Patent Application
20050164258
Methods of synthesizing polymer sequences such as nucleotide and peptide sequences are known. Methods of synthesizing oligonucleotides are found in, for example, Oligonucleotide Synthesis: A Practical Approach, Gait, ed., IRL Press, Oxford (1984), incorporated herein by reference in its entirety for all purposes. The so-called “Merrifield” solid phase peptide synthesis has been in common use for many years and is discussed in Merrifield, J. Am. Chem. Soc. (1963) 85: 2149-2154, incorporated herein by reference for all purposes. Solid-phase synthesis techniques have been provided for the synthesis of polymers, including peptides and nucleic acids on, for example, a number of “pins.” See e.g., Geysen et al., J. Immun. Meth. (1987) 102: 259-274, incorporated herein by reference for all purposes. Other solid-phase techniques involve, for example, synthesis of various peptide sequences on different cellulose disks supported in a column. See Frank and Doring, Tetrahedron (1988) 44: 6031-6040, incorporated herein by reference for all purposes. Still other solid-phase techniques are discussed in U.S. Pat. No. 4,728,502 (issued to Hamill) and PCT Publication No. WO 90/00626 (Beattie, inventor). Techniques have also been developed for the photolithographic synthesis of high density polymer arrays, including high density nucleic acid arrays. One technique that has been commercially used to produce high density oligonucleotide arrays is the use of photoprotective groups to build up nucleic acids in situ.
The present invention discloses methods for fabricating arrays of polymers. One disclosed method has the steps of providing a solid substrate having a reactive group protected by a protective group; coating the solid substrate with a film having an activatable deprotecting agent; activating the deprotecting agent in selected areas by selective application of the activator to provide an activated deprotecting agent in selected areas; and exposing the protected reactive group having the protective group to the activated deprotecting group under appropriate conditions such that the protecting group is removed to provide an exposed reactive group wherein the step of exposing does not result in substantial damage to said polymer. In preferred embodiments of the disclosed invention, the array of polymers is an array of nucleic acids or an array of oligonucleotides. The film may, according to certain aspects of the disclosed invention, contain additional materials, including a sensitizer and a base or both.
The present invention discloses the monomer in the process is preferably a nucleotide or amino acid. It is also disclosed that a nucleotide is preferably protected with a DMT protecting group at its 5′ or 3′ hydroxyl moiety. In accordance with the present invention, it is also disclosed that the monomer is preferably an amino acid which is preferably protected by a tBOC protective group at its amino terminal end.
The present invention also discloses that the activatable deprotecting agent is preferably a photoacid generator. In preferred embodiments of the present invention, the photoacid generator is 2,6-dinitrobenzyl tosylate. In another preferred embodiment of the present invention, the photoacid generator is an onium salt. In the case of photoacid generators, the activator is light. The light preferably has a wavelength of about 330 to 365 nm. In accordance with the present invention, no post-photo exposure baking step is performed. In accordance with the present invention, it has been discovered that such baking or heating is destructive of nucleic acid polymers, e.g., causes depurination.
In still other preferred embodiments of the present invention, the film contains the polymer poly(methyl methacrylate).
In still other embodiments of the present invention, the method employs additional steps of reacting the exposed reactive group with a protected monomer. The present invention discloses that these steps may be further repeated until the desired polymer array is fabricated. The present invention discloses that the array is preferably comprised of a polymer of between 20 to 75 monomers in length.
Definitions
As used herein, the following terms are intended to have the following general meanings:
Base: A base is an alkaline compound which may used in conjunction with certain photoacid generators in accordance with the present invention. Examples of bases in accordance with an aspect of the present invention include N-octylamine and di-t-butyl aniline. While applicants disclaim being held to any particular mechanistic theory, in accordance with an aspect of the present invention, the base is used a contrast enhancer. The base may act as a buffer, neutralizing, for example, the first mole equivalent of acid that's generated by the PAG. By doing this, small amounts of acid that may be generated due to stray light from the imaging system will not cause any detritylation response on the substrate where the monomer is a DMT protected monomer. In effect a “threshold” level of acid must be generated before free acid can build up in the film and detritylation can occur. High-resolution imaging systems tend to have lower contrast (ie, edge resolution profiles are sharp, but dark areas are not totally dark). Bases also serve to protect against small “background” amounts of acid that may occur from impurities in the PAG reagent or from it's thermal decomposition on storage or during processing, etc.
Film: A film as used herein refers to a layer or coating having one or more constituents, applied in a generally uniform manner over the entire surface of the substrate for example by spin coating. For example, in accordance with an aspect of the present invention, a film is, for example, a solution, suspension, dispersion, emulsion, etc., of a chosen polymer, including by way of example, a photoacid generator and optionally a base and a sensitizer.
Ligand: A ligand is a molecule that is recognized by a receptor. Examples of ligands that can be investigated by at least one aspect of the present invention include, but are not restricted to, agonists, antagonists, toxins, receptors, venoms, viral epitopes, hormones, opiates, steroids, peptides, enzyme substrates, cofactors, drugs, lectins, sugars, oligonucleotides, nucleic acids, oligosaccharides, and proteins.
Monomer: A monomer is a member of the set of small molecules which are or can be joined together to form a polymer or a compound composed of two or more members. The set of monomers includes but is not restricted to, for example, the set of common L-amino acids, the set of D-amino acids, the set of synthetic and/or natural amino acids, the set of nucleotides, and the set of pentoses and hexoses, each set of which is readily known to those of skill in the art. The particular ordering of monomers within a polymer is referred to herein as the “sequence” of the polymer. As used herein, “monomers” refers to any member of a basis set for synthesis of a polymer, and is not limited to a single “mer”. For example, dimers of the 20 naturally occurring L-amino acids form a basis set of 400 monomers for synthesis of polypeptides. Monomers can also include trimers, oligomers, polymers and so forth. Different basis sets of monomers may be used at successive steps in the synthesis of a polymer. Furthermore, each of the sets may include protected members composed of, protected amino acids as described above. Other examples of polymers within the scope of the present invention include without limitation linear and cyclic polymers of nucleic acids, polysaccharides, phospholipids, and peptides having either α-, β-, or ω-amino acids, heteropolymers in which a known drug is covalently bound to any of the above, polynucleotides, polyurethanes, polyesters, polycarbonates, polymeas, polyamides, polyethyleneimines, polyarylene sulfides, polysiloxanes, polyimides, polyacetates, or other polymers within the scope of the present invention as would be understood by a person of kill in the art of this disclosure. Such polymers are “diverse” when polymers having different monomer sequences are formed at different predefined regions of a substrate. Methods of cyclization and polymer reversal are disclosed in copending application Serial No. 796,727, filed Nov. 22, 1991, entitled “POLYMER REVERSAL ON SOLID SURFACES,” incorporated herein by reference in its entirety.
Peptide: A peptide is a polymer in which the monomers are α-amino acids and are joined together through amide bonds, alternatively referred to as a polypeptide. Amino acids may be in the L-optical isomer form or the D-optical isomer form. The term “polypeptide” as used herein refers to two or more amino acid monomers in length or greater and often includes more than 20 amino acid monomers or monomers on the order of hundreds. Standard abbreviations for amino acids are used (e.g., P for proline). Identification of amino acids and their abbreviations are well-known and are included in Stryer, Biochemistry, Third Ed., 1988, which is incorporated herein by reference in its entirety.
Receptor: A receptor is a molecule that has a specific affinity for a ligand and usually binds tightly to the ligand. Receptors may be naturally occurring or synthetic molecules. Ligands can be employed in their unaltered state or as aggregates with other molecules. Receptors may be attached, covalently or noncovalently, to a binding member or ligand, either directly or via a specific binding substance. Examples of receptors which can be employed by this invention include, but are not restricted to, antibodies, cell membrane receptors, monoclonal antibodies and antisera reactive with specific antigenic determinants, viruses, cells, drugs, polynucleotides, nucleic acids, peptides, cofactors, lectins, sugars, polysaccharides, cellular membranes, and organelles. Receptors are sometimes referred to in the art as antiligands. A “Ligand Receptor Pair” is formed when two molecules (e.g. a ligand and a receptor) have combined through molecular recognition to form a complex. Specific examples of receptors which can be investigated by this invention include but are not restricted to:
Sensitizer: A sensitizer is a compound which aids in the use of certain photoacidgenerators (“PAGs”). The sensitizer aids in this process by reacting with the energy source to initiate the photo-reaction of the PAG. For certain applications of an aspect of the present invention, it is desirable to extend the photosensitivity of the PAG. One approach to this would be to add an appropriate chromophore into the structure of the PAG. Yet another approach to this issues in accordance with an aspect of the present invention, is to add a sensitizer to the photoresist, also called a photosensitizer, which is capable of activating the PAG at, for example, a longer wavelength of light.
Substrate: A material having a rigid, semi-rigid or gelatinous surface. Typical examples include glass or suitable polymer materials. In some embodiments of the present invention, at least one surface of the substrate will be substantially flat, although in some embodiments it may be desirable to physically separate synthesis regions for different polymers with, for example, wells, raised regions, etched trenches, or the like. In some embodiments, the substrate itself contains wells, trenches, flow through regions, etc. which form all or part of the synthesis regions. According to other-embodiments, small beads may be provided on the surface, and compounds synthesized thereon optionally may be released upon completion of the synthesis. Substrates are well known in the art and are readily commercially available through vendors such as USPG, PPG Industries, AFG Industries and others.
Protective Group: A group or moiety which may be selectively removed to expose an active site such as an amino functionality in peptide or amino acid or a hydroxyl group in a nucleic acid or nucleotide. In accordance with one aspect of the present invention, protective groups may be removed under a variety of condition, for example, depending on the nature of the protective group and the mode of its connection to the active sites basic or acidic conditions may be employed as appropriate. For an extensive listing of protective groups useful in the practice of the present invention, see also Greene, T. W. and Wuts, P. G. M., Protective Groups in Organic Synthesis, (1991), incorporated herein by reference in its entirety. Useful representative acid sensitive protective groups include dimethoxytrityl (DMT), tert-butylcarbamate (tBoc) and trifluoroacetyl (tFA). Useful representative base sensitive protective groups include 9-fluorenylmethoxycarbonyl (Fmoc), isobutyrl (iBu), benzoyl (Bz) and phenoxyacetyl (pac). Other protective groups include acetamidomethyl, acetyl, tert-amyloxycarbonyl, benzyl, benzyloxycarbonyl, 2-(4-biphenylyl)-2-propyloxycarbonyl, 2-bromobenzyloxycarbonyl, tert-butyl, tert-butyloxycarbonyl, 1-carbobenzoxamido-2,2,2-trifluoroethyl, 2,6-dichlorobenzyl, 2-(3,5-dimethoxyphenyl)-2-propyloxycarbonyl, 2,4-dinitrophenyl, dithiasuccinyl, formyl, 4-methoxybenzenesulfonyl, 4-methoxybenzyl, 4-methylbenzyl, o-nitrophenylsulfenyl, 2-phenyl-2-propyloxycarbonyl, α-2,4,5-tetramethylbenzyloxycarbonyl, p-toluenesulfonyl, xanthenyl, benzyl ester, N-hydroxysuccinimide ester, p-nitrobenzyl ester, p-nitrophenyl ester, phenyl ester, p-nitrocarbonate, p-nitrobenzylcarbonate, trimethylsilyl and pentachlorophenyl ester and the like.
Predefined Region: A predefined region is a localized area on a substrate which is, was, or is intended to be used for formation of a selected polymer and is otherwise referred to herein in the alternative as “reaction” region, a “selected” region, simply a “region” or a feature. The predefined region may have any convenient shape, e.g., circular, rectangular, elliptical, wedge-shaped, etc. In accordance with the present invention, the arrays of the present invention have features on the order of 10-100 μm, i.e. 10×10 μm2 to 100×100 μm2 for approximately square features. More preferably the features will be on the order of 1-10 μm. It is also an object of the present invention to provide features having sub-micron dimensions. Such features are preferably on the order of 100-1000 nm. Within these regions, the polymer synthesized therein is preferably synthesized in a substantially pure form. However, in other embodiments of the invention, predefined regions may substantially overlap. In such embodiments, hybridization results may be resolved by software for example.
A Deprotecting Agent is a chemical or agent which causes a Protective Group to be cleaved from, for example, a protected monomer. Such cleavage, in accordance with the present invention, preferably exposes a reactive group on the monomer. The reactive group may then, in accordance with the present invention, be used to couple the deprotected monomer to the next monomer creating the polymer step by step using the appropriate chemistry. This next monomer coupled would, in accordance with one aspect of the present invention, bear a protective group which could in turn be cleaved under appropriate conditions.
An Activatable Deprotecting Agent is a chemical or agent which is relatively inert with respect to a Protective Group bound to a monomer, i.e., the activatable deprotecting agent will not cause cleavage of the protective group in any significant amount absent activation. An activatable deprotecting agent may be activated in a variety of ways depending on it's chemical and physical properties. In accordance with one aspect of the present invention, certain acitvatable deprotecting agents may be activated by exposure to some form of activator, e.g. electromagnetic radiation. In accordance with one aspect of the present invention, an activatable deprotecting agent will be activatable at only certain wave lengths of electromagnetic radiation and not at others. For example, certain activatable deprotecting reagents will be activated with visible or UV light.
Damage to the polymer: it is an object of one aspect of the present invention that the reagents and conditions used to deprotect the monomer, whether attached to a linker or growing polymer chain, do not substantially degrade or harm the polymer, monomer, linker or substrate. Preferably, the reagents and conditions used to deprotect will not damage the polymer at all or will do so only minimally such that the polymer can still be specifically recognized by its counterpart (e.g. ligand-receptor). For example, if the polymer is nucleic acid, it can only sustain damage, e.g., depurination, to the extent that it can still undergo specific Watson-Crick base pairing with a complementary nucleic acid such that specific hybridization is detectable over non-specific hybridizations. Acceptable levels of damage will be readily appreciated by those of skill in the art. In constructing an array of polymers in accordance with the present invention, it is acceptable that some polymers of a group are extensively damaged as long as there are sufficient other members of the group that are either undamaged or minimally damaged to allow specific recognition of the polymer.
A Photoacid Generator is a compound or reagent which produces an acid upon treatment with electro magnetic radiation (e.g. light) of a selected wave length.
The present invention has many preferred embodiments and relies on many patents, applications and other references for details known to those of skill in the art. Therefore, when a patent, application, or other reference is cited or repeated below, it is incorporated by reference in its entirety unless indicated otherwise.
As used in this application, the singular form “a,” “an,” and “the” include the corresponding plural references unless the context dictates otherwise. Likewise, plural references include the singular unless the context indicates otherwise.
Throughout this disclosure, various aspects of this invention can be presented in a range format. It should be understood that such description is merely for convenience and brevity and should not be construed as an unwarranted limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
The practice of the present invention may employ, unless otherwise indicated, conventional techniques of organic chemistry, polymer technology, molecular biology (including recombinant nucleic acid techniques), cell biology, biochemistry, and immunology as would be understood by one of the ordinary skill. Such conventional techniques include polymer array synthesis, hybridization, ligation, and detection of hybridization using a label. Specific illustrations of suitable techniques can be had by reference to the examples herein below. However, other equivalent conventional procedures can, of course, also be used. Such conventional techniques and descriptions can be found in standard laboratory manuals such as Genome Analysis: A Laboratory Manual Series (Vols. I-IV), Using Antibodies: A Laboratory Manual, Cells: A Laboratory Manual, PCR Primer: A Laboratory Manual, and Molecular Cloning: A Laboratory Manual (all from Cold Spring Harbor Laboratory Press), Stryer, L. (1995) Biochemistry (4th Ed.) Freeman, New York, Gait, “Oligonucleotide Synthesis: A Practical Approach” 1984, IRL Press, London, Nelson and Cox (2000), Lehninger, Principles of Biochemistry 3rd Ed., W.H. Freeman Pub., New York, N.Y. and Berg et al. (2002) Biochemistry, 5th Ed., W.H. Freeman Pub., New York, N.Y., all of which are herein incorporated by reference in their entirety.
The present invention can employ solid substrates, including arrays in some preferred embodiments. Methods and techniques applicable to polymer (including protein) array synthesis have been described in U.S. Ser. No. 09/536,841, WO 00/58516, U.S. Pat. Nos. 5,143,854, 5,242,974, 5,252,743, 5,324,633, 5,384,261, 5,405,783, 5,424,186, 5,451,683, 5,482,867, 5,491,074, 5,527,681, 5,550,215, 5,571,639, 5,578,832, 5,593,839, 5,599,695, 5,624,711, 5,631,734, 5,795,716, 5,831,070, 5,837,832, 5,856,101, 5,858,659, 5,936,324, 5,968,740, 5,974,164, 5,981,185, 5,981,956, 6,025,601, 6,033,860, 6,040,193, 6,090,555, 6,136,269, 6,269,846 and 6,428,752, in PCT Applications Nos. PCT/US99/00730 (International Publication Number WO 99/36760) and PCT/US01/04285 (International Publication Number WO 01/58593), which are all incorporated herein by reference in their entirety.
Patents that describe synthesis techniques in specific embodiments include U.S. Pat. Nos. 5,412,087, 6,147,205, 6,262,216, 6,310,189, 5,889,165, and 5,959,098, which are all incorporated by reference in their entirety. Nucleic acid arrays are described in many of the above patents, but the same general methodologies are applicable to polypeptide arrays.
The present invention also contemplates many uses for polymers attached to solid substrates. These uses include gene expression monitoring, profiling, library screening, genotyping and diagnostics. Gene expression monitoring, and profiling methods can be shown in U.S. Pat. Nos. 5,800,992, 6,013,449, 6,020,135, 6,033,860, 6,040,138, 6,177,248 and 6,309,822, which are all incorporated by reference in their entirety. Genotyping and uses therefore are shown in U.S. Ser. Nos. 60/319,253, 10/013,598 (U.S. Patent Application Publication 20030036069), and U.S. Pat. Nos. 5,856,092, 6,300,063, 5,858,659, 6,284,460, 6,361,947, 6,368,799 and 6,333,179, which are incorporated by reference in their entirety. Other uses are embodied in U.S. Pat. Nos. 5,871,928, 5,902,723, 6,045,996, 5,541,061, and 6,197,506, which are incorporated by reference in their entirety.
The present invention also contemplates sample preparation methods in certain preferred embodiments. Prior to or concurrent with genotyping, the genomic sample may be amplified by a variety of mechanisms, some of which may employ PCR. See, e.g., PCR Technology: Principles and Applications for DNA Amplification (Ed. H. A. Erlich, Freeman Press, NY, N.Y., 1992); PCR Protocols: A Guide to Methods and Applications (Eds. Innis, et al., Academic Press, San Diego, Calif., 1990); Mattila et al., Nucleic Acids Res. 19, 4967 (1991); Eckert et al., PCR Methods and Applications 1, 17 (1991); PCR (Eds. McPherson et al., IRL Press, Oxford); and U.S. Pat. Nos. 4,683,202, 4,683,195, 4,800,159 4,965,188, and 5,333,675, and each of which is incorporated herein by reference in their entirety. The sample may be amplified on the array. See, for example, U.S. Pat. No. 6,300,070 and U.S. Ser. No. 09/513,300, which are incorporated herein by reference in their entirety.
Other suitable amplification methods include the ligase chain reaction (LCR) (e.g., Wu and Wallace, Genomics 4, 560 (1989), Landegren et al., Science 241, 1077 (1988) and Barringer et al. Gene 89: 117 (1990)), transcription amplification (Kwoh et al., Proc. Natl. Acad. Sci. USA 86, 1173 (1989) and WO88/10315), self-sustained sequence replication (Guatelli et al., Proc. Nat. Acad. Sci. USA, 87, 1874 (1990) and WO90/06995), selective amplification of target polynucleotide sequences (U.S. Pat. No. 6,410,276), consensus sequence primed polymerase chain reaction (CP-PCR) (U.S. Pat. No. 4,437,975), arbitrarily primed polymerase chain reaction (AP-PCR) (U.S. Pat. Nos. 5,413,909, 5,861,245) and nucleic acid based sequence amplification (NABSA). (See, U.S. Pat. Nos. 5,409,818, 5,554,517, and 6,063,603, each of which is incorporated herein by reference). Other amplification methods that may be used are described in, U.S. Pat. Nos. 5,242,794, 5,494,810, 4,988,617 and in U.S. Ser. No. 09/854,317. Each of the above references is incorporated herein by reference in its entirety.
Additional methods of sample preparation and techniques for reducing the complexity of a nucleic sample are described in Dong et al., Genome Research 11, 1418 (2001), in U.S. Pat. Nos. 6,361,947, 6,391,592 and U.S. Ser. Nos. 09/916,135, 09/920,491 (U.S. Patent Application Publication 20030096235), 09/910,292 (U.S. Patent Application Publication 20030082543), and 10/013,598, each of which is incorporated herein by reference in its entirety.
Numerous methods for conducting polynucleotide hybridization assays have been well developed. Hybridization assay procedures and conditions will vary depending on the application and are selected in accordance with the general binding methods known including those referred to in: Maniatis et al. Molecular Cloning: A Laboratory Manual (2nd Ed. Cold Spring Harbor, N.Y, 1989); Berger and Kimmel Methods in Enzymology, Vol. 152, Guide to Molecular Cloning Techniques (Academic Press, Inc., San Diego, Calif., 1987); Young and Davism, P.N.A.S, 80: 1194 (1983). Methods and apparatus for carrying out repeated and controlled hybridization reactions have been described in U.S. Pat. Nos. 5,871,928, 5,874,219, 6,045,996 and 6,386,749, 6,391,623 each of which is hereby incorporated by reference in its entirety.
The present invention contemplates detection of hybridization between a ligand and its corresponding receptor by generation of specific signals. See U.S. Pat. Nos. 5,143,854, 5,578,832; 5,631,734; 5,834,758; 5,936,324; 5,981,956; 6,025,601; 6,141,096; 6,185,030; 6,201,639; 6,218,803; and 6,225,625, in U.S. Ser. No. 60/364,731 and in PCT Application PCT/US99/06097 (published as WO99/47964), each of which also is hereby incorporated by reference in its entirety. Each of these references is incorporated herein by reference in its entirety.
Methods and apparatus for signal detection and processing of intensity data are disclosed in, for example, U.S. Pat. Nos. 5,143,854, 5,547,839, 5,578,832, 5,631,734, 5,800,992, 5,834,758; 5,856,092, 5,902,723, 5,936,324, 5,981,956, 6,025,601, 6,090,555, 6,141,096, 6,185,030, 6,201,639; 6,218,803; and 6,225,625, in U.S. Ser. No. 60/364,731 and in PCT Application PCT/US99/06097 (published as WO99/47964), each of which also is hereby incorporated by reference in its entirety.
The practice of the present invention may also employ conventional biology methods, software and systems. Computer software products of the invention typically include computer readable medium having computer-executable instructions for performing the logic steps of the method of the invention. Suitable computer readable medium include floppy disk, CD-ROM/DVD/DVD-ROM, hard-disk drive, flash memory, ROM/RAM, magnetic tapes and etc. The computer executable instructions may be written in a suitable computer language or combination of several languages. Basic computational biology methods are described in, e.g. Setubal and Meidanis et al., Introduction to Computational Biology Methods (PWS Publishing Company, Boston, 1997); Salzberg, Searles, Kasif, (Ed.), Computational Methods in Molecular Biology, (Elsevier, Amsterdam, 1998); Rashidi and Buehler, Bioinformatics Basics: Application in Biological Science and Medicine (CRC Press, London, 2000) and Ouelette and Bzevanis Bioinformatics: A Practical Guide for Analysis of Gene and Proteins (Wiley & Sons, Inc., 2nd ed., 2001). See U.S. Pat. No. 6,420,108. Each of these references is incorporated herein by reference in its entirety.
The present invention may also make use of various computer program products and software for a variety of purposes, such as probe design, management of data, analysis, and instrument operation. See, U.S. Pat. Nos. 5,593,839, 5,795,716, 5,733,729, 5,974,164, 6,066,454, 6,090,555, 6,185,561, 6,188,783, 6,223,127, 6,229,911 and 6,308,170. Each of these references is incorporated herein by reference in its entirety.
Light patterns can also be generated using Digital Micromirrors, Light Crystal on Silicon (LCOS), light valve arrays, laser beam patterns and other devices suitable for direct-write photolithography. See. e.g., U.S. Pat. Nos. 6,271,957 and 6,480,324, incorporated herein by reference.
Additionally, the present invention may have preferred embodiments that include methods for providing genetic information over networks such as the Internet as shown in U.S. Ser. Nos. 10/063,559 (United States Publication No.U.S. 20020183936), U.S. Provisional Application 60/349,546, 60/376,003, 60/394,574 and 60/403,381). Each of these references is incorporated herein by reference in its entirety.
The present invention provides methods, devices, and compositions for the formation of arrays of large numbers of different polymer sequences. In one aspect of the present invention, the methods and compositions provided herein involve the conversion of radiation signals into chemical products that are particularly useful in polymer synthesis. The invention also includes the arrays formed using the methods and compositions disclosed herein. One aspect of the invention includes methods, compositions, and devices for the synthesis of an array of different polymers in selected and predefined regions of a substrate. Another aspect of the invention includes those arrays and various methods of using them.
Such arrays are used in, for example, in nucleic acid analysis. Polynucleotide or nucleic acid arrays are especially suitable for checking the accuracy of previously elucidated sequences and for detecting mutations and polymorphisms. Polymer arrays are also used in screening studies to evaluate their interaction with, for example, receptors such as antibodies in the case of peptide arrays or with nucleic acids in the case, for example of oligonucleotide arrays. For example, certain embodiments of the invention provide for the screening of peptides to determine which if any of a diverse set of peptides has strong binding affinity with a receptor.
In some embodiments of the present invention, the arrays formed by the present invention are used in competitive assays or other well-known techniques to screen for compounds having certain activities. For example, vast collections of synthetic or natural compounds are immobilized on predefined regions of a substrate. The reaction of the immobilized compounds (or compound) with various test compositions such as the members of a chemical library or a biological extract are tested by dispensing small aliquots of each member of the library or extract to a different region. In one embodiment, a large collection of human receptors is deposited on a substrate, one in each region to form an array. A plant or animal extract is then screened for binding to various receptors of the array.
Nucleic acid sequences can also be immobilized in specific locations or predefined regions of a substrate using the current invention. In some embodiments, such immobilized nucleic acid arrays are used in hybridization assays for gene expression monitoring, nucleic acid amplifications, nucleic acid computation, and nucleic acid analysis in general.
The present invention has certain features in common with the radiation directed methods discussed in U.S. Pat. No. 5,143,854, incorporated herein by reference. The radiation-directed methods discussed in that patent involve activating predefined regions of the substrate and then contacting the substrate with a preselected monomer solution. The predefined regions can be activated with, for example, a light source shown through a mask (much in the manner of photolithographic techniques used in integrated circuit fabrication). Other regions of the substrate remain inactive because they are blocked by the mask from illumination. Thus, a light pattern defines which regions of the substrate react with a given monomer. By repeatedly activating different sets of predefined regions and providing different monomer compositions thereto, a diverse array of polymers is produced on or near the substrate.
According to one embodiment of the present invention, linker molecules having reactive functional groups protected by protecting groups are provided on the surface of a substrate. In one preferred embodiment of the present invention a catalyst system including a photoacid generator (“PAG”) and a base, but no sensitizer, are provided on the surface, preferably in a film. In another aspect of the present invention, the catalyst system comprises a film comprising a PAG, a sensitizer and a base. A set of selected regions on the surface of the substrate is exposed to radiation using well-known lithographic methods discussed, for example, in Thompson, L. F.; Willson, C. G.; and Bowden, M. J., Introduction to Microlithography; American Chemical Society, 1994, pp. 212-232, incorporated herein by reference in its entirety. The generated acid is allowed to be exposed to the protected group for long enough and under sufficient conditions to remove the protective group, preferably a DMT group. Afterwards, the surface of the array is stripped, preferably in an appropriate solvent leaving protected and unprotected groups. Monomers having a protective group are allowed to react with the exposed groups. The surface is again coated with one of the catalyst systems described above. A second set of selected regions is exposed to radiation as above.
A second set of selected regions is, thereafter, exposed to radiation. The radiation-initiated reactions remove the protecting groups on molecules in the second set of selected regions, i.e. the linker molecules and the first-bound monomers. The substrate is then contacted with a second monomer containing a removable protective group for reaction with exposed functional groups. This process is repeated to selectively apply monomers until polymers of a desired length and desired chemical sequence are obtained. According to one aspect of the present invention, the growing chains of nucleic acid can be capped in between synthesis rounds. This procedure limits the production of nucleic acids with an undesired sequence. Side chain protective groups for exocylic amines for example, if present, are also optionally removed.
In one preferred embodiment, the monomer is a 2′-deoxynucleoside phosphoramidite containing an acid removable protecting group at its 5′ hydroxyl group. As stated previously, in an alternate embodiment, the protecting group is present at the 3′ hydroxyl group if synthesis of the polynucleotide is from the 5′ to 3′ direction. The nucleoside phosphoroamidite is represented in accordance with one aspect of the present invention by the following formula:
wherein the base is adenine, guanine. thymine, or cytosine, R1 is a protecting group which makes the 5′ hydroxyl group unavailable for reaction and includes dimethoxytrityl, tert-butyloxycarbonyl or any of the protecting groups known to those of skill in the art; R2 is cyanoethyl, methyl, t-butyl, trimethylsilyl and the like and R3 and R4 are isopropyl, cyclohexane and the like. Exocyclic amines present on the bases can also be protected with acyl protecting groups such as benzoyl, isobutyryl, phenoxyacetyl and the like. The linker molecule contains an acid- or base-removable protecting group. Useful linker molecules are well known to those skilled in the art and representative examples include oligo ethers such as hexaethylene glycol, oligomers of nucleotides, esters, carbonates, amides and the like. Useful protecting groups include those previously listed and others known to those skilled in the art.
In another preferred embodiment, the monomer is an amino acid containing an acid- or base-removable protecting group at its amino or carboxy terminus and the linker molecule terminates in an amino or carboxy acid group bearing an acid- or base removable protecting group. Protecting groups include tert-butyloxycarbonyl, 9-fluorophenylmethoxycarbonyl, and any of the protective groups previously mentioned and others known to those skilled in the art.
According to one aspect of the present invention, spatially defined polymer synthesis will be performed by depositing a photoresist such as Ghand's “VLSI Fabrication Principles,” Wiley (1983), incorporated herein by reference in its entirety. According to these embodiments, a resist is deposited, selectively exposed, leaving a portion of the substrate exposed for coupling. These steps of depositing resist, selectively removing resist and monomer coupling are repeated to form polymers of defined sequences at desired locations. In some specific embodiments, a positive tone resist comprised of diazonapthoquinone-novolac (DQN/N) is incorporated in a creasole-formaldehyde polymer matrix. This resist and its variants are used routinely in the microelectronics industry for submicron resolution lithography, as more fully discussed in Reiser, “Photoreactive Polymers: The Science and Technology of Resist,” Riley (1989), incorporated herein by reference in its entirety. However, it has been discovered in accordance with an aspect of the present invention that substantial and non-obvious refinements to the procedures developed for the microelectronics industry are necessary to allow similar procedures to work with certain polymers of the present invention, e.g., nucleic acids. It is also known to those of skill in the art that other polymers such as peptides are not stable at all conditions employed in the microelectronics industry.
High contrast detritylation of <4 microns has been demonstrated with simple contact printing with a resist. Unfortunately, the alkaline conditions needed (aqueous [OH] 0.1 M) complicates its direct use in a multistep polymer synthesis, such as polynucleotide array fabrication because of the hydrolysis of nucleobase exocylic amine protecting groups that are used to prevent side reactions during synthesis with standard phosphoramidite monomers.
As various well known methods for chemical removal of DMT protecting groups involving application of alkali conditions resulted in undesired side reactions such as removal of exo-cyclic amino protecting groups, reagents and methods were developed for light-directed synthesis of DNA probes, utilizing phosphoramidite monomers having photolabile protecting groups. These methods and reagents are described in the various references incorporated by reference above.
Under some circumstances, photodeprotection yields truncated probe sequences due to incomplete removal of the photoprotecting group following application of light. Incomplete removal of a photodeprotecting group may impose limitations on probe length. For example, if one imagines a stepwise yield of photolysis of 85% and 25 successive steps are carried out to provide 25-mer oligonucleotides, less than 2% of the probes will reach the desired length of 25.
In addition, relative to conventional DMT-protected phosphoramidite monomers, photolabile-protected phosphoramidite monomers are costly to obtain. A manufacturing process that uses DMT-protected phosphoramidite monomers should therefore be cheaper, and by analogy to well-established efficiencies of acid-mediated DMT removal, should also be higher-yielding, perhaps even approaching a 99% stepwise yield. A high-yielding synthesis method would substantially decrease the number of truncated probes and enable the ability to produce long-mer probes (e.g., 50-mer, 60-mer, 70-mer etc.) with relative ease. Shorter probes could also be constructed by the same method if desired.
In accordance with one aspect of the present invention, methods and compositions to generate localized photo-generation of appropriate acid species to effect DMT removal from growing strands of polynucleotides were developed. The traditional semiconductor field employs photoacid generator compounds (i.e., PAGs) in conjunction with “sensitizer” compounds that require elevated temperatures to achieve a suitable acidity to appropriately affect surfaces in that industry. In accordance with an aspect of the present invention, it was discovered that some polymers, for example polynucleotides, including DNA, are susceptible to depurination at elevated temperatures and low pH values, giving rise to variably degraded probes. Probes which have undergone depurination, i.e., the loss of the base structure on T and C nucleotides, will not hybridize as well to corresponding homologous DNA or RNA. Substantially, damaged probes may not hybridize at all or may hybridize without specificity, i.e., background hybridization unrelated to sequence of probe. Arrays with a substantial number of depurinated probes would be undesirable for a number of reasons including possible failure to hybridize to theoretically homologous nucleic acids in a sample, resulting in a false negative experiment. Solutions to acid induced depurination are known in the art. Analogues of standard DNA, for example 2′-OMe nucleoside modifications, are known to be more resistant to such degradation. However, utilization of such analogues is substantially more expensive than the corresponding underivatized analog. Moreover, analogues such as 2′-OMe nucleosides alter the hybridization properties of the probes, which would require changes to probe/array design.
It has been discovered in accordance with the present invention that high-yield probes may be prepared using standard DMT-containing monomers and detritylation with a photoacid generator used under appropriate conditions, i.e. conditions described in accordance with an aspect of the present invention which substantially reduce or eliminate acid induced depurination. In accordance with an aspect of the present invention, the local concentration of acid liberated by the activated PAG, which is reflected by the pKa of this molecule, is an important consideration in selecting the appropriate PAG(s) for the particular polymer to be fabricated. Also, the exposure time of the polymer to the acid is another important consideration. Another key aspect of an aspect of the invention is the photolysis time, which must be of sufficient duration to generate a suitable quantity of acid and achieve essentially quantitative detritylation, but not so long that depurination becomes a factor. It has been discovered in accordance with an aspect of the present invention that a heating step following photoactivation of the PAG, which is routinely employed and taught in the semiconductor industry, should not be used in conjunction with certain polymers contemplated by the present invention, including especially polynucleotides, e.g. DNA oligonucleotides. If growing polynucleotide chains are baked after activation of the photoacid generator, it appears that the resulting heat in conjunction with a localized low pH causes depurination. Thus, post-UV light exposure baking is to be avoided in accordance with an aspect of the present invention.
With respect to on particular aspect of the present invention, it has been discovered that certain onium salts provide excellent removal of the DMT group when used in conjunction with an appropriate base and without a post-exposure baking step. In another aspect of the present invention, a non-ionic PAG is used in conjunction with a sensitizer and a base to provide high yield DMT removal without causing unwanted depurination. These approaches, in accordance with an aspect of the present invention, substantially solve the problem of probe degradation often observed with photoacid generation, avoids the need to use DNA analogues and enables a high-yield probe synthesis process and resulting products.
In accordance with this aspect of the present invention, the photoacid causes minimal or insubstantial damage to the polymers making up the array. What damage may be endured by the polymer in question will be determined by the nature of the polymer and the assay or experiment to be conducted with the array. This will be apparent to the person of skill in the art. For example, if an array of oligonucleotides is fabricated, a certain amount of depurination may be tolerated if the probes on the array can still be used to reliably and specifically detect sequences in a sample.
In accordance with another aspect of the present invention, the PAG must be chosen such that that wavelength of light of activation is not to short. For example, many PAGs are used in the semiconductor industry which require UV light have a wavelength of less than 300 nm. Indeed, literature references speak of using “short UV” PAGs wherein wavelengths of light of 220 to 260 nm are used. In accordance with an aspect of the present invention, such short UV wavelengths are totally unacceptable with respect to certain polymers, particularly nucleic acids. For nucleic acids UV light is used on the order of preferably 330 to 365 nm. More preferably, UV light of around 365 nm is used.
According to one aspect of the present invention a process is provided for fabricating an array of polymers, the process having the steps of providing a solid substrate having a reactive group protected by a protective group; coating the solid substrate with a film having an activatable deprotecting agent; activating the deprotecting agent in selected areas by selective application of an activator to provide an activated deprotecting agent; and exposing the monomer having the protective group to the activated deprotecting group under appropriate conditions such that the protecting group is removed to provide an exposed reactive group wherein the step of exposing does not result in substantial damage to the polymer. In accordance with the present invention the reactive group may be located on a linker having one end bound to a solid substrate with the reactive group at the opposite end or other exposed site of the linker, a monomer attached to a linker or a polymer (here two or more monomers) attached to a linker.
Preferably the array of polymers is an array of nucleic acids. More preferably, the array of nucleic acids is an array of oligonucleotides. The monomer is preferably a naturally or non-naturally occurring nucleotide. More preferably the nucleotide is selected from the group consisting of G, A, T, and C. Preferably, the nucleotide is protected at its 5′ hydroxyl end by a dimethoxytrityl (“DMT”) protective group. In the most preferred embodiments, the nucleotide is selected from the group G, A, T, and C and is protected at its 5′ hydroxyl group by a DMT protective group. In another aspect of the present invention, the nucleotide is protected at its 3′ hydroxyl group with a DMT protective group. Thus, in accordance with the present invention, nucleotides may be synthesized in the 5′ to 3′ direction or a 3′ to 5′ direction. In still another preferred embodiment of the present invention, the array of polymers is an array of peptides. Also, preferably, the monomer is an amino acid. It is also a preferred embodiment of the present invention that the amino acid is a naturally occurring amino acid or a non-naturally occurring amino acid. More preferably the amino acid is selected from the group consisting of alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, praline, serine, threonine, tryptophan, tyrosine and valine.
In still another preferred embodiment, the amino acid is protected at its amino terminus functionality by a tert-butyloxycarbonyl (“tBOC”) protective group during synthesis.
In another aspect of the instant invention, the process described above has an additional step of reacting the monomer with an exposed reactive group with a second monomer having a reactive group protected by a protective group. In another preferred embodiment of the instant invention, the process has a further step of repeating all the steps to obtain the desired polymer array.
Originally the term lithography referred to a method of printing using a nonpolar ink applied to a hydrophilic master plate patterned with a hydrophobic image. As used at the present date, the term is generally used to describe a number of methods for replicating a predetermined master pattern on a substrate. Common applications of this technology involve replication effected by first coating the substrate with a radiation-sensitive polymer film (a resist) and then exposing the film to actinic radiation in a predefined pattern. The radiation induced chemical changes that result, alter the chemical properties of the exposed regions of the coated substrate such that they can be differentiated in subsequent developmental steps.
In yet another preferred embodiment of the instant invention, the step of coating is performed by applying to the substrate a film of a polymer solution containing the activatable deprotecting agent. Preferably, the polymer solution is a composition of a certain percentage of poly(methyl methacrylate). Preferably, the activatable deprotecting agent is a photoacid generator. Both ionic and non-ionic photoacid generators can be used in accordance with an aspect of the present invention. Preferably the photoacid generator is 2,6-dinitrobenzyl tosylate, a non-ionic photoacid generator. Where the activatable deprotecting agent is a photoacid generator, it is particularly preferred that the monomer is a nucleotide and the protecting group is DMT. It is also preferred in this situation that the monomer is an amino acid and the protecting group is tBOC.
Where the activatable deprotecting agent is a photoacid and the photoacid is 2,6 dinitro benzyl tosylate, the activator is preferably light having a wave length of around 365 nm. In still other preferred embodiments of the instant invention, the array of polymers comprises a polymer at least 50 monomers in length. In other preferred embodiments, the polymer is at least 60 monomers in length. In still other preferred embodiments, the polymer is at least 70 monomers in length. More preferably, each of the at least 50, 60 and 70 monomer long polymers are DNA oligonucleotides.
Still other photoacid generators (“PAGs”) are known. Common commercial ionic PAGs include onium and organometallic salts such as diaryliodonium and triarylsulfonium salts and (cyclopentadienyl)(arene)iron+ salts of the anions PF6−, SbF6−, CF3SO3−, C4F9SO3− and C8F17SO3−. Also known are sulfonium salts (e.g., triphenylsulfonium hexafluorophosphate, triflate, toslyate, and camphorsulfonate, The photochemical reaction of many onium salt generates a low concentration of a strong Brönsted acid. In this regard, numerous PAGs are known from the semiconductor industry. However, in the semi-conductor industry, the wafer is subjected to a baking step after generation of the acid by photolysis, where the exposed wafers are subjected to temperatures exceeding 100° C. for prolonged periods of time. In accordance with the present invention, it has been discovered that baking has a deleterious effect on some polymers, in particular nucleic acids. Thus, while onium salts and other PAGs used in the semiconductor industry are of interest to the present invention, protocols for the usage of these compounds must be varied significantly as described in accordance with one aspect of the present invention.
Onium salts are known to have high quantum yields of acid production, good absorption properties and good solubility in many resist films. However, it is also known in accordance with the present invention that the wavelengths of light commonly used to activate onium salts for semi-conductors can not be used with some polymers, particularly nucleic acids. In this regard, it is common in the semi-conductor industry to use low wavelength UV light (e.g. less than 300 nm) to activate onium salts. See, e.g., Wallraff, G. M. and Hinsberg, W. D., Lithographic Imaging Techniquesfor the formation of Nanoscopic Features, Chem. Rev. 1999, 99, 1801-1821, which is incorporated herein be reference for all purposes.
In accordance with the present invention, it is known that such wavelengths of light are entirely unacceptable for the synthesis of nucleic acids. Such wavelengths of UV light cause numerous forms of damage to a nucleic acid chain, including cross-linking of bases. Nucleic acids synthesized under these conditions would be unable to hybridize to their homologous counterparts. To use onium salts in accordance with the present invention, they must absorb light in the range of 330 nm to about 365 nm and generate acid at an acceptable level and rate (photospeed) at those longer wavelengths. Such onium salts are known in the literature or could be devised based on the teachings of present invention by those of skill in the art using reasonable and not undue effort.
Many onium salts can be synthesized by metathesis reactions. Thus, the acid counterion can be easily modified. In turn, this allows a ready means to vary the pKa, volatility and size of the photogenerated acid. Onium acids are described in a wide variety of published references, including Wallraff, G. M. and Hinsberg, W. D., cited above. See also Shirai, M and Tsunooka, M., “Photoacid and Photobase Generators: Chemistry and Applications to Polymeric Materials,” Prov. Polym. Sci., Vol. 21, 1-45, 1996, incorporated here by reference for all purposes.
In accordance with an aspect of the present invention, both ionic and non-ionic photoacid generators are contemplated. Both have advantages and disadvantages. Ionic PAGs are thermally stable and have a wide range of spectral absorption. However, ionic solvents have a limited solubility in organic solvents. Non-ionic PAGs have better solubility in organic solvents, but have less thermal stability than ionic PAGs. However, as discussed above, the thermal stability is less of an important consideration for the present invention.
In accordance with an aspect of the present invention, it is important that the polymers to be synthesized by the techniques of the present invention not undergo undue or substantial damage during the synthesis. In this regard, it is known that exposure of nucleic acid polymers to acids can result in damage, including for example depurination. In the context of nucleic acid microarrays, which are used to detect the hybridization of homologous species of nucleotides, the nucleic acid attached to the substrate can undergo some depurination and still act to satisfactorily hybridize homologous nucleic acids. However, if the damage is too great, the hybridization will not occur at all or will not occur reliably. A substantial number of damaged proves in a feature could result in a false negative. Thus, it is important in embodiments of the instant invention employing photoacid generators that the acid is not allowed to substantially damage the nucleic acids being synthesized. In accordance with the present invention, substantial damage means that the polymer or nucleic acid is unable to be used for the intended use for the array. Thus, in the context of a nucleic acid array, substantial damage would mean that the array could not be used to reliably detect nucleic acids. For a protein array, substantial damage would mean that the peptide was damaged to the extent that it could not be recognized by an antibody or protein receptor.
According to one aspect of the present invention, a process for fabricating an array of polymers is provided, the method having the steps of providing a solid substrate comprising a monomer having a reactive group protected by a protective group; coating the solid substrate with a film, said film comprising an activatable deprotecting agent; activating the deprotecting agent in selected areas by selective application of an activator to provide an activated deprotecting agent; exposing the monomer having the protective group to the activated deprotecting group under appropriate conditions such that the protecting group is removed to provide a monomer with an exposed reactive group wherein the step of exposure does not result in substantial damage to the polymer.
The array is preferably an array of nucleic acids or an array of oligonucleotides. The monomer is preferably a nucleotide. More preferably the nucleotide is protected at its 5′ hydroxyl end with a DMT protective group. It is also preferred that the nucleotide is protected at its 3′ hydroxyl group with a DMT protective group.
In still other preferred embodiments of the present invention the polymer is a peptide. The monomer is preferably an amino acid. More preferably, the amino acid is a naturally occurring amino acid. In still other embodiments of the instant invention, it is preferred that the amino acid is protected at its amino functionality by a tBOC protective group.
In other preferred embodiments the nucleotide, is selected from the group consisting of G, A, T and C. More preferably, the nucleotide selected from the group consisting of G, A, T, and C is protected at its 5′ hydroxyl group with a DMT protective group.
In an other preferred embodiment of the instant invention, the process comprises the further step of reacting said exposed reactive group with a monomer having a reactive group protected by a protective group; coating the solid substrate with a film having an activatable deprotecting agent, activating said deprotecting agent in selected areas by selective application of an activator to provide an activated deprotecting agent; exposing the monomer having the protective group to said activated deprotecting group under appropriate conditions such that said protecting group is removed to provide a monomer with an exposed reactive group wherein said step of exposure does not result in substantial damage to said polymer and repeating the above steps to provide the desired polymer array.
In another preferred embodiment of the present invention the step of coating is performed by applying to the substrate a film of a polymer solution containing said activatable deprotecting agent. Preferably, the activatable deprotecting agent is a photoacid generator. More preferably the photoacid generator is selected from the group consisting of a photoacid generator selected from the group consisting of an ionic photoacid generator and a non-ionic generator. In another preferred embodiment, the photoacid generator is 2,6-dinitrobenzyl tosylate. Where the activatable deprotecting agent is a photoacid generator the monomer comprises a nucleotide and the protecting group is DMT. In another preferred embodiment of the present invention, the monomer is an amino acid and the protecting group is tBOC. Where a photoacid generator is used, it is preferably dispersed in poly(methyl methacrylate) (PMMA).
Where the monomer is a nucleic acid, the activator is preferably light having a wave length of between 330 and 365 nm. It is also a preferred embodiment of the present invention that the array of polymers comprises a polymer at least 25 to 75 monomers in length. In a preferred embodiment of the present invention the photoacid generator is an onium salt. More preferably, the onium salt is Bis (4-t-butyl phenyl) iodonium PF6−.
In one preferred embodiment of the present invention, where the polymer is a nucleic acid, substantial damage is determined by the ability of the nucleic acid array to bind complementary nucleic acids.
It is also a preferred embodiment of the present invention that after exposing the photoacid generator to an activating wavelength of light, there is no post exposure baking or heating step.
In preferred embodiments of the present invention, the polymer is a nucleic acid and the monomer is a nucleotide and substantial damage is determined by determining the level of false negatives generated by hybridizing the array with a known sample having known complementary nucleic acids to said array. In accordance with this aspect of the present invention, the array could be tested by hybridizing it with a test or control sample having nucleic acids which should give a positive signal on the array if the oligonucleotides, for example, on the array have been synthesized without substantial damage. After hybridization of the control sequence, the array can be scanned and the features analyzed with the corresponding control probes. If the control probes have suffered no damage during fabrication, a high intensity result should be observed. However, if minimal damage occurred the signal might still be present, but diminished, for example by 50%. If the array were intended to detect rare species such a diminution would probably not be acceptable. The batch of arrays containing such defects would likely have to be disposed of. If no signal were seen or if the signal was diminished by 90% or more, the batch of such arrays would probably have to be disposed of regardless of the proposed end use of such arrays.
In accordance with another aspect of the present invention, an array of oligonucleotides is produced using a PAG and DMT protected nucleotides to produce features preferably on the order of 10-100 μm. More preferably, features are on the order 1-10 μm. In another preferred embodiment, features are on the order of 100-1000 nm.
In this example, a PAG was used in conjunction with standard DMT-protected phosphoramidite monomers to fabricate oligonucleotide arrays. A solution of activated DMT-protected phosphoramidite monomer was coupled to a support-bound hydroxyl functionality and oxidized in the typical manner. The support (i.e., wafer or chip) was removed from the flowcell and coated with a polymer solution that contained a photoacid generator: 2,6-dinitrobenzyl tosylate (“DBT”).
A film was prepared of 10% by weight DBT was incorporated in 15% PMMA (MW 120 k) in MEK solvent, including a base of 0.5% di-t-butyl aniline and spun coat at 2,500 RPM for 90 seconds onto the substrate, which is a convenient method to apply the polymer solution, and provides a tact-free surface. The coated support was then subjected to photolysis with (or without a mask for certain control experiments) using a dosage of about 1 Joule at 365 nm wavelength. Following photolysis, the support was promptly stripped of its coating by applying with acetonitrile, and then the support was returned to the flowcell to continue probe synthesis. This basic sequence of events was repeated to add additional monomer units, thus assembling the probe. After the desired probes had been synthesized, the substrate was base-deprotected in the normal way and then used in hybridization experiments.
Supporting data demonstrate exemplary methods described above in accordance with one aspect of the present invention. 20-mer and 50-mer probes were prepared in various patterns. Hybridization signals and profiles from these were compared to a “gold standard” method using solution-phase TCA delivery to achieve detritylation. In most respects, the behavior of the probes prepared with the photoacid generator process is identical to the behavior of the probes prepared with conventional solution-phase TCA detritylation. This observation demonstrates that the stepwise coupling yield for the probes prepared by the photo-acid generator process is comparable to that achieved with solution-phase TCA delivery (i.e., 97-99%). Moreover, the hybridization results further demonstrate that the probe is intact and not degraded as a result of depurination and subsequent chain cleavage. Particularly low background signal was obtained. The low levels of background demonstrate that this method additionally holds promise for array designs that demand extremely high-contrast, such as those that contain ultra-small features. No baking step was conducted between the photolysis step and the stripping step in the above process.
In yet another aspect of the present invention, an onium salt\ was used as a photoacid generator. Bis (4-t-butyl phenyl) iodonium PF6− (5% wt., 80 mM) was used in a polymer of 5% (wt) PMMA (15 k) in ethyl lactate. Also included in the formulation was a sensitizer and a base. The sensitizer was 2-isopropyl thioxanthone (ITX, 9.5% wt., 371 mM) and the base N-octylamine (0.85% wt., 65.8 mM). ITX has the following structure(s):
The polymer and formulation PAG, sensitizer and base was spun coat for 60 seconds at 3000 RPM on to a substrate to generate a layer of 0.1 μm thickness, followed by a prebake for 1 minute at 85 degrees centigrade.
Exposure of the spun coated, prebaked plate was at 66 mJ for non-base formulation and 120 mJ for base-added formulation. Following exposure, stripping was performed with SVC-14 (60% DMSO: 40% aliphatic ether), ACN. Hybridization to 10 nM target in 1XMES at 35 degrees C. No post baking step was performed. Scanning was performed using an Agilent instrument at 530 nm (3 μm), an ARC instrument at 570 nm (1 μm), and by SEM.
Synthesis fidelity of the onium system was analyzed. The hexamer 3′-TAGCAT-5′ was fabricated with the constituents as identified above. The total yield was 64% and the stepwise yield was 94%. The lithographic performance was also analyzed and the onium photoresist provided high contrast arrays with excellent resolution. The onium process is also robust as was demonstrated by a 75-step wafer scale synthesis. Because of the high total and stepwise yield, the onium photoacid generator can be used to generate arrays with longer oligonucleotide probes than currently available photolithographic methods. In this regard, the onium system described above was used to synthesize 50 mer probes. High intensity signals were sign on hybridization to these 50 mers. Moreover, little depurination was observed.
The feature size of onium arrays produced with different masks was measured and is shown in Table 1 below:
In summary, the onium based salt supporting data demonstrate exemplary methods described above in accordance with one aspect of the present invention. 20-mer and 50-mer probes were prepared in various patterns. Hybridization signals and profiles from these were compared to a “gold standard” method using solution-phase TCA delivery to achieve detritylation. In most respects, the behavior of the probes prepared with the photoacid generator process is identical to the behavior of the probes prepared with conventional solution-phase TCA detritylation. This observation demonstrates that the stepwise coupling yield for the probes prepared by the photo-acid generator process is comparable to that achieved with solution-phase TCA delivery (i.e., 97-99%). Moreover, the hybridization results further demonstrate that the probe is intact and not degraded as a result of depurination and subsequent chain cleavage. Particularly low background signal was obtained. The low levels of background demonstrate that this method additionally holds promise for array designs that demand extremely high-contrast, such as those that contain ultra-small features. No baking step was conducted between the photolysis step and the stripping step in the above process.
The foregoing invention has been described in some detail by way of illustration and examples, for purposes of clarity and understanding. It will be obvious to one of skill in the art that changes and modifications may be practiced within the scope of the appended claims. Therefore, it is to be understood that the above description is intended to be illustrative and not restrictive. The scope of the invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the following appended claims, along with the full scope of equivalents to which such claims are entitled.
This application claims priority to U.S. Provisional Application No. 60/532,220, filed on Dec. 22, 2003; and U.S. Provisional Application No. 60/577,050, filed on Jun. 3, 2004. The '220 and '050 applications are incorporated herein by reference in their entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 60532220 | Dec 2003 | US | |
| 60577050 | Jun 2004 | US |
