The invention relates generally to the sensing of biological agents and, more specifically, to using nano-electronic circuits as transducers to convert and to amplify signals produced by the biological agents and methods for making such nano-electronic circuits.
There is intense interest in the development of small solid-state sensors that are capable of rapidly detecting markers for human bacterial pathogens, including biological threat agents. Conventional detection methods are generally based on the use of biological reagents for specific recognition of biological targets, including the mutual recognition that complimentary oligonucleotides have for each other, and the recognition of antigens by specific antibodies. In general, recognition and binding events are coupled with some form of optical detection that relays a signal indicating detection of the target of interest.
DNA recognition techniques are quite accurate, as they are based on the principle of a DNA sequence signature that is unique to each bacterial species and strain. Sections of the DNA are tagged with markers that can be detected using fluorescent methods. However, as there is only a very small amount of DNA material in a cell or in any given sample, the technique relies on the polymerase chain reaction (PCR) technology to increase the quantity of the sample material to a level that allows detection by fluorescent techniques. The combination of these techniques is expensive, complex, and time consuming; DNA recognition techniques can require a day for identifying a typical bacterial species, and three days for identifying a typical strain.
Human bacterial pathogens belong to either the gram-positive or the gram-negative Proteobacteria divisions; within these divisions, the pathogens are classified according to Genus, Species, and Strain. A large number of specific antibodies have been identified that recognize and bind to particular species of bacterial pathogens, and thus immunoassay techniques use these specific antibodies to detect particular bacterial pathogen species. Immunoassay techniques are generally less discriminating, but faster and more economical than DNA recognition techniques. Their accuracy may be limited by the specificity of the antibody-antigen combination, more particularly by cross-reactivity, i.e., the degree to which the antibody binds to species other than the target of interest. Fluorescent detection methods are very sensitive, but the large, sensitive fluorescence detectors of laboratory systems are costly.
Rapid screening tests have also been developed that utilize colorimetric detection, wherein the changing of color within an assay solution indicates detection of a target of interest. These systems are generally more economical, but less sensitive than fluorescent methods, as the signal involves not only change in wave length, but variation in intensity of color. Such tests can be read by the human eye, or with the aid of an optical reader.
Recently, detection techniques involving nanostructures (such as nanotubes or nanowires) as sensors have been developed. A nanostructure is used as a constricted path that conductively spans the gap between two electrodes. An electrical current is forced to pass through this constriction, and the current flow is then measured across the electrodes. In another architecture, a field effect transistor (FET) is created, where the conductivity across the nanotube, or nanowire, is controlled by the application of a gate voltage. A change in the electronic properties of the nanostructured electrical pathway in either or these alternative architectures affects the electronic response measurably. In particular, if a molecule binds to the surface of the nanostructured electrical element, it can significantly change the flow of current across the constriction, and such a change in the electronic properties can be used to detect the presence of the molecule. The use of nanostructures for electronic detection of the presence of gases has been described by Bradley et al. (Physical Review Letters 85, 412-21) and by Collins et al. (Science 287, 1801). The detection of gases is based on the observation that the electrical properties of carbon nanotubes, including the resistance, thermoelectric power, and local density of states, change considerably when the nanotubes are exposed to oxygen.
Balavoine et al. (Angewandte Chemie Int. Ed. 111, p. 2036) have shown that it is possible to organize proteins on the surface of a carbon nanotube. These authors suggest that nanotubes decorated with biological macromolecules could form the basis for the development of new biosensors and bioelectronic nanomaterials, taking advantage of the specific biomolecular recognition properties associated with the bound macromolecules. For such purposes, the specific recognition protein would need to be densely packed on the surface of the carbon nanotubes and the protein would need to be functional with regard to its ability to recognize and bind with the target of interest.
Chen et al. (J. Am. Chem. Soc. 123, p. 3838) have reported a general approach to non-covalent functionalization of the sidewalls of single-walled carbon nanotubes, and the subsequent immobilization of various biological molecules onto the nanotubes, that yields a high degree of control and specificity. Cui et al. (Science vol. 293, p. 5533) have taken this approach a step further and demonstrated that it is possible to achieve very fast protein detection using silicon nanowires (SiNW) and the model provided by the well-characterized ligand-receptor binding relationship between biotin and streptavidin. These authors functionalized the surface of a SiNW with biotin and detected a change in the conductivity of these functionalized SiNWs after exposure to streptavidin. The change in conductance of the SiNWs upon exposure to streptavidin was not a general feature of the SiNWs, but was dependent on the functionalization with biotin. The sensitivity of this device was reported to be at the level of 10 ppM (part per million).
Song et al. (U.S. Pat. No. 6,297,059 B1) have described an optical biosensor that includes a substrate having a lipid bilayer membrane thereon. A recognition molecule, capable of binding a target biomolecule, is disposed within the membrane. The recognition molecule includes a fluorescent label which changes in fluorescence in response to binding between the recognition molecule and the target biomolecule. Distance-dependent fluorescence self-quenching and/or fluorescence energy transfer are used as optical signal transduction mechanisms to detect molecule-target biomolecule interactions.
There is a need for improved processes and materials that are capable of sensing analytes that represent targeted bio-molecules, or groups of related molecules, with high specificity and with high sensitivity, particularly where these bio-molecules are associated with, or representative of, or diagnostic of human pathogenic organisms. Preferably, sensing devices have fast detection response and will be amenable to being configured into portable and robust packages. There are many applications where a robust, sensitive, fast, accurate and multiply-specific architecture for recognition of biological agents, which utilizes simple electronic signal amplification technology and can be used under a wide variety of conditions, would be useful.
According to the invention, nano-sensors are presented that are capable of detecting biomolecular analytes, those particular to a human pathogen, by using an electronic nanocircuit as a transducer and amplifier. Such biomolecular analytes include DNA sequences, RNA sequences, or proteins, or any molecule whose presence is diagnostic of a particular human pathogenic organism. Such pathogens include various species of bacteria, protozoa, fungi, viruses and prions. A nanocircuit contains one or more nanostructures, examples of which include nanofibers, single-walled nanotubes, multi-walled nanotubes, nanocages, nanococoons, nanohorns, nanotopes, nanotori, nanorods, nanowires and other configurations of fullerene-like molecules constructed of carbon and/or other light elements. The nanostructures are integrated into a device that can measure changes in electrical behavior along the nanostructured conductive path.
In some embodiments, the inventive device includes a semiconductor chip with metal lines or electrodes. A nanostructure spans the gap between two electrodes, thus serving as a molecular wire electrically coupled to the electrodes through which electric current passes, as it travels from one electrode to the other. Changes in properties of the nanostructure dramatically affect features of its electrical performance, which can be measured by applying a low voltage across the device. The control circuitry of the sensor can be formed on the same semiconductor chip. The use of a semiconductor chip as the technology platform allows the utilization of standard integrated circuit fabrication technology.
In some embodiments, a biologically and chemically protective coating or membrane layer surrounds the electronic nanocircuit. One of the functions of the coating layer is to diminish, inhibit, or prevent the non-specific binding or interaction of non-targeted analytes with the nanostructure. The protective coating can include a surfactant or lipid monolayer, bilayer, multilayer, hybrid bilayer, a self-assembled monolayer of biological or non-biological material, a polymer layer (such as PEG polyethylene glycol), a micellar layer, or other macromolecular assemblies composed of amphipathic molecules. The biologically and chemically protective coating or layer can contain both hydrophobic and hydrophilic elements, as well as molecular transducers or ion channels, which respond selectively to target molecules.
In some embodiments, nanostructures are clustered into an integrated array on a single semiconductor chip. Subgroups of nanostructures are each functionalized for the detection of specific biological target molecules. In such a configuration, the range of pathogens that can be detected can be easily expanded. In some embodiments a library of pathogen specific sensors is created, which can be used as part of a larger sensor system. In still other embodiments, the sensor device is integrated into a larger instrumentation package that includes sample handling, transmission of data to remote sites, alarm capabilities, and computer control of operations.
Such a biological nano-sensor detects the presence of a biological agent through a specific binding event that is transduced by molecular mechanisms as detailed below, which create a characteristic electrical signal. As depicted in
The Biological Nanosensor Integrated into a Semiconductor Chip
In
Electrodes 32 are coupled or connected to additional circuitry (
As shown in
The functions of the protective layer 11 include preventing or inhibiting non-targeted molecules from coupling to the nanostructure 10, and, in some embodiments, to provide a cell membrane-like environment for targeted molecules. In some embodiments, highly flexible protective layers 11 are selected that can be bent with a small bending radius. The flexibility of protective layers 11 can be increased with co-surfactants, or with the addition of small alcohol molecules.
The process of binding of targeted biomolecular analyte and initial signal generation in response thereto is performed by molecular transducers 12, as illustrated in
The molecular transducer 12 further includes tether molecule 22, which is connected both to the anchor molecule 20 and the receptor molecule 24. The tether molecule 22 extends through the biologically and chemically protective coating 11, and provides a connection between the anchor 20 near the nanostructure 10 and a receptor 24 near the surface of the protective coating. The tether molecule 22 can be configured at various angles with respect to the coated nanostructure, including being approximately perpendicular to the surface of the protective coating 11. The tether molecule 22 can contain more than one kind of functional moiety, and can include lipophilic, liposoluble, and/or hydrophobic groups, and can be branched or linear in form. Candidates for tether molecules 22 include single- or poly-saturated aliphatic chains, unsaturated aliphatic chains, and aromatic chains. The length of the tether molecule 22 can be selected to fit the thickness of the protective coating 11. In some embodiments, the tether molecule is relatively stiff, in which case a movement on one end of the tether molecule causes a similar movement on the other end of the molecule, providing a mechanism for communicating or transducing the sensing of a targeted molecule to the nanostructure 10. In other embodiments, the length of the tether molecule can be between about 6 and about 7 nanometers. In still other embodiments, the anchoring and tethering functions are embodied within a single multifunctional anchor molecule that is connected both to the nanostructure and the receptor molecule.
The molecular transducer 12 further includes a receptor molecule 24 that binds specifically to a targeted biomolecule of interest for its association with a human pathogenic organism. By biomolecule is meant any molecule of biological origin, such as lipids, peptides, proteins, carbohydrates, polysaccharides, oligonucleotides, polynucleotides, conjugate molecules such as glycoproteins, and glycolipids, or molecules of biological intermediary metabolism. The receptor molecule 24 can be protein, such as an antibody, an enzyme, or the active site of an antibody or an enzyme, a polynucleotide, such as a DNA or an RNA sequence, a carbohydrate, a cyclodextrin, a crown ether, or any other molecule capable of specifically recognizing and interacting with or binding to a biomolecule of interest, or capable of being functionalized in such a way that it recognizes or binds specifically to a biomolecule of interest. The receptor molecule 24 can also be coupled to the tether molecule 20 by way of a linker molecule (not shown).
The nanotube 10 is electrically coupled or connected to contact electrodes 32, which are electrically connected to an electrical circuit 40. The nanotube 10 has an original conductivity which determines the current conducted in response to a given applied voltage. A voltage source 42 applies a voltage to the electrodes 32 and generates a current through nanotube 10 and the generated current is read by ammeter 44. In some embodiments, the voltage source 42 can apply a voltage to the substrate 13, which then can act as an undifferentiated gate electrode for the device 9. The gate voltage can be DC, AC, or both. The current is very sensitive to the electrical conducting properties of the nanotube 10; small changes in the electrical conducting properties of the nanotube are readily detectable as a change in current flow.
A processing unit 60, which may include a computer or computational device (see
The protective layer 11 includes molecular transducers 12-1, 12-2, and 12-3 that are capable of sensing one or more targeted molecules. Under control conditions, in the absence of the targeted analyte biomolecule, the anchor molecules 12-1a, 12-2a, 12-3a of the molecular transducers 12-1, 12-2, 12-3 maintain an equilibrium charge transfer with the nanotube 10 and an equilibrium distance from the nanotube 10. Under non-sensing conditions, a characteristic non-sensing equilibrium current flows through the nanotube 10, as determined by the conductance of the nanotube under control conditions, and as read by the ammeter 44. The tether molecules 12-1b, 12-2b, and 12-3b provide a mechanical link between the anchor molecules 12-1a, 12-2a, and 12-3a and the receptor molecules 12-1c, 12-2c, and 12-3c. The length of the tether molecules is selected to provide a responsive connection between the anchor molecules 12-1a, 12-2a, 12-3a and the receptor molecules 12-1c, 12-2c, 12-3c. In some embodiments the length of the tether molecules is commensurate with the thickness of the protective layer 11. In the embodiment of
The binding of the targeted molecules from a test sample to a receptor molecule creates a receptor-ligand complex with a newly present molecular configuration that exert a force on the molecular transducers 12-1, 12-2, and 12-3. The molecular configuration of the receptor-ligand complex, or of the receptor itself, as modified by its interaction with the ligand, that gives rise to the force on the molecular transducers can be of a steric or an electrostatic nature. Such an altered configuration causes repulsion or attraction between the protective layer 11 and the targeted molecule bound to receptor molecules 12-1c, 12-2c, and 12-3c. The bound ligand molecule, or the receptor-ligand complex as a unit accommodates the steric or electrostatic force by moving with respect to protective layer, moving the receptor molecules with it. The receptor molecules, in turn, exert a force on the tether molecules 12-1b, 12-2b, and 12-3b. Finally, the tethered molecules transmit the force to the anchor molecules 12-1a, 12-2a, 12-3a, thereby perturbing them and changing the nature or magnitude of their electronic interaction with the nanotube 10. Such change in the electronic relationship between the anchor molecule and the nanotube, in turn, causes a change in the electrical conductivity of the nanotube portion of the sensor circuit.
In some embodiments, for example, the interaction between the anchor molecule 12-1a and the nanotube 10 is strong enough that the transmitted force causes a structural deformation of the nanotube, such as a localized bending. In other embodiments, the binding between the anchor molecule 12-3a and the nanotube 10 is weaker, and the force results in change in the distance between the anchor molecule 12-3a and the nanotube, thus causing a change in charge transfer between the anchor molecule and the nanotube. In some embodiments, the anchor molecule affects the nanotube by a modification of the charge transfer, by a change in the local electric field, by a change in the distortion of bonds, or by a change in the π-bond overlaps.
Any changes in the relationship between the anchor molecules 12-1a, 12-2a, 12-3a and the nanotube 10 result in a change in the electrical conduction properties of the nanotube, for example, in its electrical resistance. Given the one-dimensional nature of the electrical conduction path, even a localized increase in the electrical resistance of the nanotube 10 creates a bottleneck for the conduction path and thus causes a large increase in the overall resistance of the nanotube. A large increase is resistance causes a large decrease in the current that can be sensed by ammeter 44. Some interactions can cause a decrease in resistance, leading to an increased current that can be sensed by ammeter 44. Processing unit 60, as noted above, can be used to provide more complex analyses of analyte detection, and may include ammeter 44 or be separate from it.
In embodiments where the receptors are able to bind a specific targeted molecule with high specificity, a change in current indicates the sensing and binding of the targeted molecule. In embodiments where the receptors are sensitive to more than one type of targeted molecule, a calibration is performed to relate particular changes in the measured current to the binding of particular targeted molecules.
In Step 2, the biologically and/or chemically protective coating, or membrane layer 11 is formed around at least portion of the nanostructure 10 as part of the nanostructure functionalization process. The protective layer 11 can include, for example, a surfactant or monolayer, bilayer, hybrid bilayer, a multilayer, a self-assembled monolayer of biological or non-biological material, a polymer layer (such as PEG polyethylene glycol), and/or a micellar layer The protective layer 11 can contain hydrophobic and hydrophilic elements. Molecular transducers 12-1, 12-2, and 12-3 are also situated within the protective layer 11. In this illustration, two types of molecular transducers are provided; one type is shown as 12-1 and 12-2, the other type is shown as 12-3. In other arrangements, there may be only one kind of molecular transducer or there may be any number of kinds of molecular transducers provided in the protective layer 11. The molecular transducers 12-1, 12-2, 12-3 provide communication through the protective layer 11 between the nanostructure 10 and the local environment 56 in which control or analyte test samples are applied. The molecular transducers contain receptors that bind to specific molecules of interest from the environment 56, as was discussed in more detail above with reference to
In Step 3, the functionalized nanostructure 10 is integrated into a semiconductor chip, containing a substrate 13 and electrodes 32a and 32b. Control circuitry (not shown) for the nano-sensor device 9 can be provided on the same substrate 13, as part of a silicon chip. The use of a silicon chip as the technology platform allows the utilization of standard integrated circuit fabrication technology.
In Step 2, a nanostructure 10 is formed above the surface of the semiconductor chip, extending from one electrode 32a to the other electrode 32b. The nanostructure 10 may include a nanofiber, a single-walled nanotube, a multi-walled nanotube, a nanocage, a nanococoon, a nanohorn, a nanotope, a nanotorus, a nanorod, a nanowire and/or a fullerene-like molecule. The nanostructure contains at least one, but can also contain many different nanostructures. The embodiment of
In Step 3, a biologically and chemically protective coating or membrane layer 11 is formed around the nanostructure 10 as part of the nanostructure functionalization process. The protective layer 11 can include a surfactant or lipid monolayer, bilayer, hybrid bilayer, a self-assembled monolayer of biological or non-biological material, a polymer layer (such as PEG polyethylene glycol), and a micellar layer. The protective layer 11 can contain hydrophobic and/or hydrophilic elements.
Molecular transducers 12-1, 12-2, and 12-3 are also dispersed within the protective layer 11, and extend beyond it, into the sensing environment 56. In this illustration (
In other embodiments, the nanostructure 10 can be formed in physical contact with the surface of the semiconductor chip in the region between the electrodes 32, as shown in the structure of
The advantages of biological agent detection using an electrical sensor with control circuitry integrated on the same chip are significant. These advantages include high speed of detection, low power requirements, small size, and low manufacturing costs because of the use of standard manufacturing technologies. Advantages also include high sensitivity, for example, of the order of a part-per-billion (ppb) without any need to increase the quantity of the sample material. Taken together, these advantages contribute to an enabling of remote sensing, data transmission, and ultimately a large physical area to be pervasively and effectively monitored for the presence of human pathogens.
This invention has been described herein in sufficient detail to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is understood that the invention can be carried out by different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.
This application is a continuation of co-pending U.S. patent application Ser. No. 12/634,525, filed Dec. 9, 2009, which is a continuation of U.S. patent application Ser. No. 10/345,783, filed Jan. 16, 2003, now abandoned, which claims priority to U.S. Provisional Application No. 60/349,670, filed Jan. 16, 2002. Each of the foregoing provisional and non-provisional applications are specifically incorporated herein, in their entirety, by reference.
Number | Date | Country | |
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60349670 | Jan 2002 | US |
Number | Date | Country | |
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Parent | 12634525 | Dec 2009 | US |
Child | 13047593 | US | |
Parent | 10345783 | Jan 2003 | US |
Child | 12634525 | US |