Patent Application
20090084686
The present invention relates to a biosensor for detecting presence and concentration of various bio-materials including genes and proteins by the electrical method, an interdigitated electrode sensor unit of the biosensor and a method for determining concentration of a bio-material using the biosensor.
The study of genes and proteins has provided chances to analogize noble biomarkers for diagnosis of diseases. Particularly, in case of the diseases such as cancer, accurate diagnosis in the early stage of development can complete cure of the disease and prevent relapse of the disease. Therefore, studies for development of sensors for early stage detection of biomarkers by antigen-antibody interaction have been actively proceeded. Such sensors can be applied in various fields related to public health, environment, military needs, food and the like and diverse research is in progress.
An optical apparatus can be used to determine the presence of the antigen of a small amount. However, this method has relatively many problems related to time, cost and efforts, though it is widely used. Recently, there are disclosed a method using wavelength change of absorbed light according to the presence of an antigen (Chou et al., (2004) Biosens. Bioelectron. 19, 999-1005) and a method using wavelength change of absorbed light by the change of nano particles having a surface capable of complimentarily binding to an antigen (Alivisatos et al., (2004) Nat. Biotechnol. 22, 47-52, Nam et al., (2003) Science. 301, 1884-1886; U.S. Pat. No. 6,974,669).
In recent, researches on electrical detection methods are actively conducted to develop a sensor which is portable, easily usable, cheap and rapid. Such sensors for electrical detection can be readily applied to direct combination with computers, portable equipments, household appliances and the like. There are disclosed methods for detecting concentration of a bio-material from change of the electrical conductivity using a surface-modified carbon nanotube or nanowire (Chen, R. J. et al. (2003) Proc. Natl. Acad. Sci. USA 100, 4984-4989, Zheng, G. et al. (2005) Nat. Biotechnol. 23, 1294-1301; U.S. Pat. No. 6,781,166).
However, devices using such a carbon nanotube or nanowire need arrangement techniques to position the nanotube or nanowire in a desired location. Also, since produced devices have different properties according to size and junction resistance of the carbon nanotube and nanowire, they cannot be produced in a mass quantity. Therefore, it is desired to realize a sensor using an device which can be readily integrated and be formed in a desired configuration using patterning (lithography) technology which is used commonly used in the semiconductor process.
The biosensor using nanogap is a technology to meet the above demand and recently attracts interests. According to the devices for detecting bio-material known up-to-date (U.S. Pat. Nos. 6,653,653 and 6,824,974), the bio-material connects directly between electrodes. However, they are not suitable for detection of proteins because of high resistance of the biomolecule. Therefore, there is disclosed a method for intermediating nano-particles to electrical conductivity at both ends of the nanogap electrodes (Haguet, V. et al. (2004) Appl. Phys. Lett. 84, 1213-1215). This method is useful in showing effective difference of electrical conductivity. Since this method is based on the general patterning process, it seems to be possible to realize integration of nanogap. However, since the production of nanogap by the general patterning method shows very low yield, it is substantially difficult to form an integrated structure and to provide a reliable result. Moreover, it is impossible to quantitatively analyze the concentration of a subject material.
The present inventors filed a method for preparing a nanogap electrode and a nanogap device prepared by using the method as Korean Patent Application No. 2006-0039528. The method for preparing a nanogap electrode includes growing a metal by reduction from metal ion in a solution on a surface having a metal pattern formed in a predetermined shape. The nanogap metal electrode prepared according to the method advantageously has a gap of 1 to 50 nm, which is difficult in the prior art.
Meanwhile, biosensors have problems of poor reproducibility and accurateness due to a very wide error range according to sensing level of a bio-material in detection of the bio-material. In order to solve these problems, Korean Laid-Open Patent NO. 1996-24350 discloses an interdigitated electrode type biosensor comprising at least two active indication electrodes for generating signals by independently response to a same material existing in a sample, inactive indication electrodes for correcting background signals, a reference electrode and counter electrode. By the interdigitated electrode type biosensor, it is possible to realize accurateness of measurement in only one measurement by providing an average value by processing multiple signals generated from the same subject material in a measurement. However, the disclosed multiple electrode type biosensor comprises a plurality of active indication electrodes having at least one biomaterial selected from enzymes, antigens, antibodies, nucleic acids and molecule receptors immobilized thereon, a reference electrode and a counter electrode is only for averagely measuring size of electrical signals. Also, it is a single electrode type based on the electrochemical method which can be used only in high concentration measurement. Therefore, it has a limit in quantitative analysis such as concentration measurement in a low concentration.
Therefore, in order to solve the above-described problems, it is an object of the present invention to provide a biosensor for detecting presence and concentration of various bio-materials such as genes and proteins by the electrical method, an interdigitated electrode sensor unit for forming the biosensor and a method for measuring concentration of a bio-material using the biosensor.
Also, it is another object of the present invention to provide a method for accurate, reliable, qualitative and quantitative measurement of a biomolecule such as antigens both in a low concentration range and in a high concentration range using the biosensor comprising a large area nanogap interdigitated electrode sensor unit manufactured by a simple and high yield production method. It is a further object of the present invention to provide a method for quantitative measurement of the concentration of a bio-material using correlation between concentration and signal probability via statistical measurement of integrated nanogap interdigitated electrode sensor units.
The present invention is directed to a biosensor for detecting presence and concentration of various bio-materials such as genes and proteins by the electrical method, an interdigitated electrode sensor unit for forming the biosensor and a method for measuring concentration of a bio-material using the biosensor.
The biosensor according to the present invention comprises a plurality of independently-operating interdigitated electrode sensor units integrated on a substrate, wherein each interdigitated electrode sensor unit comprise: first electrode and second electrode formed interdigitatedly and spaced from each other on the substrate; and a sensor-immobilized biomolecule receptor immobilized on the substrate exposed between the first electrode and the second electrode so that the first electrode is electrically connected to the second electrode upon binding to a biomolecule and specifically binding to the biomolecule, wherein the biomolecule is analyzed by the number of the interdigitated electrode sensor units electrically connected by the biomolecule captured by the sensor-immobilized biomolecule receptor.
Also, by the biosensor according to the present invention, the biomolecule in a sample solution is quantitatively analyzed by correlation between the concentration of the biomolecule in a sample solution and the ratio of the number of the electrically connected interdigitated electrode sensor unit to the total number of the interdigitated electrode sensor unit.
Particularly, the biosensor according to the present invention comprises interdigitated electrode sensor units provided in an n×m matrix. The interdigitated electrode sensor units are constructed to independently operate so that the interdigitated electrode sensor unit where the biomolecule binds thereto circulates current and does not circulate current where the biomolecule does not bind thereto. Therefore, the concentration of the biomolecule is determined by measuring the number of the current flowing interdigitated electrode sensor units. The number of the interdigitated electrode sensor units circulating current can be readily and automatically measured by a conventional electric circuit layout method.
The electrical conductivity increased by the binding to the biomolecule can be simply determined by measuring resistance of the interdigitated electrode sensor unit.
The voltage and current amount used in the measurement is not particularly limited. However, it is preferable to use a voltage of 100 mV or less, thereby excluding error factors such as electro-migration which can be induced by a strong voltage.
As an example, in the method for determining concentration of a subject material to be analyzed from statistical data of electrical conductivity showing the on-off state of the interdigitated electrode sensor units by integrating the sensor units with m ranks and n columns, the concentration of the subjection material existing in the sample (C) is given by a function of the rate of sensor unit showing the presence of the subject material with respect to the total number of the interdigitated electrode sensor units existing in the biosensor (Ntot), Pon=Non/Ntot=Non/(m×n), where Ntot is m×n and Non is the number of the unit sensors showing the presence of the subject material among the integrated sensor units. Here, when the number of the integrated interdigitated electrode sensor units is increased (Ntot is large), the relation between the probability and concentration has a higher reliability. Particularly, the reliability of the concentration measurement is increased when the sensor unit is constructed to have a high sensitivity and a small area to react with a subject material of a small number.
When the rate of the sensor units showing change in the electrical conductivity according to the concentration of the subject antigen existing in the sample increases, it means the increase in the concentration of the subject material. It is possible to determine the concentration of the sample from the rate of the interdigitated electrode sensor units showing change in the electrical conductivity.
The rate (Poff) of the interdigitated electrode sensor units showing the absence of the subject of the material (off sensor, not showing change in the electrical conductivity) is decreased when the concentration of the subject material is increased. Here, the micro-increment of Poff (dPoff) according to micro-increment of the concentration (dC) is proportional to micro-increment of the concentration (dC) and the instant rate of the off sensor (Poff).
dP
off
=−k·P
off
dC [k is a proportional constant]
From the above equation, the relation between the rate Pon of the sensors showing the presence of the subject material (on sensor) and the concentration can be expressed by the following equation.
P
on
=A−B exp(−kC)
[A and B refer constants reflecting non-ideal behavior of the sensor which may be caused by several factors such as imperfection of the device, immobilization efficiency of nano-particles and non-specific bonding]
The probability function may vary by various factors such as the structure and arrangement of the biosensor and the interdigitated electrode sensor unit according to the present invention and types of subject materials to be analyzed. Reliability of the concentration measurement can be affected by the size and integration of the device.
The interdigitated electrode biosensor according to the present invention comprises first electrode and second electrode formed to be spaced from and opposed to each other on the substrate, and a sensor-immobilized biomolecule receptor which is immobilized on the substrate exposed between the first electrode and the second electrode so that the first electrode is electrically connected to the second electrode upon binding to a biomolecule to be analyzed and can specifically bind to the biomolecule, in which the first electrode and the second electrode are formed by growing a metal reduced by reduction of metallic ion in a solution on a surface having a predetermined metal pattern formed thereon.
Also, the method for quantitatively analyzing a biomolecule according to the present invention comprises steps of: contacting the biosensor with a sample solution containing the biomolecule to be analyzed so that the biomolecule is captured by a sensor-immobilized biomolecule receptor immobilized on a substrate exposed between first electrode and second electrode of an independently-operating interdigitated electrode sensor unit; contacting the biomolecule bound to the sensor-immobilized biomolecule receptor with a particle-immobilized biomolecule receptor having electrically conductive particle immobilized thereon to bind to the biomolecule; measuring electrical conductivity of the biosensor; and calculating concentration of the biomolecule in the sample solution from the relation between the concentration and the rate of the sensors showing change of the electrical conductivity before and after contact with the solution. In another embodiment according the present invention the method comprises the steps of: mixing electrically conductive particle with a sample solution containing a biomolecule to be analyzed for immobilization on the subject biomolecule; contacting the biosensor with the subject biomolecule which have had electrically conductive particle immobilized thereon so that the subject biomolecule is captured by a sensor-immobilized biomolecule receptor immobilized on a substrate exposed between first electrode and second electrode of an independently-operating interdigitated electrode sensor unit; measuring electrical conductivity of the biosensor; and calculating concentration of the biomolecule in the sample solution from the relation between the concentration and the rate of the sensors showing change of the electrical conductivity before and after contact with the solution. In a further embodiment of the present invention, the method comprises the steps of: contacting the biosensor with a subject biomolecule to be analyzed so that the subject biomolecule is captured by a sensor-immobilized biomolecule receptor immobilized on a substrate exposed between first electrode and second electrode of an independently-operating interdigitated electrode sensor unit; contacting the biosensor with another biomolecule having electrically conductive particle immobilized thereon so that the electrically-conductive-particle-immobilized biomolecule is captured by the sensor-immobilized biomolecule receptor where the subject biomolecule has not been captured; measuring electrical conductivity of the biosensor; and calculating concentration of the biomolecule in the sample solution from the relation between the concentration and the rate of the sensors showing change of the electrical conductivity before and after contact with the sample solution. The another biomolecule having the electrically conductive particle immobilized thereon includes direct immobilization of the electrically conductive particle on the biomolecule or indirect immobilization of the electrically conductive particle on the biomolecule by the media of biomolecule receptor.
The biosensor according to the present invention includes both the construction, in which the subject biomolecule to be analyzed has electrically conductive particle immobilized thereon so that the first electrode and the second electrode are electrically connected by the electrically conductive particle when the biomolecule binds to the sensor-immobilized biomolecule receptor of the interdigitated electrode sensor unit and the construction, in which the subject biomolecule in the sample solution is captured by and specifically binds to the sensor-immobilized biomolecule receptor of the interdigitated electrode sensor unit and the captured biomolecule then binds to particle-immobilized biomolecule receptor comprising electrically conductive particle immobilized on biomolecule receptor so that the first electrode and the second electrode are electrically connected by the electrically conductive particle.
Here, in the region of the substrate exposed between the two electrodes, the sensor-immobilized biomolecule receptor which can specifically bind to the biomolecule is immobilized. When interdigitated electrodes are used, the area of the substrate exposed by the interdigitated electrode is increased and thus, it is possible to reduce time taken to measure concentration even though the concentration is low.
The sensor-immobilized biomolecule receptor and the particle-immobilized biomolecule receptor may be antibody and the biomolecule may be antigen. Also, as the sensor-immobilized biomolecule receptor, different types of antibodies may be immobilized on the substrate at a predetermined ratio. The antibody may be a material which can selectively react with any antigen to be detected, including genetic materials such as DNA as well as proteins which can undergo antigen-antibody interaction.
When an antibody is used as the sensor-immobilized biomolecule receptor, a monoclonal antibody is preferably used for selectivity of antigen. The reaction conditions such as concentration and time for immobilization on the substrate may follow the known method.
The electrically conductive particle which binds to the biomolecule or the particle-immobilized biomolecule receptor to form a bridge between the first electrode and the second electrode so that the first electrode and the second electrode are electrically connected has a size properly selected according to the gap between the interdigitated electrodes. However, it has preferably a size in the range of 0.5 nm to 1 μm and more preferably a size in the range of 1 nm to 100 μm, considering the nanogap space of the interdigitated electrodes.
The selection of the nano-particle for the particle-immobilized biomolecule receptor is not particularly limited, as long as it has electrical conductivity regardless of properties of semiconductors and metals. However, it is preferably metal such as gold nano-particles. The size of the nano-particle is not particularly limited but is preferably equal to or smaller than the gap space of the nanogap device, more preferably a bit smaller than the gap space.
When an antibody is selected as the particle-immobilized biomolecule receptor, it is preferably polyclonal antibody. The reaction conditions such as concentration and time for binding the electrically conductive particle may follow the known methods.
Meanwhile, the sensor-immobilized biomolecule receptor and the substrate may be fixed by a linker molecule layer such as self assembled monolayer (SAM). Though the selection of the SAM molecule may vary according to circumstances, it is preferably to select a molecule having a functional group such as —CHO, —COOH and the like for bonding to amine group in antibody in most cases.
The substrate having the interdigitated electrode and the sensor-immobilized biomolecule receptor placed thereon may be anyone that can have the biomolecule receptor immobilized and has electrically insulating property. The electrically insulating material is preferably oxides, more preferably silicon oxides.
Preferably, the first electrode and the second electrode have a height greater than the height of the biomolecule receptor immobilized on the substrate considering that the immobilized electrically conductive particle adheres closely between the first electrode and the second electrode to form a bridge for electrical connection. However, it is also possible for the first electrode and the second electrode to have a height smaller than the biomolecule receptor.
The first electrode and the second electrode may be provided with a protein adsorption blocking layer on the surface for preventing adsorption of protein by non-specific binding. The adsorption blocking layer is preferably formed using hydrophilic molecules such as glycol based compounds.
The interdigitated electrode according to the present invention may be patterned by a method selected from lithography, printing and contact printing. Here, the gap between the electrodes may be in the range of 0.5 nm to 1 μm. However, considering the size of the biomolecule and bridge formation of electrically conductive particles between the first electrode and the second electrode, the gap between the first electrode and the second electrode is preferably 1 nm to 100 nm. The electrode can be prepared following the method for preparing nanogap electrode described in Korea Patent Application No. 2006-0039528, filed by the present application.
Thus, the electrode having nanogap according to the present invention is prepared by forming an interdigitated metal pattern by lithography, printing and contact printing and growing a metal reduced by reduction of metallic ion in a solution on a surface having an interdigitated metal pattern formed thereon. More particularly, the electrode is prepared by dipping the substrate having an interdigitated metal pattern formed thereon in a solution containing metal ion and adding a reducing agent to the solution to grow the metal reduced from the metal ion in the solution on the surface with the metal pattern.
Preferably, the metal pattern is selected from Au, Ag, Al, Cu and Pt, considering electrical conductivity and the reducing agent is selected from hydroxyl amine (H2NOH), ascorbic acid, glucose, Rochelle salt (potassium sodium tartrate), formaldehyde and mixtures thereof.
Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, a preferred embodiment of the invention will be explained in detail with reference to the appended drawings. However, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
A silicon substrate having an oxide layer thereon was used. An interdigitated gold pattern in the form of a large area IDE (interdigitated electrode) having a gap of about 70 nm˜200 nm was formed by photo and e-beam lithography and then subjected to the gap narrowing process by chemical reduction to prepare 3 biosensors, each biosensor comprising 8 interdigitated electrodes having a gap distance of about 50 nm.
The gap narrowing by chemical reduction was performed by dipping the substrate having the pattern formed thereon 11 mL of 36 μM HAuCl4 aqueous solution, adding 1 mL of 640 μM NH2OH aqueous solution thereto and leaving the solution for 2 minutes at 27° C. for reaction. The above-described procedures were repeated 4 times to grow gold on the interdigitated gold pattern surface. Thus, a nanogap device having interdigitated electrode sensor units integrated thereon was prepared.
Next, a linker molecule layer was formed in the nanogap region where the substrate was exposed between the interdigitated electrodes of the interdigitated electrode sensor unit and antibody which selectively binds to antigen was introduced to form an active surface. The used antibody was anti-PSA which was an antibody which selectively binds to PSA (prostate specific antigen), a marker of prostate cancer.
Firstly, in order to fix the antibody, a molecule layer was formed using the linker molecule in the nanogap region. Since the nanogap region (silicon oxide layer) was formed a material different from the interdigitated electrode part (gold), it is possible to introduce a selective molecule layer. In order to induce selective binding of the gold nano-particle in the nanogap region, the previously prepared nanogap device was dipped in 1 mM solution of 2,5,8,11-tetraoxadocosane-22-thiol for 10 minutes to form ethyleneglycol (EG) group on the gold electrode surface.
Next, antibody was selectively attached to the SiO2 surface existing in the nanogap region. The surface was activated by O2 plasma treatment, reacted with APTES (aminopropyltriethoxysilane) to form a molecule layer having—NH2 terminal and treated with 1% glutaaldehyde buffer solution (0.1M sodium phosphate buffer, pH=7.0) for 30 minutes to bind aldehyde group to the molecule layer formed by using APTES and to form a surface having aldehyde group, which had not participated in the binding to the molecule layer, exposed thereon.
When the aldehyde surface formed on the nanogap surface was dipped in a buffer solution (10 mM PBS buffer, pH=7.4) of monoclonal antibody having a concentration of about 50 mg/mL, the —NH2 group existing in lysine peptide of the monoclonal antibody was effectively reacted with the aldehyde group exposed on the surface, whereby the antibody was fixed on the surface. Then, the unreacted —CHO group was saturated by treatment with 0.1M glycine buffer (pH=8.0) for 30 minutes.
The biosensor thus-obtained was measured for I-V properties in a low voltage range of −100 mV to 100 mV.
The biosensor was contacted with a solution containing PSA to be measured and control solution not containing PSA for about 1 hour and reacted with solution of 10 to 40 nm gold nano-particles having polyclonal anti-PSA thereon at a ratio of 1 to 10 antibodies per nano-particle. Then, in order to minimize probability of error by non-specific adsorption, washing process by buffer solution or de-ionized water was performed. Finally, the nanogap biosensor and the array thereof were dried using nitrogen and the electrical conductivity was measured again. The result of this electrical conductivity measurement was compared with the result of the previous electrical conductivity measurement before the treatment with the subject sample to confirm the change of electrical conductivity. The voltage intensity was set in a range of ˜100 mV˜100 mV to minimize possible error in the measurement such as deformation of antibody and induction of electro migration caused by high voltage.
For quantitative measurement of concentration of a subject sample, a reference curve for the relation between the concentration and the rate of sensors showing electrical conductivity change among the integrated devices was obtained prior to the determination of the concentration of an un-known sample. The relation between concentration and the rate of ‘on’ sensor needed proportional constant. In a dynamic range of every sensor array, the proportional constant was determined for use in the measurement of that region. It was expected that the dynamic region of the sensor array would vary according to gap-separation and configuration of the nanogap, size of nano-particles, type of antigen-antibody interaction and the surface immobilization method. The reliability of the concentration measurement was raised as the sensitivity of the unit sensor is high and the size of the region is small and as the units are highly integrated.
Now, the preferred embodiment of the present invention will be described in detail with reference to the attached drawings. The following examples are provided as an illustration to deliver the spirit of the present invention to those having ordinary knowledge in the art. Therefore, the present invention is not limited to the examples described below and may be embodied to another form. Also, in the drawings, length and thickness of some layers and regions may be magnified for convenience. Like reference numerals refer to the like devices throughout the specification.
Referring to
Here, the substrate area exposed between the two electrodes is an area where the sensor-immobilized biomolecule receptor which can specifically bind to the biomolecule is immobilized. When this area is increased, it is possible to reduce the time taken to measure relatively low concentration sample. The method for forming the nanogap device having such structure includes a chemical, electrochemical or physical gap narrowing step to raise yield and reduce the unit cost of production, though it may be formed by general patterning methods. As the method for increasing the area of the active surface, methods for highly integrating nanogap sensors may be selected.
The particle-immobilized biomolecule receptor having electrically conductive particles immobilized in the gap between interdigitated electrodes may induce change in electrical conductivity between two electrodes.
P
on
=A−B exp(kC)
[A and B refer constants reflecting non-ideal behavior of the sensor which may be caused by several factors such as imperfection of the device, immobilization efficiency of nano-particles and non-specific bonding]
The biosensor according to the present invention is contacted with a sample solution containing a subject biomolecule (a). The biomolecule is captured by sensor-immobilized biomolecule receptors immobilized on a substrate (b). The biosensor is contacted with another biomolecule having electrically conductive particles fixed thereon. The electrically-conductive-particle-fixed biomolecule is captured by sensor-immobilized biomolecule receptor where the subject biomolecule has not been captured. The first electrode and the second electrode are electrically connected by the electrically conductive particle (c). Therefore, the biomolecule in the sample solution can be analyzed by measuring the number of electrically connected interdigitated electrode sensor units or the number of non-connected interdigitated electrode sensor units. The method shown in
The biosensor according to the present invention can contribute to various fields such as development of material detection technique based on molecular recognition, kit for early diagnosis of diseases, environment monitoring systems, public health and hygiene supervision apparatus, sensor systems for anti-terror and against chemical, biological and radiological warfare, and development of sensor kits. The present invention can provide the highest performance by combination with technique for pre-treatment of reagent such as blood and optimized surface control technique, technique for complex treatment of signals and be conveniently manufactured in a large scale.
Also, according to the present invention, it is possible to detect a small amount of biomolecule in high concentration and low concentration ranges by producing a large area nanogap device by reducing the gap space of the nanogap device and increasing the surface area of the nanogap to shorten the detection time while maintaining detection sensitivity of the device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0065828 | Jul 2006 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2006/003357 | 8/25/2006 | WO | 00 | 2/27/2008 |
