WO2025012806A1

WO2025012806A1 - Nanoparticle monolayer-field-effect based molecular sensors

Info

Publication number: WO2025012806A1
Application number: PCT/IB2024/056663
Authority: WO
Inventors: Moh’d REZEQ; Yawar ABBAS; Firdous A. DEADER; Ahsan Ul Haq QURASHI; Mahmoud Al-Qutayri; Vincent Chan
Original assignee: Khalifa University of Science, Technology and Research (KUSTAR)
Current assignee: Khalifa University of Science, Technology and Research (KUSTAR)
Priority date: 2023-07-11
Filing date: 2024-07-09
Publication date: 2025-01-16
Anticipated expiration: 2026-01-11

Abstract

A molecular detection device can be formed with a monolayer of nanoparticles. For example, a system can include the molecular detection device. The molecular detection device can include a semiconductor substrate. Additionally, the molecular detection device can include two conducting electrodes, each formed on a surface of the semiconductor substrate. The molecular detection device can also include a monolayer of nanoparticles formed between the two conducting plates. A thin oxide layer can be formed between the monolayer of nanoparticles and the surface of the substrate.

Description

NANOPARTICLE MONOLAYER-FIELD-EFFECT BASED MOLECULAR SENSORS

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63/513,085 filed July 11, 2023, the entire contents of which are hereby incorporated for all purposes in their entirety.

BACKGROUND OF THE INVENTION

[0002] Viruses can cause human diseases, which can rapidly spread from person to person with devastating consequences, such as pandemics like COVID-19. Fast and early detection can help prevent an outbreak and hence save lives. Moreover, methods that can allow a rapid and sensitive detection and identification of abnormalities in biological samples at protein and DNA levels could have applications for both communicable and non-communicable diseases. Rapid and sensitive detection may be possible through a development of biosensors that can quickly and accurately diagnose diseases and identify different types of viruses or proteins, by producing quantitative and reliable signals.

BRIEF SUMMARY OF THE INVENTION

[0003] Field effect based molecular sensors can be formed with a monolayer of nanoparticles. For example, a system described herein can include a device for detecting molecules. The device can include a semiconductor substrate. Additionally, the device can include two conducting electrodes formed on a surface of the semiconductor substrate. The device can also include a monolayer of nanoparticles. The monolayer of nanoparticles can be formed between the two conducting electrodes.

[0004] In another example, a method for forming a monolayer of nanoparticles described herein can include preparing a solution containing the nanoparticles. The method can also include drop casting the solution onto a substrate. Additionally, the method can include exposing the substrate to an electric field for a duration of time. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a schematic of a molecular detection device that incorporates a monolayer of nanoparticles according to some aspects of the present disclosure.

[0006] FIG. 2A is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of uncharged nanoparticles according to some aspects of the present disclosure.

[0007] FIG. 2B is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of charged nanoparticles according to some aspects of the present disclosure.

[0008] FIG. 3A is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device under forward (positive) bias that incorporates a monolayer of charged nanoparticles according to some aspects of the present disclosure.

[0009] FIG. 3B is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device under reverse (negative) bias that incorporates a monolayer of charged nanoparticles according to some aspects of the present disclosure.

[0010] FIG. 4A is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of charged nanoparticles bound to positively charged molecules under both unbiased and forward biased conditions according to some aspects of the present disclosure.

[0011] FIG. 4B is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of charged nanoparticles bound to negatively charged molecules under both unbiased and forward biased conditions according to some aspects of the present disclosure.

[0012] FIG. 5 is a graph of current versus voltage (I-V) curves for a molecular detection device under different modes of operation according to some aspects of the present disclosure.

[0013] FIG. 6 is a graph of I-V curves for a molecular detection device measured at different times after exposure to a high humidity environment according to some aspects of the present disclosure. [0014] FIG. 7 is a flowchart of an example of a process for fabricating a monolayer of nanoparticles distributed uniformly on a semiconductor surface according to some aspects of the present disclosure.

[0015] FIG. 8 is a diagram of a semiconductor substrate with a drop cast nanoparticle solution coating exposed to an electric field of a parallel plate capacitor according to some aspects of the present disclosure.

[0016] FIG. 9 is a scanning electron microscope (SEM) image of a monolayer of nanoparticles formed on a semiconductor substrate according to some aspects of the present application.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Nanoparticles such as gold nanoparticles with well-defined shapes can potentially detect chemical and biological molecules with ultraprecise accuracy, due to unique properties that can be different from bulk form. Charged nanoparticles can be particularly good candidate components of molecular detectors due to an ability to load protein molecules using electrostatic enhanced binding. Methods and systems for molecular device sensing can be based on unique characteristics of nanoparticles on semiconductor substrates, such as gold nanoparticles on silicon (Si) substrates. A presence of the nanoparticles on the semiconductor surface can result in a significant enhancement of an electric field at a nano metalsemiconductor (M-S) interface, which can enable extremely sensitive and fast biosensing. Nanoparticles, such as gold nanoparticles, can be charged, either directly from an applied voltage difference between a semiconductor substrate and top electrodes on the substrate or by treating the nanoparticles in a citrate solution. Charging the nanoparticles can enhance an attachment of biological molecules and other molecules to nanoparticle surfaces.

[0018] Charge on protein molecules attached to the nanoparticles can result in modifying the electric field at the nano M-S interface and affect an associated current. Since each protein can possess a specific charge and binding affinity, based on an amino acid of the protein, the sensed current can be a direct function of protein structure. Thus, the sensed current can act as a ‘fingerprint’ and help to detect and identify protein molecules bound to the nanoparticles. The systems and methods described herein can provide a very fast and accurate diagnosing current signal due to a sensitivity of the interface electric field enhanced by surface electric charge. A biosensing or molecular sensing device based on charged nanoparticles can also detect polarized molecules, like water molecules. [0019] Illustrative examples are given to introduce the reader to the general subject matter discussed herein and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative aspects, but, like the illustrative aspects, should not be used to limit the present disclosure.

[0020] FIG. 1 is a schematic of a molecular detection device 300 that incorporates a monolayer of nanoparticles according to some aspects of the present disclosure. The molecular detection device 300 can include a semiconductor substrate, two top metal electrodes, and the monolayer of nanoparticles. The two top metal electrodes can be fabricated using known microfabrication or nanofabrication techniques. The fabrication techniques can involve photolithography methods, metal sputtering, chemical vapor deposition (CVD) methods, or some combination thereof. The top metal electrodes can be fabricated before depositing the monolayer of nanoparticles. The two top metal electrodes can be separated by a separation length that can include any length up to a width of the semiconductor substrate. For example, the separation length can be 100 micrometers. The nanoparticles can be arranged uniformly across a top surface of the semiconductor substrate between the two top metal electrodes. The monolayer of nanoparticles can include a width that is perpendicular to the separation length between the two top metal electrodes. Example values of the width can include 10-50 micrometers. The semiconductor substrate can include n-type or p-type silicon with a thin silicon oxide layer. As an example, the silicon substrate can include a resistivity of 0.1 — 10 fl ■ cm. The nanoparticles can be metal or semiconductor nanoparticles and can be charged. A layer of absorbed citrate on a surface of the nanoparticles can keep the nanoparticles electrically isolated from each other. The nanoparticles can include negatively charged gold nanoparticles.

[0021] The two top metal electrodes can include a first top electrode or ground electrode that can be connected to ground and a second top electrode or biased electrode that can be connected to a direct voltage source. When a positive DC voltage is supplied to the biased electrode (relative to ground), a current can flow from the ground electrode, through the semiconductor surface, to the second top electrode. A conventional current (described by a direction that positive charge carriers flow) would flow in an opposite direction, from the biased electrode to the ground electrode. The current can be comprised primarily of electrons, which are majority charge carriers in n-type Si. The electrons can tunnel through the silicon oxide layer but may not flow through the monolayer of electrically isolated nanoparticles. The current can be referred to as a detection current.

[0022] Molecules can bind to the charged nanoparticles and excess charge or a charge distribution on the molecules can modify an electric field and a surface conductivity at the semiconductor interface. Thus, the detection current flowing at a particular applied voltage can be modified by molecules attached to the charged nanoparticles. The type of molecules attached to the charged nanoparticles can affect the detection current. The molecules can include protein molecules, biological molecules, polar molecules, etc. A value of the detection current associated with the particular applied voltage can help determine if molecules are bound to the charged nanoparticles and can also determine a charge configuration for the attached molecules (i.e., positively charged, negatively charged, or polar). The value of the detection current can also identify a type of molecule attached to the nanoparticles, since different molecules can modify the electric field and surface conductivity differently.

[0023] FIG. 2 A is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of uncharged nanoparticles according to some aspects of the present disclosure. Examples of the semiconductor layer can include n-type silicon. A dashed line in the energy band diagram can represent a Fermi energy level for the semiconductor. A solid line below the Fermi energy level in the energy band diagram can represent a valence band. A solid line above the Fermi energy level can represent a conduction band for the semiconductor.

[0024] When the semiconductor is an n-type semiconductor (i.e., a semiconductor with more electron charge carriers than hole charge carriers), the Fermi level can be closer to the conduction band than to the valence band. The molecular detection device can include a first top electrode, a second top electrode, and the monolayer of nanoparticles uniformly distributed on the semiconductor surface between the first and second top electrodes. When the nanoparticles are uncharged the bands can be relatively flat.

[0025] FIG. 2B is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of charged nanoparticles according to some aspects of the present disclosure. Examples of the semiconductor layer can include n-type silicon. When the semiconductor is an n-type semiconductor (i.e., a semiconductor with more electron charge carriers than hole charge carriers), the Fermi level can be closer to the conduction band than to the valence band. [0026] The molecular detection device can include a first top electrode, a second top electrode, and the monolayer of nanoparticles uniformly distributed on the semiconductor surface between the first and second top electrodes. The nanoparticles can be charged nanoparticles. The nanoparticles can become charged either by charge injection or in solution when the nanoparticles are formed. When the nanoparticles possess a net negative charge, majority carrier electrons in the n-type silicon can be repelled from the surface. Directly underneath the monolayer of negatively charged nanoparticles, the conduction band can be depressed. Thus, the conduction band along the surface beneath the nanoparticles can be lower than parts of the conduction band under the first and second top electrodes, forming an electron tunnel path across the silicon surface, under the monolayer of nanoparticles.

[0027] FIG. 3A is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device under forward (positive) bias that incorporates a monolayer of charged nanoparticles according to some aspects of the present disclosure. Examples of the semiconductor layer can include n-type silicon. The molecular detection device can include a first top electrode or ground electrode, a second top electrode or biased electrode, and the monolayer of nanoparticles uniformly distributed on the semiconductor surface between the first and second top electrodes. The nanoparticles can be negatively charged. The charged nanoparticles can be electrically isolated so that current only flows through the silicon surface. For example, each nanoparticle can be electrically isolated with a coated layer of absorbed citrate.

[0028] When the biased electrode becomes positively biased (i.e., biased at a higher voltage than the ground electrode), a conduction band of the silicon at an interface with the biased electrode can be pushed down and a negative gradient can form in the band diagram, from left to right in FIG. 3 A. Further increase in the positive applied voltage can tilt the conduction band and increase the negative gradient. Since the nanoparticles are electrically isolated from each other, current flow through the nanoparticle monolayer may not occur.

[0029] The negative gradient can promote a current or flow of majority carrier electrons along the silicon surface from the ground electrode to the biased electrode (or a conventional current in the opposite direction). Electrons in the ground electrode (and electrons within the nanoparticles) can tunnel through the oxide layer, flow along the silicon surface, and tunnel back up through the oxide layer into the biased electrode. The current can be referred to as a detection current. The detection current can increase with an increase in the positive applied voltage. When the biased electrode is positively biased, the molecular detection device can be considered forward biased since the detection current can be produced under this condition.

[0030] FIG. 3B is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device under reverse (negative) bias that incorporates a monolayer of charged nanoparticles according to some aspects of the present disclosure. Examples of the semiconductor layer can include n-type silicon. The molecular detection device can include a first top electrode or ground electrode, a second top electrode or biased electrode, and the monolayer of nanoparticles uniformly distributed on the semiconductor surface between the first and second top electrodes. The nanoparticles can be negatively charged. The charged nanoparticles can be electrically isolated so that if current flows, current only flows through the silicon surface. For example, each nanoparticle can be electrically isolated with a coated layer of absorbed citrate.

[0031] When the biased electrode becomes negatively biased (i.e., biased at a lower voltage than the ground electrode), a positive gradient can form in the band diagram, from left to right in FIG. 3B. The positive gradient can represent a potential barrier to majority carrier electrons along the silicon surface and a current or flow of majority carrier electrons along the silicon surface from the ground electrode to the biased electrode can be absent or negligible. When negatively biased, the biased electrode can be considered reverse biased since the detection current can be absent or negligible under this condition.

[0032] FIG. 4A is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of charged nanoparticles bound to positively charged molecules under both unbiased and forward biased conditions according to some aspects of the present disclosure. Examples of the semiconductor layer can include n-type silicon. The molecular detection device can include a first top electrode or ground electrode, a second top electrode or biased electrode, and the monolayer of nanoparticles uniformly distributed on the semiconductor surface between the first and second top electrodes. The nanoparticles can be negatively charged.

[0033] When molecules with net positive charge bind to negatively charged nanoparticles, the negative charge on the nanoparticles can be redistributed away from the silicon surface and an electric field at the silicon surface can be reduced compared to when the positively charged molecules are not present. In an unbiased (black lines) condition, a conduction band of the n- type silicon can still be depressed, but the conduction band can be less depressed than when the positively charged molecules are not present.

[0034] In the forward biased (red lines) condition (i.e., when the biased electrode is at a higher voltage than the ground electrode), a negative gradient can form in the energy band diagram for the silicon, but the gradient can be less pronounced than when the positively charged molecules are not present. Thus, for a particular applied positive bias, a detection current can be reduced when positively charged molecules are present. The detection current can also be reduced when polar charged molecules are present, since polar molecules can also redistribute negative charges on the nanoparticles away from the silicon surface, reducing the electric field at the silicon surface. Polar molecules may be less effective at reducing the electric field than positively charged molecules, so the reduction in the detection current at a particular positive bias may not be as drastic. The silicon can appear to have an increased effective resistance when positively charged or polar molecules are bound to the nanoparticles.

[0035] FIG. 4B is a schematic for a side view of an energy band diagram of a semiconductor layer of a molecular detection device that incorporates a monolayer of charged nanoparticles bound to negatively charged molecules under both unbiased and forward biased conditions according to some aspects of the present disclosure. Examples of the semiconductor layer can include n-type silicon. The molecular detection device can include a first top electrode or ground electrode, a second top electrode or biased electrode, and the monolayer of nanoparticles uniformly distributed on the semiconductor surface between the first and second top electrodes. The nanoparticles can be negatively charged.

[0036] When molecules with net negative charge bind to negatively charged nanoparticles, additional negative charge on the nanoparticles can be redistributed near the silicon surface and an electric field at the silicon surface can be enhanced compared to when the negatively charged molecules are not present. In an unbiased (black lines) condition, a conduction band of the n- type silicon can still be depressed, but the conduction band can be more depressed than when the negatively charged molecules are not present.

[0037] In the forward biased (red lines) condition (i.e., when the biased electrode is at a higher voltage than the ground electrode), a negative gradient can form in the energy band diagram for the silicon, but the gradient can be even more pronounced than when the negatively charged molecules are not present. Thus, for a particular applied positive bias, a detection current can be increased when negatively charged molecules are present. The more negatively charged the molecules, the higher the increase in detection current. The silicon can appear to have a decreased effective resistance when negatively charged molecules are bound to the nanoparticles.

[0038] FIG. 5 is a graph 700 of current versus voltage (I-V) curves for a molecular detection device under different modes of operation according to some aspects of the present disclosure. The molecular detection device can be molecular detection device 300 described in FIG. 1. The monolayer of nanoparticles can include negatively charged gold nanoparticles that are electrically isolated with a coated layer of absorbed citrate. The molecular detection device can include a first top electrode or ground electrode and a second top electrode or biased electrode. A voltage applied to the device can be applied to the biased electrode. The molecular device can include a semiconductor substrate, such as an n-type silicon substrate (n-Si).

[0039] The graph 700 includes three I-V curves, one for each of three different modes of operation associated with the molecular detection device. A first I-V curve 702 can be associated with the molecular detection device when no molecules are attached to the gold nanoparticles. A second I-V curve 704 can be associated with the molecular detection device when negatively charged molecules are bound to the gold nanoparticles. A third I-V curve 706 can be associated with the molecular detection device when positively charged molecules or polar molecules are bound to the gold nanoparticles.

[0040] Looking at the graph from left to right (i.e., from negative applied bias to positive applied bias), each of the I-V curves transition from a reverse bias state with zero or negligible detection current to a forward bias state with a measurable and rapidly increasing detection current. The detection current under forward bias can be due to majority carriers of the n-Si substrate flowing from the ground electrode to the biased electrode. A transition between the two states for an I-V curve can occur at a threshold value called a threshold voltage. The three I-V curves: curve 702, curve 704, and curve 706 each have different threshold voltages.

[0041] Curve 704, which can be associated with negatively charged molecules attached to the gold nanoparticles, has the lowest threshold voltage. Curve 706, which can be associated with either positively charged or polar molecules attached to the gold nanoparticles, has the largest threshold voltage. Curve 702, which can be associated with just the negatively charged gold nanoparticles unbound to any molecules, has a threshold voltage in between that of curve 704 and curve 702. The detection currents can occur due to a flow of majority carrier electrons along the n-Si surface. [0042] Differences between the three curves can be observed along the vertical dashed line associated with a particular voltage referred to as V_sense . At that particular voltage, the three I- V curves can each have different detection currents. As noted above, a presence of negatively charged molecules attached to the nanoparticles can effectively reduce resistance of silicon in terms of the detection current. A presence of positively charged or polar molecules attached to the nanoparticles can effectively increase the resistance of the silicon. Therefore, Curve 704 can have the highest current at V_sense, Curve 706 can have a negligible current at that particular voltage, and Curve 702 can have a detection current in between the other two values. In some examples, the molecular detection device can detect molecules by maintaining a constant applied bias of V_sense and monitoring the detection current between the biased electrode and the ground electrode. Determining the detection current relative to the detection current for unbound gold particles can indicate a presence of molecules and a charge configuration of the molecules. The value of the detection current may indicate a specific molecular species.

[0043] Although FIG. 5 shows I-V characteristics for a molecular detection device including an n-type substrate, the molecular detection device can work with a p-type semiconductor substrate as well. The I-V characteristics for the device with a p-type substrate would look similar to the I-V characteristics of graph 700, but the device can be forward biased for negative applied voltages and threshold voltages can be negative instead of positive. Similar to the n- type detection device, different negative threshold values for the p-type detection device can be associated with a presence of attached molecules and charge configuration of the attached molecules.

[0044] FIG. 6 is a graph 800 of I-V curves for a molecular detection device measured at different times after exposure to a high humidity environment according to some aspects of the present disclosure. The molecular detection device can be molecular detection device 300 described in FIG. 1. The monolayer of nanoparticles can include negatively charged gold nanoparticles that are electrically isolated with a coated layer of absorbed citrate. The molecular detection device can include a first top electrode or ground electrode and a second top electrode or biased electrode. A voltage applied to the device can be applied to the biased electrode. The molecular device can include a semiconductor substrate, such as an n-type silicon substrate (n-Si).

[0045] The graph 800 includes six I-V curves, curve 802, curve 804, curve 806, curve 808, curve 810, and curve 812. The curve 802 was measured prior to an exposure to the high humidity environment and can depict an I-V curve for the device when no or very few molecules are attached to nanoparticles in a monolayer of nanoparticles in the molecular detection device. The other five I-V curves, which can be referred to as humidity I-V curves, were measured at various times after exposure to the high humidity environment. For example, humidity curve 804 was measured 5 seconds after the exposure to the humid environment. Humidity curve 812 was measured 40 seconds after the exposure and very closely resembles curve 802. The high-humidity environment can be characterized by a relative humidity amount of 90% and can be formed using standard saturated salt solutions such as NaCl, K2SO4, KC1, NaBr, NaOH, etc.

[0046] Humidity curve 804 has the largest threshold voltage (i.e., over +5.0 Volts) out of all of the I-V curves in graph 800. The large threshold voltage may be attributed to an increased effective resistance (as described above) of the semiconductor layer due to the presence of polar molecules attached to the negatively charged nanoparticles. As time passes after the exposure to humidity from 5 to 40 seconds, the I-V curves drift towards the left of the graph 800. As the curves drift, the threshold voltage decreases. The drift suggests that the water molecules can gradually detach from the nanoparticles. After some time (i.e., forty seconds), the humidity curve can no longer be distinguished from the I-V curve with unbound nanoparticles. The I-V curve data suggest that the molecular detection device can recover easily and can be repurposed for detection of a different molecule type in less than 40 seconds.

[0047] FIG. 7 is a flowchart of an example of a process 900 for fabricating a monolayer of nanoparticles distributed uniformly on a semiconductor surface according to some aspects of the present disclosure. Operations of processes may be performed by software, firmware, hardware, or a combination thereof. The operations of the process 900 start at block 910.

[0048] At block 910, the process 900 involves preparing a solution containing the nanoparticles. The nanoparticles can be semiconductor or metal nanoparticles. From the preparation solution, the nanoparticles can become electrically charged. Examples of charged nanoparticles formed in solution can include negatively charged gold nanoparticles. A low , nanopar Lie les . . . . . . . . . . . . concentration (e.g., 10 - — - ) solution with gold nanoparticles can be purchased

commercially. The commercially purchased nanoparticles can be dispersed in a citrate solution so the nanoparticles will be electrically isolated from one another after absorbing a citrate surface layer. The concentration of nanoparticles can be increased (e.g., 10^{13 nan}° ^^tlcles centrifuging at 1000 rpms. [0049] At block 920, the process 900 involves drop casting the solution with the nanoparticles on a semiconductor substrate. The semiconductor substrate can be n-type silicon with a thin (i.e., less than 10 nm thick) silicon oxide layer. Drop casting can involve coating the semiconductor surface with a single drop or multiple drops of the solution. An amount of drops can depend on a surface area of the substrate.

[0050] At block 930, the process involves exposing the substrate with the nanoparticle kV solution coating to a large electric field, (e.g., 0.5 — 3.0 — ). FIG. 8 is a diagram of a semiconductor substrate with a drop cast nanoparticle solution coating exposed to an electric field of a parallel plate capacitor according to some aspects of the present application. After drop casting the solution with nanoparticles on the semiconductor surface, the substrate can be placed between the plates of a parallel plate capacitor.

[0051] The parallel plates depicted in FIG. 8 are arranged vertically, but the plates can be arranged horizontally as well, or can have some combination of horizontal and vertical components. The substrate can be placed near a center of a bottom plate of the parallel plate capacitor. By placing the substrate near the center of one of the parallel plates, the substrate can be exposed to a nearly uniform electric field. A potential difference (e.g., 0.5 — 3.0 kV) can be applied between the parallel plates and the substrate and nanoparticles can be exposed to a large electric field. Examples of materials for the parallel plates can include copper. For example, the top plate can be electrically ground and the bottom plate can be connected to a power supply, function generator, or any suitable voltage source. The substrate can be exposed to the large electric field for a duration of time denoted the field exposure time. For example, the field exposure time can be two hours.

[0052] By exposing the nanoparticle solution to a large electric field, a monolayer of nanoparticles can form on the semiconductor surface. FIG. 9 is an SEM image 1100 of a monolayer of nanoparticles formed on a semiconductor substrate according to some aspects of the present application. The monolayer can be uniformly distributed across the semiconductor surface. A predetermined degree of uniformity of a distribution of nanoparticles in the monolayer can be realized by an optimization of process parameters. The process parameters can include solution concentration, magnitude of the applied electric field, field exposure time, etc. The image 1100 includes a scale bar 1102 that has a length of 100 nanometers.

[0053] In the preceding description, various embodiments have been described. For purposes of explanation, specific configurations and details have been set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the embodiments may be practiced without the specific details. Furthermore, well-known features may have been omitted or simplified in order not to obscure the embodiment being described.

[0054] Some embodiments of the present disclosure include a system including one or more data processors. In some embodiments, the system includes a non-transitory computer readable storage medium containing instructions which, when executed on the one or more data processors, cause the one or more data processors to perform part or all of one or more methods and/or part or all of one or more processes and workflows disclosed herein. Some embodiments of the present disclosure include a computer-program product tangibly embodied in a non- transitory machine-readable storage medium, including instructions configured to cause one or more data processors to perform part or all of one or more methods and/or part or all of one or more processes disclosed herein.

[0055] The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention as claimed has been specifically disclosed by embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

[0056] The description provides preferred exemplary embodiments only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing various embodiments. It is understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims.

[0057] Specific details are given in the description to provide a thorough understanding of the embodiments. However, it will be understood that the embodiments may be practiced without these specific details. For example, specific computational models, systems, networks, processes, and other components may be shown as components in block diagram form in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: a device configured to detect molecules, the device comprising: a semiconductor substrate; two conducting electrodes formed on a surface of the semiconductor substrate; and a monolayer of nanoparticles formed between the two conducting electrodes.

2. The system of claim 1, wherein the nanoparticles are electrically charged.

3. The system of claim 2, wherein the nanoparticles are electrically charged with excess negative charge.

4. The system of claim 1, wherein each nanoparticle in the monolayer of nanoparticles is electrically isolated from each other.

5. The system of claim 4, wherein each nanoparticle is electrically isolated from each other by a layer of absorbed citrate on a surface of each nanoparticle.

6. The system of claim 1, wherein the semiconductor substrate comprises a silicon substrate.

7. The system of claim 6, wherein the silicon substrate comprises at least one of an n-type or a p-type silicon substrate.

8. The system of claim 6, wherein the silicon substrate comprises a silicon oxide layer.

9. The system of claim 1, wherein the device is configured to detect electrically charged or polar molecules.

10. The system of claim 1, wherein the two conducting electrodes comprise: a ground electrode configured to be connected to ground; and a biased electrode configured to receive a voltage relative to the ground electrode from a voltage source.

11. The system of claim 10, wherein the semiconductor substrate is configured to produce a detection current when the voltage exceeds a threshold value.

12. The system of claim 11, wherein an effective resistance of the semiconductor substrate to the detection current decreases when at least one negatively charged molecule is bound to a nanoparticle in the monolayer of nanoparticles.

13. The system of claim 11, wherein an effective resistance of the semiconductor substrate to the detection current increases when at least one positive charged molecule or at least one polar molecule is bound to a nanoparticle in the monolayer of nanoparticles.

14. The system of claim 1, wherein the nanoparticles are gold nanoparticles.

15. A method for forming a monolayer of nanoparticles comprising : preparing a solution containing the nanoparticles; drop casting the solution onto a substrate; and exposing the substrate to an electric field for a duration of time.

16. The method of claim 15, wherein the solution comprises a comprises sodium citrate so the nanoparticles will be electrically isolated from one another after absorbing a citrate surface layer.

17. The method of claim 15, wherein the solution comprises a component that causes the nanoparticles to be electrically charged.

18. The method of claim 15, further comprising optimizing a concentration of nanoparticles in the solution, a magnitude of the electric field, or the duration of time to achieve a predetermined degree of uniformity for a distribution of the nanoparticles in the monolayer.

19. The method of claim 15, wherein exposing the substrate to an electric field comprises placing the substrate between two parallel plates.

20. The method of claim 15, wherein the substrate is n-type silicon and the nanoparticles are negatively charged gold nanoparticles.