BIOSENSORS WITH ONE-DIMENSIONAL CONDUCTING POLYMER SYSTEMS

Abstract

The present disclosure relates to methods for biosensing using one-dimensional conducting polymer systems. The present disclosure also relates to one-dimensional sensors having substrates coated with conducting polymers such as polyaniline. The geometry of the substrates is configured to maximize the geometrical probability of detecting pathogens, aerosols, etc.

Claims

1. A sensor for detecting the presence of a pathogen, the sensor comprising a one-dimensional substrate.

2. The sensor of claim 1, further comprising a coating on the substrate, the coating comprising an electrically-conducting polymer.

3. The sensor of claim 2, wherein the coating comprises polyaniline.

4. The sensor of claim 2, wherein the substrate comprises cellulose.

5. The sensor of claim 2, wherein the substrate comprises a single-strand filament.

6. The sensor of claim 2, wherein the substrate comprises a natural fibre.

7. The sensor of claim 6, wherein the substrate comprises one of silk thread and jute.

8. The sensor of claim 2, wherein the substrate has a width of less than about 25 microns.

9. The sensor of claim 8, wherein the substrate has a width of about 3 microns to about 25 microns.

10. The sensor of claim 9, wherein the substrate has a width of about 20 microns to about 25 microns.

11. The sensor of claim 2, wherein the substrate has a linear configuration.

12. The sensor of claim 2, wherein the substrate has a zig-zag configuration.

13. The sensor of claim 2, wherein the substrate has a criss-cross configuration.

14. The sensor of claim 2, wherein the substrate comprises paper.

15. The sensor of claim 14, wherein the substrate comprises 300 grams per square meter paper.

16. A method for detecting the presence of airborne pathogens, comprising: providing a one-dimensional sensor; and measuring a change of resistance of the sensor in response to exposure to the pathogens.

17. The method of claim 16, wherein providing a one-dimensional sensor comprises providing a sensor comprising a substrate having a width of about 25 microns or less, and a coating on the substrate, the coating comprising an electrically-conducting polymer.

18. A sensor for detecting the presence of a pathogen, comprising: a substrate having a width of about 25 microns or less; and a coating on the substrate, the coating comprising an electrically-conducting polymer.

19. The sensor of claim 18, wherein the coating comprises polyaniline.

20. A pathogen detection system comprising: a sensor; and an RC coupling circuit electrically coupled to the sensor and configured to indicate a change of resistance of the sensor based on an output frequency of the RC coupling circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The following drawings are illustrative of particular embodiments of the present disclosure and therefore do not limit the scope of the present disclosure. Embodiments of the present disclosure will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.

[0049] FIG. 1 depicts a conducting polymer (PANI) grown in-situ from a synthesis bath on a paper substrate; and a scanning electron microscope image of viral particles that have fallen on a substrate and aggregated;

[0050] FIG. 2 is a schematic illustration of two sensors, showing the lower number of electronic conducting paths in the sensor having the smaller width.

[0051] FIG. 3 shows comparative resistance measurements obtained from sensors having relatively wide and narrow substrates;

[0052] FIG. 4 is a table showing various steps in the fabrication process for the sensors shown in FIG. 5;

[0053] FIG. 5 is a schematic diagram of different types of 1D and 2D sensors;

[0054] FIG. 6 is a simplified circuit diagram of an RC oscillation circuit for determining a change in resistance of a sensor;

[0055] FIG. 7 depicts an exemplary test set-up for exposing sensors to airborne viral particles;

[0056] FIG. 8 includes graphical representations of the respective responses of a 2D paper-based sensors and a 1D paper-based sensor to exposure to an equivalent number of airborne viral particles;

[0057] FIG. 9 includes graphical representations of the responses of 1D sensors comprising silk and jute fibres, respectively, to exposure to airborne viral particles.

[0058] FIG. 10 is a diagrammatic illustration showing the chemical interaction of natural fibres in the form of silk and cellulose, i.e. jute, with polyaniline.

[0059] FIG. 11 is a graphical representation of the response of a 1D paper sensor to exposure to airborne viral particles, showing the effects of varying to the length of the sensor.

[0060] FIG. 12 includes graphical representations of the respective responses of a 2D paper-based sensor and a 1D paper paper-based sensor to exposure to an equivalent number of airborne viral particles.

[0061] FIG. 13 is a graphical representation of the response of a 1D sensor comprising silk fibres to exposure to airborne viral particles.

[0062] FIG. 14A is a graphical representation of the response of a 1D sensor to exposure to different concentrations of SARS Cov-2 viruses.

[0063] FIG. 14B is a graphical representation of the rate of change of the normalized response of the 1D sensor to the exposure to different concentrations of SARS Cov-2 viruses.

WRITTEN DESCRIPTION

[0064] The inventive concepts are described with reference to the attached figures, wherein like reference numerals represent like parts and assemblies throughout the several views. Several aspects of the inventive concepts are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the inventive concepts. One having ordinary skill in the relevant art, however, will readily recognize that the inventive concepts can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operation are not shown in detail to avoid obscuring the inventive concepts.

[0065] The inventive concepts are described with reference to the attached figures, wherein like reference numerals represent like parts and assemblies throughout the several views. Several aspects of the inventive concepts are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the inventive concepts. One having ordinary skill in the relevant art, however, will readily recognize that the inventive concepts can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operation are not shown in detail to avoid obscuring the inventive concepts.

[0066] Theoretical Advantages of 1D Sensors

[0067] Within a conductor, according to free-electron gas theory, an electron faces no barrier and thus can move in any direction. When a conductor is placed within an electric field, the electrons experience a net force in the opposite direction of the applied field, and move along the direction of force. Although there are many probable free paths, electrons follow linear free paths having larger components in the direction to travel since those free paths result in the least time for the electrons to travel from cathode to anode. Also, is possible for the electrons to travel over multiple mean free paths at one time. In case the mean free path(s) is (are) disrupted, the electrons find alternative (new) mean free paths for conduction. Thus, for any conductor subjected to electrical characterization, multiple probable parallel conduction paths exist between the two electrodes even when the conductor is in a 2D configuration, as shown in FIG. 2. According to the Landauer principle, the electric current through a material is given by:

[00001]$I=-\frac{2q}{h}T\left(E\right).Math.M\left(E\right).Math.\left(n_1-n_2\right)\mathrm{dE},$

where q is the electronic charge, h is the Plank constant, T(E) is the transport probability, M(E) is the modes available and n's are the occupation numbers at energy levels E and (E+dE). (D. Wortmann; H. Ishida; S. Blugel, Embedded Green-function formulation of tunneling conductance: Bardeen versus Landauer approaches Physical Review B, 2005, 72, 235113. (doi.org/10.1103/PhysRevB.72.235113). The current (1) depends on the area of the 3D conductor, or the width of conductor for the 2D conductor when the conductor length is constant. Thus, decreasing the width of a 2D conductor, as shown in FIG. 2, decreases the number of electronic conducting paths and thereby increases the resistance while reducing the current.

[0068] For example, FIG. 3 depicts a resistance measurement of a wide PANI-coated paper substrate on left, and a resistance measurement of a relatively narrow PANI-coated paper substrate on the right, with the narrow substrate showing much higher resistance than the wide substrate. Classically, this means a reduction of mean free path number. (For a quantum mechanical 1D conductor, however, the modes are constant of energy and the transmission probability becomes zero for a conductor which has a length much longer than the electron scattering distance.) As noted above, in the context of the present application, this description remains restricted within classical science boundaries, and one-dimensional or 1D is intended to mean the narrowest two-dimensional (2D) conductor which obeys classical scientific laws. In such a conductor, the number of electronic mean free paths within the conductor would be at a minimum. According to the development described herein, a 2D conductor with a width within the few micrometer range can be achieved, for example, using silk thread as the substrate.

[0069] From earlier reports, it is known that the virus particle and biogenic materials bind with PANI (conducting polymer) chains through imine/amine bonds. (R. Borah; A. Kumar; M. K. Das; A. Ramteke, Surface functionalization-induced enhancement in surface properties and biocompatibility of polyaniline nanofibers, RSC Advances, 2015, 5, 48971. (doi.org/10.1039/C5RA01809A)). This bond formation withdraws the excess (free) electron from the conjugated electronic pathway of PANI chain and impairs local electronic conductivity. (S. Griggs; A. Marks; H. Bristow; I. McCulloch, n-Type organic semiconducting polymers: stability limitations, design considerations and applications Journal of Materials Chemistry C, 2021, 8099. (doi.org/10.1039/D1TC02048J)). This means that virus exposure at a point on the conductor disrupts the electronic path through that point and the enclosing area (about 30 microns for a virus-containing aerosol). Thus, if the number of available electronic paths (including parallel conduction paths between the two electrodes) is at a minimum, destroying some of them immediately causes a drastic drop of conductivity and/or a drastic increase of resistance (about 1.5 to 2 times or greater). Thus, the sensitivity becomes very large and the response time very short (about 10s to 40s, due to the time taken to absorb the aerosol).

[0070] Hence, when the conducting polymer based 2D substrates are exposed to aerosolized virus particles, the incidence of the virus particles results in a significant increment of resistance of some of such paths (and not necessarily the least resistive one), thereby leading to drop in conductivity. But due to the parallel geometry of several such resistive paths, significant alteration in the equivalent resistance of the network after virus exposure is no longer a repetitive phenomenon. Restriction of the substrate dimension to 1D resists the formation of multiple parallel conduction paths, and suddenly and appreciably drops down the flow of current upon the same load of virus exposure. Hence, in theory, an almost completely resistive nature should be observed after exposure of the 1D substrate to the virus.

[0071] Experimental Verification

[0072] To confirm the above phenomena experimentally, a detection method was designed in which the sensor is coupled with RC-based electronics which provide an output in terms of frequency. In this two-electrode electronic circuit, shown in FIG. 6, the resistance of the sensor and the frequency output from the circuit maintain an inverse relationship with each other.

[0073] Sensor Fabrication

[0074] The following sensors, depicted in FIG. 5, were fabricated as follows. The senor designated Type A is a 2D sensor, and the other depicted sensors are examples to 1D sensors with different types of geometries. Various steps in the fabrication methodology are documented in the table presented in FIG. 4.

[0075] Preparation of Type-A substrate: Polyaniline (PANI) was in-situ synthesized/coated on hot pressed 300 GSM cellulose substrate (Type A) (2D) by oxidative polymerization using 0.1 M Aniline in 1M HCl and ammonium peroxodisulfate (APS) as oxidizing agent (equimolar to aniline). The polymerization reaction was performed in cooled (32 F.-37.5 F.) reactor under continuous stirring. On completion of polymerization each substrate was coated with 2 percent solution of Terephthaldehyde in ethanol.

[0076] Preparation of Type-B substrate: Polyaniline (PANI) was in-situ synthesized/coated on hot pressed 300 GSM paper cellulose (Type B) substrate by oxidative polymerization using 0.1 M Aniline in 1M HCl and ammonium peroxodisulfate (APS) as oxidizing agent (equimolar to aniline). The polymerization reaction was performed in a cooled (32 F.-37.5 F.) reactor under continuous stirring. Terephthaldhyde coating was done after polymerization as mentioned for Type A substrate. Then the sensor substrates were cut into a narrow (approximately 1 mm width) piece.

[0077] Preparation of Type-C(filament like) substrate: Polyaniline (PANI) was in-situ synthesized/coated on jute and silk thread by oxidative polymerization using 0.1 M Aniline in 1M HCl and ammonium peroxodisulfate (APS) as oxidizing agent (equimolar to aniline). The polymerization reaction was performed in cooled (32 F.-37.5 F.) reactor under continuous stirring followed by coating with 2% Terephthaldehyde solution. The threads were dried at 50 C. in a hot air oven.

[0078] Preparation of Type-D (filament like) substrate in criss-cross fashion: PANI coated Type-C substrate was arranged in criss-cross fashion around multiple arrays of pins.

[0079] Preparation of Type-E (filament like) substrate in zig-zag fashion: PANI coated Type-C substrate was pasted with silver paste on a PVC board in zig-zag fashion.

[0080] Measurement of Resistivity

[0081] As discussed above, the exposure of viral particles or biogenic material decreases the conductivity of PANI, i.e., the conducting polymer. This essentially means that the resistance of the sensor increases, and that is the sensing signature of the viral particles or biogenic materials. A detection method has been developed to determine such changes in resistance. The detection method couples the sensor with RC based electronics, to provide an output in terms of frequency.

[0082] The sensor resistance is used to generate an oscillation in an RC oscillation circuit as shown, for example, in the simplified circuit diagram of FIG. 6, with the oscillation frequency changing with the sensor resistance. Thus, the change in the resistivity/conductivity of the substrate can be measured from the change in the oscillation frequency. In the setup depicted in FIG. 6, the sensor is connected with the RC oscillator (e.g., RC timer, LMC555) in parallel with a fixed-value resistor (e.g., R=150 k), and an initial frequency (f) is generated based on the sensor resistance (R) which is in parallel with the fixed resistor. The calculation of the frequency f is as follows:

[00002]$f=\frac{1}{0.6932\stackrel{.}{R}C}$

where {dot over (R)}=R.sub.fR or

[00003]$\frac{1}{\stackrel{.}{R}}=\left(\frac{1}{R_f}+\frac{1}{R}\right),$

R.sub.f=fixed resistance, R=Sensor/substrate resistance.

[00004]$f=\frac{1}{k\left(R_f.Math..Math.R\right)},$

Where k=1.386C

[00005]$f=\frac{\frac{1}{R_f}+\frac{1}{R}}{k}f=\frac{1}{k{R}_f}+\frac{1}{kR}$

[00006]$f=481+\frac{72.15{10}^6}{R},$

for C=0.01 F and R.sub.f=150 k (used in circuit)

[00007]$f=f_0+\frac{k}{R},$

where f.sub.0=481 Hz and k=72.1510.sup.6 F.sup.1

[00008]$f=f_0+f_x\left(\frac{1}{R}\right),$

Where f.sub.x=is the additional frequency generated by the substrate which is inversely proportional to the change of R.

[0083] The addition of the virus particles on the cellulose substrate is indicated by a drop in the output frequency of the sensor.

Results

[0084] An illustrative, exemplary test set-up is depicted in FIG. 7. In the test set-up, the detection system was arranged in a box, and the sensor was placed on the box using adhesive tape. The connections were taken through wire connectors or pogo pins. A nebulizer containing the viral particles/biogenic materials in a suitable solvent was separated from the sensor by a distance of about two to about three feet.

[0085] The test results are shown in FIG. 8. In particular, FIG. 8 displays representative data showing a side-by-side comparison of the responses of a 2D paper-based sensor (on the left) and 1D paper-based sensor (on the right) upon exposure to the same number of viral particles (20 k viral particles). FIG. 8 shows that the normalized frequency drops, i.e., the figure of merit value, is higher for the 1D sensor, and the response of the 1D sensor is faster than that of the 2D sensor.

[0086] The results thus indicate that a single-strand-filament 1D sensor gives better results over a multistrand-filament 2D sensor in terms of sensitivity. Comparing the response of the 1D sensor and the 2D sensor, the sensitivity has been increased in the 1D sensor, as can be seen clearly from the larger frequency drop. Also, the response time has been decreased, as evidenced from the higher rate of frequency drop in case of the 1D sensor.

[0087] FIG. 9 exhibits responses from a single strand silk substrate with criss-cross geometry (Type D) and a jute fibre in zig-zag geometry (Type E). Although a drop in frequency can be observed, it is not as large as that of the paper sensors. The reason could be the low cross-sectional area available to capture the nebulized viral particles, because even the natural fibres like jute, cotton, silk, etc. and their threads (single or multiple strands) reduce the thickness of the substrate further. Changing the substrate geometry from that of Type C (AB [BA] as show % n in FIG. 5) to the criss-cross pattern shown in FIG. 5 (Type D: AB [B<A]), and the zig-zag pattern also shows in FIG. 5 (Type E) leads to an increase in the surface area of the sensor compared to the Type C (and Type B) substrates.

[0088] FIG. 10 diagrammatically depicts the chemical interaction between polyaniline with the natural fibres silk (upper diagram) and cellulose, i.e. jute, (lower diagrarm).

[0089] A potential issue for the 1D substrate is that its cross-sectional area, which is much lower than that of the 2D sensor, significantly reduces the capture probability of the virus or biogenic material. Thus, although narrowing the width of the sensor increases the sensitivity and decreases the response time, the droplet-capturing cross-section is compromised. Thus, in making an effective 1D sensor for virus and biogenic material, the width of the sensor should be optimized according to the conditions under which the sensor is to be used.

[0090] FIG. 11 depicts representative data showing the effect of length variation for the 1D paper sensor fabricated by in-situ coating of PANI on 300 gsm paper. The width of the sensor is fixed as 1 mm, but the length has been varied from 6 mm to 15 mm.

[0091] FIG. 12 depicts representative data showing a side-by-side comparison of a 2D paper-based sensor (on the left) and a 1D paper paper-based sensor (on the right) upon exposure to the same number of virus particles.

[0092] FIG. 13 depicts representative data representing the response of a 1D sensor based on silk fibres.

[0093] FIG. 14A is a plot of normalized sensor responses with respect to time. Responses of different concentrations of SARS Cov-2 viruses, 100 k copies (red), 50 k copies (orange) and 5 k copies (yellow) per l of AS (artificial saliva) and control (only AS, green) are shown. A one-l drop of these dispersions has been added around the 20th second of the scan.

[0094] FIG. 14B depicts statistics of the rate of change of the normalized responses. The change is defined as the difference between responses before the addition of the drop; and after the addition of the drop, once the signal stabilizes around the 30.sup.th second, calculated from the above data. For each concentration and control set, 20 experiments have been carried out. The data of FIG. 14B shows that the rate of change for the control is below a threshold, i.e., 0.005, while the rates of change in the presence of the virus samples are greater than the threshold.

[0095] Although the present solution has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the present solution may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Thus, the breadth and scope of the present solution should not be limited by any of the above described embodiments. Rather, the scope of the present solution should be defined in accordance with the following claims and their equivalents.

[0096] Although the present solution has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the present solution may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Thus, the breadth and scope of the present solution should not be limited by any of the above described embodiments. Rather, the scope of the present solution should be defined in accordance with the following claims and their equivalents.