Nanoelectronic sensor pixel
An electrical circuit element, defined as “pixel”, can include at least one silicon nanowire open for contact with a medium for sensing; a metal electrode open for contact with said medium and used for feeding a high-frequency sinusoidal stimulation in impedance measurements and for sensing properties of said medium; implanted source and drain electrodes connected to said silicon nanowire and leaving the gate area and parts of said electrode open for contact with said medium; electrical metal contacts for connecting said pixel to an electrical circuit; and a reference electrode open for contact with said medium for creating a three-electrode-cell system and providing a constant gate potential in the circuit. Some embodiments provide a microelectronic sensor and wearable-patch sensor based on the array of these pixels. Also, some embodiments provide methods for performing DC readout, AC readout and a triple readout combining both DC and AC readouts and temperature sensing.
1. An electrical circuit element, defined as “pixel”, comprising:
at least one silicon nanowire open for contact with a medium;
a metal electrode open for contact with said medium for feeding a high-frequency sinusoidal AC stimulation in impedance measurements and for sensing properties of said medium, wherein said metal electrode is a temperature sensor, or both a counter electrode and temperature sensor, simultaneously;
implanted source and drain electrodes connected to said silicon nanowire and leaving a gate area of said pixel and parts of said electrode open for contact with said medium;
electrical metal contacts for connecting said pixel to an electrical circuit; and
a reference electrode open for contact with said medium for creating a three-electrode-cell system and providing a constant gate potential in the circuit.
2. The pixel of claim 1 , further comprising a backgate contact for the full electrostatic control of said pixel and for stabilising the electronic recording in electrolyte solutions.
3. The pixel of claim 1 , wherein said silicon nanowire is low-doped p-type, low-doped n-type, drain n-doped and source p-doped, or drain p-doped and source n-doped.
4. The pixel of claim 1 , wherein said metal electrode is a noble metal counter electrode.
5. The pixel of claim 4 , wherein said noble metal is platinum, gold or copper.
6. The pixel of claim 1 , wherein said reference electrode is an Ag/AgCl reference-cell electrode.
7. The pixel of claim 1 , wherein said metal electrode and said reference electrode are not passivated and in direct contact with said medium.
8. The pixel of claim 1 , wherein the surface of said silicon nanowire is coated with pH-sensitive oxide or nitride dielectric for use as a pH-reference element.
9. The pixel of claim 8 , where said pH-sensitive oxide or nitride dielectric is made of SiO 2 , Al 2 O 3 , Ta 2 O 5 , HfO 2 , TiO 2 , ZrO 2 , TiN or Si 3 N 4 .
10. The pixel of claim 9 , where said pH-sensitive oxide dielectric is made of Al 2 O 3 or Ta 2 O 5 .
11. The pixel of claim 1 , wherein the surface of said silicon nanowire is coated with either a metal- or a molecular-passivation layer for negating the pH-sensitivity of said surface and consequently using the sensor as a solution conductivity reference element for pure ionic strength sensing.
12. The pixel of claim 11 , where said metal-passivation layer is made of Au, Pt, Al, Wo, or Cu.
13. The pixel of claim 1 , further comprising a back gate at the bottom for tuning a threshold voltage.
14. The pixel of claim 1 , wherein the surface of said silicon nanowires is functionalised with receptor (capture) molecules capable of binding to target (analyte) molecules.
15. A sensor chip comprising an array of pixels, each of claim 1 , connected in a mixed analogue/digital amplifier circuit.
16. A diagnostic method for label-free detection of a target molecule (analyte) in a liquid or gas medium by monitoring changes in an electric current recorded by the sensor comprising the pixel of claim 1 or array thereof upon contacting with said medium.
17. The method of claim 16 , wherein said method comprises affinity-based diagnostics of said target molecule by monitoring binding or unbinding interaction of said target molecule to a receptor molecule attached to said sensor surface or by monitoring the changes in the spatial molecular configuration of the bound target molecule and/or receptor molecule.
18. The method of claim 16 , wherein said method comprises metabolic diagnostics of said target molecule by monitoring the formation of a product of said target molecule in a metabolic enzymatic reaction, or by observing an electron transfer from said target molecule to said sensor surface.
19. In a method for label-free detection of a target molecule (analyte) in a medium by monitoring changes in an electric current recorded by a sensor open for contact with said medium, the improvement comprises using the sensor comprising the pixel of claim 1 or array thereof.
20. A method for performing a DC readout with the sensor comprising the pixel of claim 1 or array thereof, said method comprising:
reading the raw data of a drain-source current (I DS ) and a gate-source voltage (V GS ) from said sensor before and after addition of an analyte solution, while a drain-source voltage (V DS ) is kept constant;
sweeping the V DS voltage with a reference electrode of said sensor and repeating the previous step for different V DS voltages to generate the sets of I DS -V GS raw data, each set for one specific V DS voltage, and to plot the corresponding I DS vs V GS curves;
calculating a transconductance (g m ) by taking a first derivative of said I DS -V GS curves at the corresponding V DS voltages and plotting the calculated g m vs V GS curves, each curve for one specific V DS voltage;
finding the maximum transconductance point g m (max) (the peak) in said g m -V GS curves and extracting the V GS voltage corresponding to the g m (max) in these curves; and choosing the point on the I DS -V GS curves generated in Step 1, said point corresponding to the V GS voltage obtained in Step 3, and taking a difference between said V G voltages of said sensor before and after addition of an analyte solution, thereby calculating a voltage shift (ΔV).
21. A method for performing an AC readout with the sensor comprising the pixel of claim 1 or array thereof, said method comprising:
reading the raw data of a root-mean-square voltage (Vrms) from a lock-in amplifier of said sensor before and after addition of an analyte solution;
plotting said Vrms data vs a current frequency (ω) of said sensor before and after addition of an analyte solution, thereby obtaining two Vrms-ω curves;
calculating the amplitude and frequency differences of a resonance peak between two said Vrms-ω curves;
calculating a cut-off slope of two said Vrms-w curves;
calculating the cut-off frequency corresponding to the frequency at the lowest amplitude of the resonance peak by:
processing the first polynomial fit to said cut-off slope;
finding an x-intercept, which is equal to said cut-off frequency, of the fitted curves for said sensor before and after addition of said analyte solution; and
taking a difference between the calculated cut-off frequencies of said sensor before and after addition of said analyte solution, thereby calculating a cut-off frequency shift.
22. A method for performing a triple readout comprising:
(I) performing a DC readout by:
reading the raw data of a drain-source current (I DS ) and a gate-source voltage (V GS ) from said sensor before and after addition of an analyte solution, while a drain-source voltage (V DS ) is kept constant;
sweeping the V DS voltage with a reference electrode of said sensor and repeating the previous step for different V DS voltages to generate the sets of I DS -V GS raw data, each set for one specific V DS voltage, and to plot the corresponding I DS vs V GS curves;
calculating a transconductance (g m ) by taking a first derivative of said I DS -V GS curves at the corresponding V DS voltages and plotting the calculated g m vs V GS curves, each curve for one specific V DS voltage;
finding the maximum transconductance point g m (max) (the peak) in said g m -V GS curves and extracting the V GS voltage corresponding to the g m (max) in these curves; and
choosing the point on the I DS -V GS curves generated in Step 1, said point corresponding to the V GS voltage obtained in Step 3, and taking a difference between said V G voltages of said sensor before and after addition of an analyte solution, thereby calculating a voltage shift (ΔV);
(II) performing an AC readout by:
reading the raw data of a root-mean-square voltage (Vrms) from a lock-in amplifier of said sensor before and after addition of an analyte solution;
plotting said Vrms data vs a current frequency (ω) of said sensor before and after addition of an analyte solution, thereby obtaining two Vrms-ω curves;
calculating the amplitude and frequency differences of a resonance peak between two said Vrms-ω curves;
calculating a cut-off slope of two said Vrms-w curves;
calculating the cut-off frequency corresponding to the frequency at the lowest amplitude of the resonance peak by:
processing the first polynomial fit to said cut-off slope;
finding an x-intercept, which is equal to said cut-off frequency, of the fitted curves for said sensor before and after addition of said analyte solution; and
taking a difference between the calculated cut-off frequencies of said sensor before and after addition of said analyte solution, thereby calculating a cut-off frequency shift; and
(III) performing temperature sensing,
wherein the DC readout, the AC readout and temperature sensing are performed with the sensor comprising the pixel of claim 1 or array thereof.
23. A microelectronic sensor comprising a disposable unit mounted on a chip substrate and a reader unit mounted on a flexible printed circuit board (PCB), wherein:
said disposable unit comprises:
an array of pixels, each of claim 1 , arranged in rows and columns and open for contact with a medium,
a row decoder connected to said array for addressing said pixels arranged in rows; and
a column decoder connected to said array for addressing said pixels arranged in columns; and
said reader unit comprises:
a voltage source connected to an electric circuit for supplying electric power to the sensor;
an integrated or CMOS current amplifier connected to said array for amplification of an electric current obtained from said pixels;
an integrated waveform generator for generating frequency of a sinusoidal electric stimulation;
an analogue-to-digital converter with in-built digital input/output connected to said current amplifier for outputting the converted signal to a user interface; and
a connection module for wired connection of the sensor to said user interface, or a wireless connection module for wireless connection of the sensor to said user interface.
24. The sensor of claim 23 , wherein said sensor further comprises a microfluidic chip or lateral flow strip for supplying an analyte solution to said pixels.
25. The sensor of claim 23 , wherein said voltage source is a battery.
26. The sensor of claim 23 , wherein said sensor is powered wirelessly via an RFID (Radio-Frequency Identification) tag.
27. A wearable-patch sensor comprising a disposable unit mounted on a chip substrate and a reader unit mounted on a flexible printed circuit board (PCB), wherein:
said disposable unit comprises an array of pixels, each of claim 1 , open for contact with a medium; and
said reader unit comprises:
an ASIC (Application-Specific Integrated Circuit) chip customised for a particular use of the sensor;
a battery or power receiver connected to an electric circuit for supplying electric power to the sensor; and
a wireless connection module for wireless connection of the sensor to a user interface.
28. The sensor of claim 27 , wherein said ASIC chip comprises an amplifier for amplification of an electric current obtained from said pixels, an additional voltage source for powering the sensor, a waveform function generator for generating frequency of a sinusoidal electric stimulation, and decoders.