Process and apparatus for measuring binding events on a microarray of electrodes

• US 20070072169A1
• Filed: 09/29/2005
• Published: 03/29/2007
• Est. Priority Date: 09/29/2005
• Status: Active Grant

• Current Assignee: CustomArray, Inc. (Genscript Biotech Corp.)
• Original Assignee: CombiMatrix Corporation
• Inventors: Peyvan, Kia, CAMPBELL, COLIN, Bizak, Michael, LEE, RAND
• Granted Patent: US 8,855,955 B2
• Time in Patent Office: Days
• US Class Current: 435/4
• CPC Class Codes: G01N 27/3277 being a redox reaction, e.g. detection by cyclic voltammetry voltammetry per se G01N27/42, G01N27/48
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence

Abstract

There is disclosed a process and apparatus for reading electrical current of electrodes on a microarray of electrodes. Those electrodes having binding events are detected by a difference in electrical current flow. Enzymes on targets catalyze the conversion of substrate to product, which is detectable by electrochemical reduction at each electrode on the microarray of electrodes. The apparatus has an integration circuit that provides a voltage output that is measured and recorded over time and used to calculate an average current flow. A potentiometer equalizes voltage at electrodes undergoing measurement compared to grounded electrodes.

Claims

1. A process for reading electrical current of electrodes on a microarray of electrodes comprising:

(a) providing a measurement system having a control system, an integration circuit, a microarray chamber, a plurality of voltage lines, digital circuitry, and analog circuitry, wherein the control system, the integration circuit, and the microarray chamber are in circuit communication, wherein the microarray chamber contains a microarray having a plurality of electrodes in circuit communication with the control system and the integration circuit, wherein the voltage lines are switchably connectable to each electrode by the control system

(b) initializing measurement by setting a measurement set of the electrodes to approximately ground, setting a counter electrode voltage of at least one counter electrode, and pausing for a steady state period, wherein the at least one counter electrode is in fluid communication with the measurement set of the electrodes;

(c) measuring current for each electrode of the measurement set of electrodes current by (i) connecting a measurement electrode to the integration circuit having a reset switch closed using the first voltage line, (ii) pausing for an electrode settling period, (iii) opening the reset switch to measure and record a voltage response from the output of the integration circuit for a measurement time at a sampling rate, (iv) closing the reset switch, and (v) switching the measurement electrode back to the second voltage line; and

(d) calculating current of each of the electrodes of the measurement set.

2. The process for reading electrical current of electrodes on a microarray of electrodes of claim 1 wherein a first voltage line connects the microarray to the integration circuit and connects the integration circuit to the control system.

3. The process for reading electrical current of electrodes on a microarray of electrodes of claim 1 wherein a second voltage line is settable to ground, wherein a third voltage line is settable to a programmable fixed voltage.

4. The process for reading electrical current of electrodes on a microarray of electrodes of claim 1 wherein the integration circuit has an integrating transimpedance amplifier having a positive input and a potentiometer circuit connected to the positive input.

5. The process for reading electrical current of electrodes on a microarray of electrodes of claim 4 wherein the potentiometer circuit is adjusted using an adjusting method to maintain approximately identical voltage of electrodes having current measured and electrodes not having current measured.

6. The process for reading electrical current of electrodes on a microarray of electrodes of claim 1 wherein the setting the measurement set of electrodes step is done with the second voltage line and the setting the counter electrode voltage is done using the third voltage line.

7. The process for reading electrical current of electrodes on a microarray of electrodes of claim 1 wherein calculating the current of each electrode is by linear regression of the voltage response and time.

8. The process for reading electrical current of electrodes on a microarray of electrodes of claim 7 wherein a slope is obtained, wherein the current is equal to negative of the slope multiplied by a capacitor value of the integration circuit capacitor.

9. The process of claim 1, wherein the adjusting method for the potentiometer circuit is selected from the group consisting of manual adjustment before assembling and software adjustment using computer software and a measurement and feedback circuit having a digital to analog converter and an analog to digital converter.

10. The process of claim 1, wherein the electrode settling period is approximately 10 to 600 microseconds.

11. The process of claim 1, wherein the programmable fixed voltage of the at least one counter electrode is approximately 0.02 to 0.5 volts.

12. The process of claim 1, wherein the steady state period is approximately 4 to 60 seconds.

13. The process of claim 9, wherein the capacitor value is approximately 5 to 20 picofarads.

14. The process of claim 1, wherein the measurement time is approximately 0.5 to 5 milliseconds

15. The process of claim 1, wherein the sampling rate is approximately one data pair every 10 to 100 microseconds.

16. An apparatus for integrating voltage to measure current of electrodes on a microarray comprising:

(a) an electrical network having at least eight network terminals (A, B, C, D, E, F, G, H) comprising;

(i) an integrating transimpedance amplifier having a negative amp input connected to a network terminal (A), a positive amp input, a negative opamp input, and an opamp output connected to a network terminal (B), and an amp output connected to a network terminal (C),

(ii) an operational amplifier having a positive opamp input connected to a network terminal (D),

(iii) a programmable gain amplifier having gain G₁ and a PGA input connected to the network terminal (C) and a PGA output connected to the network terminal (H),

(iv) a first resistor having known resistance R₁ connected between the network terminals (D) and (E),

(v) a second resistor having known resistance R₂ connected between the network terminal (D) and ground,

(vi) a potentiometer having known resistance R₃, a potentiometer output connected to the network terminal (E), and potentiometer inputs connected between the network terminals (F) and (G),

(vii) a capacitor of known capacitance C₁ connected between the network terminals (A) and (C), and (viii) a reset switch connected between the network terminals (A) and (C);

(b) a plurality of voltages lines;

(c) one or more external power sources; and

(d) a computer control and data acquisition system having an input line connected to the network terminal (H) and in circuit communication with the integration circuit.

17. The apparatus for integrating voltage to measure current of electrodes on a microarray of claim 16 wherein the plurality of voltages lines comprise a measurement line, a ground line, and a counter electrode line.

18. The apparatus for integrating voltage to measure current of electrodes on a microarray of claim 16 wherein the voltages lines are switchably connectable to electrodes on a microarray of electrodes.

19. The apparatus for integrating voltage to measure current of electrodes on a microarray of claim 16 wherein during measurement the measurement line is connected between network terminal (A) and a measurement electrode, the ground line is connected to a plurality of electrodes not being measured, and the counter electrode line is connected to at least one counter electrode.

20. The apparatus for integrating voltage to measure current of electrodes on a microarray of claim 16 wherein the one or more external power sources provide a first source of potential across the network terminals (F) and (G), a second source of potential to power the operational amplifier, a third source of potential to power the integrating transimpedance amplifier, a fourth source of potential to power the programmable gain amplifier, and a fifth source of potential to power the reset switch.

21. The apparatus for integrating voltage to measure current of electrodes on a microarray of claim 16 wherein the external power sources, and the voltage lines use analog circuitry and digital circuitry.

22. The apparatus of claim 16, wherein the potentiometer is adjustable using a method selected from the group consisting of manual adjustment before assembling and software adjustment using computer software and a measurement and feedback circuit having a digital to analog converter and an analog to digital converter.

23. The apparatus of claim 16, wherein the counter electrode line is adjustable to a voltage of approximately 0.02 to 0.5 volts.

24. The apparatus of claim 16, wherein C₁ is approximately 10 picofarads.

25. The apparatus of claim 16, wherein R₁ is approximately 49,900 ohms, R₂ is approximately 100 ohms, and wherein R₃ is approximately 10,000 ohms.