Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
  • G01N27/4163—Systems checking the operation of, or calibrating, the measuring apparatus
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/483—Physical analysis of biological material
  • G01N33/487—Physical analysis of biological material of liquid biological material
  • G01N33/48707—Physical analysis of biological material of liquid biological material by electrical means
  • G01N33/48721—Investigating individual macromolecules, e.g. by translocation through nanopores
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
  • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
  • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
  • C12Q1/6869—Methods for sequencing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/28—Electrolytic cell components
  • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
  • G01N27/301—Reference electrodes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/403—Cells and electrode assemblies
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
  • G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage

Definitions

• a nanoscale electronic device for detecting and analyzing single molecules based on recognition tunneling (RT) has been described previously (see, e.g., U.S. patent application publication no. 2014/0113386), which uses a one Palladium (Pd) electrode having a layer of AI 2 O 3 (insulator). Another electrode is included which has a Pd layer deposited on top of an insulating layer. An opening or gap is established through the layers and the exposed metal functionalized with adaptor molecules serve to trap analytes in a well-defined chemical configuration.
• An example of an adaptor molecule is 4(5)-(2-mercaptoethyl)-lH-imidazole-2- carboxamide, hereafter referred to as ICA.
• a series of current spikes are generated upon which are based on molecules (e.g., analytes) which pass through the gap and bridge one electrode to the other via adaptor molecules functionalized on the electrodes.
• the current spikes are analyzed (e.g., via a machine learning algorithm) to identify the particular analyte within in the gap for an associated current spike.
• the problem may be more complex since a significant bias voltage V is applied across a relatively small gap in contact with the solution.
• Bias V can be on the order of about 0.5V, and thus, if one electrode is at a potential where interactions with the solution are small, the other electrode may not be, which can cause instability in the RT junction.
• Figure 3a where the analyte comprises the nucleotide dAMP
• Figure 3b where the analyte comprises the nucleotide dGMP
• swings in current output with slow returns to the baseline current which is understood not to be associated with a tunneling process, but rather by relatively slow, i.e., on the order of a number of seconds, adsorptions of charged species and release thereof from the solution in contact with the electrodes.
• RT apparatuses may become inactive after only a few minutes of operation. Accordingly, it is desirable to find a way to stabilize a multiple (e.g., two) electrode sensing device in contact with a conducting solution.
• An apparatus for identifying and/or sequencing one or more first molecules includes a first sensing electrode and a second sensing electrode separated from the first electrode.
• the apparatus further includes a gap established by the separated electrodes, wherein an electrolyte is contained within the gap.
• the electrode surfaces are functionalized with adaptor molecules for contacting one or more first molecules.
• the apparatus further includes a reference electrode in contact with the electrolyte and coupled to one of the sensing electrodes.
• Figure 1 illustrates an RT apparatus and reference electrode according to some embodiments, whereby separate solution compartments are provided above and below the device (the corresponding solutions therein may be labeled cis solution and trans solution).
• V is the bias applied between top and bottom electrodes and V ref is the bias applied with respect to a reference electrode.
• Figure 2 illustrates the use of a reference electrode with nanowire devices, according to the prior art.
• Figures 3a-3d illustrates current spike results of an RT apparatus which lack a reference electrode (3a and 3b), and yield unstable current outputs, and current spike results of an RT apparatus which includes a reference electrode (3c and 3d) which are stable and operate for long periods.
• Figure 4 illustrates current-voltage sweeps of an imidazole (ICA) coated Pd electrode showing the large currents that develop as a consequence of hydrogen evolution when the potential is swept negative of 0V with respect to a Ag/AgCl reference electrode.
• ICA imidazole
• Figure 5a shows cyclic voltammetry for an ICA coated Pd electrode from +50 mV with respect to a Ag/AgCl reference electrode. The system is stable against hydrogen evolution, but now shows electrochemical noise that peaks at +380mV.
• Figure 5b illustrates that a bare Pd electrode does not display the electrochemical noise of Figure 5a.
• Figure 5c shows RT signals from a junction in which the lower electrode is held at +100mV vs. Ag/AgCl. Noise spikes are evident starting around 280mV, corresponding to +380 mV as Ag/AgCl.
• An opening/gap is established through the layers and the exposed metal functionalized with adaptor molecules (e.g., ICA) 4 serve to trap analytes in a well-defined chemical configuration.
• V (6) being applied across the gap, a series of current spikes are generated upon which are based on molecules (e.g., analytes) which pass from one electrode to another via the functionalized adaptor molecules and the trapped analytes.
• an RT apparatus includes a reference electrode 8, comprising, for example, a silver wire covered in a silver chloride layer, which is placed in contact with the solution and connected to either one of the electrodes via a voltage source Vref 7, where Vref is selected to maximize the stability of the two-electrode device operated at a bias V 6.
• the reference can be connected to either one of the electrodes in the RT device, so long as the other electrode is held at a fixed potential difference with respect to the electrode that is connected to the reference electrode.
• the criteria for setting the value of Vref for stable operation are as described below.
• reference electrodes 9, 10 can be placed in contact with solution above and (and/or) below the tunnel junction with a second bias 11, which may be applied to drive charged molecules through the tunnel junction (if desired).
• electrochemical data is acquired to aid in selecting values for Vref 7, and/or V, the bias across the apparatus 6.
• Figure 4 illustrates a series of cyclic voltammograms obtained using a Pd electrode coated with a monolayer of ICA. In these sweeps, the potential range of the sweep was increased in steps around 0 V vs. Ag/AgCl. Large currents are generated at the electrode is swept further negative of 0 V, a consequence of hydrogen evolution (Burke, L.D. and J.K. Casey, An Examination of the Behcho of Palladium Electrodes in Acid. J. Electrochem. Soc, 1993. 104: p. 1284-1291).
• a device that adsorbs negatively charged molecules can be driven into the potential range where hydrogen is evolved, destabilizing the device.
• Vref is chosen such that each electrode is not at a potential where electrochemical reactions occur with the molecules or ions in the solution in contact with the electrodes.
• FIGs 3a and 3b An example of this instability is shown in Figures 3a and 3b.
• the signal spikes generated by recognition tunneling occur in bursts but are accompanied b violent current fluctuations with large changes in the background current (pointed to by arrows).
• dGMP Figure 3b
• the device generates RT signals for only a small fraction of the time. After a few minutes of operation, the devices always became inactive.
• Figure 3c (dAMP) and Figure 3d (dGMP) show how violent current fluctuations may be removed, the normal recognition-tunneling signal restored, and the baseline current stabilized, when V re f is set to about +100 mV (bottom electrode with respect to Ag/AgC l).
• Such stabilized apparatuses have operated continuously for periods of 10 h or more.
• V re f was chosen so that the electrode connected to the reference was still slightly positive of the potential for hydrogen evolution (which is about -150mV on the Ag/AgCl scale).
• the second electrode was held at a potential, V re f + Vbi as that is less than the potential for oxidation reactions to occur in this solution.
• both electrodes are held at potentials such that electrochemical reactions are avoided.
• the second electrode (3 in Figure 1) is held at a potential V re f+V with respect to the Ag/AgCl reference (8 in Figure 1). Its electrochemical stability is also important.
• Figure 5a shows cyclic voltammetry of a Pd electrode functionalized with an ICA monolayer. The sweeps start at +50 mV vs. Ag/AgCl and the upper amplitude is increased in steps up to 750 mV.
• Figure 5b shows cyclic voltammetry on bare Pd. The increase of current at the highest bias clearly reflects an oxidation process on the Pd surface (suppressed somewhat when the Pd is covered with ICA because the currents are lower - Figure 5a).
• an optimal operating point for this device is to have one electrode held at + lOOmV vs. Ag/AgCl while the second electrode should not exceed + 350 mV vs Ag/AgCl .
• a device operated in these conditions gives excellent chemical recognition signals, is stable, and substantially free of additional noise for long periods. Without the reference electrode connected as described, the device becomes noisy with large shifts in baseline, as illustrated in Figures 3 a and 3b.
• additional improvements may be made by including a thick polymer layer, which may be deposited by spin coating of PMMA resist, with an opening above the junction which may be used as both a mask, to cut the opening through the electrodes, as well as a fluid well to keep solutions from the electrodes (except in the vicinity of the tunnel junction). Accordingly, for such embodiments, this process may eliminate leakage currents when the solution (which is contacting the biased reference electrode) also made a large contact area with the tunneling apparatus by virtue of solution leakage over the surface of the apparatus.
• electrodes can be cut using, for example, reactive ion etching, with CI gas used to tech the Pd electrodes and BC1 3 gas used to etch the A1 2 0 3 .
• the reference electrode may comprise an Ag wire coated with AgCl salt, although one of skill in the art will appreciate that any electrode of substantially constant polarization will suffice.
• Non-limiting examples of such electrodes include the silver/silver chloride electrode, the saturated calomel electrode, the normal hydrogen electrode, and/or the like. Even a bare silver, palladium or platinum wire will do so long as its area is many thousands of times as large as the area of the tunneling elecrtodes exposed to the electrolyte so that its potential only changes by a small amount when ions and molecules absorb or desorb form its surface.
• any large metallic electrode in some embodiments, much larger than the sensing electrodes 1 and 3 in Figure 1 may suffice so long as it is sized so as to undergo small changes, i.e., less than a few tens of mV, in potential as charged species are absorbed and/or desorbed from its surface.
• a reference electrode can be built into a device by fabricating a large (e.g., at least a micron by a micron in area) metal pad in a position such that it is in contact with the electrolyte.
• an apparatus for identifying and/or sequencing one or more first molecules comprises a first sensing electrode, a second sensing electrode separated from the first electrode, and a gap established by the separated electrodes.
• An electrolyte is contained within the gap and the electrode surfaces are functionalized with adaptor molecules for contacting one or more first molecules.
• the apparatus also includes a reference electrode in contact with the electrolyte and coupled to one of the sensing electrodes.
• the apparatus may further comprise a voltage source for coupling the reference electrode with one of the sensing electrodes, where the voltage source is configured to hold the sensing electrode coupled to the reference electrode at a constant potential difference with respect to the reference electrode.
• a method determining the potential of a reference electrode in a recognition tunneling (RT) apparatus may comprise a first sensing electrode, a second sensing electrode separated from the first electrode, and a gap established by the separated electrodes.
• An electrolyte is contained within the gap, and the electrode surfaces are functionalized with adaptor molecules for contacting one or more first molecules.
• the apparatus may further comprise a reference electrode in contact with the electrolyte and coupled to one of the sensing electrodes, and a voltage source for coupling the reference electrode with the first sensing electrode.
• the voltage source is configured to hold the first sensing electrode at a constant potential difference with respect to the reference electrode.
• the method comprises sweeping the bias between the first sensing electrode and the reference electrode, recording a leakage current through the first sensing electrode, and the noise for each of a plurality of fixed values of potential difference between first sensing electrode and the reference electrode, and selecting the reference electrode potential corresponding to the minimum leakage current.
• embodiments of the subject disclosure may include formulations, methods, systems and devices which may further include any and all elements from any other disclosed formulations, methods, systems, and devices, including any and all elements corresponding to RT systems.
• elements from one or another disclosed embodiments may be interchangeable with elements from other disclosed embodiments.

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• 2015
  • 2015-02-25 US US15/121,148 patent/US20170016852A1/en not_active Abandoned
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• 2018
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