Digital analysis of molecular analytes using electrical methods
Electrical detection methods are used to identify and further characterize single-molecule target analytes such as proteins and nucleic acids. A composition including a probe region and a tail region is contacted with a target analyte. The probe region specifically binds to the target analyte. The tail region is coupled to the probe region, and includes a nucleic acid template for polynucleotide synthesis. When conditions are such that polynucleotide synthesis occurs along the tail region, one hydrogen ion is released for every nucleotide that is incorporated into the tail region. A transistor such as an ISFET detects and measures changes in ion concentration, and these measurements can be used to identify the tail region and thus characterize the corresponding target analyte.
1. A method of characterizing at least one target analyte, comprising:
obtaining a plurality of ordered tail region sets, each of the ordered tail region sets comprising one or more tail region, the one or more tail region comprising a homopolymeric base region comprising at least 25 consecutive nucleotides and a nucleotide adjacent to the homopolymeric base region, wherein the nucleotide comprises a base that is distinct from the bases within the homopolymeric base region and wherein the one or more tail region is directed to a defined subset of N distinct target analytes, wherein the N distinct target analytes are immobilized on spatially separate regions of a substrate;
contacting the N distinct target analytes with a probe region under conditions designed to promote specific binding of the probe region to one or more of the immobilized N distinct target analytes;
performing at least M cycles, wherein the performing comprises:
(1) a hybridization step comprising contacting the bound probe region with the one or more tail region, wherein each tail region specifically binds to a linker region of a probe region;
(2) a synthesis step, the synthesis step comprising contacting the bound tail region with a reaction mixture comprising reagents and under conditions that result in synthesis of a polynucleotide strand using the tail region as a template; and
(3) a stripping step, the stripping step comprising stripping the tail region or the probe region from the N distinct target analytes;
detecting during each of the at least M cycles a plurality of output signals from the spatially separate regions of the substrate; and
determining from the detected plurality of output signals at least K bits of information per cycle for one or more of the N distinct target analytes, wherein the at least K bits of information are used to determine L total bits of information, wherein K×M=L bits of information and L>log 2 (N), and wherein the L bits of information are used to identify one or more of the N distinct target analytes.
2. The method of claim 1 , wherein L>log 2 (N), and wherein L comprises bits of information used for correcting errors in the plurality of signals.
3. The method of claim 1 , wherein L>log 2 (N), and wherein L comprises bits of information that are ordered in a predetermined order.
4. The method of claim 3 , wherein the predetermined order is a random order.
5. The method of claim 1 , wherein L>log 2 (N), and wherein L comprises bits of information used for determining an identification code for each of the N distinct target analytes.
6. The method of claim 1 , wherein L>log 2 (N), and wherein L comprises bits of information comprising a key for decoding an order of the ordered tail region sets for each cycle in the at least M cycles.
7. The method of claim 1 , further comprising using a key to decode the identity of one or more of the N distinct target analytes.
8. The method of claim 1 , further comprising digitizing the plurality of signals to expand a dynamic range of detection of the plurality of signals.
9. The method of claim 1 , further comprising comparing the L bits of information determined for an N target analyte with an expected bits of information for provided by a key, wherein the comparison is used to determine an identity of the N target analyte.
10. The method of claim 1 , wherein the method is computer implemented.
11. The method of claim 1 , further comprising determining from the L bits of information an error correction for the plurality of output signals.
12. The method of claim 11 , wherein the error correction comprises using a Reed-Solomon code.
13. The method of claim 1 , further comprising determining a number of ordered tail region sets based on the number of N distinct target analytes.
14. The method of claim 1 , wherein the substrate contains at least one transistor, the transistor detecting the plurality of output signals.
15. The method of claim 14 , wherein the transistor is an ion-sensitive field-effect transistor (ISFET) structure.
16. The method of claim 1 , wherein the tail region comprises a homopolymeric base region comprising more than 25 consecutive nucleotides.
17. The method of claim 1 , wherein the tail region further comprises one or more nucleotides comprising more than one bases that are distinct form the bases within the homopolymeric base region.
18. The method of claim 16 , wherein the homopolymeric base region comprises a poly-A tail, a poly-T tail, a poly-C tail, or a poly-G tail.
19. The method of claim 1 , wherein the linker region is configured to specifically bind to portions of multiple tail regions.
20. The method of claim 16 , wherein the homopolymeric base region comprises at least 100 consecutive nucleotides.
21. The method of claim 20 , wherein the homopolymeric base region comprises at least 200 consecutive nucleotides.
22. The method of claim 1 , wherein the analyte comprises a protein, a peptide, or a nucleic acid.
23. The method of claim 1 , wherein the probe region comprises a protein, a peptide, or a nucleic acid.
24. The method of claim 1 , wherein the probe region comprises an antibody.
25. The method of claim 1 , wherein the linker region sequence comprises at least 10 nucleotides.
26. The method of claim 25 , wherein the linker region sequence comprises 20-25 nucleotides.
27. The method of claim 16 , wherein the tail region further comprises:
a nucleotide adjacent to the homopolymeric base region, wherein the nucleotide comprises a base that is distinct from the bases within the homopolymeric base region;
a second homopolymeric base region adjacent to the nucleotide, wherein the second homopolymeric base region comprises bases that are different from the nucleotide base; and
optionally a plurality of additional homopolymeric base regions each separated from an adjacent homopolymeric base region, by an intervening nucleotide, wherein the intervening nucleotide base is different from the bases of each adjacent homopolymeric base region.
28. The method of claim 27 , wherein each homopolymeric base region comprises the same base.
29. The method of claim 1 , wherein the one or more tail region comprises more than one tail region.
30. The method of claim 29 , wherein a length of each tail region is constant.
31. The method of claim 1 , further comprising a second probe region.