| CPC C12N 9/1252 (2013.01) [C12Q 1/6869 (2013.01); C12Y 207/07007 (2013.01)] | 15 Claims |

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1. A system for identifying a nucleotide, the system comprising:
(a) a nucleic acid binding composition comprising:
(i) a nucleic acid binding moiety comprising a polymerase or a catalytic domain thereof;
(ii) a base-pairing moiety, wherein the base-pairing moieties is connected to the nucleic acid binding moiety via a linker, and wherein the linker has a length effective to allow the base-pairing moiety to pair with a complementary nucleotide in a primed polynucleotide while precluding incorporation of the base-pairing moiety into a 3′ end of the primed polynucleotide, wherein the primed polynucleotide is unlabeled when the primed polynucleotide is disassociated from the base-pairing moiety, wherein:
(A) the polymerase or the catalytic domain thereof comprises a point mutation that renders the polymerase or the catalytic domain thereof incapable of incorporating any nucleotide into the 3′ end of the primed polynucleotide; or
(B) the nucleic acid binding composition lacks sufficient magnesium to render the polymerase or the catalytic domain thereof incapable of incorporating any nucleotide into the 3′ end of the primed polynucleotide; and
(iii) a detectable label coupled to the nucleic acid binding moiety, the base-pairing moiety, or the linker; and
(b) an imaging module comprising an optical waveguide, wherein the imaging module is configured to detect the nucleic acid binding composition bound to the complementary nucleotide in the primed polynucleotide, thereby identifying the complementary nucleotide.
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