| CPC C12Q 1/6837 (2013.01) [G01N 21/6428 (2013.01); G01N 21/6458 (2013.01); G01N 2021/6439 (2013.01)] | 17 Claims |

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1. A method of detecting completion of a template switching oligonucleotide (TSO) reaction, the method comprising:
(a) contacting (i) a tissue section with (ii) a plurality of capture probes attached to an array, wherein a capture probe of the plurality comprises a capture domain, wherein the capture domain is positioned at a 3′ end of the capture probe;
(b) releasing one or more target nucleic acids from the tissue section, wherein a target nucleic acid released from the tissue section is bound by the capture domain of the capture probe;
(c) extending the 3′ end of the capture probe using the bound target nucleic acid as a template thereby creating an extended capture probe comprising a sequence that is complementary to the bound target nucleic acid;
(d) adding to the 3′ end of the extended capture probe a first homopolynucleotide sequence;
(e) generating a second strand that comprises in a 5′ to a 3′ direction: a conjugated first agent, a second homopolynucleotide sequence, and a sequence corresponding to a portion of the bound target nucleic acid, wherein the first homopolynucleotide sequence hybridizes to the second homopolynucleotide sequence, and the step of generating the second strand comprises the use of a partially-double stranded template switching oligonucleotide sensor comprising:
(i) a first oligonucleotide comprising a conjugated second agent at its 3′ end, and
(ii) a second oligonucleotide comprising the conjugated first agent at its 5′ end and the second homopolynucleotide sequence at its 3′ end, wherein the second oligonucleotide has a single-stranded overhang at its 3′ end, and wherein:
the conjugated first agent is a fluorophore and the conjugated second agent is a fluorescence quencher; or
the conjugated first agent is a fluorescence quencher and the conjugated second agent is a fluorophore; or
the conjugated first agent is a donor fluorophore and the conjugated second agent is an acceptor fluorophore; or
the conjugated first agent is an acceptor fluorophore and the conjugated second agent is a donor fluorophore; and
(f) measuring fluorescence upon release of the first oligonucleotide from the second oligonucleotide by extension of a 3′ end of the extended first capture probe having the first homopolynucleotide sequence using the second oligonucleotide as a template, thereby detecting the completion of the TSO reaction.
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