Method of detecting or method of quantifying oligonucleotides

A method of detecting a target oligonucleotide in a sample, comprising steps of:

• (i) adding the first polynucleotide to the target oligonucleotide in the sample;
• (ii) bringing a capture probe for capturing the target oligonucleotide into contact with the target oligonucleotide,
• the capture probe containing
• (A) a nucleic acid probe,
• (B) a solid phase, or an adapter or a linker, adjacent to a nucleotide at the 3′ end or 5′ end of the nucleic acid probe,
• the nucleic acid probe containing a sequence complementary to a complete or partial sequence of the target oligonucleotide and/or a complete or partial sequence of the first polynucleotide;
• (iii) bringing a single-strand-specific nuclease into contact with the sample subjected to the step of adding the first polynucleotide and the contact step with the capture probe;
• (iv) making the capture probe in the sample single-stranded after the contact step with the single-strand-specific nuclease is performed;
• (v) bringing a pair of probes capable of self-aggregation composed of first and second oligonucleotides into contact with the sample subjected to the step of making the capture probe single-stranded to form a complex of the capture probe and an oligonucleotide polymer generated by self-aggregation of the first and second oligonucleotides;
• and
• (vi) detecting the complex, and thereby detecting the target oligonucleotide in the sample.