Methods for detecting target polynucleotides

A thermocycling method for increasing the number of tandem repeats of a unit sequence that is 1 to 60 nucleotides long in a linear polynucleotide, the method comprising the steps of:

• i) providing a solid substrate with a surface, the surface having immobilised thereon a single stranded primer polynucleotide comprising at least two tandem repeats of a unit sequence that is 1 to 60 nucleotides long;
• ii) contacting the immobilised primer polynucleotide with a single stranded template polynucleotide comprising at least two tandem repeats that are complementary to the unit sequence of the primer polynucleotide under hybridisation conditions that permit mismatched duplex formation between a unit sequence and its complement such that a 5′ overhang of the template polynucleotide is generated, wherein the 5′ overhang comprises at least one tandem repeat that is complementary to the unit sequence of the primer polynucleotide;
• and
• iii) contacting the mismatched duplexes with a thermostable 5′ to 3′ polymerase and nucleotides under extension conditions that permit polynucleotide extension in a 5′ to 3′ direction.