A method of amplifying a target polynucleotide, comprising: providing a template polynucleotide comprising a 5′ hairpin, a target polynucleotide and a 3′ hairpin, wherein the 5′ hairpin comprises one or more non-canonical nucleotides and contacting the template polynucleotide with a polymerase and canonical nucleotides, wherein the polymerase extends, using the canonical nucleotides, the target polynucleotide from its 3′ end to form a first extended polynucleotide comprising the 5′ hairpin at its 5′ end and the complement of the 5′ hairpin at its 3′ end, wherein the complement of the 5′ hairpin forms a 3′ hairpin; and the polymerase extends the first extended polynucleotide from its 3′ end to form a second extended polynucleotide comprising the 5′ hairpin at its 5′ end and the complement of the 5′ hairpin at its 3′ end, wherein the complement of the 5′ hairpin forms a 3′ hairpin.