PROBLEM TO BE SOLVED: To provide a nucleic acid analog for performing capture, recognition, detection, identification or quantification about chemically or microbiologically individual units. SOLUTION: The nucleic acid analogues provided are: (a) a PNA (peptide nucleic acid) including a polyamide backbone bearing a plurality of ligands at respective spaced locations along the backbone, where each ligand being bound directly or indirectly to a nitrogen atom in the backbone and the ligand bearing nitrogen atoms mainly being separated from one another in the backbone by 4-8 intervening atoms; (b) a nucleic acid analog capable of hybridizing to a nucleic acid of complementary sequence to form a hybrid which is more stable against denaturation by heat than a hybrid between the conventional deoxyribonucleotide and the nucleic acid; or (c) a nucleic acid analogue capable of hybridizing to double-stranded nucleic acid in which one strand has a sequence complementary to the analogue, so as to displace the other strand from one strand. COPYRIGHT: (C)2009,JPO&INPIT