nucleic acid ligand target molecule complex are then detected by any suitable method known to those skilled in the art the selex protocol used for selection of oligonucleotides ligands from combinatorial nucleic acid libraries is not suitable for generation of a random mixture of parallel duplex structures because the parallel stranded hairpins of the invention are best made empirically for a given position on the hairpin one should find the complementary base and the direction of the dna sequence should be inverted in the middle of the sequence allowing the formation of a parallel stranded hairpin one aspect of the present invention includes the study of parallel duplex hairpins as aptamers by generating and testing defined sequences individually this process may be speeded however by using dna chips technology in particular dna chip synthesizers as genion febit mannheim germany these machines are designed to produce in short time one day 40 000 dna molecules in pmol amounts in a chip using photoactive protecting groups the present invention will also encompass methods and compositions for the synthesis of a library of parallel duplexes as shown for example in fig3 in the present invention a branching phosphoramidite is used to prepare two asymmetric tracks using available phosphoramidites such as those reported in avi u00f1o a et al u201c synthesis of branched oligonucleotides suitable for triple helix studies accepted for publication 2003 helvetica chimica acta branched nucleic acids are prepared using nucleoside and or non nucleoside branching molecules one end of the track pg 1 is protected by and acid labile group including but not limited to dimethoxytrityl dmt or monomethoxytril mmt the other track is protected by a base labile orthogonal group such as but not limited to.