Scheme 1.

Schematic representation of the BioCode Au-nanobeacon. a The hairpin in its closed conformation strongly suppresses fluorescence. b A complementary target disrupts the hairpin and the donor breaks away from the AuNP surface leading to partial recovery of the donor’s fluorescence. c Hybridization to the target sequence exposes the palindromic sequence, which can then be targeted by the acceptor labeled oligonucleotide triggering the emission of fluorescence signal due to the specific FRET between the fluorophores that codify each possible target sequence (spectral codification)