Homogeneous competitive hybridization assay based on two-photon excitation fluorescence resonance energy transfer

Recently, we have successfully developed a two-photon excitation fluorescence resonance energy transfer (TPE-FRET)-based homogeneous immunoassay using two-photon excitable small organic molecule as the energy donor. In the present work, the newly emerging TPE-FRET technique was extended to the determination of oligonucleotide. A new TPE molecule with favorable two-photon action cross section was synthesized [2-(2,5-bis(4-(dimethylamino)styryl)-1H-pyrrol-1-yl)acetic acid, abbreviated as TP-COOH], with the tagged reactive carboxyl group allowing facile conjugation with streptavidin (SA). Employing the TP-COOH molecule as energy donor and black hole quencher 1 (BHQ-1) as acceptor, a TPE-FRET-based homogeneous competitive hybridization model was constructed via a biotin-streptavidin bridge. Through the hybridization between a biotinylated single-stranded DNA (ssDNA) and a BHQ-1-linked ssDNA, and the subsequent capture of the as-formed hybrid by TP-COOH labeled SA, the donor fluorescence was quenched due to the FRET between TP-COOH and BHQ-1. Upon the competition between a target ssDNA and the quencher-linked ssDNA toward the biotinylated oligonucleotide, the donor fluorescence was recovered in a target-dependent manner. Good linearity was obtained with the target oligonucleotide ranging from 0.08 to 1.52 microM. The method was applied to spiked serum and urine samples with satisfying recoveries obtained. The results of this work verified the applicability of TPE-FRET technique in hybridization assay and confirmed the advantages of TPE-FRET in complicated matrix.