An upconversion nanoparticle-based photostable FRET system for long-chain DNA sequence detection

The fluorescence resonance energy transfer (FRET)-based diagnosis method has been widely used in fast and accurate diagnosis. However, the traditional FRET-based diagnosis method is unable to detect long-chain DNA sequences, due to the limitation of the distance between the donor and acceptor, while the long-chain DNA sequence enables higher selectivity and is quite important for confirming many major diseases. Therefore, it is urgently needed to develop an efficient FRET system for long-chain DNA detection. Herein a 'head-to-tail' structure was developed using NaYF4:Yb,Er nanoparticles as the energy donor and gold nanoparticles (AuNPs) as the acceptor to detect long-chain oligonucleotides sequences (i.e., HIV DNA, 52 bp). We modified NaYF4:Yb,Er nanoparticles with carboxylic acid groups by using poly(acrylic acid) to enhance its hydrophilic and then covalently attached 5 'end of capture oligonucleotides strand to the surface of the particles. In the presence of target HIV DNA, gold nanoparticles with reported DNA were brought close to NaYF4:Yb,Er nanoparticles upon 'head-to-tail' sandwich hybridization with target HIV DNA, resulting in an efficient FRET. Moreover, benefited from both photostable nanoparticles of UCNPs and AuNPs, the photobleaching issue has also been settled down. This developed method possesses high selectivity, high sensitivity, and reached a nanomolar limitation level. To our knowledge, it is the first time to report a 'head-to-tail' structure FRET system for detecting long-chain DNA sequences.