Development of a Novel System Consisting of a Reductase-Like Nanozyme and the Reaction of Resazurin and Ammonia Borane for Sensitive Fluorometric Sensing.

We report a novel system consisting of a redox reaction and a highly efficient reductase-like nanozyme, silica-palladium nanoparticles (Pd@SiO NPs), as a novel detection platform for fluorometric sensing. In a proof-of-concept demonstration using an oligonucleotide as the detection target, a glass fiber-based sensor is fabricated by covalently conjugating two oligo probes, which are complementary to the adjacent segments of the target oligonucleotide, on Pd@SiO NPs and glass fiber, respectively. In the presence of the target oligonucleotide, the two probes are drawn together by the target through sequence-specific hybridization, bringing the Pd@SiO NPs to the glass fiber. When the glass fiber is subsequently immersed in a mixture of resazurin and ammonia borane solution, the Pd@SiO NPs on the glass fiber trigger the catalytic conversion of resazurin (blue, slightly fluorescent) to resorufin (pink, highly fluorescent) with massive signal amplification, indirectly signaling the presence of the target oligonucleotide. We show that the glass fiber-based fluorometric sensor can detect a target oligonucleotide associated with the BRAF mutation linearly in the concentration range of 20 to 400 pM with a detection limit (LOD) of 15 pM and the specificity to differentiate targets with single-base difference. These results demonstrate a new frontier for the development of a sensitive, specific, and inexpensive nonenzyme-based fluorometric sensing platform as an alternative to conventional enzyme-based assays.