Synergistic synthesis of gold nanoflowers as upconversion near-infrared nanoprobe energy acceptor and recognition unit for improved hydrogen sulfide sensing.

A highly sensitive and selective upconversion near-infrared (NIR) fluorescence and colorimetric dual readout hydrogen sulfide (H2 S) nanoprobe was constructed based on the excellent NIR fluorescence emission performance of upconversion nanomaterials (UCNPs), the specific recognition effect of synergistically synthesized gold nanoflowers (trypsin-stabled AuNFs (Try-AuNFs)) and the effective NIR fluorescence quenching capability. In this assay, the sensing strategy included three processes. First of all, the synthesized UCNPs can emit 803 nm NIR fluorescence when they were excited by 980 nm excitation light. Secondly, as a result of the principle of fluorescence resonance energy transfer (FRET), Try-AuNFs can effectively quench the NIR fluorescence of UCNPs at 803 nm, which can effectively improve the signal-to-background ratio of nanoprobes, thereby improving the sensitivity of the probes. Thirdly, in the presence of H2 S, the Try protective layer on the surface of Try-AuNFs was specifically penetrated, which will subsequently cleave Try-AuNFs via the strong S-Au bond. As such, the NIR fluorescence of UCNPs will be restored, achieving high selectivity and sensitivity detection of H2 S. Under optimized conditions, the linear response range of H2 S was 0.1-300 μM, and the detection limit was 53 nM. It is worth noting that the Try on the surface of Try-AuNFs via the synergistic effect can increase the steric hindrance of the probe, and this can effectively prevent the interaction between the probe with biothiols (cysteine (Cys), homocysteine (Hcy)) and other natural amino acids (non-thiol-containing) with resultant in the high selectivity regarding the detection of H2 S in human serum, which is unlikely to be achieved by AuNFs synthesized by the gold seed method (Se-AuNFs). This work not only provided a new type of UCNPs fluorescence quencher and recognition unit, but also exemplified that the use of the physical properties (steric hindrance) of protein ligands on the surface of nanoflowers can improve the specificity of the probe. This will provide new ideas for the design of other nanoprobes.