Scrupulous recognition of biologically important acids by fluorescent “turn off-on” mechanism of thaicalix reduced silver nanoparticles

Water dispersible silver nanoparticles (AgNps) were prepared using thiacalix4]arene tetrahydrazide (TCTH) as a reducing and stabilizing agent. TCTH-AgNps were characterized by surface plasmon resonance (SPR), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). Relatively uniform 20 nm spherical particles of TCTH-AgNps were efficiently formed over a pH range of 5-9 and from 10-40℃. The interaction behavior of TCTH-AgNps with different amino acids was investigated using spectrophotometry and spectrofluorimetry. Among the amino acids tested, only tryptophan and histidine showed fluorescence quenching and fluorescence enhancement, respectively. The linear detection range by Stern-Volmer plot was 5 nmol/L to 0.48 μmol/L for tryptophan and 4 nmol/L to 0.54 μmol/L for histidine. TCTH-AgNps were able to effectively reduce the levels of gram-positive bacteria, gram-negative bacteria, and fungi. These properties argue for the potential use of TCTH-AgNps as detectors of histidine and tryptophan and as antibiotics.