The pH-switchable agglomeration and dispersion behavior of fluorescent Ag nanoclusters and its applications in urea and glucose biosensing

Water-soluble fluorescent Ag nanoclusters (Ag NCs) with distinct pH-switchable agglomeration and spectral signal responses are prepared using a facile etching method. Increased and decreased pH cause the Ag NCs to switch between agglomeration and dispersion, accompanied by decreases in and recoveries of fluorescence intensity and absorbance. The pH switchable behavior of the Ag NCs is attributed to carboxyl groups on the nanocluster surface that are rich in the citrate and amido functional groups of ligands (glutathione), creating an easily formed, weak molecular interaction among Ag NCs (for example, hydrogen bonding) and maintaining a balance in the colloidal solution, whereas a change in pH will disrupt the balance, leading to the reversible agglomeration of Ag NCs and the switchable spectral signal response. In addition, because urea and glucose can change the pH of a solution by producing NH3 and gluconic acid in enzyme-catalyzed reactions, the pH-switchable behavior of the Ag NCs is used to develop them as an optical probe to establish a regenerated biosensing platform for the sensitive and selective detection of urea and glucose, and the test results are satisfactory.