Preparation Of Ag Nanoclusters Hydrogel And Its Applications

As the food safety issues frequently happen in recent years, the public pay more andmore attention to food safety. Therefore, ensuring the safety of food process, as well as thereliability of the late detection for food is very important. The appearance of nanotechnologyhas dramatically promoted the development of related disciplines on the basis of the materialscience. Particularly, the utilization of nanomaterials and the rapid developing nano-technology in the field of food safety has been extensively explored during the last decade.Silver (Ag) nanoclusters, one of the most important nanomaterials in nanoscience, are ofpromising applications in food, chemical detection, and bio-pharmaceutical due to its distinctoptical, electrical, and chemical properties. The preparation of Ag nanoclusters in aqueoussolutions, however, is quite difficult because of the tendency of Ag nanoclusters to aggregateinto larger particles. Therefore, it is significant to develop a simple and environmentallyfriendly synthetic method to obtain Ag nanoclusters. Incorporating Ag nanoclusters intohydrogels to make nanocomposites can not only improve their stability but also endow themwith more functions. Herein we report a simple and green synthesis of Ag nanoclustershydrogel and their related applications in the field of food safety. The specific results are asfollows:(1) Highly stable Ag nanoclusters hydrogel has been prepared by employing UVphotoreduction method with AgNO3and L-cysteine as raw materials. The successfulpreparation of Ag nanoclusters can be controlled by varying the molar ratio of AgNO3andL-cysteine, the concentration of AgNO3, and UV irradiation time.The ultraviolet–visiblespectra (UV-vis), transmission electron microscopy (TEM), scanning electron microscope(SEM), X-Ray photoelectron spectroscopy (XPS), and matrix-assisted laser desorptionionization mass spectrometry (MALDI-TOF) are performed to characterize the opticalproperties, structure and synthesis principle of Ag nanoclusters hydrogel, respectively. Inaddition, the stability of the as-prepared Ag nanoclusters hydrogel to acid and base has alsobeen investigated in this work. The results demonstrated that stable Ag nanoclusters hydrogelcan be synthesized when the mole ratio of AgNO3and L-cysteine is1.5:1, the concentrationof AgNO3is0.1mol/L, and the photoreduction time is4.5hours.(2) The antibacterial activity of Ag nanoclusters hydrogel against Escherichia coli (E.coli)and Staphylococcus aureus (S.aureus) are conducted using zones of inhibition, minimuminhibitory concentrations (MIC), minimum bactericidal concentrations (MBC), and growthcurves. The Ag nanoclusters hydrogel shows highly potent antibacterial activity toward bothE.coli and S.aureus. The MIC of Ag nanoclusters hydrogel toward E.coli and S.aureus are10.93μg/mL,21.85μg/mL; the MBC are43.75μg/mL and87.50μg/mL, respectively.(3) We demonstrate a novel colorimetric avenue for highly selective halide ions (Cl－,Br－, I－) recognition and sensing using Ag nanoclusters hydrogel. We find that Agnanoclusters hydrogel could discriminate halide ions from a wide range of environmentallydominant anions (NO－－－3, NO2, CH3COO, SO32－, etc), identified by the changes in the colorof Ag nanoclusters hydrogel and distinct absorption band changes in the UV-vis spectra. The minimum detectable concentrations are estimated to be20μmol/L for Cl－, and5μmol/L bothfor Br－and I－, respectively. Furthermore, appreciable color change of Ag nanoclustershydrogel can be also observed at200μmol/L,100μmol/L,100μmol/L with the naked eye forCl－, Br－, I－. The Ag nanoclusters hydrogel is also applied successfully to the sensing of Cl－in real water samples. The total measurement could be finished within5min, thus thiscolorimetric method based on Ag nanoclusters hydrogel could be a promising and attractiveapproach due to its rapidity, simplicity, and low cost.