Research Of Triangular Silver Nanoplates Applied In The Visual Detection

The optical, physical, and chemical properties of silver nanoplates (AgNPs)strongly depended on their size and shape, thus, it is a promising strategy to change thesize and shape of AgNPs for various applications in different fields. Recently, AgNPshave been widely used as chromogenic components in colorimetric sensing systems. Inthis paper, we applied the changes of color, morphology, maximum absorptionwavelength of the blue triangular silver nanoplates (TAg-NPs) to visual detection oftraces of deferent substances (I－, cysteine, Cu2+). In these system, the sodiumthiosulfate played a key role.(1) Based on the reaction of TAg-NPs and iodide ions (I－) in the presence ofsodium thiosulfate (Na2S2O3) coupled with UV-visible spectrophotometric detection.The blue color of TAg-NPs significantly changed in the presence of Na2S2O3becauseof the formation of [Ag(S2O3)2]3ions. The I－reacted with [Ag(S2O3)2]3ions on thesurface of TAg-NPs forming AgI, which was then adsorbed onto the TAg-NPs surfaces,thus preventing further dissolution of TAg-NPs by Na2S2O3. The color andcorresponding maximum absorption wavelength of TAg-NPs were varied depending onthe concentration of I－. Furthermore, the change of maximum absorption wavelength() of TAg-NPs, were proportional to the concentrations of iodide ions in the range of1.0109~1.0106mol/L. Thus, a method for I－detection by either UV-visiblespectrophotometry detection or naked eyes observation is established.(2) The TAg-NPs could be etched by cysteine through forming Ag-S covalentbond. However, the reaction between TAg-NPs and cysteine is not obviously,especially when the concentration of cysteine lower as the range of1.010-9~1.010-7mol/L. It was found that the color, morphology, and maximum absorption wavelengthof TAg-NPs could be changed clearly with increasing the concentrations of cysteine inthe lower level concentration in the presence of Na2S2O3. Furthermore, the shift valuesof maximum absorption wavelength of TAg-NPs solution were proportional to theconcentrations of cysteine. Thus, a method for cysteine detection by either UV-visiblespectrophotometry detection or naked eyes observation is established. (3) Na2S2O3is dissociated under heating(80℃) in the presence of Cu2+, whichleads the concentration of Na2S2O3to be decreased. Furthermore, when the reactiontime between Na2S2O3with Cu2+is fixed, the decreased concentration of Na2S2O3isproportion to the concentration of Cu2+, and as a result, the color of the mixturesolution of TAg-NPs/Cu2+/Na2S2O3-is different from the different Cu2+concentrations.At the same time, the absorbance at the position of maximum absorption peak ofTAg-NPs changed with the change of the concentrations of Cu2+, and the changevalues of the absorbance at the position of maximum absorption peak of TAg-NPswere proportional to the concentrations of Cu2+. Thus, a new method is established asimple, low cost method for Cu2+detection.(4) The establishment of the system is mainly based on the principle of theNa2S2O3could corrosion the TAg-NPs, however, O2could react with ascorbic acid (VC)and produce H2O2in the presence of low concentration of Cu2+, which could react withNa2S2O3and prevent the reaction of TAg-NPs and Na2S2O3. When the concentration ofNa2S2O3is constant, the morphology, color and the maximum absorption wavelengthof TAg-NPs changed with the change of the concentrations of Cu2+, and the shiftvalues of maximum absorption wavelength was proportional to the concentration ofCu2+. Thus, a method for Cu2+detection by either UV-visible spectrophotometrydetection or naked eyes observation is established.