Abstract
In this study, silver nanoparticles (Ag NPs), which were synthesized by biocompatible chitosan, showed strong surface plasmon resonance (SPR) effect and were used to develop a naked-eye biosensor. Human serum albumin (HSA) with different concentrations were conjugated with chitosan to demonstrate the feasibility of protein sensing. The mechanism of Ag NP synthesis by HSA-conjugated chitosan was studied via UV-Vis spectra and TEM analyses. Furthermore, the UV-Vis spectra were transformed to chromatic diagram to characterize the color of synthesized Ag NPs to correlate the HSA concentration. In this work, the mechanism of Ag NP synthesis by chitosan was discussed in the first instance, followed by the study on the effects of HSA-conjugated chitosan. The result showed that HSA with different concentrations restrained the reaction of Ag NP formation to different extent and therefore led to the color changes. Furthermore, UV-Vis and transmission electron microscopy (TEM) were used to analyze the Ag NPs to demonstrate the restraining effect caused by HSA. Moreover, the effect of HSA on restraining the chemical reduction to form Ag NPs was applied to develop colorimetric biosensor. Through synthesis of Ag NPs in chitosan, which was conjugated with HSA of different concentrations, the lighter colors of Ag NPs were observed when the conjugating concentration of HSA is higher. The severe color change occurred when the formation of Ag NPs was completely retarded. Furthermore, the detecting range is adjustable through tuning the concentration of chitosan. In summary, this study addresses a new mechanism that the synthesis of Ag NPs by chitosan would be restrained by conjugating proteins on chitosan to provide a naked-eye, convenient, instant-detecting and cost-effective biosensor for everyone.