A label-free photoelectrochemical immunosensor based on CdS-decorated dual-ligand metal-organic framework nanocomposite for sensitive detection of Salmonella typhimurium.

A label-free photoelectrochemical (PEC) immunosensor for rapid and sensitive detection of Salmonella typhimurium has been designed using a dual-ligand metal-organic framework (MOF) that was synthesized by electrochemical deposition for in-situ generating CdS nanoparticles. This novel MOF film was constructed by simultaneous introduction of perylene tetracarboxylic acid dianhydride (PTCDA) as the organic ligand and zinc phthalocyanine (ZnPc) as a guest molecule via a one-step electrochemical deposition method, yielding ZnPTC-ZnPc MOFs. This strategy relied on strong electrostatic interactions and coordination competition into influence the MOF growth process, resulting in the firm immobilization of both ZnPTC and ZnPc within the MOF structure. Then, the ZnPTC-ZnPc might catalyze the Cd ions react with thioacetamide to in-situ generate CdS nanoparticles on its surface, realizing the uniform formation of CdS to avoid the particle aggregation problem of the traditional modification. The unique porous structure of ZnPTC-ZnPc-CdS shortened transportation distance of the generating charge, accelerated surface reaction between photoelectrode and electrolyte, and broadened the light absorption into the visible region and inhibited the electron-hole complexation. The photoelectric conversion efficiency of ZnPTC-ZnPc-CdS reaches to 0.677%. Under the optimal conditions, a sensitive PEC immunosensor was developed for sensing Salmonella of concentrations linearly ranging from 1 fg/mL to 100 ng/mL, with a limit of detection of 0.27 fg/mL (S/N = 3). Therefore, the proposed strategy provides a reliable solution to realize the trace detection of Salmonella, and opens a new door to design and application of the MOF composite-based PEC biosensor.