A dual-model immobilization-free photoelectrochemical/visual colorimetric bioanalysis based on microemulsion...

Herein, a novel silver ion-loaded gold microemulsion assemblies (Au/Ag⁺ MAs) mediated multifunctional signal amplification strategy was proposed to construct a sensitive immobilization-free photoelectrochemical (PEC)/colorimetric biosensor for carcinoembryonic antigen (CEA) detection. Through the sandwiched reaction among CEA, the CEA aptamer (DNA1) loaded on the Au nanoparticles (NPs) functionalized iron oxide (Fe₃O₄) nanospheres and another CEA aptamer (DNA2) immobilized on Au/Ag⁺ MAs, a complex is formed and acquired by magnetic separation. Then, Au/Ag⁺ MAs of the complex are disassembled into Au NPs and Ag⁺ ions driven by an acetone response, and the obtained demulsification solution is transferred to the cadmium sulfide/cadmium telluride (CdS/CdTe) photoactive composites modified electrode. Based on the multiple inhibition functions (blocking effect of oleylamine; energy transfer effect of Au NPs; and electron snatching effect of Ag⁺), the photocurrent of the electrode decreases obviously, resulting in the ultrasensitive detection of CEA (a detection limit of 16 fg mL^-1). Interestingly, the ion-exchange reactions between CdS/CdTe composites and Ag⁺ ions generate silver sulfide/silver telluride (Ag₂S/Ag₂Te) composites, and a color change of composites can be distinguished directly, leading to a quick visual detection of CEA. Compared with the traditional single-modal assay for CEA, such dual-modal PEC/colorimetric assay is a more accurate and reliable due to different mechanisms and independent signal conversion. This work will offer a new perspective for the applications of various self-assemblies in PEC bioanalysis.