Engineering the Signal Transduction between CdTe and CdSe Quantum Dots for <i>in Situ</i> Ratiometric Photoelectrochemical Immunoassay of Cry1Ab Protein

Abstract

Controllable modulation of a response mode is extremely attracting to fabricate biosensor with programmable analytical performances. Here, we reported a proof-of-concept ratiometric photoelectrochemical (PEC) immunoassay of Cry1Ab protein based on the signal transduction regulation at the sensing interface. A sandwich-type PEC structure was designed so that gold nanorods sensitized quantum dots to fix primary antibody (Au NRs/QDs-Ab₁) and methylene blue sensitized QDs to combine a second antibody (MB/QDs-Ab₂), which served as photoelectric substrate and signal amplifier, respectively. Unlike common recognition element, such a sandwich-type PEC structure allowed for the <i>in situ</i> generation of two specific response signals. For analysis, Cry1Ab captured by Au NRs/QDs-Ab₁ led to a decreased photocurrent (<i>I</i>_Cry1Ab), while the subsequently anchored MB/QDs-Ab₂ produced another photocurrent (<i>I</i>_MB). Noteworthy, by taking advantage of the different energy band gaps of QDs, varying locations of CdTe and CdSe QDs could realize different signal transduction strategies (i.e., Mode 1 and Mode 2). Investigations on data analysis of <i>I</i>_Cry1Ab and <i>I</i>_MB <i>via</i> different routes demonstrated the superior analytical performances of ratiometry (Mode 1). Consequently, the ratiometric PEC immunosensor offered a linear range of 0.01-100 ng mL^-1 with a detection limit of 1.4 pg mL^-1. This work provides an efficient strategy for <i>in situ</i> collection of multiple photocurrents to design ratiometric PEC sensors.