A wavelength-resolved ratiometric photoelectrochemical technique: design and sensing applications

In this work, a wavelength-resolved ratiometric photoelectrochemical (WR-PEC) technique was investigated and employed to construct a new type of PEC sensor with good sensitivity and anti-interference ability. The WR-PEC hybrid photoelectrodes were stepwise assembled using semiconductor quantum dots (QDs) and photoactive dyes. Under continuous irradiation, the photocurrent-wavelength (I-λ) curves reveal the dependence of the photocurrent on the wavelength. By monitoring the ratios of the two different PEC peak values, a wavelength-resolved ratiometric strategy was realized. Using CdS QDs and methylene blue (MB) as photoactive models, a dual-anodic WR-PEC sensor was established for sensitive detection of Cu²⁺. This ratiometric strategy was identified to be based on the quenching effect of Cu²⁺ towards CdS QDs and enhancement of the MB photocurrent through catalytic oxidation of leuco-MB. Under continuous illumination from 400 nm to 800 nm at a 0.1 V bias potential, a WR-PEC sensor for Cu²⁺ was developed with a wide linear range and a detection limit of 0.37 nM. This WR-PEC had a greatly improved anti-interference ability in a complex environment, and showed acceptable stability. Moreover, using the CdS/magnesium phthalocyanine (MgPc) and CdTe/MgPc as photoelectrodes, anodic-cathodic and dual-cathodic WR-PEC sensors were established, respectively. The WR-PEC technique could serve as a novel concept for designing ratiometric or multi-channel PEC sensors.