Sodium Alginate Micelle-Encapsulating Zinc Phthalocyanine Dye-Sensitized Photoelectrochemical Biosensor with CdS as the Photoelectric Material for Hg²⁺ Detection

A simple and selective photoelectrochemical (PEC) biosensor was constructed for Hg²⁺ detection based on zinc phthalocyanine (ZnPc) dye-sensitized CdS using alginate not only as a carrier but also as a binder. First, CdS as a photoactive material was in situ modified on the electrode surface using a rapid and simple electrodeposition to obtain an initial photocurrent signal. Second, ZnPc was loaded in the amphiphilic alginate micelle and then was coated onto the CdS film surface via alginate as the binder. The photocurrent was subsequently enhanced due to the favorable dye sensitization effect of ZnPc to CdS. Finally, the thymine-rich probe DNA was immobilized on the modified ITO surface via coupling reaction between the carbonyl groups of the amphiphilic polymer and the amino groups of the probe DNA. In the presence of Hg²⁺, the thymine–Hg²⁺–thymine (T–Hg²⁺–T) structure was formed due to the specific bond of Hg²⁺ with thymine, resulting in the decrease of photocurrent due to the increase of steric hindrance on the modified electrode surface. The proposed PEC biosensor for Hg²⁺ detection possessed a wide linear range from 10 pM to 1.0 μM with a detection limit of 5.7 pM. This biosensor provides a promising platform for detecting other biomolecules of interest.