An ultra-sensitive photoelectrochemical aptasensor based on a CdIn₂S₄/ZnSnO₃ composite for the detection of adenosine...

Adenosine triphosphate (ATP) is an important extracellular signaling molecule in the human body. Its abnormal expression is closely related to the occurrence and development of various diseases, and accurate detection is of great significance for early disease diagnosis. However, conventional photoelectrochemical (PEC) sensors still suffer from low visible-light utilization, serious recombination of photogenerated carriers and limited detection sensitivity, making it difficult to achieve accurate detection of low-abundance ATP. In this work, an enzyme-catalyzed PEC aptasensor based on a CdIn₂S₄/ZnSnO₃ (CIS/ZSO) heterojunction was constructed. The heterojunction significantly enhances visible-light absorption and promotes the separation and transport of photogenerated carriers, with a photocurrent response approximately 10 times higher than that of pure CdIn₂S₄. In the presence of 3,3'-diaminobenzidine (DAB) and hydrogen peroxide (H₂O₂), the amino-functionalized MnFe₂O₄ (MnFe₂O₄-NH₂) nanozyme with outstanding peroxidase-like activity catalyzes the production of insoluble ox-DAB precipitates. The precipitates hinder interfacial electron transfer via steric hindrance and decrease the photocurrent. With specific recognition of ATP, the amount of MnFe₂O₄-NH₂ on the electrode surface was reduced, the photocurrent was recovered and a signal-on detection mode was achieved. The aptasensor exhibits a linear range from 10^-12 to 10^-7 g mL^-1 with a detection limit of 0.33 pg mL^-1, together with satisfactory reproducibility, stability and practical applicability. This work provides a new strategy for the efficient detection of low-abundance biological small molecules and a new approach for early clinical monitoring and diagnosis of diseases.