1：Experimental Design and Method Selection:

The biosensor is based on a cascaded quadratic amplification strategy combining catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) for signal amplification. Mn:CdS@ZnS QDs serve as the photoelectric material, and MnPP acts as a photosensitizer. The "on-off-on" strategy reduces background signals.

2：Sample Selection and Data Sources:

Oligonucleotides (HP1, HP2, S1, S2) and miRNA 141 were used, with sequences provided. Human serum samples were diluted 50-fold for practical application.

3：List of Experimental Equipment and Materials:

Equipment includes CHI 604D and CHI 440A electrochemical workstations, TEM, SEM, XPS, EDX. Materials include Cd(NO3)2, MnAc2, Na2S·9H2O, ZnAc2, Tris, MCH, TCEP, AA, TB, DEPC, oligonucleotides from specified suppliers.

4：Experimental Procedures and Operational Workflow:

GCEs were polished, modified with Mn:CdS@ZnS QDs, HP1, MCH, miRNA 141 and HP2, S1 and S2, and MnPP sequentially. PEC measurements used a white LED lamp (400-700 nm, 14 mW/cm2) with AA as a sacrificial electron donor.

5：Data Analysis Methods:

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for electrochemical characterization. Photocurrent responses were recorded, and a linear regression equation was derived for quantification.