1：Experimental Design and Method Selection:

The biosensor is based on a photoelectrochemical assay using a modified ITO electrode with CdS quantum dots and DBA. The method involves the chelation of Cu2+ by PPi, release of Cu2+ by PPase hydrolysis, and triggering of OPD-DBA reaction to shield light excitation, leading to a measurable photocurrent difference.

2：Sample Selection and Data Sources:

PPase samples with varying activities, including spiked human serum albumin (HSA) matrices, were used. Chemicals were reagent grade or higher, with solutions prepared in deionized water.

3：List of Experimental Equipment and Materials:

ITO electrodes, CdS QDs synthesized from cadmium chloride and sodium sulfide, PDDA, OPD, DBA, copper chloride, PPi, PPase, HSA, and other chemicals from suppliers like Sigma-Aldrich and J.T. Baker. Apparatus includes a CHI 609 electrochemical analyzer, Philips TUV 8W lamp, Shimadzu UV-1601 spectrometer, and JEOL JEM-ARM200FTH TEM microscope.

4：Experimental Procedures and Operational Workflow:

The ITO electrode was modified sequentially with PDDA, CdS QDs, PDDA, and DBA. A mixture of PPi-Cu2+ complex, OPD, and sample was placed on the electrode and incubated for 2 hours. Photocurrent was measured using a three-electrode system under light irradiation.

5：Data Analysis Methods:

Photocurrent differences were measured and correlated with PPase activity using calibration curves. Statistical analysis included calculation of limit of detection (LOD) based on signal-to-noise ratio and reproducibility assessments.