The invention relates to an electrochemical analysis technology, in particular to a method and a device for detecting potential change by using a photoelectrochemical method. Using electrode of modified photosensitive material as working electrode, ion selective electrode as reference electrode and Pt as auxiliary electrode; The potential of the working electrode is regulated and controlled by the potential of the reference electrode, and quantitative/qualitative determination of ions to be detected under activity change is realized according to current change output by the working electrode before and after illumination. According to the invention, the potential change of the ion selective electrode is measured by using photoelectrochemistry with current as an output signal; and unlike a classical potential method, the ion activity detection can reach a pA order of magnitude by using a current method, so that the sensitivity is greatly improved.
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