(a) Exploded view of a smartphone-based PEC sensing system for portable detection of HER2, including smartphone, LED light, Co9S8@ZnIn2S4-modified SPE, and electronic readout circuit. (b) Block diagram of electronic readout circuit. (c) Photocurrent-time curves of Co9S8@ZnIn2S4-modified SPE toward HER2 with different concentrations. (d) Corresponding calibration curve between the photocurrent intensity and HER2 concentrations. (e) Smartphone screen of photocurrent measurements and HER2 concentrations converted from linear equations.