In this work, a photoelectrochemical (PEC) sensing system was developed for chemical detection without any tags. The system is based on methylammonium lead iodide chloride perovskite as the photoelectrochemical signal-generating molecule, tin oxide nanoparticles (SnO2) as the electron transport layer, and ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) as the stabilizer and electrolyte. The photosensitizer film is formed through spin-coating followed by low-temperature sintering. Upon irradiation with 473 nm light, an anodic photocurrent is generated in a blank electrolyte and changed significantly after addition of hemin into the electrolyte. The change of photocurrent after addition of hemin suggested that the chemicals participated in a photoelectrochemical process. Our work paves the way to developing analytical methods with perovskite.