Photoelectrochemical　(PEC)　biosensors　incorporating　biomolecular　recognition　with　photon-to-electron　conversion　capabilities　of　the　photoactive　species　have　been　developed　for　molecular　diagnosis,　but　most　involve　difficulty　in　adjusting　band　gap　positions　and　are　unsuitable　for　PEC　biodetection.　In　this　work,　an　innovative　PEC　biosensor　combined　with　quantum　size-controlled　engineering　based　on　quantum　confinement　by　controlling　the　quantum　size　was　designed　for　the　detection　of　human　papillomavirus-16　(HPV-16)　through　CRISPR-Cas12a　(Cpf1)-induced　disassembly　of　Z-scheme　heterojunction.　To　the　best　of　our　knowledge,　quantum　size-controlled　engineering　that　precisely　tunes　the　properties　of　photoactive　materials　is　first　utilized　in　the　PEC　bioanalysis.　Based　on　the　quantum　size　effect,　the　light　absorption　efficiency　and　charge-transfer　rate　were　tuned　to　suitable　levels　to　obtain　the　best　PEC　performance.　After　incubation　with　target　HPV-16,　the　binding　of　Cas12a-crRNA　to　the　target　double-stranded　DNA　(dsDNA)　stimulated　the　activity　of　indiscriminate　cleavage　toward　single-stranded　DNA　(ssDNA),　resulting　in　a　decrease　in　photocurrent　due　to　the　blocking　of　electron　transfer　through　the　heterojunction.　By　optimizing　experimental　conditions,　the　Z-scheme　sensing　system　exhibited　incredible　photocurrent　response　to　HPV-16　in　the　range　from　3.0　pM　to　600　nM　with　a　detection　limit　of　1.0　pM.　Impressively,　the　application　of　the　quantum　size　effect　could　stimulate　more　interest　in　the　precise　design　of　band　gap　structure　to　improve　PEC　performance.　©　2022　American　Chemical　Society.