This　work　presented　an　innovative　and　rationally　engineered　palindromic　molecular　beacon　(PMB)　based　＂Z-scheme＂　photoelectrochemical　(PEC)　biosensing　protocol　for　the　selective　screening　of　kanamycin　(Kana)　through　DNA　hybridization-induced　conformational　conversion.　Interestingly,　the　ingeniously　designed　PMB　integrated　the　multifunctional　elements　including　recognition　region,　primer-like　palindromic　fragment,　and　polymerization-nicking　template.　The　cosensitized　structures　consisted　of　CdS　quantum　dot　functionalized　hairpin　DNA2　(QD-HP2)　and　region-selectively　deposited　gold　nanoparticles　onto　{001}　facets　of　bismuth　oxychloride　(BiOCl-Au).　Compared　with　BiOCl-Au　alone,　the　attachment　of　CdS　QDs　onto　BiOCl-Au　(i.e.,　BiOCl-Au-CdS　QDs)　exhibited　evidently　enhanced　photocurrent　intensity　thanks　to　the　synergistic　effect　of　Z-scheme　BiOCl-Au-CdS　QDs.　After　incubation　with　target　Kana,　Kana-aptamer　binding　could　induce　the　exposure　of　PMB　region　for　hairpin　DNA1　(HP1).　The　exposed　palindromic　tails　hybridized　with　each　other　(like　a　molecular　machine)　to　consume　the　substrates　(dNTPs)　and　fuels　(enzyme)　for　the　releasing　of　numerous　nick　fragments　(Nick).　The　as-generated　nick　fragments　could　specifically　hybridize　with　the　complementary　region　of　QD-HP2,　thus　resulting　in　decreasing　photocurrent　because　of　the　increasing　spatial　distance　for　electron　transfer　between　two-type　photosensitizers.　Under　optimum　conditions,　the　PMB-based　sensing　system　exhibited　satisfying　photocurrent　responses　toward　target　Kana　within　the　working　range　from　50　to　5000　fM　at　a　low　detection　limit　of　29　fM.　Impressively,　the　concept　of　a　palindromic　fragment-mediated　primer-free　biosensing　strategy　offers　a　new　avenue　for　advanced　development　of　efficient　and　convenient　biodetection　systems.　Copyright　©　2019　American　Chemical　Society.