For　rapid　and　sensitive　detection　of　miRNA-210,　which　is　important　for　improving　the　reliability　of　clinical　diagnosis　of　breast　cancer,　a　dual-signal　mode　ratiometric　photoelectrochemical　(PEC)　sensor　based　on　a　Au/GaN　photoanode　is　proposed.　First,　a　DNA　probe　was　designed　that　could　complement　the　target　miRNA-210.　Then,　another　G-rich　DNA　sequence　was　designed　to　mismatch　the　probe　and　form　a　double-stranded　DNA　(dsDNA).　Upon　addition　of　the　target,　the　dsDNA　unwinds　from　its　binding　site　and　releases　G-rich　single-stranded　DNA.　In　the　presence　of　Mg2+　and　K+,　this　single-stranded　DNA　molecule　spontaneously　forms　a　G-quadruplex　structure,　facilitating　the　rapid　transport　of　photogenerated　holes,　thereby　increasing　the　photocurrent　response　of　Au/GaN　and　enabling　sensitive　label-free　detection　of　miRNA-210.　By　control　of　different　pH　values,　a　response　signal　was　generated　at　pH　8,　while　a　reference　signal　was　produced　at　pH　5.　The　designed　PEC　system　shows　a　high　potential　for　the　development　of　miRNA-210　detection.　Ultimately,　the　response　signal-to-reference　signal　ratio　was　used　as　the　variable,　and　a　broad　linear　span　ranging　from　10　fM　to　1　nM　(R-2　=　0.993)　has　been　exhibited,　with　a　detection　threshold　of　3　fM　(S/N　=　3).　The　designed　PEC　platform　shows　potential　for　the　development　of　other　disease　markers.