Heterojunctions　are　usually　designed　as　photocatalytically　active　interfaces　to　promote　the　separation　of　photo-induced　charge　carriers.　In　situ　construction　of　a　heterojunction　using　nucleation　sites　derived　from　the　same　precursor　effectively　enhances　the　extent　to　which　there　is　heterogeneous　contact　throughout　the　whole　mixture,　compared　with　heterojunction　formation　between　two　completely　crystalline　phases.　In　this　work,　(0　0　1)TiO2/Ti3C2　heterojunctions　were　successfully　fabricated　through　simple　hydrothermal　oxidation　of　the　Ti3C2　precursor　and　used　as　an　electrode　material　for　the　photoelectrochemical　(PEC)　detection　of　dopamine.　The　(0　0　1)TiO2　formed　on　the　surface　of　Ti3C2　using　Ti3C2　itself　as　the　source　of　titanium　not　only　increases　the　catalytically　active　surface　(001　facet)　for　dopamine　adsorption,　but　also　produces　a　superior　photoelectric　response　(compared　to　TiO2)　based　on　the　coupling　effect　of　(0　0　1)TiO2　and　the　two-dimensional　Ti3C2　inhibiting　the　recombination　of　electron–hole　pairs.　The　PEC　sensor　can　detect　dopamine　from　1.0　μM　to　1000　μM　with　a　limit　of　detection　of　0.52　μM,　with　good　stability,　and　high　selectivity.　This　work　therefore　suggests　that　(0　0　1)TiO2/Ti3C2　heterojunctions　represent　a　promising　material　for　applications　in　PEC　detection.　©　2021　The　Author(s)