A　heterojunction　with　excellent　photocatalytic　performance　based　on　graphene-like　carbon　nitride　(g-C3N4)　nanosheets　and　dendritic　zinc(II)　phthalocyanine　was　proposed.　Herein,　the　g-C3N4　with　excellent　photo-activity　and　high　nitrogen　content　was　readily　available　as　a　functional　material.　The　g-C3N4　acted　as　an　electron　pair　donor　for　dendritic　zinc(II)　phthalocyanine　through　axial　coordination,　forming　the　pn　heterojunction.　Then　by　taking　advantage　of　the　distortion　of　dendritic　zinc(II)　phthalocyanine,　the　spatial　charge　separation　of　photo-generated　charge　carriers　in　this　metal　macrocycle　achieved　high　efficiency,　resulting　in　the　enhanced　photo-to-electric　conversion　efficiency.　Therefore,　the　optoelectronic　sensing　device　based　on　the　heterojunction　led　to　an　enhanced　photocurrent,　and　made　it　a　promising　candidate　for　establishing　photoelectrochemical　biosensors.　Moreover,　the　p-n　heterojunction　was　successfully　applied　to　the　detection　of　choline　with　a　wide　linear　range　from　10　nM　to　5　mu　M,　which　could　be　oxidized　by　the　photo-generated　holes.　Along　with　these　attractive　features,　the　as-proposed　biosensor　also　displayed　a　remarkable　specificity　against　other　interferents　and　could　be　successfully　used　for　detecting　choline　in　real　samples.　The　heterojunction　with　enhanced　photoelectronic　properties　provides　a　promising　format　for　the　future　development　of　photoelectrochemical　biosensors.