As　Alzheimer＇s　disease　prevalence　continues　to　rise,　there　is　an　increasing　demand　for　efficient　on　-chip　biosensors　capable　of　early　biomarker　detection.　This　study　presents　a　novel　biosensor　chip　leveraging　vertical　cavity　surface　emitting　laser　(VCSEL)　technology,　with　Parylene　C　serving　as　the　antibody　coupling　layer　and　utilizing　a　streamlined　one-step　antibody　modification　method.　Integration　of　Parylene　C　enhances　chip　sensitivity　from　34.28　mu　W/RIU　to　40.32　mu　W/RIU.　Moreover,　post　-testing　removal　of　Parylene　C　enables　chip　reusability　without　significant　alteration　of　results.　The　sensor　demonstrates　effective　detection　of　A　beta　42　,　an　Alzheimer＇s　biomarker,　exhibiting　a　linear　range　of　1-200　ng/mL　and　a　detection　limit　of　0.26　ng/mL.　These　findings　underscore　the　reusability　and　reliability　of　the　ultrathin　Parylene　C-based　VCSEL　biosensor　chip,　highlighting　its　potential　for　point-of-care　Alzheimer＇s　disease　diagnosis.