Label-free fluorescent detection of alkaline phosphatase with vegetable waste-derived green carbon probes

•A fluorescent carbon probe to detect alkaline phosphatase was prepared by modified ultrasound irradiation from vegetable waste.•Unique interaction among Cu2+, carbon probe, and pyrophosphate was used for the label-free detection of alkaline phosphatase.•The carbon probe-based biosensor showed high selectivity and sensitivity.•The biosensor showed great performance to determine alkaline phosphate levels in human serum with excellent precision.