Red-emissive carbon dots based fluorescent and smartphone-integrated paper sensors for sensitive detection of carbendazim

•A red-emissive carbon dots based fluorescent nanosensor was fabricated for sensing carbendazim.•R-CDs were synthesized by solvothermal method and surface charge engineering with excellent performance.•The novel nanosensor exhibited LOD of 3.5 ng/mL and range of 10–250 ng/mL for carbendazim.•Real application in Lotus seeds confirmed the excellent reliability with satisfactory recovery.•Visual paper-based sensor with smartphone was developed for rapid on-site carbendazim detection.