A reliable ratiometric fluorescence sensing of heparin and its antidote based on cationic carbon quantum dots and acid red 87

A reliable, selective, and sensitive ratiometric fluorescence sensor was fabricated for the detection of protamine (PROT) and heparin (HEPR). It is based on a rational combination of Acid Red 87 (AR 87) as an anionic dye and polyethyleneimine modified carbon quantum dots (PEI@CQDs) as cationic fluorescent nanoparticles via elec-trostatic interaction. Addition of positively charged PROT quenched the negatively charged AR 87 via static quenching; while, the addition of HEPR restored the fluorescence of AR 87 via the formation of PROT-HEPR complex. Simultaneously, the fluorescence emission of PEI@CQDs remained constant. Thus, a ratiometric response (FAR 87/FPEI@CQDs) was linear with the concentration of PROT and HEPR in the range of 0.006-20 mu g mL-1 and 0.018-22 mu g mL-1 with detection limits (S/N) of 1.7 ng mL-1 and 6.0 ng mL-1, respectively. The analytical sensing platform offers several advantages including good selectivity, low LOD values, low-cost, and fast-response. Importantly, the sensing platform was used to detect PROT and HEPR in human serum and urine samples with satisfactorily recoveries % and RSDs %.