Heparin-MPA dual modified CdS quantum dots used as a simple and rapid label-free fluorescent sensor for protamine and hemin detection

Hererin, we reported a fluorescent “turn-on-off” nanosensor based on mercaptopropionic acid (MPA) and heparin (Hep) dual modified CdS quantum dots (Hep-MPA-CdS QDs), which is used for protamine and hemin detection with good sensitivity and selectivity. The negatively charged modifier, heparin, caught the positively charged protamine by static interaction. The protamine filled in the surface defects of Hep-MPA-CdS QDs, resulting in the florescence enhancement. With the addition of negatively charged hemin, the protamine was withdrew from the surface of the QDs, and combined with hemin, following the florescence quenching of the system. The concentration of protamine and hemin can be determined by measuring the fluorescent intensity of Hep-MPA-CdS QDs system. The detection limit of protamine and hemin are 5.2 nmol L− 1 and 48.6 nmol L− 1 respectively. Compared with the previous reports, this method avoided expensive fluorescence labeling, complex procedures and large-scale instruments. Since the MPA-CdS QDs (the precursor of Hep-MPA-CdS) can be modified with molecules other than heparin to detect other kinds of biomolecules, the method we presented has promising application in the field of biomedical detection, environmental monitoring, and food inspection, etc.