Photoluminescence sensing of bilirubin in human serum using L-cysteine tailored manganese doped zinc sulphide quantum dots

Bilirubin (BR) is a protective antioxidant generated as end-product of heme catabolism in human. However, BR accumulation in biological tissues in connection with neonatal and hereditary jaundice causes severe hyperbilirubinemia and neurotoxicity. Herein, a fluorescence turn-off sensor for the detection of BR, a major biomarker for jaundice, is designed based on L-cysteine capped manganese doped zinc sulphide quantum dots (Mn:ZnS QDs). The QDs were synthesized by a microwave assisted chemical co-precipitation method. Under optimum conditions, the luminescence quenching response of Mn:ZnS QDs can be effectively used for detection of BR in the linear range of 10.99 mu M - 63.84 mu M BR. The limit of detection (LOD) is as low as 1.8 mu M and limit of quantification (LOQ) is 6 mu M. The plausible mechanism behind BR induced luminescence quenching is reductive photo-induced electron transfer (PET) in which Mn:ZnS QDs act as electron acceptor and BR act as electron donor. The developed sensor show good selectivity for BR over other co-existing biomolecules such as creatine, cholesterol, bisphenol, glutathione, uric acid, urea, hemoglobin, fructose, galactose and glucose. The developed sensor was validated by the detection of BR in spiked human serum and urine samples. For practical applications, a paper strip based sensor was also developed.