Carbon dots doped with sulfur and nitrogen (S,N-CDs) were utilised to design a paper-stripe based fluorescent probe for the detection of bilirubin. The S,N-CDs were synthesized through a microwave assisted route by using citric acid as carbon source and L-cysteine as a source of nitrogen and sulfur. The S,N-CDs exhibit bright blue fluorescence emission with a peak at 452 nm. Fluorescence is quenched by Fe(III) but selectively restored by bilirubin. The quenched fluorescent probe exhibit significant selectivity and sensitivity for bilirubin in the 0.2 nM to 2 nM concentration range, with a 0.12 nM detection limit. The method was applied to the determination of bilirubin in spiked human serum and urine samples. The method was used to design a paper based test stripe as a point of care device for visual bilirubin detection. Graphical abstract Schematic representation of sulphur and nitrogen doped carbon dots whose fluorescence is quenched by Fe(III) and turned on by bilirubin. Photograph of the corresponding system under day light and UV shows the feasibility of the phenomenon. The applicability of the assay was further extended by impregnating the probe on a filter paper.

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Depicting fluorescence sensing of protamine and heparin based on aggregation and disaggregation of copper nanoclusters.