Fluorescent Nitrogen-doped Carbon Dots-based Turn-off Sensor for Bilirubin.

Bilirubin (BR), a heme protein produced from breakdown of haemoglobin is present in aged red blood cells; whose abnormal concentration is associated with diseases like hyperbilirubinemia, coronary disease, iron deficiency, and so on. Herein, we have synthesized a selective, sensitive, and low-cost sensing platform using fluorescent nitrogen doped carbon dots (NCDs), prepared from precursors; citric acid and urea via a simple microwave-assisted method. The emission at 444 nm on excitation with 360 nm was well quenched in presence of BR suggesting a direct turn-off detection for BR. Characterization of developed probe was done by UV-Visible absorption studies, photoluminescence studies, SEM, TEM, ATR-FTIR, XPS, and DLS analysis. BR was detected with a Limit of Detection (LoD) and Limit of Quantification (LoQ) of 0.32 µM and 1.08 µM respectively. NCDs exhibited excellent selectivity and sensitivity towards BR in the presence of co-existing biomolecules and ions. Practical feasibility was checked by paper-strip-based sensing of BR and spiked real human samples were used for conducting real sample analysis.

Picric Acid Incorporated Fluorescent Nitrogen Doped Carbon Dot for "Turn-On" Detection of Glutathione.

Glutathione (GSH), a non-protein thiol in living cells whose abnormal level indicates the onset of diseases like Alzheimer's, HIV, diabetes, cancer, Parkinson's, Dementia, etc. Herein, we have synthesized a low-cost, selective, and sensitive detection platform by using citric acid and urea-derived fluorescent carbon dots (NCDs) via the microwave-assisted method, showing fluorescence at 444 nm. This fluorescence was quenched with picric acid (PA), and this probe, picric acid incorporated nitrogen doped carbon dot (NCDs@PA) was further used for the detection of GSH. The characterization of the probe was done by photoluminescence study, UV-Visible absorption studies, ATR-FTIR, SEM, and DLS analysis. GSH induced fluorescence recovery due to the competitive binding of GSH to PA. GSH was detected within a linear range of 0.31 mM- 2.43 mM with a Limit of Detection (LoD) and Limit of Quantification (LoQ) of 32.10 µM and 107.32 µM, respectively. The sensor exhibited good selectivity and sensitivity towards GSH among various co-existing ions and biomolecules. The paper-strip-based sensing of glutathione was conducted to check practical applicability of the probe, and a real sample analysis was also conducted from spiked human samples.