QPRTase modified N-doped carbon quantum dots: A fluorescent bioprobe for selective detection of neurotoxin quinolinic acid in human serum.

Highly fluorescent nitrogen doped carbon quantum dots (NCQDs) were synthesized using microwave assisted green method. It was characterized by Transmission Electron Microscopy (TEM), FTIR, UV-Visible absorption and Photoluminiscence (PL) techniques. The NCQDs were immobilized with an enzyme named quinolinate phoshphoribosyl transferase (QPRTase). The NCQDs immobilized by QPRTase was used as a fluorescent bioprobe for the selective detection of endogenous neurotoxin quinolinic acid (QA) whose elevated level in serum is marker of many neurological disorders such as Alzheimer's, Huntington's and HIV associated dementia (HAD) as well as deficiency of vitamin B6. Steady state PL studies were carried out to measure the PL response of the fabricated fluorescent bioprobe as a function of QA concentrations in human serum samples. This probe was found applicable in linear range [3.22-51µM] with the limit of detection ~ 6.51µM. It has desirable sensitivity ~ (0.02340±0.0001) µM-1, excellent stability for ~ 7 weeks and good reproducibility. The similar response of this fluorescent bioprobe for QA detection in triple distilled water and human serum shows that it is unaffected by variation in media. Hence, this fluorescent bioprobe can be employed for QA detection in serum sample for the early detection of many diseases.