Static quenching and inner-filter effect assisted turn-off fluorescence sensor for the determination of hepatobiliary biomarker bilirubin based on luminescent copper nanoparticles

The determination of bilirubin level is a crucial aspect of medical diagnosis and plays a significant role in assessing the health of an individual, particularly in relation to the liver and blood. This paper discusses the development of a facile, cost-effective and sensitive turn-off fluorescence sensing platform for the determination of bilirubin based on highly stable and luminescent copper nanoparticles protected by ascorbic acid (AACuNPs). The fluorophore was characterised by UV–Visible spectrophotometry, FT-IR, XPS and EDX spectroscopic techniques as well as by TEM and zeta potential analysis. Bilirubin could selectively quench the fluorescence intensity of AACuNPs linearly in the concentration range from 1.00 × 10-5 M to 5.00 × 10-7 M and the limit of detection was obtained to be 2.48 × 10-7 M. The mechanism underlying the sensing of bilirubin has been explored with the help of various experimental techniques and is found to be a static quenching mechanism assisted by the inner filter effect. Moreover, the synthesized fluorophore has proved to be successful in the determination of bilirubin in synthetic physiological fluids. High selectivity and very low interference from probably coexisting species in the physiological fluids also verify the reliability of the sensor for the determination of bilirubin.