Smartphone-integrated quantitative determination of bilirubin using luminescent carbon nanoparticles

Herein, using a green, cost-effective, and sustainable biomass precursor, luminescent carbon nanoparticles (CNP) are synthesized for selective bilirubin quantification. From high-resolution transmission electron microscopy (HRTEM) image, the prepared CNP exhibited spherical morphology and the crystallite size ranges from 8 to 16 nm. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of both sp² and sp³ hybridized carbon bonds within the carbon nanoparticles (CNP). Furthermore, Dynamic Light Scattering (DLS) analysis was performed to determine the hydrodynamic diameter of the CNP and the average particle size was found to be approximately 12.94 ± 0.19 nm. Under ultraviolet (UV) radiation of 350 nm wavelength, the CNP displayed excitation dependent emission characteristics, having an average lifetime of 4.4 ns. The fluorescence intensity of carbon nanoparticles reduced considerably in the presence of Fe³⁺ ions and fluorescence turn ON was achieved upon the addition of different concentrations of bilirubin. The probe displayed remarkable selectivity towards bilirubin over other potential interferences. Using a sensing platform based on a mobile phone application, the fluorescent probe exhibited a limit of detection (LOD) of 32 nM. Moreover, the fluorescent probe was efficiently employed for the detection of bilirubin in human serum and urine specimens. This cost-effective carbon-based "turn-off-on" fluorescent sensor makes it easy to detect bilirubin, through visual inspection under ultraviolet light, thereby enabling prompt diagnosis.