Carbon quantum dots derived from sugarcane bagasse as a functional layer in SPR sensors for interleukin detection

This study focuses on utilizing an environmentally friendly and sustainable carbon precursor: sugarcane bagasse, to synthesize Carbon Quantum Dots (CQDs) as an active SPR sensor layer. The CQDs were synthesized via a hydrothermal method. The CQDs were then uniformly deposited onto a gold (Au) substrate on the optical fiber using the Ultrasonic Spray Pyrolysis technique. Optical and morphological characterizations showed that the resulting CQDs, with a particle size of approximately 4 nm, produced a photoluminescence emission peak in the blue-green range, with a red shift that depended on the excitation wavelength and bagasse mass. UV–Vis spectra analyzed using the Tauc plot method showed an increase in the band gap from 3.28 e V to 3.55 e V with increasing bagasse mass. The gap increase indicates an increase in the refractive index due to changes in the electronic structure, thereby strengthening the interaction between the evanescent waves and the analyte. The performance testing of the SPR sensor with a CQDs layer was carried out with the human interleukin −17 isolate (IL-17) biomolecule, and showed an increase in sensor sensitivity up to 2 , 105.07 ± 0.055 n m / R I U , with a figure of merit (FOM) value of 13.507 ± 0.120 RIU - 1 and a limit of detection (LOD) reaching 0.074 ± 0.002 R I U . The resonance shift and significant decrease in transmittance prove the role of CQDs in increasing sensor sensitivity. These results demonstrate the novelty of using biomass waste-based CQDs as the active layer of an SPR sensor, which not only improves performance but also supports sustainability