Fiber-optic biosensor based on the laccase immobilization on silica-functionalized fluorescent carbon dots for the detection of dopamine and multi-color imaging applications in neuroblastoma cells

Abstract An efficient and cost-effective biosensor is of the great demand for the detection of the biologically significant neurotransmitter dopamine. In this context, enzymatic biosensors show excellent sensitivity and selectivity. In this study, we developed a laccase immobilized fiber-optic biosensor based on the fluorescence principle for the detection of dopamine. To design this biosensor, we used microwave irradiation to synthesize carbon dots (CDs) using curcumin and dimethylformamide, and the resulting CDs were called CDD-CDs. These were functionalized with a silicon precursor, 3-(aminopropyl)-triethoxysilane), and were referred to as APT-CDs. Furthermore, laccase was covalently immobilized to the APT-CDs to construct a novel bioprobe. The CDD-CDs, APT-CDs, and bioprobe showed orange (λem = 586 nm) green (λem = 533 nm), and blue-colored emissions (λem = 476 nm) at 430, 380, and 360 nm excitation wavelengths, respectively. The CDD-CDs and bioprobe showed quantum yields of 14.8% and 10.2%, respectively. The CDD-CDs displayed solvatochromism in various solvents. Bioprobe showed a significant fluorescence quenching for dopamine in the linear range of 0-30 μM with a detection limit of 41.2 nM. Bioprobe was immobilized on the tapered optical fiber using ethyl cellulose by a simple dip-coating method and investigated for multi-color imaging applications. The resulting tapered optical fiber achieved a satisfactory detection limit of 46.4 nM in the dopamine concentration range of 0-10 μM. The bioprobe demonstrated high biocompatibility, long-lasting photostability, and thermal stability, and had sufficient cytotoxicity in human neuroblastoma cells (SH-SY5Y) with excellent multi-color imaging potential. The practicality of the bioprobe was investigated in human serum and cerebrospinal fluid.