Smart-Phone-Assisted Optical Biosensors Based on Silk-Fibroin-Decorated Reduced Graphene Oxide Quantum Dots for Fluorescent Turn-On Recognition of l-Dopa

Levodopa (l-dopa) is a gold standard neurological drug for symptomatic medication of Parkinson's disease. The long-term use of l-dopa therapy frequently leads to l-dopa-induced dyskinesia and several other non-motor flocculants for fluctuating plasma concentration. To alleviate the adverse effect of dopamine replacement therapy, sensitive detection of l-dopa is still challenging. Therefore, this study presents a simple strategy to develop an inexpensive, easy-to-use, smartphone-based fluorescence turn-on sensory system based on the aggregation-induced emission enhancement phenomenon for instant low-level detection of l-dopa in biological samples. The sensor was fabricated using silk-fibroin-decorated reduced graphene oxide quantum dots, which exhibit a progressive increase of fluorescence intensity in the presence of l-dopa. By measuring the turn-on efficiency of the sensor in elevated concentrations of l-dopa, the limit of detection (LOD) was evaluated as 76.18 nM over a linear range of 0–35 μM. We have further designed a smartphone-based electronic device involving a 365 nm light emitting diode attached below the rare camera for capturing the change of fluorescent color of the solution during sensing. From these images, red, green, and blue values are analyzed using a mobile phone application, and the corresponding LOD was found to be 0.29 μM in a similar linear range of concentration. This simple, cost-effective, and rapid screening gadget is very demanding for on-spot detection of the analytes in remote areas where sophisticated instrumentation is not usually available.