Toward Non-Invasive Neurological Biomarker Monitoring: Dopamine Sensing in Tears with Laser-Induced Graphene Electrochemical Sensors.

Dopamine plays a crucial role in motor control, cognition, and emotional regulation, and its abnormal levels are associated with disorders such as Parkinson's disease and schizophrenia, highlighting the need for sensitive, selective, and noninvasive detection methods. This study reports the development of a high-performance, nonenzymatic electrochemical sensor based on laser-induced graphene, functionalized with nickel nitrate and urea, for the detection of dopamine. Cyclic voltammetry and differential pulse voltammetry were employed to assess the sensor's selectivity and overall performance. In-depth characterization by scanning electron microscopy and Raman spectroscopy confirmed the successful formation of a porous and electroactive graphene structure, uniformly functionalized with nickel ions and nitrogen-containing groups. These modifications enhanced electron transfer rates and increased the number of active sites for dopamine oxidation. Electrochemical measurements demonstrated excellent performance, with a linear detection range of 0.25-16.44 μmol·L-1, a limit of detection of 17.86 nmol·L-1, and a limit of quantification of 54.14 nmol·L-1, with R 2 = 0.98 in phosphate-buffered solution. In synthetic tear fluid, the sensor maintained a reliable response across four different concentrations ranging from 3.23 to 9.32 μmol·L-1. Furthermore, the sensor exhibited excellent analytical performance in real matrices, achieving recovery rates close to 100% in real sample analyses.