Correlation of Graphene Defect Density in Saccharide Carbon Dots for Electrochemical Dopamine Detection

Abstract

ABSTRACT A study was conducted to investigate the detection of dopamine levels in urine to diagnose neuroblastoma, a childhood cancer. A series of carbon dots (sucrose, palatinose and raffinose) were synthesized in the Leblanc lab at U. Miami-Coral Gables and applied for the electrochemical sensing of dopamine. A cobalt oxide-sucrose carbon dot (Co3O4-SucCD) composite was developed, utilizing a 1:1 mixture (by mass) suspended in absolute anhydrous ethanol, followed by sonication for 30 min. to facilitate the tethering of sucrose carbon dots (SucCDs) onto the Co3O4 nanoparticles. The electrode demonstrated selectivity towards urea, uric acid, glucose, and ascorbic acid, common interferes in urine. With a limit of detection of 1.91 µM in PBS, the electrode exhibited a linear dynamic range of 10-100 µM, R2=0.990, and successfully detected 5 µM dopamine in urine samples, suitable for identifying elevated dopamine levels indicative of neuroblastoma. Calibration curve fitting in simulated urine yielded a quadratic equation with an R2 = 0.997. The diffusion coefficient of the electrode in phosphate buffer was determined to be 5.21 x 10-5 cm2•sec-1. The correlation between graphene defect density within the saccharide carbon dots for dopamine sensing was investigated, revealing that the defect density decreased in the order of SucCDs (0.195) > PalCDs (0.115) > RafCDs (0.0975), while the electrocatalytic sensitivity followed the trend of RafCDs < PalCDs < SucCDs. The composite particles exhibit an average size of 68.47 ± 0.77 nm with a coefficient of determination R2= 0.978. SEM-EDX analysis indicates a presence of 0.6% cobalt within the composite. The data suggests that a multilayer of carbon dots (CDs) surrounds the cobalt oxide particles, rendering low atomic % cobalt as detected by EDX.