Porous Nitrogen-Doped Crumpled Graphene Nanoparticles: A Metal-Free Nanozyme for Selective Detection of Dopamine in Aqueous Medium and Human Serum

Accurate detection of trace analytes in biological samples is essential for medical diagnostics but usually requires complex and expensive instruments. Nanozymes, a series of nanosized systems with a catalytic activity mimicking that of peroxidase enzymes, offer a useful alternative for the design of sensing devices. In this article, we describe the synthesis of porous 3D nitrogen-doped crumpled graphene nanoparticles (CGNPs) and their use as a platform for the sensitive detection of dopamine (DA) in complex biological media such as blood serum. CGNPs were prepared by doping graphene oxide (GO) using ammonium hydroxide in a hydrothermal treatment. This procedure leads to the crumpling of GO sheets into porous sphere-like nanoparticles, with a diameter of 34 ± 10 nm. These nanoparticles with high surface area and improved electronic properties proved very active for the oxidation of the peroxidase substrate 3,3′,5,5′- tetramethylbenzidine (TMB). Our sensing device relied on the scavenging of hydroxyl radicals by DA, resulting in a turn-off effect for TMB oxidation. The system selectively detected DA with a limit of detection of 1.15 μM and a linearity range of 1 to 20 μM. The system also possessed good selectivity for DA in the presence of various interfering species, as well as in human blood serum.