Development of gold nanoparticle-sheathed glass capillary nanoelectrodes for sensitive detection of cerebral dopamine

To develop in vivo monitoring strategies of neurotransmitters involved in brain chemistry is a challenging work for progress in understanding the roles that biomolecules play in pathology and physiology. Here we report a new type of gold nanoparticle-sheathed glass capillary nanoelectrode (Au/GCNE) for sensing cerebral dopamine. First, a size-controlled needle-type quartz capillary was pulled with a laser puller. Then, the capillary tip exterior was chemically functionalized with colloidal gold nanoparticles by the seed-mediated growth protocol. Through insulating the above tip with cathodic electrophoretic paint followed by heating to tune the exposed area of gold-nanoparticle-film, the Au/GCNE with tip apex radius ranging from ~8.9 to ~500 nm can be prepared. Scanning electron microscopy (SEM) and steady-state voltammetry were utilized to characterize the effective radius of nanoelectrodes. The results showed that the tip apex radius of Au/GCNE was mainly affected by the pre-pulled capillary tip, the modified AuNPs and the cathodic electrophoretic paint. By taking advantage of the modified AuNPs and the enhanced electrochemical performance of the nanoelectrode, a wide dynamic linear range from 2.0×10−8 M to 5.6×10−6 M with a low detection limit of 1.0×10−8 M (S/N=3), as well as good selectivity for dopamine, were first achieved with the Nafion-modified Au/GCNE. In addition, the designed glass substrates of Au/GCNE were mechanically stronger and their sharp tips aided in membrane penetration during implantation in the in vivo experiment. As a result, the Nafion-modified Au/GCNE was successfully applied for amperometrically monitoring dopamine in the striatum of anesthetic rats.