Nanodiamond Coating Improves the Sensitivity and Antifouling Properties of Carbon Fiber Microelectrodes

Abstract

Nanodiamonds (NDs) are carbon nanomaterials with a core diamond crystalline structure and crystal defects, such as graphitic carbon and heteroatoms, on their surface. For electrochemistry, NDs are promising to increase active sites and decrease fouling, but NDs have not been studied for neurotransmitter electrochemistry. Here, we optimized ND coatings on microelectrodes and found that ND increases the sensitivity for neurotransmitters with fastscan cyclic voltammetry detection and decreases electrochemical and biofouling. Different sizes and functionalizations of NDs were tested, and ND suspensions were drop-casted onto carbon-fiber microelectrodes (CFMEs). The 5 nm ND-H and 5 nm ND-COOH formed thick coatings, while the 15 and 60 nm ND-COOH formed more sparse coatings. With electrochemical impedance spectroscopy, 5 nm ND-H and 5 nm ND-COOH had high charge-transfer resistance, while 15 and 60 nm ND-COOH had low charge-transfer resistance. ND-COOH (15 nm) was optimal, with the best electrocatalytic properties and current for dopamine. Sensitivity was enhanced 2.1 ± 0.2 times and the limit of detection for dopamine improved to 3 ± 1 nM. ND coating increased current for other cations such as serotonin, norepinephrine, and epinephrine, but not for the anion ascorbic acid. Moreover, NDs decreased electrochemical fouling from serotonin and 5-hydroxyindoleacetic acid, and they also decreased biofouling in brain slice tissue by 50%. The current at biofouled ND-coated electrodes is similar to the signal of pristine, unfouled CFMEs. The carboxylated ND-modified CFMEs are beneficial for neurotransmitter detection because of easy fabrication, improved limit of detection, and antifouling properties.

Diamond in medical devices and sensors: An overview of diamond surfaces

“…ND coatings of different chemical functionalities were applied to carbon fibre microelectrodes (CFMEs) and investigated using the technique fast scan cyclic voltammetry. Decreased fouling as well as improved sensitivity and limit of detection for neurotransmitter sensing was found with ND coatings, Figure 6 (Puthongkham & Venton, 2019). Further to forming films, NDs can be used as part of composites.…”

“…(c) CFME and (d) carboxylated ND-coated CFME. Reprinted (adapted) with permission fromPuthongkham, P., & Venton, B. J. (2019).…”

Recent Advances in In Vivo Neurochemical Monitoring

“…The Venton group optimized drop-cast ND coatings on a CFM and found that the carboxylated ND with a particle size of 15 nm gave the most sensitive DA response with FSCV detection. They showed that the ND coating reduced chemical fouling from 5-HT and 5-hydroxyindoleacetic acid and also decreased biofouling in tissue slices by 50% [ 90 ]. In addition, scientists at the Mayo Clinic reported the first use in humans of a polycrystalline boron doped diamond (BDD) microelectrode for recording in the thalamus; see Figure 2 F [ 54 ].…”

Next-Generation Diamond Electrodes for Neurochemical Sensing: Challenges and Opportunities

“…CFMEs are often fabricated through proprietary mechanisms, using low-throughput assembly methods, and are designed for industrial processes rather than electrochemical purposes [ 101 ]. Recently, boron doped diamond (BDD) deposition and growth processes were developed that enable the wafer patterning and growth of custom-deposited carbon electrodes [ 96 , 102 , 103 , 104 , 105 ]. Through these growth processes, BDD was grown on tungsten wires and carbon fiber surfaces.…”

“…Through these growth processes, BDD was grown on tungsten wires and carbon fiber surfaces. More recently, custom BDD microelectrodes (BDDMEs) encapsulated with polycrystalline diamond were developed [ 96 , 101 , 104 , 106 , 107 ]. BDD is an attractive material because it has a low background current, a wide potential window, and good biocompatibility [ 108 , 109 , 110 ].…”