Analysis of Carbon-Based Microelectrodes for Neurochemical Sensing

Abstract

The comprehensive microscopic, spectroscopic, and in vitro voltammetric analysis presented in this work, which builds on the well-studied properties of carbon-based materials, facilitates potential ways for improvement of carbon fiber microelectrodes (CFMs) for neuroscience applications. Investigations by both, scanning electron microscopy (SEM) and confocal Raman spectroscopy, confirm a higher degree of structural ordering for the fibers exposed to carbonization temperatures. An evident correlation is also identified between the extent of structural defects observed from SEM and Raman results with the CFM electrochemical performance for dopamine detection. To improve CFM physico-chemical surface stability and increase its mechanical resistance to the induced compressive stress during anticipated in vivo tissue penetration, successful coating of the carbon fiber with boron-doped diamond (BDD) is also performed and microspectroscopically analyzed here. The absence of spectral shifts of the diamond Raman vibrational signature verifies that the growth of an unstrained BDD thin film was achieved. Although more work needs to be done to identify optimal parameter values for improved BDD deposition, this study serves as a demonstration of foundational technology for the development of more sensitive electrochemical sensors, that may have been impractical previously for clinical applications, due to limitations in either safety or performance.

Structural Characterisation and Chemical Stability of Commercial Fibrous Carbons in Molten Lithium Salts

“…When the band deconvolution is performed for the second order of the Raman spectra, a clear appearance of the intense S1 band (attributed to the first overtone of D1 at around 2700 cm −1 ) has been found only for graphitised CFs. The observed intensity increase of the S1 band (as in GR4) should correspond to the lateral growth of the graphitic nanocrystallites, and to the improvement of the stacking order of the graphitic layers [41,60]. However, it is known that the S1 band splits into two bands when the structure acquires a tri-periodic stacking order of the carbon layers [39,64], which is obviously not the case for any of the studied materials, in agreement with the XRD analysis.…”

“…In contrast, the D bands observed in the first order part have been attributed to in-plane defects and to heteroatoms. The S 1 band is as an overtone of the D 1 band, and is related to the stacking order along the c-axis [41]. From the D 1 and G bands, their full width at half maximum (FWHM) values and intensity ratio (I D1 /I G ) are calculated, which gives information on the extent of structural defects and the graphitisation degree in a series of carbon materials.…”

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

“…Likewise, their long-term stability is compromised by dissolution of the carbon fiber electrode material that can result in significant degradation and loss of sensitivity over time. 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. 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 ].…”

Diamond-Based Electrodes for Detection of Metal Ions and Anions

“…A number of methods involving organic nanoprobes, covalent–organic frameworks (COFs), metal–organic frameworks (MOFs), metal nanoparticles, hybrid nanomaterials, small molecules, and polymers were engaged in the quantitation of specific analytes [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. On the other end of the spectrum, instrumental tactics, such as inductively coupled plasma mass spectrometry, high-performance liquid chromatography, gas chromatography, atomic absorption spectrometry, electrochemical studies, and immunoassays have been pronounced as the conventional cost-effective approaches [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Among them, electrochemical-based detection of specified analyte detection seems to be impressive in terms of its selectivity and sensitivity with lower detection/quantification limits [ 21 , 22 , 23 ].…”