Carbon Composite Microelectrodes: Charge Percolation and Electroanalytical Performance

3D-Printed Microelectrodes for Biological Measurement

Microelectrodes are useful electrochemical sensors that can provide spatial biological monitoring. Carbon fiber has been by far the most widely used microelectrode; however, a vast number of different materials and modification strategies have been developed to broaden the scope of microelectrodes. Carbon composite electrodes provide a simple approach to making microelectrodes with a wide range of materials, but manufacturing strategies are complex. 3D printing can provide the ability to make microelectrodes with high precision. We used fused filament fabrication to print single strands of carbon black/polylactic acid (CB/PLA) and multiwall carbon nanotube/polylactic acid (MWCNT/PLA), which were then made into microelectrodes. Microelectrodes ranged from 70 μm in diameter to 400 μm in diameter and were assessed using standard redox probes. MWCNT/PLA electrodes exhibited greater sensitivity, a lower limit of detection, and stability for the measurement of serotonin (5-HT). Both CB/PLA and MWCNT/PLA microelectrodes were able to monitor 5-HT overflow from the ex vivo ileum tissue. MWCNT/PLA microelectrodes were utilized to show differences in 5-HT overflow from ex vivo ileum and colon following exposure to odorants present in spices. These findings highlight that any conductive thermoplastic material can be fabricated into a microelectrode. This simple strategy can utilize a wide range of materials to make 3D-printed microelectrodes for a diverse range of applications.

Simultaneous detection of norepinephrine and 5-hydroxytryptophan using poly-alizarin/multi-walled carbon nanotubes-graphene modified carbon fiber microelectrode array sensor

Multi-walled carbon nanotubes, graphene and alizarin polymer composites coated carbon fiber microelectrode array sensor (p-AZ/MWCNT-GR/CFMEA) was constructed and used for the simultaneous detection of norepinephrine (NE) and 5-hydroxytryptophan (5-HT). The morphology and structural characteristics of sensor are characterized using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Its electrochemical behavior has been studied with cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibits excellent electrochemical activity for the oxidation of NE and 5-HT, two well separated oxidation peaks with the peak potential difference of 220 mV are observed on the cyclic voltammogram. NE and 5-HT both show two electrons and two protons electrochemical reaction on the p-AZ/MWCNT-GR/CFMEA. Under the optimized experiment conditions, the linear ranges of the sensor for NE and 5-HT are 0. 08- 8 μM and 0. 1-20 μM with detection limits of 4. 22 nM and 14. 2 nM (S/N = 3), respectively. In addition, the microsensor array show good reproducibility, stability and selectivity for the determination of NE and 5-HT. Finally, the p-AZ/MWCNT-GR/CFMEA is applied to the simultaneous detection of NE and 5-HT in human serum samples and macrophages.

The effects of printing orientation on the electrochemical behaviour of 3D printed acrylonitrile butadiene styrene (ABS)/carbon black electrodes

Additive manufacturing also known as 3D printing is being utilised in electrochemistry to reproducibly develop complex geometries with conductive properties. In this study, we explored if the electrochemical behavior of 3D printed acrylonitrile butadiene styrene (ABS)/carbon black electrodes was influenced by printing direction. The electrodes were printed in both horizontal and vertical directions. The horizsontal direction resulted in a smooth surface (HPSS electrode) and a comparatively rougher surface (HPRS electrode) surface. Electrodes were characterized using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. For various redox couples, the vertical printed (VP) electrode showed enhanced current response when compared the two electrode surfaces generated by horizontal print direction. No differences in the capacitive response was observed, indicating that the conductive surface area of all types of electrodes were identical. The VP electrode had reduced charge transfer resistance and uncompensated solution resistance when compared to the HPSS and HPRS electrodes. Overall, electrodes printed in a vertical direction provide enhanced electrochemical performance and our study indicates that print orientation is a key factor that can be used to enhance sensor performance.

Electrogenerated Chemiluminescence Bioanalytic System Based on Biocleavage of Probes and Homogeneous Detection

A novel electrogenerated chemiluminescence (ECL) bioanalytic system based on biocleavage of a ECL probe and homogeneous detection was designed and utilized for the first time for highly sensitive quantification of proteases to overcome drawbacks from probes directly immobilized on electrodes and commercial ECL biosystems, based on bioaffinity reactions. Prostate-specific antigen (PSA) was taken as a model analyte and ruthenium complex-tagged specific peptide (CHSSKLQK) was designed as an ECL probe (peptide-Ru1). ECL bioconjugated magnetic beads were synthesized through a simple solid-phase synthesis. When analyte PSA was introduced into the suspension of ECL bioconjugated magnetic beads, a biocleavage of the peptide occurred and the cleaved Ru1 part was released from the magnetic beads. ECL measurement was carried out in the presence of co-reactant tripropylamine, using two models. One is homogeneous ECL detection on a bare graphite pencil electrode (PGE), and the other is enriching ECL detection after the cleaved Ru1 part of the peptide was concentrated into the surface film of Nafion/gold nanoparticles modified PGE (AuNPs/Nafion/PGE). The extremely low detection limit of 80 fg/mL and high reproducibility (relative standard deviation (RSD) of 5.4% for six measurements of 0.5 pg/mL) for the detection of PSA were achieved at AuNPs/Nafion/PGE. This work demonstrates that the bioanalytic system designed can not only quantify proteases with high sensitivity and selectivity, but also diminish the complicated electrode process and improve the reproducibility by conducting the biocleavage and transduction steps at different surfaces. It can be easily extended for ECL analysis of other proteases in this system and other detection techniques, including optics and electrochemistry.

Conducting film from graphite oxide nanoplatelets and poly(acrylic acid) by layer-by-layer self-assembly

A [poly(acrylic acid)/graphite oxide]n [(PAA/GO)(n)] film with a conductivity of 60 S.cm(-1) was grown layer-by-layer (LbL) using Langmuir-Blodgett self-assembly techniques. GO nanoplatelets were prepared from natural graphite by oxidizing, ball milling, exfoliating, and modifying with cationic surfactant cetyltrimethylammonium bromide (CTAB). The X-ray diffraction pattern reveals that PAA and GO stack orderly LbL and repeatedly in the (PAA/GO)(n) films, and about three carbon molecular layers are superposed on each GO sheet. Fourier transform infrared spectra offer evidence for the interaction between the carboxylic groups on PAA and the CTAB on the surface of the GO nanoplatelets. Electrochemistry measurements show that the conductivity of the (PAA/GO)(n) film depends on the carbon-carbon interlayer height of the GO sheet, and the (PAA/GO)(n) film has a typical positive temperature coefficient effect above the PAA melting temperature. The atomic force microscopy images reveal that CTAB molecules stack in a well-ordered head-to-head structure on both surfaces of the GO nanoplatelets and the GO nanoplatelets are embeded between PAA layers.

Sol−Gel-Derived Ceramic−Carbon Nanotube Nanocomposite Electrodes: Tunable Electrode Dimension and Potential Electrochemical Applications

Nanocomposite electrodes made of sol-gel-derived ceramic-carbon nanotube are fabricated by doping mutliwalled carbon nanotubes (MWNTs) into a silicate gel matrix. The electrochemical behavior and potential electrochemical applications of the ceramic-carbon nanotube nanocomposite electrodes (CCNNEs) are also studied. The as-prepared CCNNEs exhibit a tunable dimension ranging from conventional electrode to nanoelectrode ensemble (NEE), depending on the amount of the MWNT dispersed in the silica sol and finally doped within the gel matrix. A high content of the MWNT (i.e., higher than 1.5 mg/mL in the sol) leads to the formation of the CCNNE characteristic of an electrode of conventional dimension, while a low content (typically lower than 0.10 mg/mL) essentially yields the CCNNE like a nanoelectrode ensemble. The NEE is demonstrated to possess good electrocatalytic activity toward the oxidation of ascorbic acid (AA), and the CCNNE of conventional dimension is found to possess remarkable electrocatalytic activity toward the oxidation of glutathione (both reduced and oxidized forms, GSH and GSSG). These properties of the CCNNEs essentially offer a new electrochemical approach for the detection of AA, GSH, and GSSG. The possible essence of the tailor-made dimensions of the CCNNEs is also presented and discussed.