Search Results (8)

Neurotoxic heavy metals, such as Cd²⁺, pose a significant global health concern due to their increased environmental contamination and subsequent detrimental health hazards they pose to human beings. These metal ions can breach the blood-brain barrierblood–brain barrier, leading to severe and often irreversible damage to the central nervous system and other vital organs. Therefore, developing a highly sensitive, robust, and rapid in vivo detection method for these hazardous heavy metal ions is of the utmost importance for early detection, thus initiating timely therapeutics. Detecting ultra-low levels of toxic metal ions in vivo and obtaining accurate speciation information remains a challenge with conventional analytical techniques. In this study, we fabricated a novel carbon carbon-fiber microelectrode (CFM)-based sensor that can detect Cd²⁺ ions using fast-scan cyclic voltammetry by electrodepositing gold nanoparticles (AuNP). We optimized electrochemical parameters that generate a unique cyclic voltammogram (CV) of Cd²⁺ at a temporal resolution of 100 ms with our novel sensor. All our experiments were performed in tris buffer that mimics the artificial cerebellum fluid. We established a calibration curve resulting in a limit of detection (LOD) of 0.01 µM with a corresponding sensitivity of 418.02 nA/ µM. The sensor’s selectivity was evaluated in the presence of other metal ions, and it was noteworthy to observe that the sensor retained its ability to produce the distinctive Cd²⁺ CV, even when the concentration of other metal ions was 200 times higher than that of Cd²⁺. We also found that our sensor could detect free Cd²⁺ ions in the presence of complexing agents. Furthermore, we analyzed the solution chemistry of each of those Cd²⁺–ligand solutions using a geochemical model, PHREEQC. The concentrations of free Cd²⁺ ions determined through our electrochemical data align well with geochemical modeling data, thus validating the response of our novel sensor. Furthermore, we reassessed our sensor’s LOD in tris buffer based on the concentration of free Cd²⁺ ions determined through PHREEQC analysis, revealing an LOD of 0.00132 µM. We also demonstrated the capability of our sensor to detect Cd²⁺ ions in artificial urine samples, showcasing its potential for application in actual biological samples. To the best of our knowledge, this is the first AuNP-modified, CFM-based Cd²⁺ sensor capable of detecting ultra-low concentrations of free Cd²⁺ ions in different complex matrices, including artificial urine at a temporal resolution of 100 ms, making it an excellent analytical tool for future real-time, in vivo detection, particularly in the brain. Full article

In the present work, a hybrid organic–inorganic semiconductor (HOIS) has been used to modify the surface of a graphite paste/silica (G–SiO₂) film electrode on a conducting glass substrate to fabricate a promising, sensitive voltammetric sensor for the vasoconstrictor bisartan BV6, which could possibly treat hypertension and COVID-19. The HOIS exhibits exceptional optoelectronic properties with promising applications not only in light-emitting diodes, lasers, or photovoltaics but also for the development of voltammetric sensors due to the ability of the immobilized HOIS lattice to interact with ions. This study involves the synthesis and characterization of an HOIS and its attachment on the surface of a G–SiO₂ film electrode in order to develop a nanocomposite, simple, sensitive with a fast-response, low-cost voltammetric sensor for BV6. The modified HOIS electrode was characterized using X-ray diffraction, scanning electron microscopy, and optical and photoluminescence spectroscopy, and its electrochemical behavior was examined using cyclic voltammetry. Under optimal conditions, the modified G–SiO₂ film electrode exhibited a higher electrocatalytic activity towards the oxidation of BV6 compared to a bare graphite paste electrode. The results showed that the peak current was proportional to BV6 concentration with a linear response range from 0 to 65 × 10⁻⁶ (coefficient of determination, 0.9767) and with a low detection limit of 1.5 × 10⁻⁶ M (S/N = 3), estimated based on the area under a voltammogram, while it was 3.5 × 10⁻⁶ for peak-based analysis. The sensor demonstrated good stability and reproducibility and was found to be appropriate for the determination of drug compounds such as BV6. Full article

Laser engraving is a convenient, fast, one-step, and environmentally friendly technique used to produce more conductive surfaces by local pyrolysis. The laser’s thermal treatment can also remove non-conductive materials from the electrode surfaces and improve electrochemical performance. The improvement was assessed by electrochemical tools such as cyclic voltammograms and electrochemical impedance spectroscopy using [Fe(CN)₆]^3−/4− and dopamine as redox probes. The electrochemical results observed showed that a treated surface showed an improvement in electron transfer and less resistance to charge transfer. To optimize the electrode performance, it was necessary to search for the most favorable graphite mines and optimize the parameters of the laser machine (laser power, scan rate, and output distance). The resultant material was adequately characterized by Raman spectroscopy and scanning electron microscopy (SEM), where an irregular surface composed of crystalline graphite particles was noticed. Furthermore, as a proof-of-concept, it was applied to detect indapamide (IND) in synthetic urine by flow injection analysis (FIA), a diuretic drug often used by athletes to alter urine composition to hide forbidden substance consumption in doping tests. Full article

Diffusion-controlled cyclic voltammograms at fast scan rates show peak shifts, as well as decreases in the peak currents from predicted diffusion-controlled currents, especially when the currents are large in a low concentration of supporting electrolytes. This has been conventionally recognized as an IR-drop effect due to solution resistance on the peaks, as well as a heterogeneously kinetic effect. It is also brought about by the negatively capacitive currents associated with charge transfer reactions. The reaction product generates dipoles with counterions to yield a capacitance, the current of which flows oppositely to that of the double-layer capacitance. The three effects are specified here in the oxidation of a ferrocenyl derivative using fast scan voltammetry. The expression for voltammograms complicated with IR-drop is derived analytically and yields deformed voltammograms. The peak shift is approximately linear with the IR-voltage, but exhibits a convex variation. The dependence of some parameters on the peaks due to the IR-drop is compared with those due to the negative capacitance. The latter is more conspicuous than the former under conventional conditions. The two effects cannot be distinguished specifically except for variations in the conductance of the solution. Full article

The molecular engineering of conjugated systems has proven to be an effective method for understanding structure–property relationships toward the advancement of optoelectronic properties and biosensing characteristics. Herein, a series of three thieno[3,4-c]pyrrole-4,6-dione (TPD)-based conjugated monomers, modified with electron-rich selenophene, 3,4-ethylenedioxythiophene (EDOT), or both building blocks (Se-TPD, EDOT-TPD, and EDOT-Se-TPD), were synthesized using Stille cross-coupling and electrochemically polymerized, and their electrochromic properties and applications in a glucose biosensing platform were explored. The influence of structural modification on electrochemical, electronic, optical, and biosensing properties was systematically investigated. The results showed that the cyclic voltammograms of EDOT-containing materials displayed a high charge capacity over a wide range of scan rates representing a quick charge propagation, making them appropriate materials for high-performance supercapacitor devices. UV-Vis studies revealed that EDOT-based materials presented wide-range absorptions, and thus low optical band gaps. These two EDOT-modified materials also exhibited superior optical contrasts and fast switching times, and further displayed multi-color properties in their neutral and fully oxidized states, enabling them to be promising materials for constructing advanced electrochromic devices. In the context of biosensing applications, a selenophene-containing polymer showed markedly lower performance, specifically in signal intensity and stability, which was attributed to the improper localization of biomolecules on the polymer surface. Overall, we demonstrated that relatively small changes in the structure had a significant impact on both optoelectronic and biosensing properties for TPD-based donor–acceptor polymers. Full article

Cortisol is a vital steroid hormone that has been known as the “stress hormone”, which is elevated during times of high stress and anxiety and has a significant impact on neurochemistry and brain health. The improved detection of cortisol is critically important as it will help further our understanding of stress during several physiological states. Several methods exist to detect cortisol; however, they suffer from low biocompatibility and spatiotemporal resolution, and they are relatively slow. In this study, we developed an assay to measure cortisol with carbon fiber microelectrodes (CFMEs) and fast-scan cyclic voltammetry (FSCV). FSCV is typically utilized to measure small molecule neurotransmitters by producing a readout cyclic voltammogram (CV) for the specific detection of biomolecules on a fast, subsecond timescale with biocompatible CFMEs. It has seen enhanced utility in measuring peptides and other larger compounds. We developed a waveform that scanned from −0.5 to −1.2 V at 400 V/s to electro-reduce cortisol at the surface of CFMEs. The sensitivity of cortisol was found to be 0.87 ± 0.055 nA/μM (n = 5) and was found to be adsorption controlled on the surface of CFMEs and stable over several hours. Cortisol was co-detected with several other biomolecules such as dopamine, and the waveform was fouling resistant to repeated injections of cortisol on the surface of the CFMEs. Furthermore, we also measured exogenously applied cortisol into simulated urine to demonstrate biocompatibility and potential use in vivo. The specific and biocompatible detection of cortisol with high spatiotemporal resolution will help further elucidate its biological significance and further understand its physiological importance and impact on brain health. Full article

Carbon fiber-microelectrodes (CFMEs) have been the standard for neurotransmitter detection for over forty years. However, in recent years, there have been many advances of utilizing alternative nanomaterials for neurotransmitter detection with fast scan cyclic voltammetry (FSCV). Recently, carbon nanotube (CNT) yarns have been developed as the working electrode materials for neurotransmitter sensing capabilities with fast scan cyclic voltammetry. Carbon nanotubes are ideal for neurotransmitter detection because they have higher aspect ratios enabling monoamine adsorption and lower limits of detection, faster electron transfer kinetics, and a resistance to surface fouling. Several methods to modify CFMEs with CNTs have resulted in increases in sensitivity, but have also increased noise and led to irreproducible results. In this study, we utilize commercially available CNT-yarns to make microelectrodes as enhanced neurotransmitter sensors for neurotransmitters such as serotonin. CNT-yarn microelectrodes have significantly higher sensitivities (peak oxidative currents of the cyclic voltammograms) than CFMEs and faster electron transfer kinetics as measured by peak separation (Δ_EP) values. Moreover, both serotonin and dopamine are adsorption controlled to the surface of the electrode as measured by scan rate and concentration experiments. CNT yarn microelectrodes also resisted surface fouling of serotonin onto the surface of the electrode over thirty minutes and had a wave application frequency independent response to sensitivity at the surface of the electrode. Full article

Porous MnO/C microspheres have been successfully fabricated by a fast co-precipitation method in a T-shaped microchannel reactor. The structures, compositions, and electrochemical performances of the obtained MnO/C microspheres are characterized by X-ray diffraction, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller analysis, charge-discharge testing, cyclic voltammograms, and electrochemical impedance spectra. Experimental results reveal that the as-prepared MnO/C, with a specific surface area of 96.66 m²·g⁻¹ and average pore size of 24.37 nm, exhibits excellent electrochemical performance, with a discharge capacity of 655.4 mAh·g⁻¹ after cycling 50 times at 1 C and capacities of 808.3, 743.7, 642.6, 450.1, and 803.1 mAh·g⁻¹ at 0.2, 0.5, 1, 2, and 0.2 C, respectively. Moreover, the controlled method of using a microchannel reactor, which can produce larger specific surface area porous MnO/C with improved cycling performance by shortening lithium-ion diffusion distances, can be easily applied in real production on a large scale. Full article