Simple self-referenced ratiometric electrochemical sensor for dopamine detection using electrochemically pretreated glassy carbon electrode modified by acid-treated multiwalled carbon nanotube

Facile Synthesis of Fe-Doped, Algae Residue-Derived Carbon Aerogels for Electrochemical Dopamine Biosensors

An abnormal level of dopamine (DA), a kind of neurotransmitter, correlates with a series of diseases, including Parkinson's disease, Willis-Ekbom disease, attention deficit hyperactivity disorder, and schizophrenia. Hence, it is imperative to achieve a precise, rapid detection method in clinical medicine. In this study, we synthesized nanocomposite carbon aerogels (CAs) doped with iron and iron carbide, based on algae residue-derived biomass materials, using Fe(NO3)3 as the iron source. The modified glassy carbon electrode (GCE) for DA detection, denoted as CAs-Fe/GCE, was prepared through surface modification with this composite material. X-ray photoelectron spectroscopy and X-ray diffraction characterization confirmed the successful doping of iron into the as-prepared CAs. Additionally, the electrochemical behavior of DA on the modified electrode surface was investigated and the results demonstrate that the addition of the CAs-Fe promoted the electron transfer rate, thereby enhancing their sensing performance. The fabricated electrochemical DA biosensor exhibits an accurate detection of DA in the concentration within the range of 0.01~200 µM, with a detection limit of 0.0033 µM. Furthermore, the proposed biosensor is validated in real samples, showing its high applicability for the detection of DA in beverages.

Legion: An Instrument for High-Throughput Electrochemistry

Electrochemical arrays promise utility for accelerated hypothesis testing and breakthrough discoveries. Herein, we report a new high-throughput electrochemistry platform, colloquially called "Legion," for applications in electroanalysis and electrosynthesis. Legion consists of 96 electrochemical cells dimensioned to match common 96-well plates that are independently controlled with a field-programmable gate array. We demonstrate the utility of Legion by measuring model electrochemical probes, pH-dependent electron transfers, and electrocatalytic dehalogenation reactions. We consider advantages and disadvantages of this new instrumentation, with the hope of expanding the electrochemical toolbox.

Ultrasensitive Electrochemical Platform for Dopamine Detection Based on CoNi-MOF@ERGO Composite

An electrochemical sensor applied for dopamine (DA) detection was constructed. An easy static way was used to synthesize bimetallic CoNi-MOF. Next, it was mixed with graphene oxide (GO) under ultrasound to get a uniform suspension. Subsequently, the solution was coated on the glassy carbon electrode (GCE) to form CoNi-MOF@ERGO/GCE by the electrochemical reduction method. The interaction between CoNi-MOF and electrochemically reduced graphene oxide (ERGO) enhances the electrocatalytic performance for DA detection. CoNi-MOF@ERGO/GCE has a wider linear range (0.1-400 μM) and a lower detection limit (0.086 μM) under optimum conditions. Furthermore, it has been applied to test DA in human serum samples. The results reveal that the DA sensor shows excellent performance, which will provide a novel idea for more sensitive and quicker DA detection.

Electrochemical sensor based on molecularly imprinted copolymer for selective and simultaneous determination of riboflavin, dopamine, and L-tryptophan

This research shows the exact detection of riboflavin (RF), dopamine (DA), and L-tryptophan (Trp) through molecularly imprinted polymer (MIP) based on the electropolymerization method. MIP was placed on the surface of the glassy carbon electrode (GCE) by electropolymerization of monomers such as catechol and para-aminophenol, in the presence of all three analytes. The introduced sensor was investigated using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), and electrochemical methods, for example, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The MIP/GCE performs well in terms of selectivity, reproducibility, repeatability, and stability. This sensor revealed good linear ranges of 0.005-500 μM for RF, 0.05-500 μM for DA, and 0.1-250 μM for Trp with limits of detection (LOD) as 0.0016 μM, 0.016 μM, and 0.03 μM for RF, DA, and Trp, respectively. The modified GCE was successfully applied to detect RF, DA, and Trp in serum and milk samples with satisfactory results.

Electrochemical Sensing of Gallic Acid in Beverages Using a 3D Bio-Nanocomposite Based on Carbon Nanotubes/Spongin-Atacamite

Gallic acid (GA) is one of the most important polyphenols, being widely used in the food, cosmetic, and pharmaceutical industries due to its biological effects such as antioxidant, antibacterial, anticancer, antiviral, anti-inflammatory, and cardioprotective properties. Hence, simple, fast, and sensitive determination of GA is of particular importance. Considering the fact that GA is an electroactive compound, electrochemical sensors offer great potential for GA quantitation due to their fast response time, high sensitivity, and ease of use. A simple, fast, and sensitive GA sensor was fabricated on the basis of a high-performance bio-nanocomposite using spongin as a natural 3D polymer, atacamite, and multi-walled carbon nanotubes (MWCNTs). The developed sensor showed an excellent response toward GA oxidation with remarkable electrochemical features due to the synergistic effects of 3D porous spongin and MWCNTs, which provide a large surface area and enhance the electrocatalytic activity of atacamite. At optimal conditions by differential pulse voltammetry (DPV), a good linear relationship was obtained between peak currents and GA concentrations in a wild linear range of 500 nM to 1 mM. Subsequently, the proposed sensor was used to detect GA in red wine as well as in green and black tea, confirming its great potential as a reliable alternative to conventional methods for GA determination.

Pascual L, Peltola E, Sainio J, Laurila T. Modulating the Geometry of the Carbon Nanofiber Electrodes Provides Control over Dopamine Sensor Performance

One of the major challenges for in vivo electrochemical measurements of dopamine (DA) is to achieve selectivity in the presence of interferents, such as ascorbic acid (AA) and uric acid (UA). Complicated multimaterial structures and ill-defined pretreatments have been frequently utilized to enhance selectivity. The lack of control over the realized structures has prevented establishing associations between the achieved selectivity and the electrode structure. Owing to their easily tailorable structure, carbon nanofiber (CNF) electrodes have become promising materials for neurobiological applications. Here, a novel yet simple strategy to control the sensitivity and selectivity of CNF electrodes toward DA is reported. It consists of adjusting the lengths of CNF by modulating the growth phase during the fabrication process while keeping the surface chemistries similar. It was observed that the sensitivity of the CNF electrodes toward DA was enhanced with the increase in the fiber lengths. More importantly, the increase in the fiber length induced (i) an anodic shift in the DA oxidation peak and (ii) a cathodic shift in the AA oxidation peak. As the UA oxidation peak remained unaffected at high anodic potentials, the electrodes with long CNFs showed excellent selectivity. Electrodes without proper fibers showed only a single broad peak in the solution of AA, DA, and UA, completely lacking the ability to discriminate DA. Hence, the simple strategy of controlling CNF length without the need to carry out any complex chemical treatments provides us a feasible and robust route to fabricate electrode materials for neurotransmitter detection with excellent sensitivity and selectivity.

Alprazolam Detection Using an Electrochemical Nanobiosensor Based on AuNUs/Fe-Ni@rGO Nanocomposite

Despite all the psychological advantages of alprazolam, its long list of toxic properties and interactions has caused concern and highlighted the need for a reliable sensing method. In this study, we developed a simple, highly sensitive electrochemical nanobiosensor to determine the desirable dose of alprazolam, averting the undesirable consequences of overdose. Gold nanourchins (AuNUs) and iron-nickel reduced graphene oxide (Fe-Ni@rGO) were immobilized on a glassy carbon electrode, which was treated beforehand. The electrode surface was characterized using cyclic voltammetry, Fourier transform infrared spectroscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and differential pulse voltammetry. The fabricated sensor showed two linear ranges (4 to 500 µg L^-1 and 1 to 50 mg L^-1), low limit of detection (1 µg L^-1), high sensitivity, good repeatability, and good recovery. Increased -OH and carboxyl (-COOH) groups on the electrode surface, resulting in improved the adsorption of alprazolam and thus lower limit of detection. This nanobiosensor could detect alprazolam powder dissolved in diluted blood serum; we also studied other benzodiazepine drugs (clonazepam, oxazepam, and diazepam) with this nanobiosensor, and results were sensible, with a significant difference.

A highly selective and sensitive electrochemical sensor for dopamine based on a functionalized multi-walled carbon nanotube and poly(N-methylaniline) composite

Dopamine (DA) is an important neurotransmitter used for diagnosing various diseases from its abnormal concentrations in human fluids. Herein, an electrochemical sensor based on a composite of re-doped poly(N-methylaniline) (rePNMA) and modified multi-walled carbon nanotubes (fMWCNTs), termed fMWCNT-rePNMA, was developed to measure DA concentration. The successful modification of the fMWCNT surface was confirmed by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Cyclic voltammetry (CV) displayed an excellent electrocatalytic activity of the fMWCNTs-rePNMA composite towards the oxidation of DA. The developed fMWCNTs-rePNMA composite demonstrated a broad linear range from 5 to 90 μmol L^-1 with a low limit of detection (LOD) value of 2.23 μmol L^-1, and a fast response with a high sensitivity of 251.5 nA μmol^-1 L as determined from the calibration curve of the DA determination. In addition, the fMWCNTs-rePNMA composite selectively identified and quantified DA in the presence of ascorbic acid (AA) and uric acid (UA). Therefore, the fMWCNTs-rePNMA composite sensor shows potential to determine the level of DA in human urine.

Graphene and Carbon Nanotube-based Electrochemical Sensing Platforms for Dopamine

Dopamine (DA) is an important neurotransmitter, which is created and released from the central nervous system. It plays a crucial role in human activities, like cognition, emotions, and response to anything. Maladjustment of DA in human blood serum results in different neural diseases, like Parkinson's and Schizophrenia. Consequently, researchers have started working on DA detection in blood serum, which is undoubtedly a hot research area. Electrochemical sensing techniques are more promising to detect DA in real samples. However, utilizing conventional electrodes for selective determination of DA encounters numerous problems due to the coexistence of other materials, such as uric acid and ascorbic acid, which have an oxidation potential close to DA. To overcome such problems, researchers have put their focus on the modification of bare electrodes. The aim of this review is to present recent advances in modifications of most used bare electrodes with carbonaceous materials, especially graphene, its derivatives, and carbon nanotubes, for electrochemical detection of DA. A brief discussion about the mechanistic phenomena at the electrode interface has also been included in this review.

Adsorptive Cathodic Stripping Voltammetry for Quantification of Alprazolam

A simple and highly sensitive electrochemical sensor was developed for adsorptive cathodic stripping voltammetry of alprazolam. Based on an electrochemically pretreated glassy carbon electrode, the sensor demonstrated good adsorption and electrochemical reduction of alprazolam. The morphology of the glassy carbon electrode and the electrochemically pretreated glassy carbon electrode were characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrochemical behaviors of alprazolam were determined by cyclic voltammetry, and the analytical measurements were studied by adsorptive cathodic stripping voltammetry. Optimized operational conditions included the concentration and deposition time of sulfuric acid in the electrochemical pretreatment, preconcentration potential, and preconcentration time. Under optimal conditions, the developed alprazolam sensor displayed a quantification limit of 0.1 mg L^-1, a detection limit of 0.03 mg L^-1, a sensitivity of 67 µA mg^-1 L cm^-2 and two linear ranges: 0.1 to 4 and 4 to 20 mg L^-1. Sensor selectivity was excellent, and repeatability (%RSD < 4.24%) and recovery (82.0 ± 0.2 to 109.0 ± 0.3%) were good. The results of determining alprazolam in beverages with the developed system were in good agreement with results from the gas chromatography-mass spectrometric method.

Cytotoxicity assessment of antibiotics on Ctenopharyngodon idellus kidney cells by a sensitive electrochemical method

As emerging pollutants, antibiotics are ubiquitous in the environment and pose a threat to human health, giving rise to an urgent need to assess their biological toxicity. In the present study, a cell electrochemical method based on the bromocresol violet/carbon nanotubes/glassy carbon electrode (BCP/MWCNTs/GCE) was established to evaluate the cytotoxicities of sulfamethoxazole (SMZ), ciprofloxacin (CIP), and tetracycline (TC). BCP/MWCNTs/GCE has advantages due to its excellent electrocatalytic activity for the oxidation of electroactive species of the Ctenopharyngodon idellus kidney (CIK) cells. The half-maximal inhibitory concentration (IC₅₀) values of SMZ, CIP, and TC obtained by the electrochemical method were 831.51 μM, 354.98 μM, and 184.51 μM, which were lower than those of the traditional methyl-thiazolyl-tetrazolium (MTT) assay (907.47 μM, 414.87 μM, and 208.11 μM). These results indicate the higher sensitivity of the electrochemical method. This study provided a sensitive tool for the cytotoxicity evaluation of antibiotics in the environmental toxicology field.

Ratiometric Electrochemistry: Improving the Robustness, Reproducibility and Reliability of Biosensors

Electrochemical biosensors are an increasingly attractive option for the development of a novel analyte detection method, especially when integration within a point-of-use device is the overall objective. In this context, accuracy and sensitivity are not compromised when working with opaque samples as the electrical readout signal can be directly read by a device without the need for any signal transduction. However, electrochemical detection can be susceptible to substantial signal drift and increased signal error. This is most apparent when analysing complex mixtures and when using small, single-use, screen-printed electrodes. Over recent years, analytical scientists have taken inspiration from self-referencing ratiometric fluorescence methods to counteract these problems and have begun to develop ratiometric electrochemical protocols to improve sensor accuracy and reliability. This review will provide coverage of key developments in ratiometric electrochemical (bio)sensors, highlighting innovative assay design, and the experiments performed that challenge assay robustness and reliability.

Development of a Novel Electrochemical Biosensor Based on Carbon Nanofibers-Gold Nanoparticles-Tyrosinase for the Detection of Ferulic Acid in Cosmetics

The present paper deals with the electrochemical behavior of three types of sensors based on modified screen-printed electrodes (SPEs): a sensor based on carbon nanofibers (CNF/SPE), a sensor based on nanofibers of carbon modified with gold nanoparticles (CNF-GNP/SPE) and a biosensor based on nanofibers of carbon modified with gold nanoparticles and tyrosinase (CNF-GNP-Ty/SPE). To prepare the biosensor, the tyrosinase (Ty) was immobilized on the surface of the electrode already modified with carbon nanofibers and gold nanoparticles, by the drop-and-dry technique. The electrochemical properties of the three electrodes were studied by cyclic voltammetry in electroactive solutions, and the position and shape of the active redox peaks are according to the nature of the materials modifying the electrodes. In the case of ferulic acid, a series of characteristic peaks were observed, the processes being more intense for the biosensor, with the higher sensitivity and selectivity being due to the immobilization of tyrosinase, a specific enzyme for phenolic compounds. The calibration curve was subsequently created using CNF-GNP-Ty/SPE in ferulic acid solutions of various concentrations in the range 0.1-129.6 μM. This new biosensor allowed low values of the detection threshold and quantification limit, 2.89 × 10-9 mol·L-1 and 9.64 × 10-9 mol·L-1, respectively, which shows that the electroanalytical method is feasible for quantifying ferulic acid in real samples. The ferulic acid was quantitatively determined in three cosmetic products by means of the CNF-GNP-Ty/SPE biosensor. The results obtained were validated by means of the spectrometric method in the infrared range, the differences between the values of the ferulic acid concentrations obtained by the two methods being under 5%.

Carbon nanomaterials against pathogens; the antimicrobial activity of carbon nanotubes, graphene/graphene oxide, fullerenes, and their nanocomposites

Recently, antibiotic resistance of pathogens has grown given the excessive and inappropriate usage of common antimicrobial agents. Hence, producing novel antimicrobial compounds is a necessity. Carbon nanomaterials (CNMs) such as carbon nanotubes, graphene/graphene oxide, and fullerenes, as an emerging class of novel materials, can exhibit a considerable antimicrobial activity, especially in the nanocomposite forms suitable for different fields including biomedical and food applications. These nanomaterials have attracted a great deal of interest due to their broad efficiency and novel features. The most important factor affecting the antimicrobial activity of CNMs is their size. Smaller particles with a higher surface to volume ratio can easily attach onto the microbial cells and affect their cell membrane integrity, metabolic procedures, and structural components. As these unique characteristics are found in CNMs, a wide range of possibilities have raised in terms of antimicrobial applications. This study aims to cover the antimicrobial activities of CNMs (both as individual forms and in nanocomposites) and comprehensively explain their mechanisms of action. The results of this review will present a broad perspective, summarizes the most remarkable findings, and provides an outlook regarding the antimicrobial properties of CNMs and their potential applications.