A novel sensor made of Antimony Doped Tin Oxide-silica composite sol on a glassy carbon electrode modified by single-walled carbon nanotubes for detection of norepinephrine

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.

Bibliometric research analysis of molecularly imprinted polymers (MIPs): evidence and research activity dynamics

The escalating issue of water pollution has become a worldwide issue that has captured the attention of numerous scientists. Molecularly imprinted polymers (MIPs) have emerged as adaptable materials with exceptional attributes, including easy synthesis, low cost, remarkable durability, long life, and accessibility. These attributes have motivated researchers to develop novel materials based on MIPs to tackle hazardous contaminants in environmental matrices. The purpose of this paper was to conduct a bibliometric analysis on MIPs' publications, in order to shed light on the developments and focus points of the field. The selected publications were obtained from Scopus database and subjected to a filtering process, resulting in 11,131 relevant publications. The analysis revealed that the leading publication source (journal) is Biosensors and Bioelectronics; the mostly employed keywords are solid-phase extraction, electrochemical sensor, and molecular recognition; and the top contributing countries are China, Iran, and the USA. The Latent Dirichlet Allocation (LDA) algorithm was used for extracting thematic axes from the textual content of the publications. The results of the LDA model showcase that the topic of synthesis and performance of MIPs for environmental applications can be considered as the most dominant topic with a share value of 72.71%. From the analysis, it can be concluded that MIPs are a cross-disciplinary research field.

Honeycomb-like nickel oxide-reduced graphene oxide based sensor for the electrochemical tracking of norepinephrine in neuronal cells

Highly sensitive and specific detection and monitoring of trace norepinephrine (NE) in biological fluids and neuronal cell lines is essential for the investigation of pathogenesis of certain neurological diseases. Herein, we constructed a novel electrochemical sensor for real-time monitoring of NE released by PC12 cells based on glassy carbon electrode (GCE) modified with honeycomb-like nickel oxide (NiO)-reduced graphene oxide (RGO) nanocomposite. The synthesized NiO, RGO and the NiO-RGO nanocomposite were characterized using X-ray diffraction spectrogram (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The porous three-dimensional honeycomb-like structure of NiO and high charge transfer kinetics of RGO endowed the nanocomposite with excellent electrocatalytic activity, large surface area and good conductivity. The developed sensor exhibited superior sensitivity and specificity towards NE in a wide linear range from 20 nM to 14 μM and 14 μM-80 μM, with a low detection limit of 5 nM. The performances of the sensor in terms of excellent biocompatibility and high sensitivity allow it to be successfully employed in the tracking of NE release from PC12 cells under the stimulation of K⁺, providing an effective strategy for the real-time monitoring of cellular NE.

Sensitive detection of noradrenaline in human whole blood based on Au nanoparticles embedded vertically-ordered silica nanochannels modified pre-activated glassy carbon electrodes

Sensitive determination of noradrenaline (NE), the pain-related neurotransmitters and hormone, in complex whole blood is of great significance. In this work, an electrochemical sensor was simply constructed on the pre-activated glassy carbon electrode (p-GCE) modified with vertically-ordered silica nanochannels thin film bearing amine groups (NH₂-VMSF) and in-situ deposited Au nanoparticles (AuNPs). The simple and green electrochemical polarization was employed to pre-activate GCE to realize the stable binding of NH₂-VMSF on the surface of electrode without the use of any adhesive layer. NH₂-VMSF was conveniently and rapidly grown on p-GCE by electrochemically assisted self-assembly (EASA). With amine group as the anchor sites, AuNPs were in-situ electrochemically deposited on the nanochannels to improve the electrochemical signals of NE. Owing to signal amplification from gold nanoparticles, the fabricated AuNPs@NH₂-VMSF/p-GCE sensor can achieve electrochemical detection of NE ranged from 50 nM to 2 μM and from 2 μM to 50 μM with a low limit of detection (LOD) of 10 nM. The constructed sensor exhibited high selectivity and can be easily regenerated and reused. Owing to the anti-fouling ability of nanochannel array, direct electroanalysis of NE in human whole blood was also realized.

A colorimetric paper-based ATONP-ALP nanobiosensor for selective detection of Cd2+ ions in clams and mussels

A colorimetric paper-based enzyme-coupled antimony tin oxide nanoparticle (ATONP) nanobiosensor for selective detection of Cd²⁺ ions in clams and mussels is presented. Alkaline phosphatase (ALP) was immobilized on ATONPs via 16-phosphonohexadecanoic acid (16-PHA) to develop ATONP-ALP nanobiosensor. The biosensor was characterized using XPS, Raman spectroscopy, SEM, and EDX. ATONP-ALP nanobiosensor exhibited high selectivity towards detection of Cd²⁺ ion with a LOD 0.006 μg L^-1 and linear range of detection 0.005-1 μg L^-1. The developed biosensor was further integrated into a low-cost paper-based format. A visual color change was obtained for Cd²⁺ ion in the range 0.1-10 μg L^-1. The developed biosensor was successfully demonstrated for the analysis of Cd²⁺ ions in clams with recoveries 101-104%. The ATONP-ALP nanobiosensor was validated using mussel tissue (BCR-668) and the conventional ICP-OES and ICP-MS techniques.

"Nano": An Emerging Avenue in Electrochemical Detection of Neurotransmitters

The growing importance of nanomaterials toward the detection of neurotransmitter molecules has been chronicled in this review. Neurotransmitters (NTs) are chemicals that serve as messengers in synaptic transmission and are key players in brain functions. Abnormal levels of NTs are associated with numerous psychotic and neurodegenerative diseases. Therefore, their sensitive and robust detection is of great significance in clinical diagnostics. For more than three decades, electrochemical sensors have made a mark toward clinical detection of NTs. The superiority of these electrochemical sensors lies in their ability to enable sensitive, simple, rapid, and selective determination of analyte molecules while remaining relatively inexpensive. Additionally, these sensors are capable of being integrated in robust, portable, and miniaturized devices to establish point-of-care diagnostic platforms. Nanomaterials have emerged as promising materials with significant implications for electrochemical sensing due to their inherent capability to achieve high surface coverage, superior sensitivity, and rapid response in addition to simple device architecture and miniaturization. Considering the enormous significance of the levels of NTs in biological systems and the advances in sensing ushered in with the integration of nanotechnology in electrochemistry, the analysis of NTs by employing nanomaterials as interface materials in various matrices has emerged as an active area of research. This review explores the advancements made in the field of electrochemical sensors for the sensitive and selective determination of NTs which have been described in the past two decades with a distinctive focus on extremely innovative attributes introduced by nanotechnology.

A novel electrochemical platform based on mesoporous silica/titania and gold nanoparticles for simultaneous determination of norepinephrine and dopamine

An amorphous and mesoporous silica/titania (SiTi) material was synthesized by sol-gel method and its surface was modified with gold nanoparticles (AuNP) previously stabilized in a chitosan solution. The presence of small AuNP, with diameter lower than 10 nm was confirmed by transmission electron microscopy (TEM) and UV-Vis spectroscopy. Carbon paste electrodes were prepared to test the electrochemical properties by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in [Fe(CN)₆]^3-/4- solution probe whereby the material silica-titania/gold nanoparticles (SiTi/AuNP) showed a huge improvement in the redox peak current and low charge transfer resistance. This electrode presented a good response for both norepinephrine and dopamine by means of square wave voltammetry (SWV) measurements; great sensitivity for both analytes, in an extensive linear range, was obtained. The limits of detection were 0.35 μmol L^-1 and 0.57 μmol L^-1 for norepinephrine and dopamine, respectively. Additionally, this electrode showed high selectivity for both analytes and it was applied in the simultaneous determination of norepinephrine and dopamine. The sensor was also tested in simulated biological fluids presenting a good recovery. The SWV electrochemical response of norepinephrine was also investigated in the presence of possible interferers such as uric acid, ascorbic acid and glucose and there was no significant interference. The prepared electrode also exhibits good reproducibility for norepinephrine detection, with relative standard deviation of 5.19%.

Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †

The oxides of transition, post-transition and rare-earth metals have a long history of robust and fast responsive recognition elements for electronic, optical, and gravimetric devices. A wide range of applications successfully utilized pristine or doped metal oxides and polymer-oxide hybrids as nanostructured recognition elements for the detection of biologically relevant molecules, harmful organic substances, and drugs as well as for the investigative process control applications. An overview of the selected recognition applications of molecularly imprinted sol-gel phases, metal oxides and hybrid nanomaterials composed of molecularly imprinted polymers (MIP) and metal oxides is presented herein. The formation and fabrication processes for imprinted sol-gel layers, metal oxides, MIP-coated oxide nanoparticles and other MIP/oxide nanohybrids are discussed along with their applications in monitoring bioorganic analytes and processes. The sensor characteristics such as dynamic detection range and limit of detection are compared as the performance criterion and the miniaturization and commercialization possibilities are critically discussed.

Electrochemical Determination of Norepinephrine by Means of Modified Glassy Carbon Electrodes with Carbon Nanotubes and Magnetic Nanoparticles of Cobalt Ferrite

This study describes the electrochemical preparation of the electrocatalytic oxidation/reduction of noradrenaline in modified glassy carbon of cobalt ferrite nanoparticles and carbon nanotubes (GC/MWCNT/FCo₉₈). The cobalt ferrite powder was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optimum conditions found in an electrode composition were 4 μL of cobalt ferrite and 10 μL of carbon nanotubes in 0.1 mol L⁻¹ PBS at pH 7.0. The electrode displays electrochemical behavior in a wide potential range (−0.4 to 1.0 V vs. Ag/AgCl), high conductivity, and electrode stability/durability in 0.1 mol L⁻¹ PBS. Catalytic oxidation of noradrenaline was performed at the unmodified GC electrode at +0.60 V vs. Ag/AgCl and current of 0.17 μA and modified GC with cobalt ferrite nanoparticles and carbon nanotubes at +0.54 V vs. Ag/AgCl and current of 0.23 mA. With regard to the anodic peak current (I_pa) versus noradrenaline concentration by means of the amperometric method at the modified electrode, (which is linear in the 0.16 and 1.91 mmol L⁻¹ concentration range), the concentration limit was 0.76 μmol L⁻¹. In this way, the modified electrode GC/MWCNT/FCo₉₈ was found to be a promising application for the determination of this neurotransmitter in the area of neuroscience.