Electrochemical Sensor Applications Research Articles

Single‐atom metal‐nitrogen‐carbon catalysts energize single molecule detection for biosensing

AbstractBiosensors featuring single molecule detection present huge opportunities as well as challenges in food safety inspection, disease diagnosis, and environmental monitoring. Single‐molecule detection is largely lacking of high enough activity, precision molecule selectivity, and understanding in the exact operating mechanism. Single‐atom catalysts (SACs), especially those metals‐nitrogen‐carbon that mimic the natural metalloenzyme structure, and with well‐defined metal atom bond configurations, high level of molecular selectivity, and easy fabrication, endow single molecule detections with practical‐use feasibilities. The recent advances in single‐atom catalysts also present new pathways in the key mechanism understandings. In this short review, we will first visit the brief history and advantages of SACs that have been explored only recently for molecule‐scale biosensors, where they are analogous and also differentiated from those nanozymes and natural metalloenzymes. Their applications in electrochemical, photochemical, and photoelectrochemical sensors are then discussed comprehensively by focusing on the different molecule‐scale sensing modes in achieving local coordination‐modulated signal amplifications. Finally, we identify new opportunities and challenges faced by these SACs‐based single molecule detections in the further development of biosensors.image

Application of a new electrochemical sensor for voltammetric determination of p-nitrophenol and betulin

A highly sensitive electrochemical sensor based on a Surface Active Modifier (SAM) consisting of Taunit-M carbon nanotubes and mesoporous carbon (NanoTechCenter LLC, Tambov, Russia) is developed for the voltammetric determination of betulin and p-nitrophenol. The effect of the modifier concentration on the electrode surface on the analytical signal of betulin was studied, and a method for modifying the surface of the SAM graphite electrode was developed. The developed method is easy to use, fast, stable, sensitive, and cost-effective procedure, which can be used to detect these analytes in real samples. Voltammograms of p-nitrophenol were obtained for the first time on the developed modified electrochemical sensor and the dependence of the height of its analytical signal on the pH of a phosphate buffer thus obtained was studied in a wide pH range from 4 to 12, a background electrolyte with optimal pH was also chosen. Proceeding from the calibration dependences of the height of the betulin analytical signal on the concentration obtained for various background electrolytes with different pH and cation-anion composition, a background electrolyte with the maximum sensitivity of the analytical signal was selected on a modified electrochemical sensor. Study of cyclic voltammograms was carried out to understand the electrode processes, exhibiting a pronounced peak of anodic oxidation observed in a potential range from 0.7 to 0.9 V. However, there was no peak in the cathodic direction which indicates the irreversible nature of the electrode process. When determining the nature of currents, the Semerano criterion equal to 1.6 was calculated, which indicates the absence of the contribution of the diffusion component of the current. Verification of the correctness of the voltammetric method for determining betulin on a new electrochemical sensor was carried out using the «spike-test» method. The data obtained show that the voltammetric determination of betulin can be carried out with a measurement error not exceeding 15%. The proposed modified electrodes were compared with previously known electrodes for the determination of pentacyclic triterpenoids and pesticides at concentrations of 0.5 × 10–3 – 8.0 × 10–3 mg/dm3.

Recent advances in nanomaterials-based electrochemical sensors for tramadol analysis.

Tramadol is a centrally-acting analgesic used for treating moderate to severe acute and chronic pain. Pain is an unpleasant sensation that occurs most commonly as a result of tissue injury. Tramadol possesses agonist actions at the μ-opioid receptor and effects reuptake at the noradrenergic and serotonergic systems. In the last years, several analytical procedures have been published in the literature for the determination of tramadol from pharmaceutical formulations and biological matrices. Electrochemical methods have attracted tremendous attention for the quantification of this drug owing to their demonstrated potential for quick response, real-time measurements, elevated selectivity and sensitivity. In this review, we highlighted the recent advances and applications of nanomaterials-based electrochemical sensors for the analysis and detection of tramadol, which is extremely important for the indication of effective diagnoses and for quality control analyses in order to protect human health. Also, the main challenges in developing nanomaterials-based electrochemical sensors for the determination of tramadol will be discussed. At last, this review offers prospects for the future research and development needed for modified electrode sensing technology for the detection of tramadol.

Green engineered synthesis of PbxZn1-xO NPs: An efficient electrochemical sensor and UV light-driven photocatalytic applications

The present work deals with preparation of PbxZn1-xO nanoparticles (NPs) (x = 0, 0.1, 0.3 & 0.5 M) first time using Zingiber officinale leaf as green fuel by solution combustion route and its structural confirmation was achieved by different spectral techniques. Powder-X-ray diffraction (P-XRD) analysis confirmed the switching of dopant Pb ions into host lattice without altering hexagonal wurtzite phase of host ZnO. The impact of Pb dopant directly affects crystallinity of ZnO host lattice changes the surface morphology with noticeable voids and pores with agglomeration examined by Scanning Electron Microscopy (SEM). The decreasing energy band gap of prepared nanoparticles from 3.3 eV − 2.4 eV due to increasing Pb content examined by UV–Visible absorption spectral technique hinders the recombination of electron-holes pairs by trapping e- and h+, which influence the enhanced photocatalytic activities. This optical characterization influences the achieved NPs used as excellent photocatalyst to remove malachite green (MG) dye under visible-light irradiation, which shows 98.5 % dye degradation at 160 min confirmed by its low kinetic constants of photocatalytic degradation of MG dye for Pb doped ZnO (17.42x10-3 min−1) than host ZnO (10.82×10-3 min−1) nanoparticles. The thermodynamics of redox reaction and capacitance measurement of prepared NPs-graphite paste electrode was investigated by electrochemical analysis in a 3-electrode system using 0.1 M KCl in the different scan rates 0.01–0.05 V/s. The excellent variation of redox peak potentials performance on sensor detections, the Pb-ZnO NPS shows an excellent chemical (Paracetamol) and biomolecule (Dextrose) sensing activity due to the region of Pb+2 ions effect.

Design and Application of Thymol Electrochemical Sensor Based on the PtNPs-CPOFs-MWCNTs Composite.

In this study, the preparation of covalent polyoxometalate organic frameworks (CPOFs) is introduced using the idea of polyoxometalate and covalent organic frameworks. Firstly, the prepared polyoxometalate was functionalized with an amine group (NH2-POM-NH2), and then the CPOFs were prepared by a solvothermal Schiff base reaction with NH2-POM-NH2 and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) as monomers. After the incorporation of PtNPs and MWCNTs into the CPOFs material, the PtNPs-CPOFs-MWCNTs nanocomposites, which possess excellent catalytic activity and electrical conductivity, were formed and utilized as new electrode materials for the electrochemical thymol sensors. The obtained PtNPs-CPOFs-MWCNTs composite exhibits excellent activity toward thymol, which is attributable to its large special surface area, good conductivity and the synergistic catalysis of each component. Under optimal experimental conditions, the sensor presented a good electrochemical response to thymol. The sensor shows two good linear relationships between the current and thymol concentration in the range of 2-65 μM (R2 = 0.996) and 65-810 μM (R2 = 0.997), with the corresponding sensitivity of 72.7 μA mM-1 and 30.5 μA mM-1, respectively. Additionally, the limit of detection (LOD) was calculated to be 0.2 μM (S/N = 3). At the same time, the prepared thymol electrochemical sensor revealed superior stability and selectivity. The constructed PtNPs-CPOFs-MWCNT electrochemical sensor is the first example of thymol detection.

Synthesis of praseodymium vanadate in deep eutectic solvent medium for electrochemical detection of furaltadone

The fabrication of electrode material with unique physiochemical properties is significant to enhance electrochemical performance. In this work, we synthesized praseodymium vanadate (PrVO4) through green deep eutectic solvents (DES) by the solvothermal approach and explored it as an electrochemical sensor for furaltadone (FLD) detection. The as-prepared PrVO4 was characterized by using appropriate microscopic and spectrophotometric techniques. The modification of the electrode on PrVO4 showed excellent electrochemical performance due to its high conductivity, active sites, and fast electron transfer ability. The PrVO4-modified electrode displayed a dynamic linear range (0.008–91 μM), trace-level detection limit (0.002 μM), high sensitivity (4.276 μA µM–1 cm–2), and strong selectivity for FLD detection under optimum experimental conditions. The practical applicability of PrVO4 modified electrode was successfully investigated for the effective determination of FLD in pond water, human urine, and fish samples, revealing its potential application for real samples analysis. This work provide applicable guidelines for the design and development of DES-based electrode materials for the electrochemical sensor application.

Layered 2D MOF nanosheets grown on CNTs substrates for efficient nitrite sensing

In this work, we report a ligand-deficient layered cerium-based metal-organic framework (MOF) nanosheets grown on carbon nanotube (CNT) substrates and its application in electrochemical sensors. The construction of layered MOF nanosheet materials is based on CNTs as the backbone and relies on the low ligand-metal ratios which is controlled by the loaded organic ligands on the surface of CNTs, providing a new approach for the application of 2D MOFs in the field of electrochemical sensing. The obtained 2D MOFs possess unique layered structure and hierarchical connectivity channels, providing highly efficient and stable pathways for electron, ion, and mass transport. The synthesized layered 2D CNTs@Ce-MOF nanosheet hybrid material uses Ce as the center ion and electrocatalytic active material for nitrite sensing. This material exhibits excellent nitrite detection performance within two wider linear ranges of 0.65–3.25 μM and 3.25–7000 μM with the sensitivity of 87.65 ± 0.6 μA·μM−1·cm2 and 0.35 ± 0.03 μA·μM−1·cm−2, respectively. The detection limit is estimated to be 0.12 μM according to signal to noise ratio (S/N) = 3. As the result, the prepared sensors possess advantages in aspects of reproducibility, stability, selectivity and responsiveness in comparison to the reported ones.

Hierarchical Structures Formed in an Atmospheric Pressure Plasma Jet by Polymerization from an Aerosol of Oxalic Acid Stabilized WO3–x Nanosheet Colloids: Toward High-Performance Electrochemical Devices and Sensors

The development of microstructures which combine high total surface area and high porosity is crucial for technologies such as electrocatalysis, electrochromics, and sensors. High deposition rate, composition control of deposition, and low processing temperature to retain active compositions are also desirable. To this end, this study describes combining colloidal sol chemistry with a nonthermal atmospheric pressure dielectric barrier discharge plasma jet to print hybrid inorganic/organic tungsten trioxide/oxalic acid (WO3–x/OA) microspheres. Injection of an aerosol of oxalic acid stabilized colloidal tungstic acid into an atmospheric pressure plasma jet results in the deposition of spherical structures in which the colloid is trapped within a plasma-polymerized organic shell. Subsequent low-temperature sintering produces hierarchical spherical shell-like structures comprising tungsten oxide nanosheets. Alteration of the gas flow rate changes the composition of the deposited material. The method has promise for the general preparation from colloidal precursors of porous materials of controlled morphology and composition with hierarchical microstructures, such as are required for applications in electrochemical devices and sensors which need a high ratio of surface area to volume and connectivity throughout the structure, yet also need a microstructure which is open for rapid exchange of reactants.

Self-assembled multilayer Nb2C MXene/MnFe2O4 electrochemical sensor with Schottky junctions for the detection of acetaminophen and dopamine

The electrochemical sensors with the ability of biomolecule detection can be used for human life and health monitoring. In this work, we developed an electrochemical sensor with a Schottky junction by electrostatic interaction, composed of Nb2C MXene and MnFe2O4. Large reactive groups (O, OH, Cl, or F) are observed at the ends of the Nb2C MXene surface. Meanwhile, there are abundant oxygen vacancies and surfaces of MnFe2O4 which bring it favorable heterogeneous catalytic properties. Among them, the chemical self-assembly of MnFe2O4 nanoparticles on Nb2C MXene enhances the binding strength of the material through electrostatic interaction, promotes charge transfer across the interface, and modulates the electronic and nanostructural characteristics of the N-MFO (MnFe2O4/Nb2C MXene). The results demonstrate that the sensing performance of N-MFO4 for Acetaminophen (AP) and Dopamine (DA) is significantly improved compared to Nb2C MXene and MnFe2O4 modified electrodes, respectively. The obtained limits of detection (LOD) of N-MFO4 modified electrode for AP and DA being 0.079 and 0.070 μM, respectively. The combination of electrodes modified with highly active nanomaterials is supposed to build a portable electrochemical analysis system with high sensitivity, good selectivity, favorable stability, simple operation and low cost, and promote the application of electrochemical sensors in related fields.

Development of mixed spinel metal oxide (Co-Mn-O) integrated functionalized boron nitride: Nanomolar electrochemical detection of herbicide diuron

The crystal phase influences the electrochemical activity of electrode materials. In particular, mixed phases contain metal ions with different oxidation states which enable conductivity and enhance the electrochemical activity. Moreover, 2D nanomaterials enhance the adsorption of target molecules owing to their surface properties. Based on that, the nanocomposite of mixed spinel metal oxide [Co, Mn oxides (CMO NPs)]/and functionalized boron nitride (f-BN) was prepared first time for the electrochemical sensor applications towards herbicide diuron determination. The CMO NPs/f-BN composite has been confirmed by various spectroscopic and microscopic analyses such as p-XRD, FT-IR, FE-SEM, and HR-TEM techniques. p-XRD and FTIR analysis proved the formation of mixed spinel of Co, Mn oxides. Interestingly, morphological investigations revealed that CMO NPs formed as an irregular cubic shape with ± 120 nm in size and f-BN existed in lateral flake-like morphology. FT-IR exhibits, that functionalization promotes the transmittance of functional groups (-OH) of h-BN. The CMO NPs/f-BN/GCE exhibits the well-resolved DU oxidation peak in the CV experiments, owing to the synergetic effect between the CMO NPs and well-functionalized f-BN. In addition, CMO NPs/f-BN/GCE exhibits a low detection limit of 13 nM along with a sensitivity of 0.323 μA µM−1 cm−2 between the two linear ranges of 0.01–419 µM and 569–1770 µM. The proposed sensor showed good repeatability, reproducibility, and stability in DPV analysis. The fabricated DU sensor was successfully applied to real sample analysis in environmental water samples with acceptable recovery results, suggesting CMO NPs/f-BN composite as a beneficial electrode material for the determination of DU.

Application of Monoferrocenylsumanenes Derived from Sonogashira Cross-Coupling or Click Chemistry Reactions in Highly Sensitive and Selective Cesium Cation Electrochemical Sensors.

This paper reports the synthesis and characterization of novel monoferrocenylsumanenes obtained by means of the Sonogashira cross-coupling or click chemistry reaction as well as their application in cesium cation electrochemical sensors. A new synthetic protocol based on Sonogashira cross-coupling was developed for the synthesis of monoferrocenylsumanene or ethynylsumanene. The click chemistry reaction was introduced to the sumanene chemistry through the synthesis of 1,2,3-triazole containing monoferrocenylsumanene. The designed synthetic methods for the modification of sumanene at the aromatic position proved to be efficient and proceeded under mild conditions. The synthesized sumanene derivatives were characterized by detailed spectroscopic analyses of the synthesized sumanene derivatives. The supramolecular interactions between cesium cations and the synthesized monoferrocenylsumanenes were spectroscopically and electrochemically investigated. Furthermore, the design of the highly selective and sensitive cesium cation fluorescence and electrochemical sensors comprising the synthesized monoferrocenylsumanenes as receptor compounds was analyzed. The tested cesium cation electrochemical sensors showed excellent limit of detection values in the range of 6.0-9.0 nM. In addition, the interactions between the synthesized monoferrocenylsumanenes and cesium cations were highly selective, which was confirmed by emission spectroscopy, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and cyclic voltammetry.

Self‐supporting flexible poly(1‐naphaneneboronic acid) film as green light‐emitting material

AbstractThe flexible conducting polymer films (FCPs) with fused ring structure is of great significance in the field of flexible electronics, yet their preparation is challenging. The mechanical properties can be improved by introducing boric acid groups to FCPs. Herein, free‐standing poly (1‐naphaneneboronic acid) (PNBA) film with a conductivity of 3 × 10−4 S cm−1 is readily prepared by electrochemical polymerization of 1‐naphaneneboronic acid. The PNBA film exhibits good redox activity and electrochemical stability. Fourier transform infrared spectrum proves that polymerization site of the as‐prepared PNBA occurs at C5 and C8 positions. The UV–Vis spectrum proves that the optical band gap of PNBA is 2.76 eV. In addition, thermal analysis reveals that the polymer displays excellent thermal stability. Fluorescence spectroscopy results show that PNBA film is a good green light‐emitting material. These characteristics indicate that free‐standing flexible PNBA film has potential applications in flexible electronic semiconductors, fluorescent materials and electrochemical sensors.

Synergetic effects of Mo2C sphere/SCN nanocatalysts interface for nanomolar detection of uric acid and folic acid in presence of interferences

Till to date, the application of sulfur-doped graphitic carbon nitride supported transition metal carbide interface for electrochemical sensor fabrication was less explored. In this work, we designed a simple synthesis of molybdenum carbide sphere embedded sulfur doped graphitic carbon nitride (Mo2C/SCN) catalyst for the nanomolar electrochemical sensor application. The synthesized Mo2C/SCN nanocatalyst was systematically characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with elemental mapping. The SEM images show that the porous SCN network adhered uniformly on Mo2C, causing a loss of crystallinity in the diffractogram. The corresponding elemental mapping of Mo2C/SCN shows distinct peaks for carbon (41.47%), nitrogen (32.54%), sulfur (1.37%), and molybdenum (24.62%) with no additional impurity peaks, reflecting the successful synthesis. Later, the glassy carbon electrode (GCE) was modified by Mo2C/SCN nanocatalyst for simultaneous sensing of uric acid (UA) and folic acid (FA). The fabricated Mo2C/SCN/GCE is capable of simultaneous and interference free electrochemical detection of UA and FA in a binary mixture. The limit of detection (LOD) calculated at Mo2C/SCN/GCE for UA and FA was 21.5 nM (0.09 – 47.0 μM) and 14.7 nM (0.09 – 167.25 μM) respectively by differential pulse voltammetric (DPV) technique. The presence of interferons has no significant effect on the sensor’s performance, making it suitable for real sample analysis. The present method can be extended to fabricate an electrochemical sensor for various molecules.

One-step laser synthesis platinum nanostructured 3D porous graphene: A flexible dual-functional electrochemical biosensor for glucose and pH detection in human perspiration

There has been a recent increase in the demand for wearable sensors for sweat glucose monitoring to facilitate diabetes management in a patient-friendly and non-invasive manner. To address this issue, the key challenge lies in the design of flexible sensors with high conductivity, miniaturized patterning, and environmental friendliness. Herein, we introduce a flexible electrochemical sensing system for glucose and pH detection based on one-step laser-scribed PtNPs nanostructured 3D porous laser-scribed graphene (LSG). The as-prepared nanocomposites can synchronously possess hierarchical porous graphene architectures, whereas PtNPs can significantly enhance their sensitivity and electrocatalytic activity. Benefiting from these advantages, the fabricated Pt-HEC/LSG biosensor exhibited a high sensitivity of 69.64 μA mM−1 cm−2 as well as a low limit of detection (LOD) of 0.23 μM at a detection range of 5–3000 μM (covering the glucose range in sweat). Moreover, the pH sensor was functionalized with polyaniline (PANI) on a Pt-HEC/LSG electrode, and it also exhibited high sensitivity (72.4 mV/pH) in the linear range of pH 4–8. The feasibility of the biosensor was confirmed by analyzing human perspiration during physical exercise. This dual-functional electrochemical biosensor displayed excellent performance, including a low detection limit, high selectivity, and great flexibility. These results confirm that the proposed dual-functional flexible electrode and fabrication process are highly promising for application in human sweat-based electrochemical glucose and pH sensors.

Porous-Pt-CuO-driven electrochemical biosensor for tracking of endogenous H2S biomessenger molecules

Hydrogen sulfide (H2S) is considered to be the third endogenous gas messenger after nitric oxide and carbon monoxide, and is closely related to physiological and pathological functions of human being. Rapid and real-time monitoring of endogenous H2S production in living cells is of great significance for clinical diagnoses of related disease and in-depth investigation of pathological processes. The application of electrochemical sensors has become a promising method to achieve real-time H2S monitoring comparing to other methods. Up to now, low-cost, and highly sensitive electrocatalysts for H2S detection are conspicuously scarce. Herein, we developed a high-efficient method to construct a H2S electrochemical sensor, which configure dissolved–H2S–sensitive electrochemical sensor using porous Pt-modified copper oxide (Pt–CuO) as electrocatalyst. The obtained sensor possessed remarkable H2S detection performance, achieving the detection limit of 0.5 ppm and apparent selectivity toward various gases (e.g., ammonia, nitrogen dioxide, and carbon dioxide). The electrochemical sensor was also applied for monitoring H2S released from mesenchymal stem cells. The enhanced sensing performance was attributed to: (1) electrocatalytic reaction between CuO and [H2S] (H2S and HS−) was observed in the cyclic voltammetry curves with oxidation current peaks; (2) Pt catalytic activity promoted electron transfer during the detection process and further decreasing Pt–CuO resistance; and (3) enhanced diffusion of detection molecules/ions, which increased the reactivity sites through forming cross porous structures using sodium carbonate as sacrifice template. The proposed Pt–CuO-based electrochemical sensor shows great potential for applications in clinical diagnoses, and provides effective means to understand the role of H2S in biological processes.

Conductivity and transport number of Sc and Ce co-doped CaHfO3

CaZrO3-based proton conductors possess high transport numbers, and can thereby yield accurate Nernst concentration electromotive force. These features make them suitable for use in commercialized hydrogen sensors for gas and aluminum melts. Since CaHfO3-based proton conductors have higher transport numbers than CaZrO3, they are more suitable for the fabrication of electrochemical hydrogen sensors. Therefore, CaHf0.9Sc0.1O3 was employed in the present work as base material followed by further modification with Ce co-doping. Accordingly, CaHf0.9-xCexSc0.1O3-δ (x ​= ​0, 0.1, and 0.2) samples were prepared by solid-state reaction sintering process. Conductivities and transport properties of resulting materials were systematically investigated by AC-impedance spectroscopy and defect equilibria model. Standard molar hydration enthalpies of CaHf0.9-xCexSc0.1O3-δ (x ​= ​0, 0.1, and 0.2) were recorded as −61.1 ​kJ/mol, −59.3 ​kJ/mol, and −77.1 ​kJ/mol, respectively. Activation energies for conduction of protons, oxygen ions, and holes were estimated to be 0.56–0.77 ​eV, 1.15–1.26 ​eV, and 1.02–1.49 ​eV, respectively. Among the materials, CaHf0.8Ce0.1Sc0.1O3-δ displayed the highest protonic transport number reaching 0.961–0.512 under 2.5%H2O+21%O2 atmosphere. Overall, CaHf0.8Ce0.1Sc0.1O3-δ is promising for applications in electrochemical hydrogen sensors.

MOF-Derived Ni-P Bundle-Like Nanorods as High-Performance Substrate for Design of Electrochemical Aptasensor Toward Cortisol Detection

The preparation of hierarchical nanostructures based on metal–organic frameworks (MOFs)-derived transition-metal phosphides (TMPs) have received much attention due to its attractive properties in the application of electrochemical sensors. In this research, a label-free and ultrasensitive electrochemical aptasensor for cortisol detection using MOF-derived Ni-P bundle-like nanorods (Ni-P) was presented as an efficient substrate for loading aptamer strings. Ni-MOF was synthesized using a facile hydrothermal method and, then, the Ni-P was obtained using a simple phosphorization of Ni-MOF precursor in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{N}_{{2}}$ </tex-math></inline-formula> atmosphere; it was found that it is made of bundle-like nanorods. The designed aptasensor showed a wide linear sensing range between charge transfer resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {ct}}{)}$ </tex-math></inline-formula> and increasing cortisol concentration in the range of 0.1 fM–700 nM with a low detection limit of 10 aM. It is noteworthy that the efficiency of the aptasensor designed by real urine sample was evaluated and the results were compared with the standard enzyme-linked immunosorbent assay (ELISA) method and acceptable results were obtained.

Electron Transport through Nanoconfined Ferrocene Solution: Density Functional Theory─Nonequilibrium Green Function Approach

We investigate the transport of electrons in a ferrocene aqueous solution nanoconfined between two Pt electrodes using density functional theory and a nonequilibrium Green function method. The system consists of three characteristic phases: metal electrodes, the electrode–solution interface, and the nanoconfined solution phase. By performing the geometry optimization of such systems, it is found that the molecular configuration of water molecules at the Pt surface is adjusted due to the Pt–water interaction, and the charges at the Pt surface are redistributed. Next, by applying the external bias potential via the effective screening medium method during ab initio molecular dynamics simulations, it is revealed that water molecules are packed at the Pt–water interfacial region, and the electrostatic potential profile in the water phase is significantly changed due to aligned water layers. From the analysis of the electron transport characteristics, it is discovered that the ferrocene molecule generates a strong transmission function near the Fermi level and high electron density of states spatially connecting both electrodes through the water phase. These features explain the drastic enhancement in electrical current–voltage characteristics. Therefore, it is concluded that ferrocene enhances electron transport through nanoconfined solutions, indicating that it can be used as a signaling molecule in nanoscale systems for electrochemical sensor applications.

Advanced growth of 2D MXene for electrochemical sensors

Over the last few years, electroanalysis has made significant advancements, particularly in developing electrochemical sensors. Electrochemical sensors generally include emerging Photoelectrochemical and Electrochemiluminescence sensors, which combine optical techniques and traditional electrochemical bio/non-biosensors. Numerous EC-detecting methods have also been designed for commercial applications to detect biological and non-biological markers for various diseases. Analytical applications have recently focused significantly on one of the novel nanomaterials, the MXene. This material is being extensively investigated for applications in electrochemical sensors due to its unique mechanical, electronic, optical, active functional groups and thermal characteristics. This study extensively discusses the salient features of MXene-based electrochemical sensors, photoelectrochemical sensors, enzyme-based biosensors, immunosensors, aptasensors, electrochemiluminescence sensors, and electrochemical non-biosensors. In addition, their performance in detecting various substances and contaminants is thoroughly discussed. Furthermore, the challenges and prospects the MXene-based electrochemical sensors are elaborated.

Localized formation of highly surface-active gold nanoparticle on intrinsic Nickel containing carbon black and its scanning electrochemical microscopy interrogation and electrocatalytic oxidation of hydrazine

Gold nanoparticles (AuNPs) anchored carbon-nanomaterial chemically modified electrodes have been widely used for electrocatalytic applications. Indeed, only a fraction of AuNPs surface is found to be active, while most of the surface is inactive in nature. Thus, it is a challenging research to prepare active AuNPs suitable for electrocatalytic applications. Herein, we present a low-cost intrinsic nickel-containing carbon black (CB-Niint, int= intrinsic nickel) modified glassy carbon electrode as an efficient matrix for forming highly active AuNPs (GCE/CB-Niint@AuNPs). Specific electrocatalytic oxidation of hydrazine has been used as a model system to compare the active sites of the AuNPs. Various carbon nanomaterials like SWCNT, MWCNT, carbon nanofiber, and graphite nanopower-modified electrodes and externally deposited Ni (Niext) on the carbon-modified electrodes were examined as controls for the AuNPs formation and hydrazine electrocatalytic activity. Amongst all, the CB-Niint matrix-modified electrode has shown the best electrocatalytic activity. The GCE/CB-Niint@AuNPs was subjected to various physicochemical characterizations like FESEM, TEM, Raman, IR, XPS, and scanning electrochemical microscopy (SECM) using a Eu3+/2+ redox probe. Meanwhile, with Fe(CN)63−, ex-situ derivatization of Niext as Ni-hexacyanoferrate, CB@Niext-HCF, was specifically inferred. It has been revealed that AuNPs form an intrinsic Au-Niint alloy system on the interstitial position of CB-Niint. On the other hand, a bulk layer-like AuNPs morphology was observed with the CB-Niext modified electrode case. This unique structural feature of the CB-Niint@AuNPs sets a new trend in AuNPs-based chemically modified electrode preparation and electrochemical applications. As a proof of concept, selective electrochemical sensor application of hydrazine with a current sensitivity of 4.37 mA mM−1 cm−2, which is about 5-10 times higher than the majority of the conventional AuNPs-modified electrodes, without any common interference from H2O2, uric acid, ascorbic acid, dopamine, and cysteine, was demonstrated.