Novel ruthenium doped TiO2/reduced graphene oxide hybrid as highly selective sensor for the determination of ambroxol

Instant water toxicity detection based on magnetically-constructed electrochemically active biofilm

Water toxicity determination with electrochemically active bacteria (EAB) is promising in the early warning of water pollution. However, limited by tedious biofilm formation, natural EAB biofilms are uncapable of the instant detection of water toxicity, resulting in the failure for the emergency monitoring of water pollution. To solve this problem, a novel method for the rapid construction of EAB biofilms using magnetic adsorption was established, and the performance of instant water toxicity detection with magnetically-constructed EAB biofilm was investigated. The results demonstrate that EAB biofilms were magnetically constructed in less than 30 min, and magnetically-constructed EAB biofilm generated stable currents even under continuous flow conditions. Magnetically-constructed EAB biofilms realized instant water toxicity detection, and the sensitivity increased with the decrease of magnetic field intensity. Low magnetic field intensity resulted in a loose biofilm structure, which is conducive to toxic pollutant penetration. The detection limit for Cu2+, phenol, and Cd2+ achieved 0.07 mg/L with optimal magnetic field intensity, and the detection time was less than 30 min. This study broadens the application of water toxicity determination with EAB, and establishes a foundation for the instant and continuous detection of water toxicity with EAB.

Novel rhombus Co3O4-nanocapsule CuO heterohybrids for efficient photocatalytic water splitting and electrochemical energy storage applications

The most appealing and prominent approach for improving energy storage and conversion performance is the development of heterojunction interfaces with efficient and unique metal oxide nanostructures. Rhombus Co₃O₄, nanocapsule CuO, and their heterojunction composites were synthesized using a single-step hydrothermal process. The resulting heterojunction Co₃O₄-CuO nanocomposite outperformed the pristine Co₃O₄ and CuO nanostructures for the electrochemical supercapacitor and water splitting performances. The composite showed 2.4 and 1.3 times higher specific capacitance than the associated pristine CuO and Co₃O₄ nanostructures, while its capacitance was 395 F g^-1 at a current density of 0.5 A g^-1. In addition, long-term GCD results with more than 90% stability and significant capacity retention at higher scan rates revealed the unaffected structures interfaced during the electrochemical reactions. The composite photoelectrode demonstrated more than 20% of photocurrent response with light illumination than the dark condition in water splitting. Co₃O₄-CuO heterostructured composite electrode showed a 0.16 mA/cm² photocurrent density, which is 3.2 and 1.7 times higher than the pristine CuO and Co₃O₄ electrodes, respectively. This performance was attributed to its unique structural composition, high reactive sites, strong ion diffusion, and fast electron accessibility. Electron microscopic and spectroscopic techniques confirmed the properties of the electrodes as well as their morphological properties. Overall, the heterojunction interface with novel rhombus and capsule structured architectures showed good electrochemical performance, suggesting their energy storage and conversion applications.

Graphene and Its Derivatives: Synthesis and Application in the Electrochemical Detection of Analytes in Sweat

Wearable sensors and invasive devices have been studied extensively in recent years as the demand for real-time human healthcare applications and seamless human-machine interaction has risen exponentially. An explosion in sensor research throughout the globe has been ignited by the unique features such as thermal, electrical, and mechanical properties of graphene. This includes wearable sensors and implants, which can detect a wide range of data, including body temperature, pulse oxygenation, blood pressure, glucose, and the other analytes present in sweat. Graphene-based sensors for real-time human health monitoring are also being developed. This review is a comprehensive discussion about the properties of graphene, routes to its synthesis, derivatives of graphene, etc. Moreover, the basic features of a biosensor along with the chemistry of sweat are also discussed in detail. The review mainly focusses on the graphene and its derivative-based wearable sensors for the detection of analytes in sweat. Graphene-based sensors for health monitoring will be examined and explained in this study as an overview of the most current innovations in sensor designs, sensing processes, technological advancements, sensor system components, and potential hurdles. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat.

Zinc Oxide–Graphene Nanocomposite-Based Sensor for the Electrochemical Determination of Cetirizine

A nanocomposite electrode of graphene (Gr) and zinc oxide (ZnO) nanoparticles was fabricated to study the electrochemical oxidation behavior of an anti-inflammatory drug, i.e., cetirizine (CET). The voltametric response of CET for bare CPE, Gr/CPE, ZnO/CPE, and the ZnO-Gr nanocomposite electrode was studied. The modifier materials were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) to comprehend the surface morphology of the utilized modifiers. The influence of pH, scan rate, and accumulation time on the electrooxidation of CET was examined. It was found that the electrochemical oxidation of CET was diffusion-controlled, in which two protons and two electrons participated. The detection limit was found to be 2.8 × 10−8 M in a linearity range of 0.05–4.0 µM. Study of excipients was also performed, and it was found that they had negligible interference with the peak potential of CET. The validation and utility of the fabricated nanocomposite sensor material were examined by analyzing clinical and biological samples. Stability testing of the nanocomposite electrode was conducted to assess the reproducibility, determining that the developed biosensor has good stability and high efficiency in producing reproducible results.

Review of the Design of Ruthenium-Based Nanomaterials and Their Sensing Applications in Electrochemistry

In this review, ruthenium nanoparticles (Ru NPs)-based functional nanomaterials have attractive electrocatalytic characteristics and they offer considerable potential in a number of fields. Ru-based binary or multimetallic NPs are widely utilized for electrode modification because of their unique electrocatalytic properties, enhanced surface-area-to-volume ratio, and synergistic effect between two metals provides as an effective improved electrode sensor. This perspective review suggests the current research and development of Ru-based nanomaterials as a platform for electrochemical (EC) sensing of harmful substances, biomolecules, insecticides, pharmaceuticals, and environmental pollutants. The advantages and limitations of mono-, bi-, and multimetallic Ru-based nanocomposites for EC sensors are discussed. Besides, the relevant EC properties and analyte sensing approaches are also presented. On the basis of these insights, we highlighted recent results for synthesizing techniques and EC environmental pollutant sensors from the perspectives of diverse supports, including graphene, carbon nanotubes, silica, semiconductors, metal sulfides, and polymers. Finally, this work overviews the modern improvements in the utilization of Ru-based nanocomposites on the basis for electroanalytical sensors as well as suggestions for the field's future development.

Rapid detection of nitrite based on nitrite-oxidizing bacteria biosensor and its application in surface water monitoring

Timely and sensitive detection of nitrite is of great significance for human health protection and water pollution treatment. However, many biosensors can only determine the comprehensive toxicity of the water, and there are few electroactive biofilm (EAB) sensors for the specific detection of pollutants. Biofilms formed by bacteria with specific functions can improve the specificity of nitrite identification by biosensors. This study developed a novel, rapidly responding, high sensitivity (958.6 μAμM^-1cm^-2), wide detection range and anti-interference electrochemical biosensor based on electroactive nitrite-oxidizing bacteria. The biosensor could accurately detect nitrite in the range of 0.3-100 mg/L within 3 min by the cyclic voltammetry (CV) method. The bioelectrode could perform stable detection of nitrite over 200 cycles. The specificity of the biosensor for detecting nitrite was demonstrated by the presence of nitrite oxidizing bacteria (NOB) and nitrite oxidase enzyme (NXR) on the electrode biofilm. The biosensor performed well in wetlands and rivers, with an RSD <14.8% in the detection of nitrite at low concentrations, and further revealed the nitrification occurrence. Our study provided a feasible way for the development of a highly sensitive, rapidly responding and stable electrochemical biosensor, which also exhibited potential applications for long-term detection of nitrite and assessment of ecological function in surface water (rivers, lakes, wetlands, marshes, etc.).

Biomarkers for Early Diagnosis of Ovarian Carcinoma

The leading cause of gynecological cancer-related morbidity and mortality is ovarian cancer (OC), which is dubbed a silent killer. Currently, OC is a target of intense biomarker research, because it is often not discovered until the disease is advanced. The goal of OC research is to develop effective tests using biomarkers that can detect the disease at the earliest stages, which would eventually decrease the mortality, thereby preventing recurrence. Therefore, there is a pressing need to revisit the existing biomarkers to recognize the potential biomarkers that can lead to efficient predictors for the OC diagnosis. This Perspective covers an update on the currently available biomarkers used in the triaging of OC to gain certain insights into the potential role of these biomarkers and their estimation that are crucial to the understanding of neoplasm progression, diagnostics, and therapy.

Strategies, advances, and challenges associated with the use of graphene-based nanocomposites for electrochemical biosensors

Graphene is an intriguing two-dimensional honeycomb-like carbon material with a unique basal plane structure, charge carrier mobility, thermal conductivity, wide electrochemical spectrum, and unusual physicochemical properties. Therefore, it has attracted considerable scientific interest in the field of nanoscience and bionanotechnology. The high specific surface area of graphene allows it to support high biomolecule loading for good detection sensitivity. As such, graphene, graphene oxide (GO), and reduced GO are excellent materials for the fabrication of new nanocomposites and electrochemical sensors. Graphene has been widely used as a chemical building block and/or scaffold with various materials to create highly sensitive and selective electrochemical sensing microdevices. Over the past decade, significant advancements have been made by utilizing graphene and graphene-based nanocomposites to design electrochemical sensors with enhanced analytical performance. This review focus on the synthetic strategies, as well as the structure-to-function studies of graphene, electrochemistry, novel multi nanocomposites combining graphene, limit of detection, stability, sensitivity, assay time. Finally, the review describes the challenges, strategies and outlook on the future development of graphene sensors technology that would be usable for the internet of things are also highlighted.

COF-43 based voltammetric sensor for Ag(I) determination: optimization of experimental conditions by Box-Behnken design

Hydrazone-linked covalent organic framework-43 (COF-43) was synthesized and the carbon paste electrode (CPE) modified with this COF was used as a voltammetric sensor to measure silver(I). Various characterization tests (XRD, FTIR, BET, SEM/EDX, electrochemical impedance (EIS), and cyclic voltammetry (CV)) were performed on the synthesized COF-43 and the prepared COF-43/CPE. Box-Behnken design was used to optimize the preparation and operation conditions of the sensor. EIS and CV investigations reveal the diffusive characteristics of silver transport in the electrode matrix. An appropriate mechanism for the sensor procedure has been suggested and ratified by electrochemical and SEM/EDX techniques. The COF-43 used has several recognition elements for the selective binding of silver ion and due to its high porosity provides a large space for the deposition and reduction of large amounts of silver. Therefore, due to the correct selection of COF used in the construction of the sensor, high selectivity and sensitivity for the prepared sensor has been achieved. The obtained data disclosed that the modification of the carbon paste electrode by COF-43 significantly improves the analytical characteristics of the sensor, which specifies the performance of COF-43 as a sensory material for determining silver(I). The obtained calibration curve is linear in the concentration range from 0.001 μM to 10.0 μM and the detection limit is 1.5 × 10^-10 M. Various statistical tests have been employed to evaluate the sensor performance. The appropriate accuracy and precision of the proposed method were confirmed using the analysis of variance (ANOVA) approach. Potential interferences were investigated and it was found that the other species did not have a significant effect on the sensor performance. The prepared sensor has been successfully used to measure silver in two samples of photographic effluents, bleaching, and fixing agents. The results from the analysis of real samples demonstrate the reliable applicability of the fabricated sensor.

Development of a SAW poly(epichlorohydrin) gas sensor for detection of harmful chemicals

The uniformity and compactness of the surface of a viscoelastic sensitive film are among the most important factors that influence the characteristics of a surface acoustic wave (SAW) gas sensor, directly affecting the detection sensitivity of a SAW sensor on a target gas. In this paper, poly(epichlorohydrin) (PECH) with viscoelastic properties was used as sensitive film for the detection of 2-chloroethyl ethyl sulfide (CEES), a common simulant of the chemical agent mustard gas. Nanoscale films were prepared using a spin coating technology on a SAW delay line of 200 MHz. Films were evaluated using polarizing microscopy and atomic force microscopy and observed with uniform surface states and particle diameter in the cluster region of 4.52-5.22 μm. The interface parameters, including contact angle, surface tension, Gibbs free energy, work of adhesion, work of immersion, and spreading coefficient values were 9.31° to 39.63°, 22.475 to 29.945 mN m^-1, -85.70 to -78.08 J m^-2, 78.08 to 85.70 J m^-2, -42.62 to -35.00 J m^-2, and 0.46 to 8.08 J m^-1, respectively. These values were obtained by experiments combined with the Young T equation and Gibbs adsorption isotherm, and the surface analysis was carried out theoretically. The glass transition temperature (-22.4 °C), viscosity, pyrolysis, and other physical characteristics of the prepared PECH were discussed. Five SAW sensors prepared at the same time were used to test the repeatability of CEES measurements at one concentration, where the consistency of the sensor preparation was confirmed. At a concentration of 13.6 mg m^-3 for CEES, 10 consecutive detection results showed good repeatability (i.e., standard deviation = 0.295, coefficient of variance = 0.021, and population mean deviation = 0.364). At room temperature (20 °C ± 5 °C), different concentrations of CEES were detected using the developed sensor, which showed good linearity in the concentration range of 1.9-19.6 mg m^-3 (y = 0.0309 + 1.13x, r = 0.99478). The limit of detection was 0.85 mg m^-3, the limit of quantitation was 1.91 mg m^-3, and the sensitivity of the SAW sensor was 1.13 mV (mg m^-3). The adsorption mechanism related to PECH in the detection of CEES was also discussed.

A high-sensitive and durable electrochemical sensor based on Geobacter-dominated biofilms for heavy metal toxicity detection

A highly sensitive electrochemical sensor for detecting low concentrations of heavy metals (Cd²⁺, Ni²⁺, Pb²⁺ and Cu²⁺) based on Geobacter-dominated biofilms was developed. The biosensor showed a high sensitivity for the determination of Cd²⁺ (109.7 μAμM^-1cm^-2) and the determination of Pb²⁺ (161.7 μAμM^-1cm^-2). The performance of three fitting models for biosensor response to heavy metal toxicity was investigated based on the relationship between total coulomb yield and heavy metal concentration. The full-area model (Equation a) provided the best fit, and the response times tended to be the fastest based on the peak current model (Equation c). Recovery methods were proposed to ensure the electrical activity of the biofilm for long-term monitoring. 16S rRNA gene sequence analysis showed that the most dominant genus in the anodic biofilm was Geobacter (44.1%-45.8%), indicating a stable community structure after continuous toxicity shock for 22 days. The confocal laser scanning microscope (CLSM) further proved the restorable and reusability of the biosensor. Thanks to the thin and electrically active Geobacter-dominated biofilms, it could be a good alternative biosensor for groundwater analysis etc. The results of this study contribute to the development of a highly sensitive and accurate biosensor with long-term usage towards on-site monitoring of heavy metals at low concentrations, improving the test performance of the biosensor for practical application.

Skin Patchable Sensor Surveillance for Continuous Glucose Monitoring

Diabetes mellitus is a physiological and metabolic disorder affecting millions of people worldwide, associated with global morbidity, mortality, and financial expenses. Long-term complications can be avoided by frequent, continuous self-monitoring of blood glucose. Therefore, this review summarizes the current state-of-art glycemic control regimes involving measurement approaches and basic concepts. Following an introduction to the significance of continuous glucose sensing, we have tracked the evolution of glucose monitoring devices from minimally invasive to non-invasive methods to present an overview of the spectrum of continuous glucose monitoring (CGM) technologies. The conveniences, accuracy, and cost-effectiveness of the real-time CGM systems (rt-CGMs) are the factors considered for discussion. Transdermal biosensing and drug delivery routes have recently emerged as an innovative approach to substitute hypodermal needles. This work reviews skin-patchable glucose monitoring sensors for the first time, providing specifics of all the major findings in the past 6 years. Skin patch sensors and their progressive form, i.e., microneedle (MN) array sensory and delivery systems, are elaborated, covering self-powered, enzymatic, and non-enzymatic devices. The critical aspects reviewed are material design and assembly techniques focusing on flexibility, sensitivity, selectivity, biocompatibility, and user-end comfort. The review highlights the advantages of patchable MNs' multi-sensor technology designed to maintain precise blood glucose levels and administer diabetes drugs or insulin through a "sense and act" feedback loop. Subsequently, the limitations and potential challenges encountered from the MN array as rt-CGMs are listed. Furthermore, the current statuses of working prototype glucose-responsive "closed-loop" insulin delivery systems are discussed. Finally, the expected future developments and outlooks in clinical applications are discussed.

Disposable biosensors based on metal nanoparticles

The coronavirus disease2019 (COVID-19) pandemic has highlighted the need for disposable biosensors that can detect viruses in infected patients quickly due to fast response and also at a low cost.The present review provides an overview of the applications of disposable biosensors based on metal nanoparticles in enzymatic and non-enzymatic sensors with special reference to glucose and H₂O₂, immunosensors as well as genosensors (DNA biosensors in which the recognized event consists of the hybridization reaction)for point-of-care diagnostics. The disposable biosensors for COVID19 have also been discussed.

Biosensors as Nano-Analytical Tools for COVID-19 Detection

Selective, sensitive and affordable techniques to detect disease and underlying health issues have been developed recently. Biosensors as nanoanalytical tools have taken a front seat in this context. Nanotechnology-enabled progress in the health sector has aided in disease and pandemic management at a very early stage efficiently. This report reflects the state-of-the-art of nanobiosensor-based virus detection technology in terms of their detection methods, targets, limits of detection, range, sensitivity, assay time, etc. The article effectively summarizes the challenges with traditional technologies and newly emerging biosensors, including the nanotechnology-based detection kit for COVID-19; optically enhanced technology; and electrochemical, smart and wearable enabled nanobiosensors. The less explored but crucial piezoelectric nanobiosensor and the reverse transcription-loop mediated isothermal amplification (RT-LAMP)-based biosensor are also discussed here. The article could be of significance to researchers and doctors dedicated to developing potent, versatile biosensors for the rapid identification of COVID-19. This kind of report is needed for selecting suitable treatments and to avert epidemics.

Electrochemical investigations for COVID-19 detection-A comparison with other viral detection methods

Virus-induced infection such as SARS-CoV-2 is a serious threat to human health and the economic setback of the world. Continued advances in the development of technologies are required before the viruses undergo mutation. The low concentration of viruses in environmental samples makes the detection extremely challenging; simple, accurate and rapid detection methods are in urgent need. Of all the analytical techniques, electrochemical methods have the established capabilities to address the issues. Particularly, the integration of nanotechnology would allow miniature devices to be made available at the point-of-care. This review outlines the capabilities of electrochemical methods in conjunction with nanotechnology for the detection of SARS-CoV-2. Future directions and challenges of the electrochemical biosensors for pathogen detection are covered including wearable and conformal biosensors, detection of plant pathogens, multiplexed detection, and reusable biosensors for on-site monitoring, thereby providing low-cost and disposable biosensors.

Synthesis of POMOFs with 8-fold helix and its composite with carboxyl functionalized SWCNTs for the voltammetric determination of dopamine

Although many satisfactory studies have been developed for biomolecule detection, the complexity of biofluids still poses a major challenge to improve the performance of nanomaterials as electrochemical sensors. Herein, unprecedented polyoxometalate-based metal-organic frameworks (POMOFs) with 8-fold meso-helical feature, [Ag₅(trz)₄]₂[PMo₁₂O₄₀] (PAZ), were synthesized and explored as electrochemical sensors to detect dopamine (DA). To improve the conductivity of PAZ and the binding ability with single-walled carbon nanotubes (SWCNTs), the nanocomposite of carboxyl functionalized SWCNTs (SWCNTs-COOH) with nano-PAZ (NPAZ), NPAZ@SWCNTs-COOH, was fabricated, and transmission electron microscopy (TEM) shows that NPAZ can interact stably and uniformly with SWCNTs-COOH, owing to more defect sites on the surface of SWCNTs-COOH. The electrochemical result of NPAZ@SWCNTs-COOH/GCE towards detecting DA shows that the linear range was from 0.05 to 100 μM with a detection limit (LOD) of 8.6 nM (S/N = 3). A new electrochemical biosensing platform by combining 8-fold helical POMOFs with SWCNTs-COOH was developed for enhancing detection of dopamine for the first time, exhibiting the lowest detection limit to date.

Point of care detection of COVID-19: Advancement in biosensing and diagnostic methods

The recent outbreak of COVID-19 has created much inconvenience and fear that the virus can seriously affect humans, causing health hazards and death. This pandemic has created much worry and as per the report by World Health Organization (WHO), more than 43 million individuals in 215 countries and territories were affected. People around the world are still struggling to overcome the problems associated with this pandemic. Of all the available methods, reverse-transcriptase polymerase chain reaction (RT-PCR) has been widely practiced for the pandemic detection even though several diagnostic tools are available having varying accuracy and sensitivity. The method offers many advantages making it a life-saving tool, but the method has the limitation of transporting to the nearest pathology lab, thus limiting its application in resource limited settings. This has a risen a crucial need for point-of-care devices for on-site detection. In this venture, biosensors have been used, since they can be applied immediately at the point-of-care. This review will discuss about the available diagnostic methods and biosensors for COVID-19 detection.

Conventional and Nanotechnology-Based Sensing Methods for SARS Coronavirus (2019-nCoV)

Ongoing pandemic coronavirus (COVID-19) has affected over 218 countries and infected 88,512,243 and 1,906,853 deaths reported by Jan. 8, 2021. At present, vaccines are being developed in Europe, Russia, USA, and China, although some of these are in phase III of trials, which are waiting to be available for the general public. The only option available now is by vigorous testing, isolation of the infected cases, and maintaining physical and social distances. Numerous methods are now available or being developed for testing the suspected cases, which may act as carriers of the virus. In this review, efforts have been made to discuss the conventional as well as fast, rapid, and efficient testing methods developed for the diagnosis of 2019-nCoV.Testing methods can be based on the sensing of targets, which include RNA, spike proteins and antibodies such as IgG and IgM. Apart from the development of RNA targeted PCR, antibody and VSV pseudovirus neutralization assay along with several other diagnostic techniques have been developed. Additionally, nanotechnology-based sensors are being developed for the diagnosis of the virus, and these are also discussed.

A facile, sensitive and rapid sensing platform based on CoZnO for detection of fipronil; an environmental toxin

A sensitive detection of extremely toxic phenylpyrazole insecticide, 'Fipronil' is presented. Currently, the advancement of approaches for the detection of insecticides at low concentrations with less time is important for environmental safety assurance. Considering this fact, an effort has been made to develop an electrospun CoZnO nanofiber (NF) based label-free electrochemical system for the detection of fipronil. The CoZnO NF were characterized using different techniques including field emission scanning electron microscopy (FE-SEM), Energy Dispersive X-Ray Analysis (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman Spectroscopy. Based on the experimental results, the proposed platform displayed a linear response for fipronil in the attogram/mL range despite the multiple interfering agents. The sensitivity of the device was found to be 3.99 Kῼ (g/ml)^-1 cm^-2. Limit of detection (LOD) and limit of quantification (LOQ) were calculated and found to be 112 ag mL^-1 and 340 ag mL^-1 respectively. Further, this proposed sensor will be implemented in the fields for the rapid and proficient detection of the real samples.

Selective nanomolar electrochemical detection of serotonin, dopamine and tryptophan using TiO2/RGO/CPE – influence of reducing agents

TiO2/RGO nanocomposites were synthesised via a simple one-pot hydrothermal method and used as a modifier in carbon paste electrode for the sensitive determination of serotonin.

Metal-organic frameworks for virus detection

Virus severely endangers human life and health, and the detection of viruses is essential for the prevention and treatment of associated diseases. Metal-organic framework (MOF), a novel hybrid porous material which is bridged by the metal clusters and organic linkers, has become a promising biosensor platform for virus detection due to its outstanding properties including high surface area, adjustable pore size, easy modification, etc. However, the MOF-based sensing platforms for virus detection are rarely summarized. This review systematically divided the detection platforms into nucleic acid and immunological (antigen and antibody) detection, and the underlying sensing mechanisms were interpreted. The nucleic acid sensing was discussed based on the properties of MOF (such as metal ion, functional group, geometry structure, size, porosity, stability, etc.), revealing the relationship between the sensing performance and properties of MOF. Moreover, antibodies sensing based on the fluorescence detection and antigens sensing based on molecular imprinting or electrochemical immunoassay were highlighted. Furthermore, the remaining challenges and future development of MOF for virus detection were further discussed and proposed. This review will provide valuable references for the construction of sophisticated sensing platform for the detection of viruses, especially the 2019 coronavirus.