Chloride ion sensors based on low-dimensional α-MnO2–Co3O4 nanoparticles fabricated glassy carbon electrodes by simple I–V technique

Silver-manganese nanocomposite modified screen-printed carbon electrode in the fabrication of an electrochemical, disposable biosensor strip for cystic fibrosis

A silver-manganese nanocomposite was successfully prepared by the urea hydrolysis method and used to detect chloride ions in sweat electrochemically. The synthesis involves the reaction of manganese sulphate, silver nitrate, and urea at 100 °C for 24 h. The crystalline nature of the particle was studied by diffraction analysis and found to be mixed-phase oxides of manganese alongside the oxides of silver. Morphological studies revealed the presence of quasi-prism-like structures, which is characteristic of β-MnO₂. A disposable sensor was fabricated by screen-printing the catalyst and used for the electrochemical detection of chloride ions in sweat. The sensor exhibited good selectivity, a sensitivity of 22.93 ± 0.64 µA mM^-1 cm^-2 in solution and 3010 ± 60 µA (log mM) ^-1 cm^-2 for the fabricated sensor strip with a detection range from 5 mM up to 200 mM. The detection limit is 207 ± 7 µM (S/N = 3) in solution and 17 ± 6 µM for the fabricated sensor strip. The relative standard deviation (RSD) of sensor response is 2.38%. A prototype of the biosensor strip was fabricated and validated using real samples. This brings the possibility of developing a real-time biosensor strip for cystic fibrosis in point-of-care testing applications.

A Review on Flexible Electrochemical Biosensors to Monitor Alcohol in Sweat

The continued focus on improving the quality of human life has encouraged the development of increasingly efficient, durable, and cost-effective products in healthcare. Over the last decade, there has been substantial development in the field of technical and interactive textiles that combine expertise in electronics, biology, chemistry, and physics. Most recently, the creation of textile biosensors capable of quantifying biometric data in biological fluids is being studied, to detect a specific disease or the physical condition of an individual. The ultimate goal is to provide access to medical diagnosis anytime and anywhere. Presently, alcohol is considered the most commonly used addictive substance worldwide, being one of the main causes of death in road accidents. Thus, it is important to think of solutions capable of minimizing this public health problem. Alcohol biosensors constitute an excellent tool to aid at improving road safety. Hence, this review explores concepts about alcohol biomarkers, the composition of human sweat and the correlation between alcohol and blood. Different components and requirements of a biosensor are reviewed, along with the electrochemical techniques to evaluate its performance, in addition to construction techniques of textile-based biosensors. Special attention is given to the determination of biomarkers that must be low cost and fast, so the use of biomimetic materials to recognize and detect the target analyte is turning into an attractive option to improve electrochemical behavior.

The fast nucleation/growth of Co3O4 nanowires on cotton silk: the facile development of a potentiometric uric acid biosensor

In this study, we have used cotton silk as a source of abundant hydroxyl groups for the fast nucleation/growth of cobalt oxide (Co₃O₄) nanowires via a hydrothermal method. The crystal planes of the Co₃O₄ nanowires well matched the cubic phase. The as-synthesized Co₃O₄ nanowires mainly contained cobalt and oxygen elements and were found to be highly sensitive towards uric acid in 0.01 M phosphate buffer solution at pH 7.4. Importantly, the Co₃O₄ nanowires exhibited a large surface area, which was heavily utilized during the immobilization of the enzyme uricase via a physical adsorption method. The potentiometric response of the uricase-immobilizing Co₃O₄ nanowires was measured in the presence of uric acid (UA) against a silver/silver chloride (Ag/AgCl) reference electrode. The newly fabricated uric acid biosensor possessed a low limit of detection of 1.0 ± 0.2 nM with a wide linear range of 5 nM to 10 mM and sensitivity of 30.6 mV dec⁻¹. Additionally, several related parameters of the developed uric acid biosensor were investigated, such as the repeatability, reproducibility, storage stability, selectivity, and dynamic response time, and these were found to be satisfactory. The good performance of the Co₃O₄ nanowires was verified based on the fast charge-transfer kinetics, as confirmed via electrochemical impedance spectroscopy. The successful practical use of the uric acid biosensor was demonstrated based on the recovery method. The observed performance of the uricase-immobilizing Co₃O₄ nanowires revealed that they could be considered as a promising and alternative tool for the detection of uric acid under both in vitro and in vivo conditions. Also, the use of cotton silk as a source of abundant hydroxyl groups may be considered for the remarkably fast nucleation/growth of other metal-oxide nanostructures, thereby facilitating the fabrication of functional electrochemical devices, such as batteries, water-splitting devices, and supercapacitors.

In this study, we have used cotton silk as a source of abundant hydroxyl groups for the fast nucleation/growth of cobalt oxide (Co₃O₄) nanowires via a hydrothermal method.

One-Step Synthesis of Green Fluorescent Carbon Dots for Chloride Detecting and for Bioimaging

The chloride ion is an essential ion in organisms, which plays an important role in maintaining normal cell functions. It is involved in many cell activities, such as cell proliferation, cell excitability regulation, immune response, and volume regulation. Accurate detection of the chloride ion can balance its concentration in vivo, which is of great significance. In this study, we developed a green fluorescent carbon quantum dot to detect chloride concentration through the “off–on” mechanism. First, the fluorescence of carbon dots is quenched by the complex of sulfhydryl and silver ions on the surface of carbon dots. Then, the addition of chloride ions pulls away the silver ions and restores the fluorescence. The fluorescence recovery is linearly related to the concentration of chloride ions, and the limit of detection is 2.817 μM, which is much lower than those of other reported chloride probes. Besides, cell and zebrafish experiments confirmed the biosafety and biocompatibility of the carbon dots, which provided a possibility for further applications in bioimaging in vivo.

Rapid and sensitive detection of selective 1,2-diaminobenzene based on facile hydrothermally prepared doped Co3O4/Yb2O3 nanoparticles

In this approach, the performance of a newly developed sensor probe coated with low-dimensional Co₃O₄/Yb₂O₃ nanoparticles (NPs) in rapidly detecting 1,2-diaminobenzene was evaluated by an electrochemical technique. The sensor probe was fabricated by depositing a very thin layer consisting of synthesized Co₃O₄/Yb₂O₃ NPs using a 5% Nafion conducting binder onto a glassy carbon electrode (GCE). The facile hydrothermally prepared Co₃O₄/Yb₂O₃ NPs were totally characterized by conventional methods such as FTIR, UV-vis, TEM, XPS, EDS, and XRD analyses. The fabricated chemical sensor probe was found to exhibit long-term activity, stability in electrochemical response, good sensitivity (5.6962 μAμM^-1cm^-2), lowest detection limit (0.02±0.001 pM), and broad linear dynamic range (0.1 pM to 0.01 mM). The observed performances suggest that the newly introduced sensor could play an efficient role in detecting 1,2-diaminobenzene especially in healthcare and environmental applications on a broad scale.

Colorimetric sensing of chloride in sweat based on fluorescence wavelength shift via halide exchange of CsPbBr3 perovskite nanocrystals

Considering the high importance of the rapid detection of chloride ion (Cl^-) in sweat for the diagnosis of fibrotic cysts, we have investigated the heterogeneous halide exchange between CsPbBr₃ perovskite nanocrystals (PNCs) in n-hexane and Cl^- in aqueous solution. The results show that CsPbBr₃ PNCs could achieve fast halide exchange with Cl^- in the aqueous phase under magnetic stirring at pH = 1, accompanied by a significant wavelength blue shift and vivid fluorescence color changes from green to blue. Therefore, a fluorescence wavelength shift-based colorimetric sensing of Cl^- based on the halide exchange of CsPbBr₃ PNCs has been developed to realize the rapid detection of Cl^- in sweat. Compared with the conventional fluorescence intensity-based method, this method is of high convenience since the whole procedure could be achieved within 5 min without any sample pretreatment (even no dilution), demonstrating promising application prospects. Graphical Abstract Fluorescence wavelength-shift based colorimetric sensing of chloride in sweat via halide exchange of CsPbBr₃ perovskite nanocrystals.

Textile sensors platform for the selective and simultaneous detection of chloride ion and pH in sweat

The development of wearable sensors, in particular fully-textile ones, is one of the most interesting open challenges in bioelectronics. Several and significant steps forward have been taken in the last decade in order to achieve a compact, lightweight, cost-effective, and easy to wear platform for healthcare and sport activities real-time monitoring. We have developed a fully textile, multi-thread biosensing platform that can detect different bioanalytes simultaneously without interference, and, as an example, we propose it for testing chloride ions (Cl^-) concentration and pH level. The textile sensors are simple threads, based on natural and synthetic fibers, coated with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and properly functionalized with either a nano-composite material or a chemical sensitive dye to obtain Cl^- and pH selective sensing functionality, respectively. The single-thread sensors show excellent sensitivity, reproducibility, selectivity, long term stability and the ability to work with small volumes of solution. The performance of the developed textile devices is demonstrated both in buffer solution and in artificial human perspiration to perform on-demand and point-of-care epidermal fluids analysis. The possibility to easily knit or sew the thread sensors into fabrics opens up a new vision for a textile wearable multi-sensing platform achievable in the near future.

Fabrication of an (α-Mn2O3:Co)-decorated CNT highly sensitive screen printed electrode for the optimization and electrochemical determination of cyclobenzaprine hydrochloride using response surface methodology

A new chemically optimized screen-printed electrode modified with a cobalt-doped α-Mn2O3 nanostructure on carbon nanotube paste (α-Mn2O3:Co@CNTs) has been constructed for the recognition of cyclobenzaprine hydrochloride. The prepared paste is based on the incorporation of oxide ion conductors, such as the α-Mn2O3 nanostructure with cobalt and ion pairs (tetraphenyl borate coupled with the drug), as electroactive species in the screen-printed electrode to increase the sensor surface area and decrease electrical resistance. The central composite design is a useful methodology for the estimation and modeling of the exact optimum parameters specifically designed for this process. This is a good way to graphically clarify the relationship between various experimental variables and the slope response. The proposed sensor, α-Mn2O3:Co@CNTs, possesses very good sensitivity and the ability to recognize the drug over the concentration range of 1 × 10-6 to 1 × 10-2 mol L-1 at 25 ± °C with a detection limit of 2.84 × 10-7 mol L-1. It exhibits a reproducible potential and stable linear response for six months at a Nernstian slope of 58.96 ± 0.76 mV per decade. The proposed electrode approach has been successfully applied in the direct determination of the drug in its pure and dosage forms.

Ag nanoparticles decorated into metal-organic framework (Ag NPs/ZIF-8) for electrochemical sensing of chloride ion

In this work, silver nanoparticles (Ag NPs) were decorated into the cavities of ZIF-8 to fabricate a novel Ag NPs/ZIF-8 modified glassy carbon electrode (GCE) for electrochemical sensing of chloride ion. Benefiting from the synergistic properties of ZIF-8 and Ag NPs, the Ag NPs/ZIF-8/GCE showed favorable performance towards chloride ion. For comparison, the electrochemical activity of Ag NPs wrapped by ZIF-8 (Ag NPs@ZIF-8) and Ag NPs coating on ZIF-8 (Ag NPs-on-ZIF-8) were also investigated and it was found that Ag NPs/ZIF-8 possessed the best performance. Some experimental parameters including pH of the supporting electrolyte and scan rate were also investigated. Under optimal conditions, the proposed sensor exhibited excellent stability, reproducibility and selectivity for the determination of chloride ion with a wide linear detection range from 5 to 4000 μmol dm^-3 and a low detection limit of 0.61 μmol dm^-3 (S/N = 3). The proposed sensor was successfully applied to the determination of chloride ion spiked in human serum. All these results indicated that the developed Ag NPs/ZIF-8/GCE sensor was superior.

FeMn layered double hydroxides: an efficient bifunctional electrocatalyst for real-time tracking of cysteine in whole blood and dopamine in biological samples

A peculiar clock-regulated design of FeMn-LDHs (FMH) with specific physiochemical attributes has been developed and used for highly sensitive detection of cysteine (CySH) and dopamine (DA).

Thermally stable hybrid polyarylidene(azomethine-ether)s polymers (PAAP): an ultrasensitive arsenic(III) sensor approach

A new category of thermally stable hybrid polyarylidene(azomethine-ether)s and copolyarylidene(azomethine-ether)s (PAAP) based on diarylidenecycloalkanones has been synthesized using solution polycondensation method. For potential cationic sensor development, a thin layer of PAAP onto a flat glassy carbon electrode (GCE, surface area: 0.0316 cm²) was prepared with conducting nafion (5%) coating agent to fabricate a sensitive and selective arsenic (III) [As³⁺] ion in short response time in neutral buffer system. The fabricated cationic sensor was measured the analytical performances such as higher sensitivity, linear dynamic range, detection limit, reproducibility, and long-term stability towards As³⁺ ions. The sensitivity and detection limit were calculated as 2.714 μAμM^-1cm^-2 and 6.8 ± 0.1 nM (SNR of 3; 3N/S) respectively from the calibration curve. This novel approach can be initiated a well-organized route of an efficient development of heavy selective arsenic sensor for hazardous pollutants in biological, environmental, and health care fields. Real sample analysis for various environmental sample was performed with PAAP-modified-GCE.

2-Nitrophenol sensor-based wet-chemically prepared binary doped Co3O4/Al2O3 nanosheets by an electrochemical approach

Herein, the wet-chemical process (co-precipitation) was used to prepare nanosheets (NSs) of Co₃O₄/Al₂O₃ in an alkaline medium (pH ∼ 10.5). The synthesized NSs were totally characterized by Fourier-transform infrared spectroscopy (FTIR), ultraviolet visible spectroscopy (UV/vis), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). The synthesized NSs were deposited onto a glassy carbon electrode (GCE) to prepare a very thin layer with a conducting binder for detecting 2-nitrophenol (2-NP) selectively by a reliable electrochemical method. The proposed chemical sensor exhibits good sensitivity (54.9842 μA μM⁻¹ cm⁻²), long-term stability, and enhanced chemical response by electrochemical approaches. The resultant current is found to be linear over the concentration range (LDR) from 0.01 nM to 0.01 mM. The estimated detection limit (DL) is equal to 1.73 ± 0.02 pM. This study introduces a potential route for future sensitive sensor development with Co₃O₄/Al₂O₃ NSs by an electrochemical approach for the selective detection of hazardous and carcinogenic chemicals in environmental and health care fields.

This potential research work introduces a route of future sensitive sensor development with Co₃O₄/Al₂O₃ NSs by electrochemical approach to selective detection of hazardous and carcinogenic chemicals in environmental and health care fields.

Fabrication of a 2,4-dinitrophenol sensor based on Fe3O4@Ag@Ni nanomaterials and studies on their antibacterial properties

Scheme representing (a) MO coated GCE, (b) theoretical I–V response, (c) observed I–V responses by the MO/Nafion/GCE, and (d) proposed detection mechanism of 2,4-DNP.

3,4-Diaminotoluene sensor development based on hydrothermally prepared MnCoxOy nanoparticles

A facile hydrothermal process was used to prepare MnCo_xO_y nanoparticles (NPs) in alkaline medium (pH~10.5) at room temperature. The NPs were characterized by Fourier-transform infrared spectroscopy (FTIR), ultraviolet visible spectroscopy (UV/vis), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and powder X-ray diffraction (XRD). A thin layer of NPs film as a chemical sensor was fabricated on a glassy carbon electrode (GCE) with the help of a conducting binder. The sensor was implemented successfully for the detection 3,4-DAT with reliable I-V approach at low potential. The sensor-features include good sensitivity (0.37 mAµmolL^-1cm^-2), low detection limit (LOD=0.26±0.01 pmolL^-1 at a signal to noise ratio of 3), low limit of quantification (LOQ=7.80±0.01 pmolL^-1), good reliability, good reproducibility, ease of integration, and long-term stability were investigated. The sensor response towards 3,4-DAT is linear in logarithmic scale over a large concentration range (1.0 pmolL^-1 to 1.0 µmolL^-1). This work is introduced a route for future sensitive sensor development based on MnCo_xO_y NPs by reliable I-V method for the detection of hazardous and carcinogenic toxins in environmental and health care fields.

Ultrasensitive and selective 4-aminophenol chemical sensor development based on nickel oxide nanoparticles decorated carbon nanotube nanocomposites for green environment

Nickel oxide nanoparticles decorated carbon nanotube nanocomposites (NiO·CNT NCs) were prepared in a basic medium by using facile wet-chemical routes. The optical, morphological, and structural properties of NiO·CNT NCs were characterized using Fourier transformed infra-red (FT-IR), Ultra-violet visible (UV/Vis) spectroscopy, field-emission scanning electron microscopy (FESEM), X-ray energy dispersed spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD) methods. Selective 4-aminophenol (4-AP) chemical sensor was developed by a flat glassy carbon electrode (GCE, surface area: 0.0316cm²) fabricated with a thin-layer of NCs. Electrochemical responses including higher sensitivity, large dynamic range (LDR), limit of detection (LOD), and long-term stability towards 4-AP were obtained using the fabricated chemical sensors. The calibration curve was found linear (R²=0.914) over a wide range of 4-AP concentration (0.1nmol/L-0.1mol/L). In perspective of slope (2×10^-5μA/μM), LOD and sensitivity were calculated as 15.0±0.1pM and ~6.33×10^-4μA/(μM·cm) respectively. The synthesized NiO·CNT NCs using a wet-chemical method is a significant route for the development of ultrasensitive and selective phenolic sensor based on nano-materials for environmental toxic substances. It is suggested that a pioneer and selective development of 4-AP sensitive sensor using NiO·CNT NCs by a facile and reliable current vs voltage (I-V) method for the major application of toxic agents in biological, green environmental, and health-care fields in near future.

Phenolic sensor development based on chromium oxide-decorated carbon nanotubes for environmental safety

A nanocomposite (NC) composed of chromium(III)oxide nanomaterials decorated carbon nanotubes (Cr₂O₃-CNT NC) was prepared via a simple solution method with reducing agents in an alkaline medium. The Cr₂O₃-CNT NC was characterized using ultraviolet-visible (UV/Vs.) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, energy-dispersive X-ray spectroscopy (XEDS), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscopy (FESEM). The Cr₂O₃-CNT composite was deposited on a flat glassy carbon electrode (GCE) with conducting nafion (5%) binders to produce a sensor that exhibited fast response and high selectivity toward 4-methoxyphenol (4MP) in phosphate buffer phase at pH 7. Furthermore, the sensor performance parameters, including the sensitivity, lower detection range, reliability, and reproducibility, ease of integration, long-term stability, and selectivity were investigated in detail. The calibration plot was found to be linear in the concentration range of 0.01 nM-0.1 μM. The sensitivity and detection limit were calculated as 1.4768 μA cm^-2 μM^-1 and 0.06428 ± 0.0002 nM (at a signal-to-noise ratio of 3), respectively. Thus, it was concluded that the proposed selective and efficient sensor represents a promising approach to effectively detect toxic phenolic compounds in the environment with acceptable and reliable results.

Sensor development of 1,2 Dichlorobenzene based on polypyrole/Cu-doped ZnO (PPY/CZO) nanocomposite embedded silver electrode and their antimicrobial studies

Cu-doped ZnO nanopowders and their composites of polypyrole (PPY)/CZO were prepared by a gel combustion method and an in-situ polymerization process, respectively. The synthesized nanocomposite are characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), FTIR, and TGA studies. Then the PPY/CZO/AgE nanocomposites were used for potential application in chemical sensing by easy and reliable I-V method, where 1,2 dichlorobenzene (1,2-DCB) is considered as a model target compound. The chemical sensor performances are exhibited the higher sensitivity, good stability, and repeatability of the sensor enhanced significantly using PPY/CZO/AgE of thin-film with conducting binders on silver electrodes (AgE; Surface area: 0.0216cm²). The calibration plot is linear over the large dynamic range (0.35nM∼3.5mM), where the sensitivity (∼2.702μAmM^-1cm^-2) and detection limit (∼0.34nM) is calculated based on signal/noise ratio (∼^3N/_S) in short response time. Finally, it is concluded that the structural and optical characteristics could be encompassed to a broad-scale in PPY/CZO/AgE composites and efficient chemical sensor applications for environmental fields. Simultaneously PPY/CZO composites was also evaluated against Gram positive bacteria Bacillus subtilis, Gram negative bacteria Escherichia coli and antibiotics (Amoxicillin) using the agar plate.

Xanthine sensor development based on ZnO–CNT, ZnO–CB, ZnO–GO and ZnO nanoparticles: an electrochemical approach

The wet-chemical method was used to prepare the various ZnO–CNT, ZnO–CB, ZnO–GO nanocomposites, and ZnO nanoparticles in higher pH medium, which were finally utilized with 5% nafion to produce a thin film of NCs/Nafion/GCE sensor that has a faster response towards selected xanthine with higher sensitivity, lower detection limit, and large linear dynamic range by electrochemical approach.

Fabrication of a selective 4-amino phenol sensor based on H-ZSM-5 zeolites deposited silver electrodes

A promising sensitive phenolic chemical sensor was developed using a porous pentasil type framework of protonated H-ZSM-5 zeolite by the reliable I–V method.

Ultrasensitive and selective hydrazine sensor development based on Sn/ZnO nanoparticles

Fabrication of highly sensitive (∼5.0108 μA cm⁻² μM⁻¹) and selective hydrazine chemical sensor based on wet-chemically prepared Sn/ZnO nanoparticles deposited glassy carbon electrodes with a detection limit as low as 18.95 ± 0.02 pM (at an S/N of 3).

Development of Hg2+ sensor based on N′-[1-(pyridin-2-yl)ethylidene]benzenesulfono-hydrazide (PEBSH) fabricated silver electrode for environmental remediation

N′-[1-(Pyridin-2-yl)ethylidene]benzenesulfonohydrazide (PEBSH) was synthesized via a simple condensation of 2-acetyl pyridine and benzene sulfonyl hydrazide in very good yield and crystallized, and then used in the formation of a Hg²⁺ sensor.

Preparation of polyaniline grafted graphene oxide–WO3 nanocomposite and its application as a chromium(iii) chemi-sensor

Polyaniline-grafted-GO@WO₃ was prepared and deposited on a Ag electrode with conducting binders to give a sensor with a fast selective response for Cr³⁺ in the liquid phase. The sensitivity and detection limit are ∼4.4251 mA mM⁻¹ cm⁻² and 0.031 ± 0.010 nM.

Chemical sensor development based on poly(o-anisidine)silverized–MWCNT nanocomposites deposited on glassy carbon electrodes for environmental remediation

POAS–Ag/MWCNT nanocomposites were prepared by an adsorption process. A selective 3-methoxyphenolic sensor was developed by an I–V technique for the first time. It displays the highest sensitivity (∼3.829 μA cm⁻² mM⁻¹) ever published in the literature.