Search

The separation efficiency of charge carriers determines the analytical sensitivity of the paper-based photoelectrochemical sensor. Herein, the Lewis base modification strategy is proposed to promote the carrier separation through an in-situ ion exchange method. Firstly, three-dimensional paper-based hierarchically TiO2 (PHT) arrays are prepared with the one-step hydrothermal method. With the aid of Lewis base, the photoinduced charge separation efficiency and the photocurrent signal are obviously increased. Ultimately, sensitive sensing of prostate specific antigen (PSA) is achieved and the linear range is 1 pg/mL-100 ng/mL with the detection limitation of 0.3 pg/mL. [ABSTRACT FROM AUTHOR]

A paper‐based potentiometric sensor was constructed and characterized for the detection of glucose in saliva. Dilution of the samples was optimized to afford the optimum experimental conditions of measurements. The performance allows for detecting abnormal high glucose concentrations observed in diabetes patients. Repeatability data were presented and the performance of the sensor compared to literature examples showing suitable characteristics at a much lower cost. The validation in real saliva samples was performed against a commercial colorimetric kit showing that glucose could be effectively determined in the 4–10 mM range based on the comparison with a reference method. [ABSTRACT FROM AUTHOR]

A new, simple and low‐cost method for patterning hydrophobic barriers in porous support such as paper by Parafilm® has been introduced. This method is then used for electrochemical paper‐based ammonia sensor construction. Ammonia sensor is based on electrochemical concentration cell which ammonia reaction with electrolyte in halves cell caused in concentration gradient and therefore potential difference dependent on ammonia concentration. The effect of concentrations of the involved chemicals, time periods of the required processes, the presence of Faraday cage as well as the effects of different salts used in the salt bridge on the response of the sensor, were investigated in order to find the optimized conditions. [ABSTRACT FROM AUTHOR]

The pursuit of ultraflexible sensors has arisen from the recent implementation of electrochemical sensors into wearable clothing where extensive mechanical stress upon the sensing platform is likely to occur. Such scenarios have witnessed screen-printed electrodes being incorporated into the waistband of undergarments for the determination of key analytes while others have reported incorporation into a neoprene wetsuit. In these conformations, the substrates which the sensors are printed upon need to be ultraflexible and capable of withstanding extensive individual mechanical stress. Therefore the composition, thickness and its combination of screen-printed ink require extensive consideration. A common short-coming within the field of screen-printed derived sensors is the lack of consideration towards the substrate material employed, and is rather in favour of the development of new electrode geometries and screen-printing inks. In this paper we explore the screen-printing of graphite based electroanalytical sensing platforms onto graphic paper commonly used in house-hold printers, and for the first time both tracing paper and ultraflexible polyester-based substrates are used. These sensors are electrochemically benchmarked with the redox probes hexaammine-ruthenium(III) chloride and potassium ferrocyanide(II). The effect of mechanical contortion upon two types of electrode substrates is also performed where it was found that these ultraflexible based polyester-based electrodes are superior to the previously reported ultraflexible paper electrodes since they can withstand extensive mechanical contortion, yet they still give rise to useful electrochemical performances. Most importantly the ultraflexible polyester electrodes do not suffer from capillary action as observed in the case of paper-based sensors causing the solution to wick-up the electrode towards the electrical connections resulting in electrical shorting, therefore compromising the electrochemical measurement; as such this new substrate can be used as a replacement for paper-based substrates and yet still be resilient to extreme mechanical contortion. A new configuration is also explored using these electrode substrate supports where the working carbon electrode contains the electrocatalyst, cobalt(II) phthalocyanine (CoPC), and is benchmarked towards the electroanalytical sensing of the model analytes citric acid and hydrazine which demonstrate excellent sensing capabilities in comparison to previously reported screen-printed electrodes. [ABSTRACT FROM AUTHOR]

In this paper the effect of different solvents (ethanol, acetone, dichloromethane and hexane) in the surface treatment of graphite for the construction of voltammetric sensors was evaluated. During voltammetric experiments of the graphite powder‐based sensor treated with ethanol, it was possible to observe a significant increase in current signals for the redox process of the model analyte (acetaminophen), as well as an increase in the area density of this sensor compared to its unmodified electrode. Theoretical studies involving Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM) showed greater interaction and stability when graphite was treated with ethanol solvent. Moreover, the theoretical calculations indicated that treating the voltammetric sensor with ethanol offers improvements in the electrochemical response of the model analyte mainly due to a higher spin density, and a partially covalent interaction between solvent and graphite surface. Therefore, graphite powder‐based sensors treated with ethanol were used for determination of acetaminophen in pharmaceutical samples and their results were in good agreement with those obtained by using spectrophotometric method recommended by Pharmacopoeia. [ABSTRACT FROM AUTHOR]

The growing demand for low cost and easy to use analytical devices requires the development of reliable and rapid deposition strategies suitable for changing easily planned designs and applicable to a wide range of materials for assembling conductive tracks and sensitive elements. Further important challenges to be pursued are the possibility of using readily available instrumentation and reducing power consumption and hazardous chemical waste. This review provides an overview of the use of portable day-to-day writing tools, such as pencils and pens, for the rapid and on-demand deposition of conductive patterns on different substrates, with particular emphasis on the assembly of 'Do It Yourself' sensors. Moreover, layer-by-layer deposition of simple or even complex three dimensional (3D) circuits, resorting to pressure driven extrusion of conductive filaments is considered. Future perspectives and potentiality of these emerging technologies for assembling sensors are also explored. [ABSTRACT FROM AUTHOR]

In this paper, novel and stable acetylcholinesterase (AChE) sensor with patterned structure for detecting organophosphorus pesticides (OPs) based on titanium dioxide sol‐gel carrier was proposed and prepared. Biosensor was assembled by dropping titanium oxide, chitosan (CS) and enzyme to the surface of the glass carbon step by step. The concentration range of the sensor detection for dichlorvos (DDVP) is 1.13 nM to 22.6 μM, and the limit of detection (LOD) is 0.23 nM. It can also detect dichlorvos in cabbage juice samples accurately. The preparation of biosensor adopted a patterned novel structure for the first time, which opens a new way for the structure optimization of organophosphorus pesticide sensor. [ABSTRACT FROM AUTHOR]

In recent years, photoelectrochemical (PEC) sensors have attracted much attention due to their inherent advantages, such as ease of operation, high sensitivity, and structural diversity. Compared with conventional PEC detection methods, self‐illuminated PEC sensors do not require an external light source, which makes them more attractive in terms of instrument miniaturization and simplified operation. Chemiluminescence (CL), a straightforward and efficient excitation source, can be harnessed for PEC sensors. In this review, we provide a summary on the recently reported chemiluminescence‐driven PEC sensors. Initially, we briefly describe the current chemiluminescent systems employed in PEC sensors, including luminol and peroxyoxalate CL systems. Subsequently, the CL‐exciting modes and the design strategies for self‐excited PEC sensors are explored. The subsequent sections of the paper predominantly focus on discussing the applications of such PEC sensors in the detection of various target analytes. Furthermore, future prospects for advancing these PEC sensors are discussed. [ABSTRACT FROM AUTHOR]

This paper describes the preparation of a new sensor based on Zn-ferrite modified glassy carbon paste electrode and its electrochemical application for the determination of trace Cd(II) ions in waste waters using differential pulse anodic stripping voltammetry (DPASV). Different Zn/Ni ferrite nanoparticles were synthesized and characterized using scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). The prepared ferrite nanoparticles were used for the preparation of Zn-ferrite-modified glassy carbon paste electrode (ZnMGCPE) for determination of Cd(II) at nanomolar levels in waste water at pH 5. The different parameters such as conditions of preparation, Zn2+/Ni2+/Fe2+ ratio and electrochemical parameters, percentage of modifier, accumulation time, pH and accumulation potential were investigated. Besides, interference measurements were also evaluated under optimized parameters. The best voltammetric response was observed for ZnFe2O4 modifier, when the percentage of modifier was 3 %, accumulation time 9 min, pH of supporting electrolyte 5 and accumulation potential −1.05 V. Thus prepared electrode displays excellent response to Cd(II) with a detection limit of 0.38 ppb, and selective detection toward Cd(II) was achieved. [ABSTRACT FROM AUTHOR]

In this study, we present a strategy for the specific electrochemical detection of NADH in human blood serums using modified electrode fabricated by intercalation of tetrabutylammonium ions (TBA+) into pencil graphite electrode (TBA+/PGE). In order to implement this protocol, a modification process in the potential range (−0.2) to (−2.75) V was performed in DMSO containing 0.1 M TBAP by CV method. The characterization processes of the prepared sensor were carried out using CV, EIS, FT‐IR, XPS, and SEM methods. The electrode fabricated by intercalation of TBA+ was found to be able to analyze NADH at +0.32 V applied potential by the amperometric method. The LOD was detected as 0.46 μM. The analysis results of human blood serums which are taken from healthy individuals show that TBA+/PGE can be used for real samples. The results indicated that TBA+/PGE can be easily fabricated by one‐step and one‐pot electrochemical method and TBA+/PGE can be used as a potential sensor for the NADH determination. [ABSTRACT FROM AUTHOR]

Interleukins proved to be valuable biomarkers for different diseases. Interleukins 1β, 6, and 12 can be used as biomarkers for brain cancer diagnosis, and therefore this paper proposed a needle stochastic sensor based on protoporphyrin IX immobilized in nanodiamond paste for fast screening of biological samples such as whole blood, urine and brain tumoral tissue for these interleukins. The results obtained using this needle stochastic sensor proved that the interleukins 1β, 6, and 12 can be reliable determined from whole blood, urine and brain tumoral tissue, with recoveries higher than 96.00 %, with relative standard deviations lower than 1.00 %. [ABSTRACT FROM AUTHOR]

The paper describes the first electrochemical method (differential pulse adsorptive stripping voltammetry, DPAdSV) using a screen‐printed sensor with a carbon/carbon nanofibers working electrode (SPCE/CNFs) for the direct determination of low (real) concentrations of paracetamol (PA) in environmental water samples. By applying this sensor together with DPAdSV, two linear PA concentration ranges from 2.0×10−9 to 5.0×10−8 mol L−1 (r=0.9991) and 1.0×10−7–2.0×10−6 mol L−1 (r=0.9994) were obtained. For the accumulation time of 90 s, the limit of detection was 5.4×10−10 mol L−1. Moreover, the SPCE/CNFs sensor and the DPADSV procedure for PA determination are potentially applicable in field analysis. The process of PA adsorption at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and theoretical studies. In the theoretical study of the interaction of CNF and PA, the first species was modelled by graphene‐like clusters containing up to 37 rings. It was found that the preferable orientation of PA is parallel to the carbon surface with the binding energy of about −68 kJ/mol calculated by symmetry‐adapted perturbation theory (SAPT). Both the selectivity and the accuracy of the developed sensor for real sample analysis were also investigated using Polish river and sea samples. [ABSTRACT FROM AUTHOR]

While most electrochemical uric acid (UA) sensors are developed on the conventional electrodes and involve either multiple steps based synthesis routes and/or complicated fabrication processes, this paper is the first demonstration of direct growth of pyrite FeS2 on pencil‐graphite electrode (PGE) for non‐enzymatic UA sensing. FESEM images of the pyrite FeS2‐PGE reveal mesoporous microspherical structure of pyrite FeS2 along with graphite flakes of PGE and EDX, Raman spectroscopic data validate growing of pyrite FeS2 on PGE. The pyrite FeS2‐PGE sensor exhibited detection limit of 6.7 μM, excellent linearity, reproducibility, selectivity over glucose, urea, ascorbic acid with the sensitivity of 370 μA mM−1 cm−2 in the range of 10–725 μM of UA. These improved analytical performances can be attributed to high conductivity of the pyrite FeS2, larger electro‐active surface area of the mesoporous microspherical pyrite FeS2 grown on PGE (than only PGE) and abundance in defect sites originating from both the pyrite FeS2 as well as functional groups of pencil graphite. Furthermore, the sensor was validated against UA in urine sample and the result supports well with the UA concentration achieved from colorimetric technique. Development of this low cost, non‐enzymatic, sensitive and highly selective pyrite FeS2‐PGE bases UA sensor is a significant step in the development of practically viable sensors for point‐of‐care applications in clinical and pharmaceutical analyses. [ABSTRACT FROM AUTHOR]

The paper presents the first report on application of a 'hybrid' lead film electrode for the adsorptive stripping voltammetric determination of Ni(II) in the presence of nioxime as a complexing agent. The strategy to create a 'hybrid' electrode is based on the combination of ex situ and in situ plating methods and the use of a reversibly deposited mediator metal (Zn) for the lead film formation. The surface morphology of a new sensor was characterized by atomic force microscopy. The detection limit for Ni(II) obtained at 120 s of accumulation time was 3.9×10−11 mol L−1. The proposed method was validated for the determination of nickel in water certified reference materials with good results. [ABSTRACT FROM AUTHOR]

Tripropylamine (TPA) is a highly toxic and carcinogenic compound, therefore, TPA concentration in water must be monitored to protect health and the environment. In this paper, an electrochemiluminescent (ECL) sensor was fabricated by immobilising Ru(bpy)32+-modified CuO nanoparticles (NPs) on a TiO2 nanotube array (TN) electrode. Compared to an ECL sensor fabricated by immobilising Ru(bpy)32+ on a TN only electrode, the as-prepared sensor displays a 30 % enhanced ECL signal and a detection limit of 9.6×10−10 M at a signal-to-noise ratio=3 with the concentration of TPA in a range 1×10−9 to 1×10−5 M. The results from this study indicated a new approach for the enhancement of performance of ECL sensor in detecting TPA in water. [ABSTRACT FROM AUTHOR]

This paper describes the development of a new sensor based on an ionic organic film. The amphiphilic molecule, 4-[(4-decyloxyphenyl)-ethynyl]-1-methylpyridinium iodide (10PyI), which has liquid-crystalline properties, was synthesized and applied in the construction of a GCE/10PyI sensor. Analytical parameters for caffeic acid, repeatability (4.8 %), reproducibility (2.8 %), linearity (two ranges: 9.9×10−7 to 3.8×10−5 mol L−1 and 4.7×10−5 to 9.9×10−5 mol L−1) and detection limits (9.0×10−7 mol L−1 and 8.7×10−6 mol L−1), were determined. The method was successfully applied in the determination of total phenolic compounds (TPC) in mate herb extracts. [ABSTRACT FROM AUTHOR]

Substrate plays an essential role in the construction of flexible electrode and related wearable sensors. Compared with conventional flexible substrates such as Polyethylene terephthalate (PET), the common transparent adhesive tape exhibits the unique advantages in the non‐adhesive surface with good printability, allowing the conductive layer to be deposited directly on its surface, and in another adhesive surface with good fastening, thus facilitating the fabrication of as‐prepared electrode in subsequent wearable sensors. Herein, we constructed a new type of flexible sensor to detect ascorbic acid which is closely related to human health in sweat by integrating flexible electrode based on transparent adhesive tape with potentiostat that incorporate the critical signal conditioning, processing, and transmission functions. Experiment results show that resulting electrode still has the good electrochemistry performance even after 1000 bending cycles (20 % bending degrees). By connecting as‐prepared flexible electrode to the potentiostat to carry out real time analysis, the resulting sensor exhibits excellent sensitivity, detection limit and repeatability (0.15 V detection potential vs printed Ag/AgCl reference electrode, 3.8 μM detection limit, 25 μM‐1 mM linearity, and good selectivity). [ABSTRACT FROM AUTHOR]

Solid‐contact ion‐selective electrodes with thin membranes can more easily achieve complete ion exchange at the sample‐membrane interface, giving unbiased selectivity coefficients. The calculated reconditioning rate corresponds well to experimental data. Alternatively, the redox state of the conducting polymer may be electrochemically switched resulting in primary ion expulsion from the membrane and interfering ion uptake from the sample. Both approaches were tested for tetrabutylammonium‐selective electrodes. The approach's limitations are identified, which includes primary ions impurities in interfering ion salts and an interaction between primary ion and redox polymer. These limitations are visualized with ionophore‐based sodium‐ and silver‐selective electrodes. [ABSTRACT FROM AUTHOR]

A new electrochemical method for the identification and quantification of Fenamiphos pesticide's major metabolite in biological samples – Fenamiphos Sulphoxide (FNX) was developed. Computational calculations, Density Functional Theory (DFT) and semi‐empirical models (PM3) were performed to determine the best monomer, pyrrole, and a ratio of 1 : 5 (template: monomer) was chosen for the fabrication of the FNX−MIP sensor obtained by electropolymerization. The FNX−MIP sensor responded well to increasing FNX concentrations (range of 1–30 μM). Limit of detection and quantification (LOD=0.183 μM, LOQ=0.601 μM), respectively, selectivity, and repeatability were also investigated for the developed method. The obtained percentage of recovery showed good agreement compared to reference values obtained from GC‐MS, which was used as a reference method. The FXN−MIP sensor proved selective in the presence of potential interferents. The developed sensor was successfully applied for the determination of FNX in spiked plasma and urine matrixes with acceptable recovery rates. The proposed method also proved successful in detecting FNX prepared from the in vitro metabolism of FNP using liver microsomes to metabolize it. [ABSTRACT FROM AUTHOR]

A sensing platform was developed based on the molybdenum disulfide‐reduced graphene oxide (MoS2‐RGO). The flower‐like MoS2‐RGO nanocomposite had a large number of active sites such as oxygen‐containing groups and highly reactive sulfur that contributed to the adsorption and preconcentration of heavy metal ions (HMIs). MoS2‐RGO was synthesized by one‐step reduction method. Under optimized conditions, the limits of detection (LODs) for Pb(II) and Cd(II) was 0.13 μg/L and 0.59 μg/L with a linear range of 4.1–207.2 μg/L and 2.2–112.4 μg/L, respectively. The modified sensors had been successfully applied to detect Pb(II) and Cd(II) in three kinds of edible mushrooms. [ABSTRACT FROM AUTHOR]

The quality of pharmaceutical products is critical for human health. Drug development requires tools to assess the presence of degradation products and contaminants during the manufacturing and storage processes. Accelerated stress degradation and kinetic studies play a vital role in predicting final product stability. This work describes the design of potentiometric sensor based on copper microfabricated electrodes for in‐line tracking the degradation kinetics of neostigmine. The proposed electrochemical technique provides a continuous profile for the hydrolysis of NEO under different temperatures and pH. The hydrolysis activation energy was found to be 18.88 kcal mol−1 which was aligned with the reported hydrolysable ester values. Consequently, the kinetic data analysis is crucial to predict the optimum analysis and storage conditions. [ABSTRACT FROM AUTHOR]

Chitosan (CH) is one of the most abundant biopolymers with multiple applications. Polyvinyl pyrrolidone (PVP) has specific binding and detoxification properties that are of great interest in health care. Hence, it arises a crucial urge to develop economic sensors to analyze CH and PVP in pharmaceutical formulations and biological samples. Two portable sensors were fabricated using precipitation‐based technique, and nanoparticles‐based technique, for determination of CH and PVP in sensor 1 and 2; respectively. Linear responses of 10−5 to10−7 M and 10−2 to10−7 M at pH 3.6–4.8 and 7.2–8.4, with ideal Nernstian slopes of 60.00 and 59.83 mV /decade, and nanomolar LODs of 94.90 and 81.20 nM were observed for CH and PVP; respectively. The percentage recoveries were 100.40±1.03 and 100.19±0.64 for sensors 1 and 2; respectively. Both sensors were successfully applied in biological fluids without pre‐treatment. Accurate results were obtained using sensor 1, in pure form, pharmaceutical formulations, human plasma, rat liver and rat brain, as well as sensor 2, in pure form, pharmaceutical formulations and urine samples. The results were statistically compared with the reported methods and no significant difference was observed. [ABSTRACT FROM AUTHOR]

Here, human serum albumin conjugated gold nanoparticles (HSA−AuNPs) were synthesized by a simple route to develop an impedimetric sensor for miRNA‐200c detection based on a selective oligo‐hybridization process without any labeling. The synthetic DNA capture probe for miRNA‐200c was decorated onto the HSA−AuNPs modified pencil graphite electrodes. Impedimetric signals were monitored after the hybridization process between the DNA probe and target miRNA‐200c. HSA−AuNPs adsorption time, incubation time of the capture probe and hybridization time‐temperature were optimized. The proposed miRNA‐200c biosensor demonstrated proper sensitivity and selectivity, low detection limit (1.13 fM), good reproducibility and simple direct detection of miRNA‐200c in serum. [ABSTRACT FROM AUTHOR]

In this work, a modified 3D‐rGO/MWCNT with nickel and copper oxide nanoparticles were synthesized. The structural properties of this nanocomposite were investigated by several techniques. The fabricated sensor at optimum condition potential of +0.60 V (vs. Ag/AgCl) and a rotational rate of 1800 rpm gave a detection limit of 0.04 μmol L−1 with two dynamic ranges of 0.10–300 and 300–900 μmol L−1 glucose with high stability. The good accuracy of the fabricated sensor was proved in the determination of glucose in a blood sample (with recoveries between 95 % to 105 % and RSDs of 1.2 to 2.5 %). [ABSTRACT FROM AUTHOR]

The mycotoxin zearalenone (ZEA) prompts reproductive toxicity due to its strong estrogenic effects. In this work, an electrochemical sensor for determination of ZEA was developed by electropolymerization of a molecularly imprinted poly (o‐phenylenediamine) (PPD) film on screen‐printed gold electrode (SPGE) surface. The sensor was examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using K3[Fe(CN)6]/K4[Fe(CN)6] as redox probe. The molecularly imprinted polymer (MIP) sensor showed a wide determination range from 2.50 to 200.00 ngmL−1 for ZEA. The Limit of detection (LOD) was calculated to be 0.20 ngmL−1, based on the signal to noise (S/N) ratio equal to 3.0. The sensor displayed good repeatability, with RSD values≤4.6 %, and maintained 93.2 % of its initial response after storage for 10 days in air at room temperature. The developed method was successfully applied for the determination of ZEA in corn flakes with mean recoveries ranged from 96.2 % to 103.8 % and RSDs within the interval of 2.1 % to 3.8 %. [ABSTRACT FROM AUTHOR]

Based on hemin-MWCNTs nanocomposite and hemin-catalyzed luminol-H2O2 reaction, a sensitive electrogenerated chemiluminescence (ECL) cholesterol biosensor was proposed in this paper. Firstly, hemin-MWCNTs was prepared via π-π stacking and modified on the surface of GCE. Subsequently, cholesterol oxidase (ChOx) was adsorbed on the modified electrode to achieve a cholesterol biosensor. Hemin-MWCNTs nanocomposite provided the electrode with a large surface area to load ChOx, and endowed the nanostructured interface on the electrode surface to enhance the performance of biosensor. The biosensor responded to cholesterol in the linear range from 0.3 µM to 1.2 mM with a detection limit of 0.1 µM ( S/ N=3). [ABSTRACT FROM AUTHOR]

A description of the performances of new electrochemical sensors is important for evaluating their novelty and potential applicability to the analysis of real samples. However, it was noticed that quite often some figures of merit were ill-defined or reported in an inadequate format. Based on some well-known books and guidelines, some simple approaches are briefly reviewed which allow a better estimation of the most frequently reported figures of merit. Adopting these approaches implies a certain increase of cost and time of the given investigations. But the results would benefit from an easier acceptance by the scientific community. [ABSTRACT FROM AUTHOR]

This research represents a novel detection method of acetone level in the exhaled breath samples (RH=88 %) based on polypyrrole/tungsten oxide (PPy/WO3) nanocomposite sensor. The PPy/WO3 sensor was fabricated by the deposition of nanocomposite on/between interdigitated electrodes (IDEs) through electrospray coating and was then characterized by FE‐SEM imaging. In this detection method, the coulometric signal of the sensor was calculated using Fast Fourier Continuous Cyclic Voltammetry (FFTCCV), where cyclic voltammetry (CV) was applied to the sensor in the defined potential rang and then charge changes of the sensor was obtained by integration of the current in all scanned potential ranges. FFTCCV method enhances the sensitivity of the sensor when exposed to the gas mixtures containing acetone. In addition to its fast coulometric response time (≤5 s) in the two linear ranges of 0.7–2.8 ppm and 2.8–28.2 ppm (R2=0.99), FFTCCV method provides the low detection limit of 70 ppb, and high sensitivity toward acetone at the optimum values of the parameters. The fabricated sensor showed great selectivity toward acetone when exposed to humid air and some exhaled gas like carbon dioxide, ammonia, methanol, ethanol and alkyl amines. The results were very satisfying as the sensor was capable to detect different acetone levels in human exhaled breath as non‐invasive diagnosis of diabetes with a good correlation (R2≃0.9) to the routine blood sugar test taken by different commercial glucometers results. [ABSTRACT FROM AUTHOR]

Nowadays, carbon‐based materials applied to the development of chemically modified sensors have been highlighted once they can generate methods with high sensitivity, stability, conductivity, accuracy and low cost. Hence, these sensors have been used in environmental monitoring in aneco‐friendlyy, sensitive, fast, efficient, inexpensive and robust way. In this review, firstly we described about carbon‐based materials and their derivatives, followed by the chemically modified carbon‐based sensors manufacturing overview and their applications in environmental analytical chemistry related to inorganic and organic compounds determinations. Future perspectives on trends of the carbon‐based materials applications in the sensor modifications are also described. [ABSTRACT FROM AUTHOR]

There is a continuous increasing demand for more sensitive and selective non-enzymatic glucose sensor applications ranging from medical diagnostics to food quality assurance. Here, we deposited gold nanostructures (referred to as Au nanospikes) on Au thin-film substrates under different electrodeposition conditions in order to determine the optimal growth parameters to obtain an enhanced glucose sensor. A modified chronoamperometric technique was employed to determine the glucose electrooxidation and sensing capabilities of the developed Au nanospikes toward 20 µM-10 mM glucose concentrations. The sensing method used here allowed for accurate determination of glucose concentrations whilst providing reproducible and stable response profiles. The sensor produced a low detection limit of 20 µM, a very high sensitivity of 201 µA mM−1 ⋅ cm−2 compared to 16.19 µA mM−1 ⋅ cm−2 for the unmodified Au substrate. The sensor also showed good selectivity when analysed against common physiological contaminants that usually interfere with conventional sensors. [ABSTRACT FROM AUTHOR]

A glutamate biosensor based on cross-linked glutamate oxidase with chitosan (CHIT) on a carbon nanotube (CNT)-modified gold nanowire (AuNW) was constructed and applied in a flow injection analysis (FIA) system. The AuNW was produced using an alumina template membrane and characterized using scanning electron microscopy (SEM) with a 120-nm diameter. The CHIT cross-linked CNT slurry was mixed with AuNW and cast on the surface of a glassy carbon electrode (GCE), followed by immobilization with the glutamate oxidase. Optimization of the experimental parameters, including the applied potential, enzyme loading, flow rate, type of buffer and pH, resulted in values of 0.7 V, 30 μL, 1.0 mL min−1, phosphate buffer, and pH 7.4, respectively. The analytical working curve was linear in the ranges from 10 to 100 (R2=0.9981) and 100 to 20,000 μM glutamate (R2=0.9821) with a low detection limit of 1.2 μM (S/N=3). A glutamate biosensor with an FIA system was used to determine glutamate in samples of Thai commercial food products. [ABSTRACT FROM AUTHOR]

In this study, a non-enzymatic hydrogen peroxide photoelectrochemical (PEC) sensor based on nanoporous BiVO4 film electrode is fabricated by electrodeposit of nanoporous BiOI film on fluorine-doped tin oxide glass (FTO) and subsequent conversion to BiVO4 by annealing at elevated temperature. The electrode exhibits excellent visible light photoelectrochemical activity, and H2O2 works as a hole scavenger to react with light-induced electron holes on the valence band of BiVO4. Upon illumination and at applied bias potential of +0.2 V, the photocurrent density is linearly correlated to the concentration of H2O2. The linear determination range of H2O2 is 9.54-764.76 μM with a corresponding correlation coefficient of 0.9997, a detection limit of 1.59 μM (S/N=3), and sensitivity of 182.6 μA mM−1 cm−2. The optimum bias potential, most suitable film thickness, anti-interference performance, and impedance are also explored. The sensor shows good response towards H2O2 and displays a promising prospect for non-enzyme PEC H2O2 sensor. [ABSTRACT FROM AUTHOR]

The measurement of low concentrations of ammonia in small sample volumes is required in biological, biomedical and environmental measurement applications. However, achieving this without instrumentation remains challenging. Here, sensor devices for the measurement of ammonia in a liquid were developed. These were based on the fabrication of polyaniline nanoparticle films onto screen printed interdigitated electrodes using inkjet printing and their integration into a polymer microfabricated device with polytetrafluroethylene membrane and air flow path between the membrane and the sensor. Samples of ammonia in phosphate buffered saline of 52 μL were measured using electrochemical impedance. While water vapour and ions from the buffer did result in a decrease in sensor impedance, this was eradicated by displacement of the headspace above the sensor with air. This, in combination with the adjustment of the sample to pH to 11 allowed the quantification of ammonia from 0 to 200 μM with a limit of detection of 25 μM. The device has the potential to be used for sensitive, low volume measurement applications of ammonia at point-of-test and point-of-care. [ABSTRACT FROM AUTHOR]

Nitrate sensing is an important application for potentiometry in environmental applications. Its recognition is by ion‐exchangers whose selectivity is governed by the lipophilicity of the ions in solution. Yet, considerable research efforts have been dedicated to the development of such ionophores and some have already been commercialized. This work examines two commercially available nitrate ionophores, nitrate ionophores V and VI, and compares their performance with widely used ion‐exchangers by determining the resulting membrane selectivity and complexation to nitrate. Unfortunately, adding a nitrate ionophore to the membrane did not result in improved selectivity. Sandwich membrane experiments indicated that binding interaction is too weak to be measurable, with a logarithmic formation constant of just 1.36±0.14 for ionophore V with nitrate. Ways to improve the reporting of relevant data are suggested. [ABSTRACT FROM AUTHOR]

Solid contact sensors were designed for determination of the antibiotic prodrug tedizolid phosphate. The sensors are based on; microfabricated copper as cost‐effective electrode substrate and graphene layer as a transducer. The ion sensing PVC polymeric membrane was optimized by proper selection of the anion exchanger. The graphene layer was characterized by scanning electron microscopy, Raman spectroscopy, FT‐IR, besides measuring electrochemical impedance for the fabricated sensors. The potential drift decreased down to 0.133 mV h−1 compared to 6.67 mV h−1 for graphene free sensor. The sensors have been used to determine tedizolid phosphate in its pharmaceutical formulation and content uniformity testing applications. [ABSTRACT FROM AUTHOR]

This work represents first attempt for potentiometric determination of the most recent antidiabetic; omarigliptin. Three sensors, employing potassium tetrakis (p‐chlorophenyl) borate as a lipophilic cation exchanger, were developed and compared. One liquid contact ion‐selective electrode and two carbon paste‐based solid contact ones, plain one and another one modified with polyaniline nanoparticles, were employed. Performances of fabricated sensors were assessed as per IUPAC recommendations. Incorporation of hydrophobic polyaniline nanoparticles as ion‐to‐electron transducer layer at solid contact/ion‐sensitive membrane interface enhanced sensitivity and stability of the third sensor showing LOD of 2.5×10−7 mol L−1 and slope of 58.57 mV decade−1. The three sensors were applied for omarigliptin determination in presence of its degradation products, in dosage form and spiked human plasma. [ABSTRACT FROM AUTHOR]

In this study, gold nanoparticles (AuNP) were synthesized using a novel stabilizer based on dialdehyde starch polymer (DAS) and dimethyl sulfoxide (DMSO) and the nanomaterial was applied to develop a sensor for methyldopa detection. The nanoparticles were characterized by transmission electron microscopy and the proposed sensor was electrochemically characterized by electrochemical impedance spectroscopy, chronocoulometry and square‐wave voltammetry. Under optimized conditions (0.1 mol L−1 McIlvaine buffer solution at pH 3.5 and 50 μL AuNP/DAS‐DMSO), using square‐wave voltammetry, the calibration curve presented a linear range of 0.99 to 19.60 μmol L−1, with a detection limit of 0.50 μmol L−1. The sensor showed good accuracy, with coefficients of variation of 7.8 % (inter‐day; n=6) and 5.9 % (intra‐day; n=3), and recovery values in the range of 95.3 to 105.2 %. The methyldopa content in a pharmaceutical sample was determined and the results show good correlation with the label value and the method recommended by the Pharmacopoeia, representing a fast and accurate alternative for detecting methyldopa in pharmaceutical products. [ABSTRACT FROM AUTHOR]

A urinary pCO2 measurement system with a miniature planar CO2 probe has been developed for monitoring pCO2 levels in the urine (U‐pCO2) of catheterized septic shock patients. U‐pCO2 may provide timely recognition of changes in the microcirculatory status of patients and used as an "early" warning of metabolic‐cellular dysfunction. The utility of the U‐pCO2 sensor has been demonstrated in monitoring experiments in a model bladder. The agreement between U‐pCO2 values measured with the planar pCO2 probe and a commercial pCO2 probe in pooled urine samples projects the possibility of the implementation of the U‐pCO2 measurement system for bedside monitoring. [ABSTRACT FROM AUTHOR]

Nickel acetate tetrahydrate (NAT) sample series were used to modify screen‐printed carbon electrodes (SPCE). The samples were hybrid Ni/NiO nanocomposites, where the NiO phase increased with an applied treatment temperature. Results of electrochemical measurements pointed that the Ni/NiO550/SPCE‐modified electrode had the best analytical performance toward the detection of riboflavin (RF). The Ni/NiO550/SPCE‐based sensor showed linear response with RF in the concentration range of 0.5–75 μM and 0.15 μM LOD in BRBS. Sensor offered fast response time, good repeatability, and selectivity with an RSD of 1.4 %. Our results show that the Ni:NiO nanocomposite ratio strongly influenced the electroanalytical performance of SPCE. [ABSTRACT FROM AUTHOR]

The following study reports the development of modified electrode with reduced graphene oxide (ErGO) for the voltammetric determination of 17α‐ethinylestradiol (EE2). The structural and morphological characterizations of the rGO were carried out by FTIR, Raman, UV‐Vis, TEM and SEM, and showed the typical formation of the nanomaterial. Electrochemical analyses were performed using Differential Pulse Voltammetry (DPV). Under optimized conditions, an analytical curve was generated for the sensor, which presented a linear dynamic range (LDR) from 0.04 to 8.28 μmol L−1 (R2=0.9999), with limit of detection (LOD) of 6.79 nmol L−1 and limit of quantification (LOQ) of 22.60 nmol L−1. The reproducibility and repeatability studies showed relative standard deviations (RSD) of 2.31 % and 5.23 %, respectively. ErGO was used to determine EE2 in wastewater, tablets, and synthetic urine samples with recovery values between 94.8 % and 110.1 %. The results obtained with ErGO show that the developed sensor can be used for the identification and quantification of EE2 in several matrices, due the excellent analytical performance presented. [ABSTRACT FROM AUTHOR]

In this review, we analyze several types of graphene-based sensors for glucose detection with respect to their preparation, properties and efficiency in electrochemical processes. Graphene may display different types of defects, which play a role in the electron transfer processes. Oxygenated groups on the edges of graphene planes reduce the graphene in-plane conductivity, but may enhance the heterogeneous electron/proton transfer constant. Other positive effects of defects are related to the shortening of the distance between active centers and electrodes upon enzyme or protein immobilization. However, though by different mechanisms, all types of graphene enhance the electrochemical response at the electrode. [ABSTRACT FROM AUTHOR]

This work summarizes the electrochemical response of flavanone carbon composite electrodes in comparison with Nafion®‐coated flavanone carbon composite electrodes, for use as voltammetric pH sensors in both buffered and low‐buffered media. Square wave voltammetric measurements suggest the peak potential achieved from the electrochemical polymerization after the electron‐proton oxidation responds with accuracy to buffered pH solutions for both coated and non‐coated electrodes, with a potential shift of 55.1 mV and 54.6 mV per pH unit respectively. However, a considerable improvement in stability, accuracy and sensitivity is provided by the proton‐transfer Nafion® layer in CO2 bubbled sea water. Furthermore, Nafion®‐coated flavanone carbon composite electrodes predicted a pH of 8.04 for the commercial seawater, which is in excellent agreement with the measured pH 8.05 value. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) light‐driven photoelectrochemical (PEC) sensing is a highly promising analytical technique, especially for in situ bioanalysis, due to the deep penetration capability and minimal invasiveness of NIR light. In this mini review, we provide a brief overview of recently developed NIR PEC sensors, focusing on NIR light‐responsive materials and the representative applications of this type of PEC sensor. Future perspectives for NIR PEC sensors are also described. [ABSTRACT FROM AUTHOR]

A method of capillary electrophoresis (CE) with capacitively coupled contactless conductivity detector (C4D) was developed to detect Cu-EDTA and its degradation intermediates simultaneously. The target compounds included oxalic acid, EDTA, Cu-EDTA, glyoxylic acid, iminodiacetic acid, formic acid and copper ion. The optimum electrophoretic conditions were determined by varying the running solution, injection voltage, injection time, and separation voltage. The anions in the reaction solution were separated and detected successfully under the conditions of 20 mmol L−1 acetate acid, electrokinetic injection of −13 kV×10 s, and separation voltage of −15 kV. Furthermore, copper ion was detected when 20 mmol L−1 acetate acid solution, electrokinetic injection of +11 kV×6 s and separation voltage of +13 kV were applied. The detection method was verified to track the degradation of Cu-EDTA with H2O2/UV. [ABSTRACT FROM AUTHOR]

For the first time the direct electron transfer of an enzyme - cellobiose dehydrogenase, CDH - has been coupled with the hexokinase catalyzed competition for glucose in a sensor for ATP. To enhance the signal output for ATP, pyruvate kinase was coimmobilized to recycle ADP by the phosphoenolpyruvate driven reaction. The new sensor overcomes the limit of 1 : 1 stoichiometry of the sequential or competitive conversion of ATP by effective enzymatic recycling of the analyte. The anodic oxidation of the glucose converting CDH proceeds at electrode potentials below 0 mV vs. Ag|AgCl thus potentially interfering substances like ascorbic acid or catecholamines do not influence the measuring signal. The combination of direct electron transfer of CDH with the enzymatic recycling results in an interference-free and oxygen-independent measurement of ATP in the lower µmolar concentration range with a lower limit of detection of 63.3 nM ( S/ N=3). [ABSTRACT FROM AUTHOR]

Herein, we report a template free and surfactant less electrochemical approach for the preparation of flower-like yttrium hexacyanoferrate (YHCF) particles on reduced graphene oxide (RGO) modified glassy carbon electrode (GCE). The morphology of YHCF particles has been controlled by varying the molar ratio of Y(NO3)2 and K3Fe(CN)6 for the first time. The surface morphology of as-prepared RGO/YHCF composite was characterized using SEM, EDX, IR and XRD methods. The electrocatalytic activity of the RGO/YHCF composite modified GCE towards Paracetamol (PA) oxidation has been investigated by using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Besides, the practical feasibility of the fabricated modified GCE has been demonstrated through the determination of PA from commercially purchased Paracetamol tablets. [ABSTRACT FROM AUTHOR]

Polypyrrole was used as sensitive material in the development of a new device employed for the indirect detection of OH radicals. The polypyrrole film was electrosynthesized on glassy carbon. The modified electrode was exposed to the OH radicals generated by Fenton reaction. As a result of the overoxidation the conductivity of the polymer diminished very much. The overoxidation (%) was directly proportional to the .OH amount that reached the electrode surface. ABTS.+, superoxide and alkylperoxy radicals did not interfere in the determination. The applicability of the device was demonstrated by estimating the .OH scavenging ability of ascorbic acid. [ABSTRACT FROM AUTHOR]

A novel strategy to improve the sensitivity of molecularly imprinted polymer (MIP) sensors was proposed for the determination of β2-agonists. The imprinted sol-gel film was prepared by mixing silica sol with a functional monomer of antimony-doped tin oxide (ATO) and a template of β2-agonists. ATO, which was embedded in the surface of the molecularly imprinted sol-gel film, not only provides the excellent conductivity for biosensor but also increases the stability and the surface area of the MIP film. The imprinted sensor was characterised by field emission scanning electron microscope, fourier transform infrared spectroscopy and electrochemical methods. Under the optimal experimental conditions, the peak current was linear with the logarithm of the concentration of clenbuterol (CLB) in the range of 5.5 nM-6.3 µM, and a detection limit of 1.7 nM was obtained. Meanwhile, the electrochemical sensor showed excellent specific recognition of the template molecule among structurally similar coexisting substances. Furthermore, the proposed sensor was satisfactorily applied to determine β2-agonists in human serum samples. The good results indicated that highly effective molecularly imprinted sol-gel films doped with ATO can be employed for other analytes. [ABSTRACT FROM AUTHOR]

A novel potentiometric strategy based on functionalized magnetite nanoparticles and microparticles were compared with the classical potentiometric strategy. This strategy provided nano- and microsized particles that were highly dispersed and coated with ionophore and plasticizer to promote an in situ cooperative ion-pairing interaction between the ionophore and the analyte present in inner solution of sensor membrane, compared to the classical technique. Three amlodipine (AML) sensors were constructed using functionalized nanoparticles in sensor 1; microparticles in sensor 2, as ionophores, and the polymeric membrane ionophoric property in sensor 3. [ABSTRACT FROM AUTHOR]

A novel and sensitive electrochemiluminescence (ECL) method for ethanol biosensor was developed by co-immobilizing the enzyme and ECL reagent Ru(bpy)32+ on the poly-(3,4-ethylene dioxythiophene) and polystyrene sulfonate functionalized graphene (PEDOT-PSS-G) nanocomposite film. Positively charged Ru(bpy)32+ could be immobilized effectively on the electrode surface with the negatively charged PSS and graphene, which provided a stable ECL platform for further modification with the enzyme. Moreover, the introduction of PEDOT and graphene can be acted as a conducting pathway to accelerate the electron transfer due to the high conductivity. Such biosensor combined enzymatic selectivity with the amplification of PEDOT-PSS-G performed well with a wide linear range, high sensitivity and good stability. The sensing platform was successfully applied to determine the amounts of alcohol in real samples. [ABSTRACT FROM AUTHOR]