An electrocatalytic transducer for l-cysteine detection based on cobalt hexacyanoferrate nanoparticles with a core–shell structure

Oxidation of Cysteine by Electrogenerated Hexacyanoferrate(III) in Microliter Droplets

Chemical reactivity in droplets is often assumed to mimic reactivity in bulk, continuous water. Here, we study the catalytic oxidation of cysteine by electrogenerated hexacyanoferrate(III) in microliter droplets. These droplets are adsorbed onto glassy carbon macroelectrodes and placed into an immiscible 1,2-dichloroethane phase. We combined cyclic voltammetry, optical microscopy, and finite element simulations to quantify the apparent bimolecular rate constant, k_c,app, in microdroplets and bulk water. Statistical analyses reveal that the apparent bimolecular rate constant (k_c,app) values formicrodroplets are larger than those in the continuous phase. Reactant adsorption to the droplet boundary has previously been implicated as the cause of such rate accelerations. Finite element modeling of this system suggests that molecular adsorption to the liquid|liquid interface cannot alone account for our observations, implicating kinetics of the bimolecular reaction either at the boundary or throughout the microliter volume. Our results indicate that cysteine oxidation by electrogenerated hexacyanoferrate(III) can be accelerated within a microenvironment, which may have profound implications on understanding biological processes within a cell.

Tellurium-based chemical sensors

The various tellurium-based chemical sensors are described. This article focuses on four types of Tellurium sensors such as CdTe quantum dots-based sensor, Te thin films-based sensor, Te nanostructures or nanoparticles-based sensor, and TeO2-based sensor.

Electrochemical Amino Acid Sensing: A Review on Challenges and Achievements

The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.

A novel non-enzymatic sensor for prostate cancer biomarker sensing based on electrocatalytic oxidation of sarcosine at nanostructured NiMn2O4 impregnated carbon paste electrode

This work addresses the electrocatalytic activity of a binary metal oxide catalyst of NiMn₂O₄ for electroxidation of sarcosine, the well-known prostate cancer biomarker. The nanocatalyst described was prepared via hydrothermal synthesis route, followed by calcination at 800 °C. Field emission scanning electron microscopy and X-ray diffraction were applied to obtain information about the material morphology and structure. A carbon paste electrode modified with nano-NiMn₂O₄ showed unique catalytic activity in sarcosine electroxidation which led to a significant rise in oxidation current (about four times) in comparison with the blank electrode. However, the carbon paste electrodes containing single oxides of NiO and Mn₂O₃ exhibited no considerable enhancement in sarcosine signal. The cyclic voltammetry results indicated that the Mn³⁺/Mn⁴⁺ couple was responsible for sarcosine oxidation, and NiO may enhance the content of Mn⁴⁺species in NiMn₂O₄ material. The carbon paste-based NiMn₂O₄ electrode was applied in the sensitive determination of sarcosine in the concentration range of 0.01-5.0 μM with the relative standard deviation of 3.49% (n = 5). The detection limit and quantification limit of the probe were determined to be 3.8 and 12 nM, respectively. The remarkable sensitivity and high selectivity of the method approved the sensor applicability in measurement of sarcosine content in urine samples.

Highly active catalyst using zeolitic imidazolate framework derived nano-polyhedron for the electro-oxidation of l-cysteine and amperometric sensing

Herein, N-doped porous carbon nano-polyhedron embedded with Co₃O₄ (Co₃O₄-NPCN) was reported for the electro-catalytic oxidation and amperometric detection of l-cysteine. Co₃O₄-NPCN was synthesized by the two-step redox calcination of zeolitic imidazolate framework (ZIF). Surface morphology characterization revealed that Co₃O₄-NPCN displayed a uniform size and rhombic dodecahedral shape. Structure and composition analysis found that Co₃O₄-NPCN was a N-doped carbon polyhedral matrix with hollow and porous structure, and Co₃O₄ nano-spheres were evenly distributed into the polyhedral matrix. Due to the hollow and porous structure, N-doped carbon matrix and embedded Co₃O₄ nano-spheres, Co₃O₄-NPCN performed a remarkable electro-catalysis towards the oxidation of l-cysteine at a very low potential of 0.10 V. A diffusion-controlled l-cysteine oxidation process was observed at Co₃O₄-NPCN prepared electrode. Accordingly, amperometric method was established for l-cysteine detection with a very fast current response in 2 s, wide linear range of 0.05 μM- 5.2 mM and low detection limit of 6.9 nM. Besides, notable selectivity, repeatability, reproducibility and long-term stability were also achieved. Moreover, Co₃O₄-NPCN sensor was successfully applied to the l-cysteine detection in human serum samples indicating the practical application of the as-developed sensor.

An innovative highly sensitive electrochemical sensor based on modified electrode with carbon quantum dots and multiwall carbon nanotubes for determination of methadone hydrochloride in real samples

In the present work, to enhance the properties of a pencil graphite electrode (PGE), highly functionalized carbon quantum dots (CQDs) were synthesized and mixed with multiwall carbon nanotubes (MWCNTs) as novel modifiers for the preparation of working electrodes. These modifiers exhibited unique characteristics owing to the fascinating and well-defined properties of the CQD-MWCNT nanocomposite, including high surface to volume ratio, high conductivity, high stability and excellent electrocatalytic activity. Consequently, a modified pencil graphite electrode based on poly (diallyldimethylammonium chloride) (PDDA)/MWCNT/CQD was used to monitor the oxidation signals of methadone hydrochloride. Notably, field emission scanning electron microscopy (FE-SEM) was used to characterize the morphology and features of the different modifiers on the electrode surface. The proposed sensor was characterized via electrochemical studies including differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under the optimum experimental conditions, the current response and concentration of methadone exhibited a linear relationship in the range of 0.1-225 μM with a detection limit of 0.03 μM. Furthermore, this sensor was successfully applied to determine methadone in human urine and plasma samples.

Nanomaterials: Electrochemical Properties and Application in Sensors

The unique properties of nanoparticles make them an extremely valuable modifying material, being used in electrochemical sensors. The features of nanoparticles affect the kinetics and thermodynamics of electrode processes of both nanoparticles and redox reactions occurring on their surface. The paper describes theoretical background and experimental studies of these processes. During the transition from macro- to micro- and nanostructures, the analytical characteristics of sensors modify. These features of metal nanoparticles are related to their size and energy effects, which affects the analytical characteristics of developed sensors. Modification of the macroelectrode with nanoparticles and other nanomaterials reduces the detection limit and improves the degree of sensitivity and selectivity of measurements. The use of nanoparticles as transducers, catalytic constituents, parts of electrochemical sensors for antioxidant detection, adsorbents, analyte transporters, and labels in electrochemical immunosensors and signal-generating elements is described.

An Aptamer-based Biosensor for Troponin I Detection in Diagnosis of Myocardial Infarction

BACKGROUND

Acute myocardial infarction (MI) accounts for one third of deaths. Cardiac troponin I (TnI) is a reliable biomarker of cardiac muscle tissue injury and is employed in the early diagnosis of MI.

OBJECTIVE

In this study, a molecular method is introduced to early diagnosis of MI by rapid detection of TnI.

MATERIALS AND METHODS

The detection method was based on electrochemical aptasensing, being developed using different methods and evaluation steps. A gold electrode was used as a transducer to successful immobilize 76base aptamer to fabricate a TnI biosensor.

RESULTS

The designed aptasensor could detect TnI in a range of 0.03 to 2.0 ng mL-1 without using any label, pre-concentration or amplification steps. The limit of detection was attained as 10 pg mL-1 without significant trouble of interfering species. The TnI biosensor demonestrated a stable, regenerative and reproducible function. 89 human samples were used to evaluate the performance of the TnI biosensor, and it represented 100% and 81%, diagnostic sensitivity and specificity, respectively.

CONCLUSION

This aptasensor may be used as an applicable tool in the future of early medical diagnosis of MI.

A colorimetric sensor of cysteine based on self-assembly nanostructures of Fe3+-H2O2/Tetramethylbenzidine system with "On-Off" switching function

Many strategies have been explored for selectively and sensitively detecting cysteine in different samples. Here, a novel colorimetric sensor based on self-assembly nanostructures of Fe³⁺-H₂O₂/Tetramethylbenzidine system with dual-level logic gate function and colorimetric determination of cysteine were firstly explored. The proposed Fe³⁺-H₂O₂-TMB system provides a sensitive optical signal due to the selectively reductive ability of cysteine to the oxidized TMB and thus could be successfully applied to the construction of instant on-site visual detection method with a paper based test strip for cysteine determination in a sample solution as well as for a dual-level logic gate fabrication.

Cysteine determination via adsorptive stripping voltammetry using a bare glassy carbon electrode

The electrochemical determination of cysteine is investigated by adsorptive stripping voltammetric detection of a copper-cysteine complex compound using a bare glassy carbon electrode. In acidic 0.1 M KNO3 solution (pH 4), the electrochemical oxidation of this complex compound generates a characteristic anodic peak ca. -0.17 V vs. a standard mercury/mercurous sulphate reference electrode. The voltammetric response is highly reproducible within 2.1% error (n = 3). A linear dynamic range is obtained for a cysteine concentration of 1.0 μM to 10.0 μM. The sensitivity of 0.18 ± 0.006 μA μM(-1) and the limit of detection of 0.03 μM (n = 3) make our methodology highly applicable for practical applications. Successful determination of cysteine concentration in the presence of glutathione has also been demonstrated by the sequential determination of the concentrations of total thiol and the tripeptide alone.

A novel cysteine sensor based on modification of carbon paste electrode by Fe(II)-exchanged zeolite X nanoparticles

An electrochemical sensor based on carbon paste electrode (CPE) modified with iron(II) doped into a synthesized nano-particles of zeolite X (Fe(II)-NX/ZCME) was constructed, which is highly sensitive for detection of cysteine (Cys). The modified electrode showed an excellent electro-activity for oxidation of Cys in phosphate buffer at pH7.4. It has been found that anodic peak potential of Cys oxidation, compared with the unmodified CPE (UCPE), was shifted towards negative values at the surface of the modified electrode under the optimum condition. The peak current increased linearly with the Cys concentration in the wide range of 5.0 × 10(-9)-3.0 × 10(-3) mol L(-1). The very low detection limit was obtained to be 1.5 × 10(-10) mol L(-1). Finally, the modified electrode was used as a selective, simple and precise new electrochemical sensor for the determination of Cys in the real samples, such as pharmaceutical and biological fluids.

Biomedical Probes Based on Inorganic Nanoparticles for Electrochemical and Optical Spectroscopy Applications

Inorganic nanoparticles usually provide novel and unique physical properties as their size approaches nanometer scale dimensions. The unique physical and optical properties of nanoparticles may lead to applications in a variety of areas, including biomedical detection. Therefore, current research is now increasingly focused on the use of the high surface-to-volume ratios of nanoparticles to fabricate superb chemical- or biosensors for various detection applications. This article highlights various kinds of inorganic nanoparticles, including metal nanoparticles, magnetic nanoparticles, nanocomposites, and semiconductor nanoparticles that can be perceived as useful materials for biomedical probes and points to the outstanding results arising from their use in such probes. The progress in the use of inorganic nanoparticle-based electrochemical, colorimetric and spectrophotometric detection in recent applications, especially bioanalysis, and the main functions of inorganic nanoparticles in detection are reviewed. The article begins with a conceptual discussion of nanoparticles according to types, followed by numerous applications to analytes including biomolecules, disease markers, and pharmaceutical substances. Most of the references cited herein, dating from 2010 to 2015, generally mention one or more of the following characteristics: a low detection limit, good signal amplification and simultaneous detection capabilities.

A sensitive and selective voltammetric sensor based on multiwall carbon nanotubes decorated with MgCr₂O₄ for the determination of azithromycin

In this report, we synthesized MgCr(2)O(4) nanoparticles and then multiwall carbon nanotubes were decorated with the MgCr(2)O(4) nanoparticles. The characteristics of the new materials were studied with different techniques such as transmission electron microscopy, Fourier transform infrared spectroscopy, atomic force microscopy and electrochemical impedance spectroscopy. The multiwall carbon nanotubes decorated with MgCr(2)O(4) nanoparticles were used as a new mediator for voltammetric determination of azithromycin. The oxidation peak of azithromycin was appeared at a potential of about 720 mV at a surface of the modified electrode. Differential pulse voltammetry exhibited two wide linear dynamic ranges of 0.25-4.0 and 4.0-10.0 μmol L(-1) azithromycin with a detection limit of 0.07 μmol L(-1) at pH 7.0. The influence of potential interfering compounds on the selectivity was studied. Finally, the modified electrode showed good sensitivity, selectivity and stability for the determination of azithromycin in real samples.

Voltammetric determination of cysteine using carbon paste electrode modified with Co(II)-Y zeolite

A novel zeolite modified electrode for use in voltammetric determination of l-cysteine (CySH) was described. The electrode comprises a Co(II)-exchanged zeolite Y as modifier in carbon paste matrix. First, the electrochemical behavior of Co(II) in modified carbon paste electrode was studied. The results demonstrated that diffusion can control the redox process of cobalt cations at the surface of the modified electrode. Then, the behavior of the electrode in the presence of CySH was studied by using cyclic voltammetry and a novel behavior was observed. In high concentration of CySH (above 10 mmol L(-1)), one pair of semi-reversible electrochemical extra peak was observed which was assigned to the processes of oxidation-reduction of CySH at the unmodified and modified electrode. Acidic conditions with respect to the neutral one cause an increase in the electrode response. The modified electrode showed a suitable linear calibration graph in the concentration range of 1.0×10(-9)-1.0×10(-3)mol L(-1) cysteine with a detection limit of 2.37×10(-10)mol L(-1). The influence of potential interfering substances on the peak current was studied and the results showed that the method was highly selective for determination of CySH. Thus, the proposed electrode was used for the determination of CySH in real samples including human blood serum, urine, N-acetylcysteine tablet and powdered poultry feed and the satisfactory results were obtained. Typical features of the sensor can be summarized as: low cost, simple preparation, fast response, good stability and selectivity, wide linear range, low detection limit and high reproducibility.