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Amperometry is a commonly used electrochemical method for studying the process of exocytosis in real-time. Given the high precision of recording that amperometry procedures offer, the volume of data generated can span over several hundreds of megabytes to a few gigabytes and therefore necessitates systematic and reproducible methods for analysis. Though the spike characteristics of amperometry traces in the time domain hold information about the dynamics of exocytosis, these biochemical signals are, more often than not, characterized by time-varying signal properties. Such signals with time-variant properties may occur at different frequencies and therefore analyzing them in the frequency domain may provide statistical validation for observations already established in the time domain. This necessitates the use of time-variant, frequency-selective signal processing methods as well, which can adeptly quantify the dominant or mean frequencies in the signal. The Fast Fourier Transform (FFT) is a well-established computational tool that is commonly used to find the frequency components of a signal buried in noise. In this work, we outline a method for spike-based frequency analysis of amperometry traces using FFT that also provides statistical validation of observations on spike characteristics in the time domain. We demonstrate the method by utilizing simulated signals and by subsequently testing it on diverse amperometry datasets generated from different experiments with various chemical stimulations. To our knowledge, this is the first fully automated open-source tool available dedicated to the analysis of spikes extracted from amperometry signals in the frequency domain. [ABSTRACT FROM AUTHOR]

A novel sandwich-type electrochemical aptasensor based on supramolecularly immobilized affinity bioreceptor was prepared via host–guest interactions. This method utilizes an adamantane-modified, target-responsive hairpin DNA aptamer as a capture molecular receptor, along with a perthiolated β-cyclodextrin (CD) covalently attached to a gold-modified electrode surface as the transduction element. The proposed sensing strategy employed an enzyme-modified aptamer as the signalling element to develop a sandwich-type aptasensor for detecting prostate-specific antigen (PSA). To achieve this, screen-printed carbon electrodes (SPCEs) with electrodeposited reduced graphene oxide (RGO) and gold nanoferns (AuNFs) were modified with the CD derivative to subsequently anchor the adamantane-modified anti-PSA aptamer via supramolecular associations. The sensing mechanism involves the affinity recognition of PSA molecules on the aptamer-enriched electrode surface, followed by the binding of an anti-PSA aptamer–horseradish peroxidase complex as a labelling element. This sandwich-type arrangement produces an analytical signal upon the addition of H2O2 and hydroquinone as enzyme substrates. The aptasensor successfully detected the biomarker within a concentration range of 0.5 ng/mL to 50 ng/mL, exhibiting high selectivity and a detection limit of 0.11 ng/mL in PBS. [ABSTRACT FROM AUTHOR]

Here we illustrate the use of dimethylglyoximate (DMG) as shape directing agent for the synthesis of nickel oxide nanowires (NiONWs) via hydrothermal process followed by calcination at elevated temperature. As-prepared NiONWs were characterized through scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) techniques and Fourier Transform Infra-red (FTIR) spectroscopy. The surface area of 27 m2 g–1 and pore diameter of 22 nm was true for the product. The prepared NiONWs were drop casted over the active surface of glassy carbon electrode (GCE) to apply it for the electrochemical sensing of hydroquinone based on cyclic voltammetry (CV) and amperometry techniques. The phosphate buffer solution (PBS) of pH 5.8 was used for the measurement of hydroquinone during electrochemical investigation. The developed sensor displayed a wide linear range of 0.5 to 11 µM for hydroquinone detection with sensitivity of 200 µA mM–1 cm–2 and limit of detection (LOD) equal to 0.01 µM. The sensor was further examined and found to be highly stable and extremely selective for the oxidation of hydroquinone. The sensor was successfully applied for amperometric detection of hydroquinone from water samples. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) were decorated on the Prussian blue nanocubes (PBNCs) using the in situ method. The synthesized nanocomposite PBNCs/AuNPs show enhanced electrocatalytic activity for H2O2 detection compared to the bare Prussian blue and gold nanoparticles due to the synergistic effect of AuNPs and PBNCs. The synthesized composites were characterized using XRD, SEM, TEM, FTIR, and Raman spectroscopy. In contrast, the electrochemical measurements used cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry. The PBNC/AuNP-based electrode shows improved electrochemical performance for H2O2 sensing, such as high sensitivity (up to 2138.2 µA/mM cm2) and limit of detection (LOD = up to 8.9 nM). Thus, the synthesized PBNC/AuNP material provides a simple, promising, cost-effective sensing platform for developing non-enzymatic electrochemical sensors. [ABSTRACT FROM AUTHOR]

This study reports the development of an innovative electrochemical bioplatform for the indirect determination of acrylamide (AM) based on its inhibitory effect on the hybridization of nucleic acids through the formation of AM‐guanine single‐stranded (ssDNA) adducts. The method combines the advantages of the formation and selective immunorecognition of DNA/RNA heteroduplex, with the use of MBs and amperometric transduction using disposable SPCEs. Increasing concentrations of acrylamide prevented the efficient hybridization of a synthetic biotinylated DNA probe immobilized on streptavidin‐coated magnetic beads with its complementary RNA target and the as‐formed heteroduplex recognition with a specific antibody and a secondary HRP‐labeled antibody used for electrochemical readout. The resulting magnetic bioconjugates were magnetically trapped on the surface of the working electrode of a SPCE and the amperometric transduction was carried out in the presence of the H2O2/HQ system, recording a cathodic response inversely proportional to the AM concentration. The developed bioplatform is more competitive with other reported methods in terms of simplicity and assay time, allowing the selective detection of 1 nM AM in 60 min. In addition, the bioplatform was applied to the analysis of potato crisp water extracts. [ABSTRACT FROM AUTHOR]

Dynamins are large GTPases whose primary function is not only to catalyze membrane scission during endocytosis but also to modulate other cellular processes, such as actin polymerization and vesicle trafficking. Recently, we reported that centronuclear myopathy associated dynamin‐2 mutations, p.A618T, and p.S619L, impair Ca2+‐induced exocytosis of the glucose transporter GLUT4 containing vesicles in immortalized human myoblasts. As exocytosis and endocytosis occur within rapid timescales, here we applied high‐temporal resolution techniques, such as patch‐clamp capacitance measurements and carbon‐fiber amperometry to assess the effects of these mutations on these two cellular processes, using bovine chromaffin cells as a study model. We found that the expression of any of these dynamin‐2 mutants inhibits a dynamin and F‐actin‐dependent form of fast endocytosis triggered by single action potential stimulus, as well as inhibits a slow compensatory endocytosis induced by 500 ms square depolarization. Both dynamin‐2 mutants further reduced the exocytosis induced by 500 ms depolarizations, and the frequency of release events and the recruitment of neuropeptide Y (NPY)‐labeled vesicles to the cell cortex after stimulation of nicotinic acetylcholine receptors with 1,1‐dimethyl‐4‐phenyl piperazine iodide (DMPP). They also provoked a significant decrease in the Ca2+‐induced formation of new actin filaments in permeabilized chromaffin cells. In summary, our results indicate that the centronuclear myopathy (CNM)‐linked p.A618T and p.S619L mutations in dynamin‐2 affect exocytosis and endocytosis, being the disruption of F‐actin dynamics a possible explanation for these results. These impaired cellular processes might underlie the pathogenic mechanisms associated with these mutations. [ABSTRACT FROM AUTHOR]

For the first time the sensitive determination of carbendatim (CRB) is reported utilizing a well-designed sensing architecture based on vanadium diselenide-multiwalled carbon nanotube (VSMC). FTIR, XRD, FESEM, EDS, and EIS were employed to evaluate the sensor's structural integrity, and the results demonstrated the successful integration of nanomaterials, resulting in a robust and sensitive electrochemical sensor. Cyclic voltammetry (CV) and chronoamperometric (CA) investigations showed that the sensor best performed at pH 8.0 (BRB) with an excellent detection limit of 9.80 nM with a wide linear range of 0.1 to 10.0 µM. A more thermodynamically viable oxidation of CRB was observed at the VSMC/GCE, with a shift of 200 mV in peak potential towards the less positive side compared with the unmodified GCE. In addition, the sensor demonstrated facile heterogeneous electron transfer, favorable anti-fouling traits in the presence of a wide range of interferents, good stability, and reproducible analytical performance. Finally, the developed sensor was validated for real-time quantification of CRB from spiked water, food, and bio-samples, which depicted acceptable recoveries (98.6 to 101.5%) with RSD values between 0.35 and 2.23%. Further, to derive the possible sensing mechanism, the valence orbitals projected density of states (PDOS) for C, H, and N atoms of an isolated CRB molecule, VSe2 + CNT and VSe2 + CNT + CRB were calculated using density functional theory (DFT) calculations. The dominant charge transfer from the valence 2p-orbitals of the C and N atoms of CRB to CNT is responsible for the electrochemical sensing of CRB molecules. [ABSTRACT FROM AUTHOR]

An innovative supramolecular architecture is reported for bienzymatic glucose biosensing based on the use of a nanohybrid made of multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with a Schiff base modified with two phenylboronic acid residues (SB-dBA) as platform for the site-specific immobilization of the glycoproteins glucose oxidase (GOx) and horseradish peroxidase (HRP). The analytical signal was obtained from amperometric experiments at − 0.050 V in the presence of 5.0 × 10−4 M hydroquinone as redox mediator. The concentration of GOx and HRP and the interaction time between the enzymes and the nanohybrid MWCNT–SB-dBA deposited at glassy carbon electrodes (GCEs) were optimized through a central composite design (CCD)/response surface methodology (RSM). The optimal concentrations of GOx and HRP were 3.0 mg mL−1 and 1.50 mg mL−1, respectively, while the optimum interaction time was 3.0 min. The bienzymatic biosensor presented a sensitivity of (24 ± 2) × 102 µA dL mg−1 ((44 ± 4) × 102 µA M−1), a linear range between 0.06 mg dL−1 and 21.6 mg dL−1 (3.1 µM–1.2 mM) (R2 = 0.9991), and detection and quantification limits of 0.02 mg dL−1 (1.0 µM) and 0.06 mg dL−1 (3.1 µM), respectively. The reproducibility for five sensors prepared with the same MWCNT–SB-dBA nanohybrid was 6.3%, while the reproducibility for sensors prepared with five different nanohybrids and five electrodes each was 7.9%. The GCE/MWCNT–SB-dBA/GOx-HRP was successfully used for the quantification of glucose in artificial human urine and commercial human serum samples. [ABSTRACT FROM AUTHOR]

Screen-printed carbon electrodes (SPCE) functionalized with MXene-based three-dimensional nanomaterials are reported for rapid determination of creatinine. Ti3C2TX MXene with in situ reduced AuNPs (MXene@AuNP) were used as a coreactant accelerator for efficient immobilization of enzymes. Creatinine could be oxidized by chitosan-embedded creatinine amidohydrolase, creatine amidinohydrolase, or sarcosine oxidase to generate H2O2, which could be electrochemically detected enhanced by Prussian blue (PB). The enzyme@CS/PB/MXene@AuNP/SPCE detected creatinine within the range 0.03–4.0 mM, with a limit of detection of 0.01 mM, with an average recovery of 96.8–103.7%. This indicates that the proposed biosensor is capable of detecting creatinine in a short amount of time (4 min) within a ± 5% percentage error, in contrast with the standard clinical colorimetric method. With this approach, reproducible and stable electrochemical responses could be achieved for determination of creatinine in serum, urine, or saliva. These results demonstrated its potential for deployment in resource-limited settings for early diagnosis and tracking the progression of chronic kidney disease (CKD). [ABSTRACT FROM AUTHOR]

Abstract Amperometry is a commonly used electrochemical method for studying the process of exocytosis in real-time. Given the high precision of recording that amperometry procedures offer, the volume of data generated can span over several hundreds of megabytes to a few gigabytes and therefore necessitates systematic and reproducible methods for analysis. Though the spike characteristics of amperometry traces in the time domain hold information about the dynamics of exocytosis, these biochemical signals are, more often than not, characterized by time-varying signal properties. Such signals with time-variant properties may occur at different frequencies and therefore analyzing them in the frequency domain may provide statistical validation for observations already established in the time domain. This necessitates the use of time-variant, frequency-selective signal processing methods as well, which can adeptly quantify the dominant or mean frequencies in the signal. The Fast Fourier Transform (FFT) is a well-established computational tool that is commonly used to find the frequency components of a signal buried in noise. In this work, we outline a method for spike-based frequency analysis of amperometry traces using FFT that also provides statistical validation of observations on spike characteristics in the time domain. We demonstrate the method by utilizing simulated signals and by subsequently testing it on diverse amperometry datasets generated from different experiments with various chemical stimulations. To our knowledge, this is the first fully automated open-source tool available dedicated to the analysis of spikes extracted from amperometry signals in the frequency domain.

Abstract This paper introduces a novel solid-state electrolyte-based enzymatic sensor designed for the detection of acetone, along with an examination of its performance under various surface modifications aimed at optimizing its sensing capabilities. To measure acetone concentrations in both liquid and vapor states, cyclic voltammetry and amperometry techniques were employed, utilizing disposable screen-printed electrodes consisting of a platinum working electrode, a platinum counter electrode, and a silver reference electrode. Four different surface modifications, involving different combinations of Nafion (N) and enzyme (E) layers (N + E; N + E + N; N + N + E; N + N + E + N), were tested to identify the most effective configuration for a sensor that can be used for breath acetone detection. The sensor's essential characteristics, including linearity, sensitivity, reproducibility, and limit of detection, were thoroughly evaluated through a range of experiments spanning concentrations from 1 µM to 25 mM. Changes in acetone concentration were monitored by comparing currents readings at different acetone concentrations. The sensor exhibited high sensitivity, and a linear response to acetone concentration in both liquid and gas phases within the specified concentration range, with correlation coefficients ranging from 0.92 to 0.98. Furthermore, the sensor achieved a rapid response time of 30–50 s and an impressive detection limit as low as 0.03 µM. The results indicated that the sensor exhibited the best linearity, sensitivity, and limit of detection when four layers were employed (N + N + E + N).

Key points Somatostatin, a peptide hormone that activates G‐protein‐coupled receptors, inhibits the secretion of many hormones. This study investigated the mechanisms of this inhibition using amperometry recording of Ca2+‐triggered catecholamine secretion from mouse chromaffin cells. Two distinct stimulation protocols, high‐KCl depolarization and caffeine, were used to trigger exocytosis, and confocal fluorescence imaging was used to monitor the rise in intracellular free Ca2+. Analysis of single‐vesicle fusion events (spikes) resolved the action of somatostatin on fusion pores at different stages. Somatostatin reduced spike frequency, and this reduction was accompanied by prolongation of pre‐spike feet and slowing of spike rise times. This indicates that somatostatin stabilizes initial fusion pores and slows their expansion. This action on the initial fusion pore impacted the release mode to favour kiss‐and‐run over full‐fusion. During a spike the permeability of a fusion pore peaks, declines and then settles into a plateau. Somatostatin had no effect on the plateau, suggesting no influence on late‐stage fusion pores. These actions of somatostatin were indistinguishable between exocytosis triggered by high‐KCl and caffeine, and fluorescence imaging showed that somatostatin had no effect on stimulus‐induced rises in cytosolic Ca2+. Our findings thus demonstrate that the signalling cascades activated by somatostatin target the exocytotic machinery that controls the initial and expanding stages of fusion pores, while having no effect on late‐stage fusion pores. As a result of its stronger inhibition of full‐fusion compared to kiss‐and‐run, somatostatin will preferentially inhibit the secretion of large peptides over the secretion of small catecholamines. Somatostatin inhibits the secretion of various hormones by activating G‐protein‐coupled receptors. In this study, we used amperometry to investigate the mechanism by which somatostatin inhibits catecholamine release from mouse chromaffin cells. Somatostatin increased pre‐spike foot lifetime and slowed fusion pore expansion. Somatostatin inhibited full‐fusion more strongly than kiss‐and‐run. Our results suggest that the initial fusion pore is the target of somatostatin‐mediated regulation of hormone release. The stronger inhibition of full‐fusion by somatostatin will result in preferential inhibition of peptide release. [ABSTRACT FROM AUTHOR]

Ti3C2Tx MXene/CuxO composites were prepared by acid etching combined with electrochemical technique. The abundant active sites on the surface of MXene greatly increase the loading of CuxO nanoparticles, and the synergistic effect between the different components of the composite can accelerate the oxidation reaction of glucose. The results indicate that at the working potential of 0.55 V (vs. Ag/AgCl), the glucose sensor based on Ti3C2Tx MXene/CuxO composite presents large linear concentration ranges from 1 µM to 4.655 mM (sensitivity of 361 µA mM−1 cm−2) and from 5.155 mM to 16.155 mM (sensitivity of 133 µA mM−1 cm−2). The limit of detection is 0.065 µM. In addition, the sensor effectively avoids the oxidative interference of common interfering species such as ascorbic acid, dopamine and uric acid. The sensor has good reproducibility, stability and acceptable recoveries for the detection of glucose in human sweat sample (97.5-103.3%) with RSD values less than 4%. Based on these excellent properties it has great potential for the detection of glucose in real samples. [ABSTRACT FROM AUTHOR]

This study demonstrated a unique method for quantifying β-glucan in edible mushrooms by immobilizing glucose oxidase (GOx) and β-glucanase (βg) on Multi-Walled Carbon Nanotubes (MWCNTs) modified glassy carbon electrode (GCE)-Nafion composite. Utilizing the special qualities of MWCNTs and Nafion, the electrochemical sensor's performance was improved. A sensitive and precise measurement of β-glucan was made possible by the sensor's design, which made use of βg and GOx. βg-GOx/MWCNTs/Nafion/GCE were evaluated for their efficacy in determining β-glucan. The findings indicated that the βg-GOx/MWCNTs/Nafion/GCE reacted only to β-glucan determination and not to other substances that could interfere. Peak current changed in a manner that was exactly proportional to β-glucan concentration in the 1–181 µg/mL range; this suggests a sensitivity of 2.14808 µA/µg mL− 1 and a detection limit of 0.7 ng/mL. By comparing seven identical biosensors made under the same circumstances, the suggested biosensor's homogeneity was assessed. The biosensor's repeatability was verified with a 4.40% relative standard deviation (RSD). Using edible mushroom samples, the βg-GOx/MWCNTs/Nafion/GCE was utilized and verified as a β-glucan sensor. Relative standard deviations of less than 4.88% and excellent recoveries ranging from 97.00 to 99.70% were obtained from the amperometric study. This confirmed that the results of βg-GOx/MWCNTs/Nafion/GCE for determining β-glucan concentration in edible mushroom samples were adequate and validated. The results of this study have the potential to greatly improve our knowledge of polysaccharides and how to use them in food science and agriculture. [ABSTRACT FROM AUTHOR]

A trendsetting direct competitive-based biosensing tool has been developed and implemented for the determination of the polyunsaturated fatty acid arachidonic acid (ARA), a highly significant biological regulator with decisive roles in viral infections. The designed methodology involves a competitive reaction between the target endogenous ARA and a biotin-ARA competitor for the recognition sites of anti-ARA antibodies covalently attached to the surface of carboxylic acid-coated magnetic microbeads (HOOC-MµBs), followed by the enzymatic label of the biotin-ARA residues with streptavidin-horseradish peroxidase (Strep-HRP) conjugate. The resulting bioconjugates were magnetically trapped onto the sensing surface of disposable screen-printed carbon transducers (SPCEs) to monitor the extent of the biorecognition reaction through amperometry. The operational functioning of the exhaustively optimized and characterized immunosensing bioplatform was highly convenient for the quantitative determination of ARA in serum samples from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2-) and respiratory syncytial virus (RSV)-infected individuals in a rapid, affordable, trustful, and sensitive manner. [ABSTRACT FROM AUTHOR]

In order to accurately determine the amount of sulphite in food samples, this study focuses on the fabrication and modification of electrochemical sensors employing NiCo2O4 adorned graphene composite electrodes. The glassy carbon electrode (GCE) was modified using a drop-casting technique using a NiCo2O4/reduced graphene oxide (rGO) nanocomposite (NiCo2O4/rGO/GCE). SEM, XPS, XRD, CV, and amperometry investigations were used to characterize the structural and electrochemical properties. The results of the analyses validated the nanocomposite's effective synthesis and its potential for improved electrochemical performance as a result of the interaction between rGO and NiCo2O4. After adding sulphite, the modified electrode showed a noticeable reduction in peak current, indicating effective catalysis. The sensor was found to have a sensitivity of 0.32341 µA/µM, a limit of quantification (LOQ) of 12 nM, and a limit of detection (LOD) of 3 nM. In terms of recovery rates for sulphite, NiCo2O4/rGO/GCE showed strong selectivity, reproducibility, and stability; the relative standard deviation (RSD) ranged from 3.22 to 4.73%. According to good recovery rates and RSD values in real sample tests, the NiCo2O4/rGO composite sensor shows increased sensitivity and specificity, making it a suitable option for real-world applications in food sample sulphite detection. [ABSTRACT FROM AUTHOR]

This paper compares materials potentially suitable for preparing solid reference electrodes, which could be used in miniaturized flow electrochemical cells. The tested electrodes are based on Sb, Bi, Pd, Pt, and Ag. The stable potential of the reference electrodes was maintained by the pH of the electrolyte, except for the AgCl electrode, whose potential was given by the concentration of chlorides. The performance of the reference electrodes was evaluated through a series of experiments focusing on potential dependences, long‐term and short‐term stability, cyclic voltammetry, and flow injection analysis with amperometric detection. Potentiometric experiments showed that Sb‐based electrodes had the closest slope to theoretical values with minor changes over five weeks. Theory‐consistent results of potential dependence were also observed for AgCl electrodes. The results of the voltammetric and flow amperometric experiment suggest that Sb‐based reference electrodes are the most suitable tools for electrochemical measurement. AgCl electrodes are limited by the necessity of maintaining a high chloride concentration. Bi‐based and PdH electrodes provide unstable results, the latter particularly due to hydrogen desorption. Although able to provide the stable potential to some extent, Pt electrodes are not suitable as the reference electrodes due to the deformation of mainly hydrodynamic voltammograms. [ABSTRACT FROM AUTHOR]

Flow injection amperometry provides an opportunity to avoid common drawbacks of classical potentiometry for solid-contact ion-selective electrodes. The current is generated by solid-contact in course of the polymer chain recharging in response to an excess of cations or anions in the polymer film. Cations cause cathodic peaks on the chronoamperogram, while anions result in anodic peaks. For polyaniline with negatively charged substituents, a response to cations is observed, whereas the presence of uncharged ones results in anion detection. Moreover, in the case of the protonated –SO3H group, this compensating current is an order of magnitude lower than that for the deprotonated one. For electroactive self-doped polyanilines, the maximal amperometric signal is achieved at the working potential within the electroactivity range. The proposed constant potential amperometric approach was validated by the successful analysis of human serum with a Na+-selective electrode based on polyaniline. [ABSTRACT FROM AUTHOR]

A novel enzyme-free sensor, constructed on a glassy carbon electrode (GCE) and featuring 2-dimensional (2-D) nanoporous magnesium oxide nanosheets (MgO-NSs), has been fabricated to enable the highly sensitive and selective detection of hydrogen peroxide (H2O2). MgO-NSs were successfully synthesized through a single-step, non-hazardous, and cost-effective sugar-blowing technique. The microstructure, porosity, thermal stability, and morphology of MgO-NSs were analyzed under XRD, FT-IR, FESEM, HR-TEM, TGA, and BET surface area. The electrochemical properties of MgO-NSs modified glassy carbon electrode (GCE) (MgO-NSs/GCE) were probed toward H2O2 sensing using CV, DPV, EIS, and amperometry techniques at varying concentrations, pH of the solution, and different scan rates. The fabricated electrode displayed remarkable selectivity, high sensitivity, and a linear response toward H2O2 in a wide concentration range of 20 µM-1000 µM at neutral pH with 0.224 µM limit of detection (LOD) and 0.753 µM limit of quantification (LOQ). The proposed electrochemical sensor based on MgO-NSs/GCE demonstrates multiple advantages like exceptionally high sensitivity, high selectivity, great stability, reproducibility, and excellent response toward the detection of hydrogen peroxide in milk and mixed-fruit juice samples as compared to the reports available in the literature. [ABSTRACT FROM AUTHOR]

The accurate and sensitive determination of tyrosine is of paramount value. In this work, we reported the synthesis and characterization of a new nanohybrid composed of silver nanoparticles and hollow carbon nanospheres (Ag/HMCS) for the amperometric sensing of tyrosine. The Ag/HMCS nanohybrid was used to modify electrodes and to fabricate an amperometric sensor for tyrosine at a working potential of 450 mV in aqueous 0.1 M phosphate buffer at pH 7.0. Under optimal conditions, the sensor determined tyrosine from 0.08 to 100 μM with a detection limit of 0.02 μM. [ABSTRACT FROM AUTHOR]

Developing convenient and reliable methods for Hg2+ monitoring is highly important. Some precious metal nanomaterials with intriguing peroxidase-like activity have been used for highly sensitive Hg2+ detection. However, H2O2 must be added during these detections, which impedes practical applications of Hg2+ sensors due to its susceptible decomposition by environmental factors. Herein, we discovered that the combination of Hg2+ and palladium metal-organic framework@graphene (Pd-MOF@GNs) exhibits oxidase-like activity (OXD). In the absence of H2O2, this activity not only catalyzes the oxidation of chromogenic substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) or o-phenylenediamine (OPD) to produce a color change but also enhances the electrical signals during OPD oxidation. Based on these properties, an effective and convenient dual-mode colorimetric and electrochemical sensor for Hg2+ has been developed. The colorimetric and amperometric linear relationships for Hg2+ were 0.045 μM—0.25 mM and 0.020 μM—2.0 mM, respectively. The proposed strategy shows good recovery in real sample tests, indicating promising prospects for multiple environmental sample detection of Hg2+ without relying on H2O2. The colorimetric and electrochemical dual-mode Hg2+ sensor is expected to hold great potentials in applications such as environmental monitoring, rapid field detection, and integration into smartphone detection of Hg2+. [ABSTRACT FROM AUTHOR]

Single atom catalysts (SACs) have attracted attention due to their excellent catalysis activity under specific reactions and conditions. However, the low density of SACs greatly limits catalytic performance. The three-dimensional graphene hollow nanospheres (GHSs) with very thin shell structure can be used as excellent carrier materials. Not only can its outer surface be used to anchor metal single atoms, but its inner surface can also provide rich sites. Here, a novel step-by-step assembly strategy is reported to anchor nickel single atoms (Ni SAs) on the inner and outer surfaces of GHSs (Ni SAs/GHSs/Ni SAs), which significantly increases the loading capacity of Ni SAs (4.8 wt%). Compared to conventional materials that only anchor Ni SAs to the outer surface of the carrier (Ni SAs/GHSs), Ni SAs/GHSs/Ni SAs exhibits significantly higher electrocatalytic activity toward glucose oxidation in alkaline media. The sensitivity of Ni SAs/GHSs/Ni SAs/GCE is nearly five times higher than that of Ni SAs/GHSs/GCE. Moreover, the sensor based on Ni SAs/GHSs/Ni SAs can detect glucose in a wide concentration range of 0.8 µM–1.1244 mM with a low detection limit of 0.19 µM (S/N = 3). This study not only provides an effective sensing material for glucose detection, but also opens a new avenue to construct high-density metal SACs. [ABSTRACT FROM AUTHOR]

This paper presents the characterization and testing of electrochemical sensor using microfluidic system. Various geometric patterns were laser cut into the platinum working electrode of a biosensor. In this work, a microfluidic chamber was designed that allows phosphate buffer solution (PBS) to flow across the sensor, using a peristaltic pump, while varying the concentration of hydrogen peroxide. The amperometric characterization of the electrochemical sensor with 25, 50, 75, and 100 μ m perforation and 75 μ m spacing showed the highest sensitivity. This result was to be expected the purpose of patterning the sensors was to provide a 3-dimensional structure to the planar electrode in order for the enzyme, glucose oxidase, to be immobilized. Future work will include selecting one of the patterns for immobilization of glucose oxidase allowing us to realize a fully functional glucose sensor. [ABSTRACT FROM AUTHOR]

In this study, donepezil hydrochloride (DZ HCl), a crucial medication for the treatment of Alzheimer's disease, is detected using a new sensor built on CuO-TiO2 hybrid nanostructures. The sensor showed improved performance characteristics with a computed limit of quantitation of 0.211 and a limit of detection of 0.063. These qualities included improved stability, selectivity, and sensitivity. The fabrication process demonstrated repeatability, with a 4.27% relative standard deviation. After 10 successive readings, the sensor maintained 95% of its initial response, demonstrating its long-term stability. By quantifying DZ HCl in urine samples, the practical applicability of the sensor was confirmed. Remarkably, the sensor achieved a remarkable recovery rate of 97.00–99.41% and a suitable relative standard deviation range of 3.29–4.71%. The results of this work contribute to the development of trustworthy electrochemical sensors for medicinal chemicals and have prospective uses in pharmacological, biological, and therapeutic fields.

The goal of this work is to create highly sensitive and selective electrochemical sensors that can detect lactate, an essential substance in the body's anaerobic breakdown of carbohydrates, by utilizing lactate oxidase (LOx) and glutaraldehyde (GA)-modified indium-doped zinc oxide (ZnO) nanorods. Several structural investigations validated the effective immobilization of LOx and GA on the modified glassy carbon electrode (GCE) with indium-doped ZnO nanorods. Lactate was detected with the LOx-GA/In-doped ZnO biosensor, which showed linear range of 0.1–36 mM, sensitivity value of 0.73301 µA/mM, and quantification and detection limits of 2.7 μM and 0.8 μM, respectively. The biosensor also displayed stability, repeatability, and selectivity. The sensor demonstrated remarkable lactate recovery rates when applied to real serum and urine specimens from athletes. The serum samples ranged from 96.00% to 99.28% with a relative standard deviation (RSD%) of 3.77–4.25, and the urine samples from 94.00 to 98.58 with an RSD% of 3.55–4.62. These results point to the LOx-GA/In-doped ZnO/GCE sensor platform's potential for a range of biomedical uses.

In this study, donepezil hydrochloride (DZ HCl), a crucial medication for the treatment of Alzheimer's disease, is detected using a new sensor built on CuO-TiO 2 hybrid nanostructures. The sensor showed improved performance characteristics with a computed limit of quantitation of 0.211 and a limit of detection of 0.063. These qualities included improved stability, selectivity, and sensitivity. The fabrication process demonstrated repeatability, with a 4.27% relative standard deviation. After 10 successive readings, the sensor maintained 95% of its initial response, demonstrating its long-term stability. By quantifying DZ HCl in urine samples, the practical applicability of the sensor was confirmed. Remarkably, the sensor achieved a remarkable recovery rate of 97.00–99.41% and a suitable relative standard deviation range of 3.29–4.71%. The results of this work contribute to the development of trustworthy electrochemical sensors for medicinal chemicals and have prospective uses in pharmacological, biological, and therapeutic fields. [ABSTRACT FROM AUTHOR]

In this paper, the evaluation of a boron‐doped ultrananocrystalline diamond (BD‐UNCD) electrode for the determination of ibuprofen (IBU) in pharmaceutical formulations using batch‐injection analysis with amperometric detection (BIA‐AD) is presented. The BD‐UNCD electrode was characterized by Raman spectroscopy and the electrochemical measurements were carried out before and after anodic pretreatment. An improved electrochemical response for IBU oxidation was observed using BD‐UNCD as compared to commercial boron‐doped diamond electrode. The optimized method based on the BIA‐AD system was carried out by using 2.0 V as the detection potential, a dispensing rate of 211.9 μL s−1, and an injection volume of 40 μL in an electrochemical cell containing 30.0 mL of 1.0 mol L−1 HClO4 as the supporting electrolyte. The proposed method provided an analytical curve within a linear dynamic range from 1.84 to 20.0 μmol L−1 (R2=0.9967) and a limit of detection of 0.55 μmol L−1. The intra‐day (n=10) and inter‐day (n=2) precisions for IBU concentrations of 5.0 and 10.0 μmol L−1 assessed as relative standard deviation (%RSD) ranged from 2.65 to 5.84 %. The accuracy of the method was assessed through the determination of IBU in pharmaceutical samples (tablets and solutions), yielding results that were consistent with those obtained through the comparative method (HPLC‐DAD). [ABSTRACT FROM AUTHOR]

An interfacial galvanic replacement strategy to controllable synthesize palladium nanoparticles (Pd NPs)-modified NiFe MOF nanocomposite on nickel foam, which served as an efficient sensing platform for quantitative determination of dopamine (DA). Pd NPs grown in situ on the nanosheets of NiFe MOF via self-driven galvanic replacement reaction (GRR) and well uniform distribution was achieved. This method effectively reduced the aggregation of metallic nanoparticles and significantly promoted the electron transfer rate during the electrochemical process, leading to improved electrocatalytic activity for DA oxidation. Remarkably, the precisely constructed biosensor achieved a low detection limit (LOD) of 0.068 µM and recovery of 94.1% (RSD 6.7%, N = 3) for simulated real sample detection and also exhibited superior selectivity and stability. The results confirmed that the as-fabricated Pd-NiFe/NF composite electrode could realize the quantitative determination of DA and showed promising prospects in real sample biosensing. [ABSTRACT FROM AUTHOR]

A novel non-enzymatic electrochemical sensor was developed with high selectivity and sensitivity for detecting biologically significant hydrogen peroxide (H2O2). The sensor utilized an electrode modified with graphite oxide/Nafion/Azure A (GO/Nf/AzA) fabricated by simple chemical adsorption method. The incorporation of AzA into the GO/Nf matrix was verified through UV–Vis and FTIR spectroscopy. Electrochemical investigations via cyclic voltammetry and differential pulse voltammetry elucidated the modified electrode's properties. Optimization of experimental parameters, including pH and scan rates, enhanced its electrochemical behavior. Cyclic voltammetry analysis revealed an apparent electron transfer rate constant (Ks) of 1.14 cm/s and a charge transfer coefficient (α) of 0.74. Compared to the bare graphite electrode, the modified electrode exhibited significantly higher current densities in response to H2O2 with reduced overvoltage. The reduction peak currents for H2O2 demonstrated a linear correlation with concentrations ranging from 1.3 × 10−6 M to 3.6 × 10−3 M, with a detection limit of 4.3 × 10−7 M (S/N = 3). Notably, the proposed modified electrode displayed excellent sensitivity and selectivity, presenting a promising avenue for H2O2 determination. In amperometric methods, it showcased stable and rapid responses, indicating potential for application in flow system analysis. Real sample analysis involving two distinct milk samples validated the electrodes' good recovery capabilities. [ABSTRACT FROM AUTHOR]

An overreactive stress granule (SG) pathway and long‐lived, stable SGs formation are thought to participate in the progress of neurodegenerative diseases (NDs). To understand if and how SGs contribute to disorders of neurotransmitter release in NDs, we examined the interaction between extracellular isolated SGs and vesicles. Amperometry shows that the vesicular content increases and dynamics of vesicle opening slow down after vesicles are treated with SGs, suggesting larger vesicles are formed. Data from transmission electron microscopy (TEM) clearly shows that a portion of large dense‐core vesicles (LDCVs) with double/multiple cores appear, thus confirming that SGs induce homotypic fusion between LDCVs. This might be a protective step to help cells to survive following high oxidative stress. A hypothetical mechanism is proposed whereby enriched mRNA or protein in the shell of SGs is likely to bind intrinsically disordered protein (IDP) regions of vesicle associated membrane protein (VAMP) driving a disrupted membrane between two closely buddled vesicles to fuse with each other to form double‐core vesicles. Our results show that SGs induce homotypic fusion of LDCVs, providing better understanding of how SGs intervene in pathological processes and opening a new direction to investigations of SGs involved neurodegenerative disease. [ABSTRACT FROM AUTHOR]

Here, we report the fabrication of Heterometallo‐supramolecular polymer (H‐SMP) for the selective oxidation of nitrite with the investigation of some kinetic parameters by the complex formation of Co(II) and Fe(II) salts with the symmetrical ligand which is composed of terpyridine moieties specially referred to as [4′,4′′′′‐(1,4‐Phenylene)bis(2,2′:6′,2′′‐terpyridine)] to form polyCoFe. The characterization of polyCoFe was carried out using UV‐Vis titration, FT‐IR and SEM. The viscosity measurement of H‐SMP was utilized to calculate its molecular weight using Mark‐Houwink‐Sakurada equation. The electrochemical performance of polyCoFe_GCE was evaluated using the CV and EIS techniques. The kinetics of the irreversible electro‐oxidation mechanism were investigated by introducing variations in scan‐rate and pH. The concurrence observed between the experimental and simulated CV results provided additional evidence supporting the accuracy and reliability of the determined kinetic parameters. We investigated the efficiency of polyCoFe_GCE for nitrite detection at various concentrations using CV as well as amperometry methods. The amperometric technique showed a wide linear range of 0.66 to 194.15 μM and a low detection limit of 0.11 μM. In addition, modified electrode underwent interference, stability, and reproducibility tests. Real samples were analyzed using both CV and amperometry methods, and the obtained results were compared with those obtained from standard solutions. [ABSTRACT FROM AUTHOR]

A fully reusable electrochemical device is proposed for the first time made from laser cutting and a homemade conductive ink composed of carbon and nail polish. As a sensor substrate, we applied polymethyl methacrylate, which allows the surface to be renewed by simply removing and reapplying a new layer of ink. In addition to the ease of renewing the sensor’s conductive surface, the design of the device has allowed for the integration of different forms of analysis. The determination of L-Dopa was performed using DPV, which presented a linear response range between 5.0 and 1000.0 μmol L−1, and a LOD of 0.11 μmol L−1. For dopamine, a flow injection analysis system was employed, and using the amperometric technique measurements were performed with a linear ranging from 2.0 to 100.0 μmol L−1 and a LOD of 0.26 μmol L−1. To demonstrate its applicability, the device was used in the quantification of analytes in pharmaceutical drug and synthetic urine samples. [ABSTRACT FROM AUTHOR]

The goal of this work is to create highly sensitive and selective electrochemical sensors that can detect lactate, an essential substance in the body's anaerobic breakdown of carbohydrates, by utilizing lactate oxidase (LOx) and glutaraldehyde (GA)-modified indium-doped zinc oxide (ZnO) nanorods. Several structural investigations validated the effective immobilization of LOx and GA on the modified glassy carbon electrode (GCE) with indium-doped ZnO nanorods. Lactate was detected with the LOx-GA/In-doped ZnO biosensor, which showed linear range of 0.1–36 mM, sensitivity value of 0.73301 µA/mM, and quantification and detection limits of 2.7 μM and 0.8 μM, respectively. The biosensor also displayed stability, repeatability, and selectivity. The sensor demonstrated remarkable lactate recovery rates when applied to real serum and urine specimens from athletes. The serum samples ranged from 96.00% to 99.28% with a relative standard deviation (RSD%) of 3.77–4.25, and the urine samples from 94.00 to 98.58 with an RSD% of 3.55–4.62. These results point to the LOx-GA/In-doped ZnO/GCE sensor platform's potential for a range of biomedical uses. [ABSTRACT FROM AUTHOR]

Electrochemical method is used for glycated hemoglobin (HbA1c) detection using a new configuration of working electrodes coated by ZnO nanorods. HbA1c reflects the average plasma glucose over two months. In this work, HbA1c is directly detected electrochemically without any proteolytic digestion for the first time. ZnO nanorods modify the working electrode to increase the surface of sensing, leading to amplifying the electrochemical signal and providing a stable enzyme bed for GOx immobilization. The limit of detection (LOD) is 0.32 μg/μl which can be achieved in 40 seconds as the sensor's response time. The range of detection is 0.32 μg/μl (0.21% of HbA1c)-22.4 μg/μl (14.93% of HbA1c) that covers the standard diagnosis range. Due to embedded nanostructures, a small amount of about 2 μl GOx solution and 50 nl of blood is required for detection. The low response time makes this sensor suitable for fast tests such as diabetic population enumeration and screening. [ABSTRACT FROM AUTHOR]

In vitro bioequivalence assessment of paracetamol tablets was carried out by differential pulse voltammetry (DPV) and amperometry using a multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNT). For the DPV developed method, samples were collected from the USP paddle apparatus, while amperometric measurements were carried out in situ. The DPV method was validated in three supporting electrolytes (per in vitro bioequivalence guidelines) by measuring the recovery from standard solutions and paracetamol tablet solutions, while precision was evaluated through the RSD (n=6). In HCl pH 1.2 solution the LOD and LOQ were 48 nM and 160 nM, respectively and the linear range was between 0.18–2.2 μM. In acetate buffer pH 4.5 the LOD and LOQ were 15 nM and 51 nM, respectively and the linear range was between 88 nM–880 nM. And in phosphate buffer pH 6.8 the LOD and LOQ were 4.6 nM and 15 nM, respectively and the linear range was between 88 nM–880 nM. Recovery values were between 95 and 105 % and precision values were less than 5 %. Results showed that both methods were effectively applied for the analysis of samples. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation of levamisole, a glassy carbon electrode, was investigated over the pH range 2.0–10.0. Cyclic voltammetric investigations showed a single oxidation process was recorded, with a peak potential (Ep) shown to be pH-dependent in the range 5.0–8.0; between pH 2.0 and pH 5.0, and above pH 8.0, the Ep was found to be independent of pH, indicating apparent pKa values of 5.0 and 8.0. Peak currents were found to increase with increasing pH values. This voltammetric oxidation process was found to be consistent with a two-electron, two-proton oxidation to the corresponding sulfoxide. Based on these findings, the development of a of method based on the high-performance liquid chromatography separation of levamisole, with electrochemical detection being used for its determination, was explored. The chromatographic conditions required for the separation of levamisole were first investigated and optimized using UV detection. The conditions were identified as a 150 mm × 4.6 mm, 5 µm C18 column with a mobile phase consisting of 50% methanol, and 50%, 50 mM, pH 8.0 phosphate buffer. The technique of hydrodynamic voltammetry was applied to optimize the applied potential required for the determination of levamisole, identified as +2.3 V versus a stainless-steel pseudo-reference counter-electrode. Under the optimized conditions, levamisole exhibited a linear response of 1.00–20 mg/L (R2 = 0.999), with a detection limit of 0.27 mg/L. The possibility of determining levamisole in artificial urine was shown to be possible via simple dilution in the mobile phase. Mean recoveries of 99.7%, and 94.6%, with associated coefficients of variation of 8.2% and 10.2%, respectively, were obtained for 1.25 µg/mL (n = 5) and 2.50 µg/mL (n = 5). [ABSTRACT FROM AUTHOR]

The modification of graphite screen-printed electrodes (SPEs) is reported using an eco-friendly and extremely fast method based on the direct cobalt pin electrode-to-SPE spark discharge at ambient conditions. This approach does not utilize any liquids or chemical templates, does not produce any waste, and allows the in-situ generation of CoxOy nanoparticles onto the electrode surface and the development of efficient electrocatalytic sensing surfaces for the determination of H2O2. Co-spark SPEs were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy and x-ray photoelectron spectroscopy (XPS), revealing the formation of surface confined CoxOy nanoparticles and the diverse oxidation states of cobalt species. Co-spark SPEs were also characterized with cyclic voltammetry and electrochemical impedance spectroscopy. Redox transitions of the surface confined electrocatalysts are demonstrated by electrochemical polarization studies, showing the formation of different oxides (CoxOy), varying the XPS results. Amperometric measurements at 0.3 V vs. Ag/AgCl revealed a linear relationship between the current response and the concentration of H2O2 over the range 1 − 102 μM, achieving a limit of detection (3σ/m) of 0.6 μM. The interference effect of various electroactive species was effectively addressed by employing dual measurements in the absence and presence of the enzyme catalase. The analytical utility of the method was evaluated in antioxidant rich real-world samples, such as energy drinks, demonstrating sufficient recovery. [ABSTRACT FROM AUTHOR]

The successful synthesis of La-doped CoFe LDH@rGO nanocomposite is reported combining the advantages of LDH and rGO and shows promising performances in electrochemical sensors. The structure of the obtained nanocomposite was investigated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction pattern (XRD), and field emission scanning electron microscope images (FE-SEM). Then, it was directly utilized to construct a carbon paste electrode (CPE) for urea detection. The electrochemical performance of the sensor was evaluated by various electrochemical methods. The La-CoFe LDH@rGO electrode exhibited excellent electrocatalytic properties, including a wide linear working range of 0.001–23.5 mM, very high sensitivity of 1.07 ± 0.023 µA µM-1 cm-2, a low detection limit of 0.33 ± 0.11 µM, and rapid response time of 5 s towards urea detection at the working potential of 0.4 V. Furthermore, the sensor displayed a high selectivity in different matrices, appropriate reproducibility, and long shelf life without activity loss during 3 months of storage under ambient conditions. Further tests were performed on serum and milk samples to confirm the capability of the proposed sensor for practical applications, demonstrating a reasonable recovery of 94.8 to 102% with an RSD value below 3%. Consequently, the synergistic effect of each component led to the good electrocatalytic activity of the modified electrode towards urea. [ABSTRACT FROM AUTHOR]

A diffusion model for the analysis of chronoamperometric data in response to a concentration step is developed for amperometric gas sensors. This analysis avoids the difficulties with standard potentiodynamic measurements at the large specific area, high capacitance electrodes employed in these sensors. Despite the fact that typical devices comprise multiple layers with varying thicknesses and diffusivities, we show that typical chronoamperometric traces can be fitted to a simple diffusion model with a single parameter τ=L2D ${\tau ={{{L}^{2}}\over{D}}}$ where L is an overall effective thickness of the diffusion barrier and D is an effective diffusion coefficient. Through a comparison of the transient and steady‐state current, independent estimates of L and D in the devices can be made. The model is also extended to cover cases with interfacial kinetic barriers; such kinetic limitations lead to a change in the effective values L and D, but the simple diffusion model remains a good fit to the data. This analysis shows that transient sensor responses can be characterised by a single parameter τ and conversely that deviations from this regression model cannot be assigned to (i) complex layer architectures or (ii) interlayer kinetic barriers. Instead, we show that non‐uniform accessibility effects arising from a distribution of diffusion rates across the device lead to deviations from the simple regression model, but that they may be captured approximately by a more complex model in which τ has a probability distribution. [ABSTRACT FROM AUTHOR]

A novel sandwich-type electrochemical aptasensor based on supramolecularly immobilized affinity bioreceptor was prepared via host–guest interactions. This method utilizes an adamantane-modified, target-responsive hairpin DNA aptamer as a capture molecular receptor, along with a perthiolated β-cyclodextrin (CD) covalently attached to a gold-modified electrode surface as the transduction element. The proposed sensing strategy employed an enzyme-modified aptamer as the signalling element to develop a sandwich-type aptasensor for detecting prostate-specific antigen (PSA). To achieve this, screen-printed carbon electrodes (SPCEs) with electrodeposited reduced graphene oxide (RGO) and gold nanoferns (AuNFs) were modified with the CD derivative to subsequently anchor the adamantane-modified anti-PSA aptamer via supramolecular associations. The sensing mechanism involves the affinity recognition of PSA molecules on the aptamer-enriched electrode surface, followed by the binding of an anti-PSA aptamer–horseradish peroxidase complex as a labelling element. This sandwich-type arrangement produces an analytical signal upon the addition of H2O2 and hydroquinone as enzyme substrates. The aptasensor successfully detected the biomarker within a concentration range of 0.5 ng/mL to 50 ng/mL, exhibiting high selectivity and a detection limit of 0.11 ng/mL in PBS.

Amperometry is arguably the most widely used technique for studying the exocytosis of biological amines. However, the scarcity of human tissues, particularly in the context of neurological diseases, poses a challenge for exocytosis research. Human platelets, which accumulate 90% of blood serotonin, release it through exocytosis. Nevertheless, single-cell amperometry with encapsulated carbon fibers is impractical due to the small size of platelets and the limited number of secretory granules on each platelet. The recent technological improvements in amperometric multi-electrode array (MEA) devices allow simultaneous recordings from several high-performance electrodes. In this paper, we present a comparison of three MEA boron-doped diamond (BDD) devices for studying serotonin exocytosis in human platelets: (i) the BDD-on-glass MEA, (ii) the BDD-on-silicon MEA, and (iii) the BDD on amorphous quartz MEA (BDD-on-quartz MEA). Transparent electrodes offer several advantages for observing living cells, and in the case of platelets, they control activation/aggregation. BDD-on-quartz offers the advantage over previous materials of combining excellent electrochemical properties with transparency for microscopic observation. These devices are opening exciting perspectives for clinical applications. [ABSTRACT FROM AUTHOR]

Implantable cell replacement therapies promise to completely restore the function of neural structures, possibly changing how we currently perceive the onset of neurodegenerative diseases. One of the major clinical hurdles for the routine implementation of stem cell therapies is poor cell retention and survival, demanding the need to better understand these mechanisms while providing precise and scalable approaches to monitor these cell-based therapies in both pre-clinical and clinical scenarios. This poses significant multidisciplinary challenges regarding planning, defining the methodology and requirements, prototyping and different stages of testing. Aiming toward an optogenetic neural stem cell implant controlled by a smart wireless electronic frontend, we show how an iterative development methodology coupled with a modular design philosophy can mitigate some of these challenges. In this study, we present a miniaturized, wireless-controlled, modular multisensor platform with fully interfaced electronics featuring three different modules: an impedance analyzer, a potentiostat and an optical stimulator. We show the application of the platform for electrical impedance spectroscopy-based cell monitoring, optical stimulation to induce dopamine release from optogenetically modified neurons and a potentiostat for cyclic voltammetry and amperometric detection of dopamine release. The multisensor platform is designed to be used as an opto-electric headstage for future in vivo animal experiments. [ABSTRACT FROM AUTHOR]

The present work describes the electrocatalytic oxidation of nitrite in the presence of a composite of coordination polymer of cobalt‐4‐pyridylporphyrin and electrochemically reduced graphene oxide. The electrode was modified by drop‐casting a suspension of graphene oxide and polymeric cobalt‐4‐pyridylporphyrin followed by reduction through cyclic voltammetry in the potential range 0.0 V to −1.5 V. The electrocatalytic investigations were carried out by voltammetric (cyclic, linear sweep, differential pulse and hydrodynamic) and by amperometric methods. The LOD and the working range obtained through different techniques are compared. The rate constant for this heterogeneous electron transfer reaction is 2.45×10−2 cms−1. [ABSTRACT FROM AUTHOR]

In this paper, a simple, sensitive, and precise flow injection system was optimized and applied to ascorbic acid determination with a carbon paste electrode modified with the Schiff base copper complex. The modified sensor showed increased sensitivity toward ascorbic acid oxidation with a decrease of oxidation potential by 200 mV. Under optimized flow parameters, working potential, gasket thickness, sample and reaction coil volumes, and flow rate, the developed flow system gave a linear response from 5 to 75 μmol/L of ascorbic acid. The calculated limit of detection was 4.5 μmol/L, calculated as 3σ/s which corresponds to the absolute value of 40 ng for the 50 μL sample coil. The precision for six consecutive injections of 5 and 75 μmol/L ascorbic acid solutions was determined as a relative standard deviation of 5.8 % and 1.5 %, respectively. The flow injection system enabled up to 120 analyses per hour. An optimized flow system was applied to the determination of ascorbic acid in dietary supplements, after simple preparation. [ABSTRACT FROM AUTHOR]