A novel flow injection amperometric sensor based on carbon black and graphene oxide modified screen-printed carbon electrode for highly sensitive determination of uric acid

Iron-based metal-organic framework/graphene oxide composite electrodes for efficient flow-injection amperometric detection of dexamethasone

A highly stable flow-injection amperometric sensor for dexamethasone (DEX) was developed using a pencil graphite electrode (PGE) modified with Fe-based metal organic frameworks, MIL-100(Fe) and graphene oxide composite materials (MIL-100(Fe)/GO). Scanning electron microscopy and energy-dispersive X-ray spectroscopy, transmission electron microscopy, powder X-ray diffraction, and Fourier-transform infrared spectroscopy were used to characterize the MIL-100(Fe) composites. The MIL-100(Fe)/GO-modified PGE (denoted MIL-100(Fe)/GO/PGE) was further electrochemically characterized using cyclic voltammetry. As an electrode material, MIL-100(Fe) is a sensing element that undergoes oxidation from Fe(ii)-MOF to Fe(iii)-MOF, and GO possesses high conductivity and a large surface area, which exhibits high absorbability. In the presence of DEX, Fe(iii) is reduced, which accelerates electron transfer at the electrode interface. Therefore, DEX can be quantitatively detected by analyzing the anodic current of MIL-100(Fe). When coupled with amperometric flow injection analysis, excellent performance can be obtained even when a low detection potential is applied (+0.10 V vs. Ag/AgCl). The concentration was linear in the range 0.10-5.0 μM and 0.010-5.0 mM with LOD of 0.030 μM based on 3(sd/slope). The modified electrode also exhibited a remarkably stable response under optimized conditions, and up to 55 injections can be used per electrode. The sensor exhibits high repeatability, reproducibility, and anti-interference properties when used for DEX detection. The effective determination of dexamethasone in real pharmaceutical and cosmetic samples demonstrated the feasibility of the electrochemical sensor, and the results were in good agreement with those obtained from the HPLC-DAD analysis. Acceptable percentage recoveries from the spiked pharmaceutical and cosmetic samples were obtained, ranging from 93-111% for this new method compared with 84-107% for the HPLC-DAD standard method.

Sensitive electrochemical flow injection analysis of H2O2 released from cells with a pass-through mode

Conventional plate electrodes were commonly used in electrochemical flow injection analysis and only part of molecules diffused to the plane of electrodes could be detected, which would limit the performance of electrochemical detection. In this study, a low-cost native stainless steel wire mesh (SSWM) electrode was integrated into a 3D-printed device for electrochemical flow injection analysis with a pass-through mode, which is different compared with previous flow-through mode. This strategy was applied for sensitive analysis of hydrogen peroxide (H2O2) released from cells. Under the optimal conditions (the applied potentials, the flow rate and the sample volume), the device exhibits high sensitivity toward H2O2. Linear relationships could be achieved between electrochemical responses and the concentration of H2O2 ranging from 1 nM to 1 mM. The excellent analytical performance of the SSWM-based device could be attributed to the pass-through mode based on the mesh microstructure and intrinsic catalytic properties for H2O2 by stainless steel. This approach could be further successfully extended for screening of H2O2 released from HeLa cells with electrochemical responses linear to the number of cells in a range of 3 - 1.35 × 104 cells with an injection volume of 30 μL. This study revealed the potential of mesh electrodes in electrochemical flow injection analysis for cellular function and pathology and its possible extension in cell counting and on-line analysis.

Development of a sensitive electrochemical method to determine amitraz based on perylene tetracarboxylic acid/mesoporous carbon/Nafion@SPCEs

A cutting-edge electrochemical method is presented for precise quantification of amitraz (AMZ), a commonly used acaricide in veterinary medicine and agriculture. Leveraging a lab-made screen-printed carbon electrode modified with a synergistic blend of perylene tetracarboxylic acid (PTCA), mesoporous carbon (MC), and Nafion, the sensor's sensitivity was significantly improved. Fine-tuning of PTCA, MC, and Nafion ratios, alongside optimization of the pH of the supporting electrolyte and accumulation time, resulted in remarkable sensitivity enhancements. The sensor exhibited a linear response within the concentration range 0.01 to 0.70 μg mL-1, boasting an exceptionally low limit of detection of 0.002 μg mL-1 and a limit of quantification of 0.10 μg mL-1, surpassing maximum residue levels permitted in honey, tomato, and longan samples. Validation with real samples demonstrated high recoveries ranging from 80.8 to 104.8%, with a relative standard deviation below 10%, affirming the method's robustness and precision. The modified PTCA/MC/Nafion@SPCE-based electrochemical sensor not only offers superior sensitivity but also simplicity and cost-effectiveness, making it a pivotal tool for accurate AMZ detection in food samples. Furthermore, beyond the scope of this study, the sensor presents promising prospects for wider application across various electrochemical analytical fields, thereby significantly contributing to food safety and advancing agricultural practices.

Sonoelectrochemical exfoliation of defective black phosphorus nanosheet with black phosphorus quantum dots as a uric acid sensor

To maintain human health, the development of rapid uric acid (UA) sensing is crucial. In this study, defective black phosphorus nanosheets with black phosphorus quantum dots (dBPN/BPQDs) were successfully and rapidly prepared by sonoelectrochemical exfoliation. In this process, the intercalation of phosphate ions into the black phosphorus working electrode was improved by coupling ultrasonic radiation with a high intercalating potential (8 V vs. Ag/AgCl/3M). The dBPN/BPQDs with various vacancies (5-9 defects, 5-7-7-5 defects, and 5-8-5 defect vacancies) exhibited a remarkable mass activity (jm, 1.22 × 10-3 mA μg-1) for uric acid oxidation, which was 5.92 times greater than that of reduced graphene oxide (rGO) (2.06 × 10-4 mA μg-1). In addition, the sensitivity of the dBPN/BPQD UA sensor was 474.2 μA mM-1 cm-2 in the linear analysis range of 0.1-1.3 mM. The sensitivity of the sensor was apparently higher than 67.7 μA mM-1cm-2 for rGO. The data from real sample experiments using serum showed that the dBPN/BPQD catalyst had high recoveries (97.3 %-100.2 %) and low related standard deviation (0.44 %-1.52 %). The dBPN/BPQDs exhibited the potential as an amperometric sensor to detect UA without needing enzymes.

A rapid and reliable electrochemical determination of 5- hydroxymethylfurfural in honey exploiting nickel oxide nanoparticles modified electrode

This study presents a novel approach for the rapid and reliable electrochemical determination of 5-hydroxymethylfurfural (5-HMF) in honey using a screen-printed carbon electrode modified with nickel oxide nanoparticles (NiONPs/SPCE). The NiONPs were synthesized using a simple method and characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The NiONPs/SPCE demonstrated enhanced sensitivity and selectivity for 5-HMF detection. The electrochemical behavior of 5-HMF on the NiONPs/SPCE was investigated using techniques such as cyclic voltammetry (CV) and square wave voltammetry (SWV). The optimum experimental conditions were obtained including a 5 μL of 5.0 mg/mL NiONPs modifier, the voltammetric response of step potential 15 mV, amplitude 50 mV and frequency 50 Hz in 0.1 M BR buffer pH 13 as supporting electrolyte. The proposed method exhibited a linear relationship between the cathodic peak current and the concentration of 5-HMF in the concentration ranges of 0.5-5.0 ppm, with a limit of detection (LOD) of 0.24 ppm. The selectivity of the NiONPs/SPCE was evaluated by studying potential interferences commonly found in honey samples, and the results demonstrated excellent selectivity for 5-HMF detection. The reproducibility and stability of the NiONPs/SPCE were also assessed, with low relative standard deviations (RSD) obtained for both the cathodic peak current (2.94 %) and long-term stability (3.14 %). The developed NiONPs/SPCE method was successfully applied to the determination of 5-HMF in real honey samples, yielding comparable results to the standard HPLC method. This work showcases the potential of the NiONPs/SPCE as a practical and cost-effective electrochemical sensor for the accurate analysis of 5-HMF in honey samples.

Impact of nanotechnology on progress of flow methods in chemical analysis: A review

In evolution of instrumentation for analytical chemistry as crucial technological breakthroughs should be considered a common introduction of electronics with all its progress in integration, and then microprocessors which was followed by a widespread computerization. It is seems that a similar role can be attributed to the introduction of various elements of modern nanotechnology, observed with a fast progress since beginning of this century. It concerns all areas of the applications of analytical chemistry, including also progress in flow analysis, which are being developed since the middle of 20th century. Obviously, it should not be omitted the developed earlier and analytically applied planar structures like lipid membranes or self-assembled monolayers They had essential impact prior to discoveries of numerous extraordinary nanoparticles such as fullerenes, carbon nanotubes and graphene, or nanocrystalline semiconductors (quantum dots). Mostly, due to catalytic effects, significantly developed surface and the possibility of easy functionalization, their application in various stages of flow analytical procedures can significantly improve them. The application of new nanomaterials may be used for the development of new detection methods for flow analytical systems in macro-flow setups as well as in microfluidics and lateral flow immunoassay tests. It is also advantageous that quick flow conditions of measurements may be helpful in preventing unfavorable agglomeration of nanoparticles. A vast literature published already on this subject (e.g. almost 1000 papers about carbon nanotubes and flow-injection analytical systems) implies that for this reviews it was necessary to make an arbitrary selection of reported examples of this trend, focused mainly on achievements reported in the recent decade.

Sonoelectrochemical nitrided graphene nanosheets with vacancies and their applications for catalysis and sensing of uric acid oxidation

A sonoelectrochemical method for preparing N-doped defective graphene nanosheets (N/O-dGNs) with point defects and 5-9 or 5-8-5 vacancies and oxygen-containing groups was successfully demonstrated. In this one-pot approach, the N-bonding configuration and N content of N/O-dGNs were finely tuned by the ultrasonic power (192, 320, and 640 W). The N content in atomic percentage (at%) for N/O-dGN (N/O-dGN320W) with point defects and 5-8-5 vacancy prepared at 320 W power was 5.6 at%, greater than 3.0 at% and 2.6 at% for N/O-dGN with point defects and 5-9 vacancies at 192 W and 640 W power (N/O-dGN192W and N/O-dGN640W), respectively. N-bonding sites on N/O-dGN320W were dominantly amine N (2.1 at%) and pyrrolic N (2.4 at%). Additionally, the electrocatalytic activity of N/O-dGN192W, N/O-dGN320W, and N/O-dGN640W was successfully demonstrated for the sequential uric acid (UA) oxidation reaction (UOR), in which N/O-dGN320W displayed a significant mass activity (2.51 A/g). As in the transient catalysis of UOR, N/O-dGN320W with amine N showed 400.8 μA mM-1 cm-2 in sensitivity within a wide linear analysis range (1.5 × 10-2-6 mM) for amperometrically sensing UA. The results of real sample experiments using serum samples further demonstrated the potential of N/O-dGN320W as a non-enzymatic UA sensor.

Microneedle coupled epidermal sensor for multiplexed electrochemical detection of kidney disease biomarkers

Early diagnosis of chronic kidney disease (CKD) and constant monitoring to guide optimal intervention is critical to prevent renal failure and other critical diseases. However, the conventional blood tests in hospital are time-consuming and have poor patient compliance. Herein, we demonstrate a real-time, minimally invasive, and self-administrable approach to detect kidney biomarkers in the skin interstitial fluid (ISF) using a polymeric microneedle coupled electrochemical sensor array (MNESA). Microneedles can readily penetrate stratum corneum and quickly extract ISF onto the sensors. Four biomarkers are simultaneously detected to avoid false positive and provide an accurate assessment of kidney functions. Using an artificial skin model, it is shown that MNSEA gives specific and sensitive responses to these kidney biomarkers in physiologically relevant ranges (phosphate: 0.3-1.8 mM, 3.62 μA/mM; uric acid: 50-550 μM, 4.19 nA/μM; creatinine: 50-550 μM, 12.58 nA/μM; urea: 1-16 mM, 44.6 mV/decade). Using a mouse model, we demonstrate that this approach is as reliable as the commercial assays and is feasible to readily monitor the progression of CDK.

Autonomous capillary electrophoresis processing and analysis of dried blood spots for high-throughput determination of uric acid

A new set-up for fully autonomous and high-throughput capillary electrophoresis (CE) analyses of dried blood spot (DBS) samples is presented. The DBS samples were prepared by collecting exactly 5 μL of capillary blood from a finger-prick onto a pre-punched DBS disc in a disposable plastic CE vial and by in-vial blood drying. The vials with the DBS samples were then loaded into a commercial CE instrument for a fully unmanned sample processing and analysis. A fused-silica capillary of the CE instrument was first used for the transfer of 100 μL of elution solvent to each vial, in-vial DBS elution, and in-vial eluate homogenization. The same capillary was also used for at-line injection, separation, and selective analysis of the resulting eluates. Novel CE sequences were tailor-programmed for consecutive processing and analyses of multiple DBSs, which facilitated a fully autonomous determination of uric acid with a throughput of 240 DBS samples per day (24 h). The presented analytical protocol (using 100 μm i. d./30 cm capillary; 30 mM 2-(N-morpholino)-ethanesulfonic acid, 30 mM l-histidine, and 30 μM cetyltrimethylammonium bromide background electrolyte solution; and UV detection at 292 nm) provided excellent precision at endogenous and spiked uric acid concentrations with RSD values of peak areas below 3.2%. Calibration curves were linear over the 33.3 - 1200 μM range (R² better than 0.998), limits of detection and quantification in the original capillary blood were 10 and 33.3 μM, respectively, and were well below the uric acid clinical range (140-420 μM). The stability of uric acid in DBS samples stored at laboratory temperature for up to 2 months was also excellent demonstrating less than a 4.2% decrease in uric acid concentrations. The actual set-up might thus be highly attractive for clinical subjects and laboratories because it is minimally invasive and requires minimum intervention from laboratory staff.

Carbon Nanomaterials-Based Screen-Printed Electrodes for Sensing Applications

Electrochemical sensors consisting of screen-printed electrodes (SPEs) are recurrent devices in the recent literature for applications in different fields of interest and contribute to the expanding electroanalytical chemistry field. This is due to inherent characteristics that can be better (or only) achieved with the use of SPEs, including miniaturization, cost reduction, lower sample consumption, compatibility with portable equipment, and disposability. SPEs are also quite versatile; they can be manufactured using different formulations of conductive inks and substrates, and are of varied designs. Naturally, the analytical performance of SPEs is directly affected by the quality of the material used for printing and modifying the electrodes. In this sense, the most varied carbon nanomaterials have been explored for the preparation and modification of SPEs, providing devices with an enhanced electrochemical response and greater sensitivity, in addition to functionalized surfaces that can immobilize biological agents for the manufacture of biosensors. Considering the relevance and timeliness of the topic, this review aimed to provide an overview of the current scenario of the use of carbonaceous nanomaterials in the context of making electrochemical SPE sensors, from which different approaches will be presented, exploring materials traditionally investigated in electrochemistry, such as graphene, carbon nanotubes, carbon black, and those more recently investigated for this (carbon quantum dots, graphitic carbon nitride, and biochar). Perspectives on the use and expansion of these devices are also considered.

Construction of cationic polyfluorinated azobenzene/reduced graphene oxide for simultaneous determination of dopamine, uric acid and ascorbic acid

A highly sensitive cationic polyfluorinated azobenzene/reduced graphene oxide (C₃F₇-azo⁺/RGO) nanocomposite electrochemical sensor for simultaneous detection of dopamine (DA), ascorbic acid (AA) and uric acid (UA) was successfully synthesized using a facile exfoliation/restacking method. The nanocomposite is self-assembled from oppositely charged graphene oxide nanosheets (GO) and polyfluorinated azobenzene cations (C₃F₇-azo⁺), and then obtained by electrochemical reduction. The structure and electrochemical properties were characterized by X-ray diffraction (XRD), energy dispersive spectrometer analysis (EDS), transmission electron microscope (TEM) and scanning electron microscope (SEM). The electrochemical property of C₃F₇-azo⁺/RGO was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). It can be clearly seen from experimental results that C₃F₇-azo⁺/RGO-modified electrode (C₃F₇-azo⁺/RGO/GCE) can detect DA, AA and UA simultaneously, and has good stability and anti-interference performance. The detection limits are 65 nM, 8 nM and 11 nM for DA, AA and UA in the ranges 57.28-134.28 μM, 0.04-6.01 μM, 9.23-23.45 μM, respectively.

Metal Nanoparticles and Carbon-Based Nanomaterials for Improved Performances of Electrochemical (Bio)Sensors with Biomedical Applications

Monitoring human health for early detection of disease conditions or health disorders is of major clinical importance for maintaining a healthy life. Sensors are small devices employed for qualitative and quantitative determination of various analytes by monitoring their properties using a certain transduction method. A "real-time" biosensor includes a biological recognition receptor (such as an antibody, enzyme, nucleic acid or whole cell) and a transducer to convert the biological binding event to a detectable signal, which is read out indicating both the presence and concentration of the analyte molecule. A wide range of specific analytes with biomedical significance at ultralow concentration can be sensitively detected. In nano(bio)sensors, nanoparticles (NPs) are incorporated into the (bio)sensor design by attachment to the suitably modified platforms. For this purpose, metal nanoparticles have many advantageous properties making them useful in the transducer component of the (bio)sensors. Gold, silver and platinum NPs have been the most popular ones, each form of these metallic NPs exhibiting special surface and interface features, which significantly improve the biocompatibility and transduction of the (bio)sensor compared to the same process in the absence of these NPs. This comprehensive review is focused on the main types of NPs used for electrochemical (bio)sensors design, especially screen-printed electrodes, with their specific medical application due to their improved analytical performances and miniaturized form. Other advantages such as supporting real-time decision and rapid manipulation are pointed out. A special attention is paid to carbon-based nanomaterials (especially carbon nanotubes and graphene), used by themselves or decorated with metal nanoparticles, with excellent features such as high surface area, excellent conductivity, effective catalytic properties and biocompatibility, which confer to these hybrid nanocomposites a wide biomedical applicability.