An electrochemical sensor based on a Co3O4-ERGO nanocomposite modified screen-printed electrode for detection of uric acid in artificial saliva

Voltammetric Determination of Salbutamol, Sulfamethoxazole, and Trimethoprim as Anthropogenic Impact Indicators Using Commercial Screen-Printed Electrodes

A voltammetric method based on the use of screen-printed carbon electrodes (SPCEs) is presented for the simultaneous determination of salbutamol (SAL), sulfamethoxazole (SMX), and trimethoprim (TMP), with high sensitivity, fast response, and excellent repeatability and reproducibility. Under the optimal voltammetric conditions, the simultaneous analysis showed linear ranges of 0.3-2.5 mg L-1, 0.3-11.1 mg L-1, and 0.5-9.0 mg L-1 for SAL, SMX, and TMP, respectively, and detection limits of 83.8 μg L-1, 88.7 μg L-1, and 139.2 μg L-1, respectively. Additionally, the developed method was successfully validated by the analysis of a spiked river water sample with satisfactory recovery values in the range of 97.0-98.8%. The added value of the presented method relays in combining cost-effective disposable SPCEs with rapid analysis (<30 s), providing portable electrochemical tools for the on-site monitoring of pharmaceutical residues, which is critical for addressing contamination linked to anthropogenic activity.

Advanced detection of the protozoacide dimetridazole in complex fluids using cassiterite nanoparticles incorporated carbon black composite

Dimetridazole (DMT), a nitroimidazole used in veterinary medicine for treating protozoan infections, poses significant carcinogenic and mutagenic risks, necessitating precise monitoring to ensure food safety. We report the development of an advanced electrochemical sensor based on a glassy carbon electrode (GCE) modified with a nanostructured cassiterite (SnO2)/carbon black (CB) composite, synthesized via hydrothermal and sonochemical techniques. The sensor benefits from SnO2's high electrical conductivity, chemical stability, and large bandgap, while CB enhances its performance with superior conductivity. Characterization through various techniques confirmed the composite's nanostructured morphology with an average particle size of 18 nm. Electrochemical analyses revealed a limit of detection (LOD) of 0.004 μM, a limit of quantification (LOQ) of 0.011 μM, and a wide linear range from 0.29 to 204.6 μM. The sensor demonstrated excellent repeatability and reproducibility, with a relative standard deviation (RSD) of 1.6 % and 2.3 %. It also exhibited notable storage stability, retaining 95.8 % of its initial response after 12 days. Real sample analyses showed impressive recovery rates of 97.5 % to 106.4 % for DMT in complex fluids such as food products, biological fluids, synthetic fluids, and environmental samples.

Fluid-specific detection of environmental pollutant moxifloxacin hydrochloride utilizing a rare-earth niobate decorated functionalized carbon nanofiber sensor platform

The development of precise and efficient detection methods is essential for the real-time monitoring of antibiotics, especially in environmental and biological matrices. This study aims to address this challenge by introducing a novel electrochemical sensor for the targeted detection of moxifloxacin hydrochloride (MFN), a fourth-generation fluoroquinolone. The sensor is based on a holmium niobate (HNO) and functionalized carbon nanofiber (f-CNF) nanocomposite, synthesized via a hydrothermal approach and subsequently characterized for its structural and electrochemical properties. When deposited onto a glassy carbon electrode (GCE), the HNO/f-CNF nanocomposite demonstrated exceptional electrochemical performance, as assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The sensor exhibited remarkable sensitivity, with a detection limit of 0.034 μM, a quantification limit of 0.11 μM, and a sensitivity of 0.69 μA μM-1 cm-2. It also achieved a broad linear detection range from 0.001 μM to 1166.11 μM, making it highly effective for MFN detection across various complex matrices, including environmental waters, biological fluids, and artificial saliva, with recovery rates between 98.15% and 101.75%. The novelty of this work lies in the unique combination of HNO's catalytic properties and f-CNF's enhanced electron transport, establishing a highly selective and sensitive platform for MFN detection. This sensor not only advances the field of electrochemical sensing but also offers a promising tool for real-time environmental and pharmaceutical monitoring.

Nanocubic cobalt-containing Prussian blue analogue-derived carbon-coated CoFe alloy nanoparticles for noninvasive uric acid sensing

This work describes an electrochemical sensor for the fast noninvasive detection of uric acid (UA) in saliva. The sensing material was based on a cobalt-containing Prussian blue analogue (Na2-xCo[Fe(CN)6]1-y, PCF). By optimizing the ratio of Co and Fe as 1.5 : 1 in PCF (PCF1.5,0), particles with a regular nanocubic morphology were formed. The calcination of PCF1.5,0 produced a carbon-coated CoFe alloy (CCF1.5), which possessed abundant defects and achieved an excellent electrochemical performance. Subsequently, CCF1.5 was modified on a screen-printed carbon electrode (SPCE) to fabricate the electrochemical sensor, CCF1.5/SPCE, which showed a sensitive and selective response toward salivary UA owing to its good conductivity, sufficient surface active sites and efficient catalytic activity. The determination of UA in artificial saliva achieved the wide linear range of 40 nM-30 μM and the low limit of detection (LOD) of 15.3 nM (3σ/s of 3). The performances of the sensor including its reproducibility, stability and selectivity were estimated to be satisfactory. The content of UA in human saliva was determined and the recovery was in the range of 98-107% and the total RSD was 4.14%. The results confirmed the reliability of CCF1.5/SPCE for application in noninvasive detection.

Thiacalix[4]arene-based metal-organic framework/reduced graphene oxide composite for electrochemical detection of chlorogenic acid

A novel metal-organic framework [Co2LCl4]·2DMF (Co-L) based on thiacalix[4]arene derivative was synthesized using the solvothermal method. Then Co-L was respectively mixed with reduced graphene oxide (RGO), multi-walled carbon nanotubes (MWCNT) and mesoporous carbon (MC) to prepare corresponding composite materials. PXRD, SEM and N2 adsorption-desorption illustrated that composite materials have been successfully prepared. After optimizing experimental conditions for detecting chlorogenic acid (CGA), the Co-L@RGO(1:1) composite material showed the optimal electrocatalytic activity for CGA, which may be because RGO possessed large specific surface area and hydroxyl and carboxyl groups that could form hydrogen-bonding with the oxide of CGA. Benefiting from the synergetic effect of Co-L and RGO, the glassy carbon electrode modified with Co-L@RGO(1:1) (Co-L@RGO(1:1)/GCE) exhibited a low limit of detection (LOD) of 7.24 nM for CGA within the concentration of 0.1-2 μM and 2-20 μM. Co-L@RGO(1:1)/GCE also showed excellent selectivity, stability, and reproducibility for the CGA detection. Co-L@RGO(1:1)/GCE could detect the CGA in honeysuckle with satisfactory results. This work provided a great example for the thiacalix[4]arene-based MOF in the application of electrochemical sensors.

A lab-made screen-printed sensing strip for sensitive and selective electrochemical detection of butylated hydroxyanisole

This study describes the fabrication of a lab-made screen-printed electrode (LabSPE) and its sensing ability for the detection of butylated hydroxyanisole (BHA) which is a synthetic antioxidant utilized widely in food industries. The lab-made screen-printed electrodes were printed on a polycarbonate substrate stepwise via a screen-printing technique using various inks suitable for electrode templates and then modified for the detection of BHA. As for the design of the sensor, firstly, graphitic carbon nitride (g-C₃N₄) was synthesized electrochemically through the one-pot synthesis method. After the synthesis of Fe₃O₄ nanoparticles (Fe₃O₄ NPs), the surface of SPE was modified with the dual composite consisting of g-C₃N₄ and Fe₃O₄ NPs. Lastly, platinum nanoparticles (Pt NPs) were deposited electrochemically on the modified electrode in 0.5 M HCl solution containing 2 mM H₂PtCl₆ at a constant potential of 0.25 V for 45 s. After optimization of varied parameters such as pH of the electrolyte solution, deposition time, and deposition potential, the current responses of the sensor (Pt/g-C₃N₄-Fe₃O₄/LabSPE) toward BHA displayed linearity in the wide concentration range of 0.25 μM to 90 μM with a low detection limit of 0.053 μM. The selectivity of Pt/g-C₃N₄-Fe₃O₄/SPE was tested successfully in the presence of other antioxidants (BHT, TBHQ, GA, and PG). Moreover, the applicability of the proposed sensor for practical tests was verified by the detection of BHA in commercial samples.

Highly Sensitive Electrochemical Non-Enzymatic Uric Acid Sensor Based on Cobalt Oxide Puffy Balls-like Nanostructure

Early-stage uric acid (UA) abnormality detection is crucial for a healthy human. With the evolution of nanoscience, metal oxide nanostructure-based sensors have become a potential candidate for health monitoring due to their low-cost, easy-to-handle, and portability. Herein, we demonstrate the synthesis of puffy balls-like cobalt oxide nanostructure using a hydrothermal method and utilize them to modify the working electrode for non-enzymatic electrochemical sensor fabrication. The non-enzymatic electrochemical sensor was utilized for UA determination using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The puffy balls-shaped cobalt oxide nanostructure-modified glassy carbon (GC) electrode exhibited excellent electro-catalytic activity during UA detection. Interestingly, when we compared the sensitivity of non-enzymatic electrochemical UA sensors, the DPV technique resulted in high sensitivity (2158 µA/mM.cm²) compared to the CV technique (sensitivity = 307 µA/mM.cm²). The developed non-enzymatic electrochemical UA sensor showed good selectivity, stability, reproducibility, and applicability in the human serum. Moreover, this study indicates that the puffy balls-shaped cobalt oxide nanostructure can be utilized as electrode material for designing (bio)sensors to detect a specific analyte.

Electrochemical Ultrasensitive Sensing of Uric Acid on Non-Enzymatic Porous Cobalt Oxide Nanosheets-Based Sensor

Transition metal oxide (TMO)-based nanomaterials are effectively utilized to fabricate clinically useful ultra-sensitive sensors. Different nanostructured nanomaterials of TMO have attracted a lot of interest from researchers for diverse applications. Herein, we utilized a hydrothermal method to develop porous nanosheets of cobalt oxide. This synthesis method is simple and low temperature-based. The morphology of the porous nanosheets like cobalt oxide was investigated in detail using FESEM and TEM. The morphological investigation confirmed the successful formation of the porous nanosheet-like nanostructure. The crystal characteristic of porous cobalt oxide nanosheets was evaluated by XRD analysis, which confirmed the crystallinity of as-synthesized cobalt oxide nanosheets. The uric acid sensor fabrication involves the fixing of porous cobalt oxide nanosheets onto the GCE (glassy carbon electrode). The non-enzymatic electrochemical sensing was measured using CV and DPV analysis. The application of DPV technique during electrochemical testing for uric acid resulted in ultra-high sensitivity (3566.5 µAmM^-1cm^-2), which is ~7.58 times better than CV-based sensitivity (470.4 µAmM^-1cm^-2). Additionally, uric acid sensors were tested for their selectivity and storage ability. The applicability of the uric acid sensors was tested in the serum sample through standard addition and recovery of known uric acid concentration. This ultrasensitive nature of porous cobalt oxide nanosheets could be utilized to realize the sensing of other biomolecules.

Straw-sheaf-like Co3O4 for preparation of an electrochemical non-enzymatic glucose sensor

3D straw-sheaf-like cobalt oxide (SS-Co₃O₄) was prepared via the hydrothermal method and inert gas calcination of precursors without the assistance of any template or surfactant. It was composed of numerous nanoneedles with a length of ~ 8 µm and a diameter of ~ 30 nm strongly tied in the center. The SS-Co₃O₄ exhibited high crystallinity, a large surface area (39.01 m².g^-1), a smaller pore size (6 nm), and lower charge transfer resistance (R_ct = 9.35 Ω) at the electrode/electrolyte interface. A non-enzymatic glucose oxidizing electrode fabricated with SS-Co₃O₄ showed a high sensitivity (669 µA.mM^-1.cm^-2), wide linear range (0.04-4.85 mM), low limit of detection (0.31 µM), good selectivity, fast response time (5 s), and high reproducibility with a relative standard deviation of 2.25%. In addition, its robust structure demonstrated excellent electrochemical stability by retaining 83.8% of the initial sensitivity when its current density vs. time response was measured for 75 min in bare electrolytes prior to the glucose-sensing test. Furthermore, it demonstrated excellent repeatability performance by retaining 87.0% of the initial sensitivity when a single electrode was tested for 4 cycles. The proposed robust structured 3D SS-Co₃O₄ electrode successfully responds to the content of glucose in human saliva, which substantially proves its suitability in practical application. The synthesis technique is advantageous to prepare other metal oxides with interesting morphology and robust structure for the development of more reliable non-enzymatic glucometers and other electrochemical devices.

Point-of-care biochemical assays using electrochemical technologies: approaches, applications, and opportunities

Against the backdrop of hidden symptoms of diseases and limited medical resources of their investigation, in vitro diagnosis has become a popular mode of real-time healthcare monitoring. Electrochemical biosensors have considerable potential for use in wearable products since they can consistently monitor the physiological information of the patient. This review classifies and briefly compares commonly available electrochemical biosensors and the techniques of detection used. Following this, the authors focus on recent studies and applications of various types of sensors based on a variety of methods to detect common compounds and cancer biomarkers in humans. The primary gaps in research are discussed and strategies for improvement are proposed along the dimensions of hardware and software. The work here provides new guidelines for advanced research on and a wider scope of applications of electrochemical biosensors to in vitro diagnosis.

Electrochemical Sensor Nanoarchitectonics for Sensitive Detection of Uric Acid in Human Whole Blood Based on Screen-Printed Carbon Electrode Equipped with Vertically-Ordered Mesoporous Silica-Nanochannel Film

Screen-printed carbon electrodes (SPCEs) bear great potential in the detection of biomarker in clinical samples with low sample consumption. However, modification of electrode surfaces to improve the anti-interference ability and sensitivity is highly desirable for direct electroanalysis of whole blood samples. Here, a reliable and miniaturized electrochemical sensor is demonstrated based on SPCE equipped with vertically-ordered mesoporous silica-nanochannel film (VMSF). To achieve stable binding of VMSF and improve the electrocatalytic performance, electrochemically reduced graphene oxide (ErGO) is applied as a conductive adhesion layer, that is in situ reduced from GO nanosheets during fast growth (less than 10 s) of amino groups modified VMSF (NH2-VMSF) using electrochemically assisted self-assembly (EASA). In comparison with bare SPCE, NH2-VMSF/ErGO/SPCE exhibits decreased oxidation potential of uric acid (UA) by 147 mV owing to significant electrocatalytic ability of ErGO. The dual signal amplification based on electrocatalysis of ErGO and enrichment of nanochannels leads to enhanced peak current by 3.9 times. Thus, the developed NH2-VMSF/ErGO/SPCE sensor enables sensitive detection of UA in the range from 0.5 μM to 180 μM with a low limit of detection (LOD, 129 nM, S/N = 3). Owing to good anti-fouling ability and high selectivity of the sensor, direct and rapid detection of UA in human whole blood is realized with very low sample consumption (50 μL).

A non-enzymatic electrochemical sensor composed of nano-berry shaped cobalt oxide nanostructures on a glassy carbon electrode for uric acid detection

Non-enzymatic electrochemical uric acid sensor fabrication with excellent performance using nano-berry shaped cobalt oxide nanostructures on a glassy carbon electrode.