Eliminating the Interference of Ascorbic Acid and Uric Acid to the Amperometric Glucose Biosensor by Cation Exchangers Membrane and Size Exclusion Membrane

Development of a nanocopper-decorated laser-scribed sensor for organophosphorus pesticide monitoring in aqueous samples

Organophosphorus pesticides are widely used in industrial agriculture and have been associated with water pollution and negative impacts on local ecosystems and communities. There is a need for testing technologies to detect the presence of pesticide residues in water sources, especially in developing countries where access to standard laboratory methods is cost prohibitive. Herein, we outline the development of a facile electrochemical sensor for amperometric determination of organophosphorus pesticides in environmental water samples. A three-electrode system was fabricated via UV laser-inscribing on a polyimide film. The working electrode was functionalized with copper nanoparticles with affinity toward organophosphate compounds. The sensor showed a limit of detection (LOD) of 3.42 ± 1.69 µM for glyphosate, 7.28 ± 1.20 µM for glufosinate, and 17.78 ± 7.68 µM for aminomethylphosphonic acid (AMPA). Sensitivity was highest for glyphosate (145.52 ± 36.73 nA⋅µM^-1⋅cm^-2) followed by glufosinate (56.98 ± 10.87 nA⋅µM^-1⋅cm^-2), and AMPA (30.92 ± 8.51 nA⋅µM^-1⋅cm^-2). The response of the sensor is not significantly affected by the presence of several ions and organic molecules commonly present in natural water samples. The developed sensor shows promising potential for facilitating environmental monitoring of organophosphorus pesticide residues, which is a current need in several parts of the world.

Glucose Biosensor Based on Dendritic Gold Nanostructures Electrodeposited on Graphite Electrode by Different Electrochemical Methods

In this research, we have demonstrated a one-step electrochemical deposition of dendritic gold nanostructures (DGNs) on a graphite rod (GR) electrode without any template, seeds, surfactants, or stabilizers. Three electrochemical methods, namely, constant potential amperometry (CPA), pulse amperometry, and differential pulse voltammetry, were used for DGN synthesis on GR electrode and further application in enzymatic glucose biosensors. Formed gold nanostructures, including DGNs, were characterized by a field emission scanning electron microscopy. The optimal concentration of HAuCl4 (6.0 mmol L−1), duration of DGNs synthesis (400 s), electrodeposition potential (−0.4 V), and the best electrochemical method (CPA) were determined experimentally. Then the enzyme, glucose oxidase, was adsorbed on the surface of DGNs and covalently cross-linked with glutaraldehyde vapor. The enzymatic glucose biosensor based on DGNs electrodeposited at optimal conditions and modified with glucose oxidase showed a quick response (less than 3 s), a high saturation current (291 μA), appropriate linear range (up to 9.97 mmol L−1 of glucose, R2 = 0.9994), good repeatability (RSD 2.4, 2.2 and 1.5% for 2, 30, 97 mmol L−1 of glucose), low limit of detection (0.059 mmol L−1, S/N = 3) and good stability. Additionally, this biosensor could be successfully applied for glucose determination in real samples with good accuracy. These results proved the principle of enzymatic glucose biosensor development based on DGNs as the basis for further investigations.

Catalytic effects of magnetic and conductive nanoparticles on immobilized glucose oxidase in skin sensors

Wearable skin sensors is a promising technology for real-time health care monitoring. They are of particular interest for monitoring glucose in diabetic patients. The concentration of glucose in sweat can be more than two orders of magnitude lower than in blood. In consequence, the scientific and technological efforts are focused in developing new concepts to enhance the sensitivity, decrease the limit of detection (LOD) and reduce the response time (RT) of glucose skin sensors. This work explores the effect of adsorbed superparamagnetic magnetite nanoparticles (MNPs) and conductive nanoparticles (CNPs) on carbon nanotube substrates (CNTs) used to immobilize glucose oxidase enzyme in the working electrode of skin sensors. MNPs and CNPs are made of magnetite and gold, respectively. The performance of the sensors was tested in standard buffer solution, artificial sweat, fresh sweat and on the skin of a healthy volunteer during an exercise session. In the case of artificial sweat, the presence of MNPs accelerated the RT from 7 to 5 s at the expense of increasing the LOD from 0.017 to 0.022 mM with slight increase of the sensitivity from 4.90 to 5.09μAm M^-1cm^-2. The presence of CNPs greatly accelerated the RT from 7 to 2 s and lowered the LOD from 0.017 to 0.014 mM at the expense of a great diminution of the sensitivity from 4.90 to 4.09μAm M^-1cm^-2. These effects were explained mechanistically by analyzing the changes in the concentration of free oxygen and electrons promoted by MNPs and CNPs in the CNTs and its consequences on the the glucose oxidation process.

Bis(2,2'-bipyridil)Copper(II) Chloride Complex: Tyrosinase Biomimetic Catalyst or Redox Mediator?

In this article, construction of amperometric sensor(s) based on screen-printed carbon electrodes covered by thin layers of two types of carbon nanomaterials serving as amplifiers, and containing [Cu(bipy)₂Cl]Cl∙5H₂O complex is reported. Their performance and biomimetic activity towards two selected neurotransmitters (dopamine and serotonin) was studied mainly using flow injection analysis (FIA). The important parameters of FIA such as working potential, flow rate, and pH were optimized. The mechanism of the catalytic activity is explained and experimentally confirmed. It reveals that presence of hydrogen peroxide plays a crucial role which leads to answer the title question: can presented complex really be considered as a tyrosinase biomimetic catalyst or only as a redox mediator?

Electrochemically Activated Conductive Ni-Based MOFs for Non-enzymatic Sensors Toward Long-Term Glucose Monitoring

Continuous intensive monitoring of glucose is one of the most important approaches in recovering the quality of life of diabetic patients. One challenge for electrochemical enzymatic glucose sensors is their short lifespan for continuous glucose monitoring. Therefore, it is of great significance to develop non-enzymatic glucose sensors as an alternative approach for long-term glucose monitoring. This study presented a highly sensitive and selective electrochemical non-enzymatic glucose sensor using the electrochemically activated conductive Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 MOFs as sensing materials. The morphology and structure of the MOFs were investigated by scanning SEM and FTIR, respectively. The performance of the activated electrode toward the electrooxidation of glucose in alkaline solution was evaluated with cyclic voltammetry technology in the potential range from 0.2 V to 0.6 V. The electrochemical activated Ni-MOFs exhibited obvious anodic (0.46 V) and cathodic peaks (0.37 V) in the 0.1 M NaOH solution due to the Ni(II)/Ni(III) transfer. A linear relationship between the glucose concentrations (ranging from 0 to 10 mM) and anodic peak currents with R2 = 0.954 was obtained. It was found that the diffusion of glucose was the limiting step in the electrochemical reaction. The sensor exhibited good selectivity toward glucose in the presence of 10-folds uric acid and ascorbic acid. Moreover, this sensor showed good long-term stability for continuous glucose monitoring. The good selectivity, stability, and rapid response of this sensor suggests that it could have potential applications in long-term non-enzymatic blood glucose monitoring.

Protein-Polymer Block Copolymer Thin Films for Highly Sensitive Detection of Small Proteins in Biological Fluids

In nearly all biosensors, sensitivity is greatly reduced for measurements conducted in biological matrices due to nonspecific binding from off-target molecules. One method to overcome this issue is to design a sensor that enables selective size-based uptake of proteins. Herein, a protein-polymer conjugate thin-film biosensor is fabricated that self-assembles into lamellae containing alternating domains of protein and polymer. Analyte is captured in protein regions while polymer domains restrict diffusion of large molecules. Device sensitivity and size-based exclusion properties are probed using two analytes: streptavidin (SA, 52.8 kDa) and monomeric streptavidin (mSA2, 15.6 kDa). Tuning domain spacing by adjusting polymer molecular weight allows the design of films that relatively freely uptake mSA2 and largely restrict SA diffusion. Furthermore, when detecting the smaller mSA2, no reduction in the limit of detection (LOD) is observed when transitioning from detection in the buffer to detection in biological fluids. As a result, LOD measured in fluid samples is reduced by 2 orders of magnitude compared to a traditional surface-immobilized protein monolayer.

A novel Cu-metal-organic framework with two-dimensional layered topology for electrochemical detection using flexible sensors

We present a novel Cu-metal-organic framework (MOF) with two-dimensional layered topology and techniques to integrate it with flexible sensors for electrochemical detection. The unique Cu-MOF is formed by coordinating Cu²⁺ ions with carboxylic oxygen groups, resulting in layered structures interlayerly connected by hydrogen bonds. The resulting flexible sensors exhibit capability in detecting ascorbic acid (AA), hydrogen peroxide (H₂O₂) and L-Histidine (L-His) with detection limits of 2.94, 4.1 and 5.3 μM, respectively. The linear ranges of the sensors compare favorably with other sensors based on rigid platforms that offer similar sensitivity. According to the result of cytotoxicity study, the MOFs-modified flexible sensors exhibit good biocompatibility to cells, suggesting potential use in in vivo chemical detection. The results presented here demonstrate applications of MOFs in facilitating highly stable electrochemical detection in flexible electronics, and provide fundamental knowledge about structure-dependent electrochemical properties of MOFs and changing behaviors of flexible MOFs membranes under external strain. More MOFs-based flexible sensors may be developed to explore different properties of MOFs by varying their compositions and structures for healthcare and clinic applications.

α-MoO3 nanostructure on carbon cloth substrate for dopamine detection

Orthorhombic molybdenum oxide (α-MoO₃) nanostructures were deposited on the surface of carbon cloth (CC) as a flexible and high conductive scaffold by reactive RF magnetron sputtering technique. Structure and morphology of the as prepared molybdenum coated carbon cloth (MoO₃CC) were thoroughly characterized with field emission scanning electron microscopy, x-ray diffraction, energy dispersive x-ray and Raman spectroscopy. Benefiting from high surface area and superior conductivity of CC as well as electrocatalytic activity of α-MoO₃ nanostructures, an electrochemical sensor was fabricated. The electrochemical behavior of this new sensor toward determination of dopamine was studied in detail by cyclic voltammetry, amperometry (AM) and square wave voltammetry (SWV). Results reported here reveal that using SWV not only enhances the sensitivity of sensors to dopamine by more than 14 times compared to AM, but also offers higher linear dynamic range (1-700 μM compared to 5-550 μM). Limit of detection, for signal to noise ratio 3, was calculated to be 0.48 μM. Applicability of the proposed sensor for measurement of dopamine in real samples, like urine and pharmaceutical formulation, was also evaluated that concluded to satisfactory results.

Three-Dimensional CeO2 Woodpile Nanostructures To Enhance Performance of Enzymatic Glucose Biosensors

Fabrication of detection elements with ultrahigh surface area is essential for improving the sensitivity of analyte detection. Here, we report a direct patterning technique to fabricate three-dimensional CeO₂ nanoelectrode arrays for biosensor application over relatively large areas. The fabrication approach, which employs nanoimprint lithography and a CeO₂ nanoparticle-based ink, enables the direct, high-throughput patterning of nanostructures and is scalable, integrable, and of low cost. With the convenience of sequential imprinting, multilayered woodpile nanostructures with prescribed numbers of layers were achieved in a "stacked-up" architecture and were successfully fabricated over large areas. To demonstrate application as a biosensor, an enzymatic glucose sensor was developed. The sensitivity of glucose sensors can be enhanced simply by increasing the number of layers, which multiplies surface area while maintaining a constant footprint. The four-layer woodpile nanostructure of CeO₂ glucose sensor exhibited enhanced sensitivity (42.8 μA mM^-1 cm^-2) and good selectivity. This direct imprinting strategy for three-dimensional sensing architectures is potentially extendable to other electroactive materials and other sensing applications.

Enzyme-Based Glucose Sensor: From Invasive to Wearable Device

Blood glucose concentration is a key indicator of patients' health, particularly for symptoms associated with diabetes mellitus. Because of the large number of diabetic patients, many approaches for glucose measurement have been studied to enable continuous and accurate glucose level monitoring. Among them, electrochemical analysis is prominent because it is simple and quantitative. This technology has been incorporated into commercialized and research-level devices from simple test strips to wearable devices and implantable systems. Although directly monitoring blood glucose assures accurate information, the invasive needle-pinching step to collect blood often results in patients (particularly young patients) being reluctant to adopt the process. An implantable glucose sensor may avoid the burden of repeated blood collections, but it is quite invasive and requires periodic replacement of the sensor owing to biofouling and its short lifetime. Therefore, noninvasive methods to estimate blood glucose levels from tears, saliva, interstitial fluid (ISF), and sweat are currently being studied. This review discusses the evolution of enzyme-based electrochemical glucose sensors, including materials, device structures, fabrication processes, and system engineering. Furthermore, invasive and noninvasive blood glucose monitoring methods using various biofluids or blood are described, highlighting the recent progress in the development of enzyme-based glucose sensors and their integrated systems.

Application of Semipermeable Membranes in Glucose Biosensing

Glucose biosensors have received significant attention in recent years due to the escalating mortality rate of diabetes mellitus. Although there is currently no cure for diabetes mellitus, individuals living with diabetes can lead a normal life by maintaining tight control of their blood glucose levels using glucose biosensors (e.g., glucometers). Current research in the field is focused on the optimization and improvement in the performance of glucose biosensors by employing a variety of glucose selective enzymes, mediators and semipermeable membranes to improve the electron transfer between the active center of the enzyme and the electrode substrate. Herein, we summarize the different semipermeable membranes used in the fabrication of the glucose biosensor, that result in improved biosensor sensitivity, selectivity, dynamic range, response time and stability.

Enzyme Biosensors for Biomedical Applications: Strategies for Safeguarding Analytical Performances in Biological Fluids

Enzyme-based chemical biosensors are based on biological recognition. In order to operate, the enzymes must be available to catalyze a specific biochemical reaction and be stable under the normal operating conditions of the biosensor. Design of biosensors is based on knowledge about the target analyte, as well as the complexity of the matrix in which the analyte has to be quantified. This article reviews the problems resulting from the interaction of enzyme-based amperometric biosensors with complex biological matrices containing the target analyte(s). One of the most challenging disadvantages of amperometric enzyme-based biosensor detection is signal reduction from fouling agents and interference from chemicals present in the sample matrix. This article, therefore, investigates the principles of functioning of enzymatic biosensors, their analytical performance over time and the strategies used to optimize their performance. Moreover, the composition of biological fluids as a function of their interaction with biosensing will be presented.

Sensitive electrochemical detection of vaccinia virus in a solution containing a high concentration of l-ascorbic acid

A new redox cycling scheme allows sensitive detection of vaccinia virus in a solution containing a high concentration of l-ascorbic acid.

Use of mercaptophenylboronic acid functionalized gold nanoparticles in a sensitive and selective dynamic light scattering assay for glucose detection in serum

A highly sensitive dynamic light scattering (DLS) assay for glucose detection without interference from ascorbic acid was demonstrated based on mercaptophenylboronic acid functionalized gold nanoparticles (MPBA-AuNPs). The stable, water-solubility MPBA-AuNPs were synthesized using facile and mild method. In the presence of glucose, specific binding between glucose and boronic acids resulted in the aggregation of MPBA-AuNPs. Thus, glucose could be detected by monitoring the average particle size change of the assay solution using DLS analysis. The detection limit was estimated to be around 10 nM. This assay also showed good selectivity, and glucose could be detected without interference even if 1 mM ascorbic acid was present. Furthermore, glucose in human serum was successfully detected here. Therefore, this sensitive and selective approach has the potential to become a new key for glucose detection.

Multilayer assembly of positively charged polyelectrolyte and negatively charged glucose oxidase on a 3D Nafion network for detecting glucose

In this paper, a novel amperometric glucose biosensor was constructed by alternative self-assembly of positively charged poly(diallydimethylammonium chloride) (PDDA) and negatively charged glucose oxidase (GOx) onto a 3D Nafion network via electrostatic adsorption. The amount of Nafion in the electrode and the number of the (PDDA/GOx)(n) multilayers were optimized to develop a sensitive and selective glucose biosensor. Under optimal conditions, the glucose biosensor with (PDDA/GOx)(5) multilayers exhibited remarkable electrocatalytic activity, capable of detecting glucose with enhanced sensitivity of 9.55 microA/mM cm(2) and a commendably low detection limit of 20 microM (S/N=3). A linear response range of 0.05-7 mM (a linear correlation coefficient of 0.9984, n=20) was achieved. In addition, the glucose biosensor demonstrated superior selectivity towards glucose over some interferents, such as ascorbic acid (AA) and uric acid (UA), at an optimized detection potential of 0.6 V versus Ag/AgCl reference.

Comparison of amperometric biosensors fabricated by palladium sputtering, palladium electrodeposition and Nafion/carbon nanotube casting on screen-printed carbon electrodes

Different strategies, including palladium electrodeposition (Pd(CV)), Pd sputtering (Pd(S)) and Nafion-solubilized carbon nanotube casting (Nafion/CNT), were used to modify screen-printed carbon electrodes (SPCEs) for the fabrication of amperometric enzyme biosensors. The electrochemical properties of the bare and modified SPCEs and the optimal conditions for surface modification were determined. The electrochemical response of the bare SPCE to H(2)O(2) under the potential of 0.3 V could be improved about 100-fold by Pd modification by electrodeposition or sputtering. By contrast, the electrochemical response of the bare SPCE was enhanced by only about 11-fold by Nafion/CNT casting. Moreover, the Pd(CV)-SPCEs exhibited better reproducibility of electrochemical response (a relative standard deviation (R.S.D.)<6.0%) than freshly prepared Pd(S)-SPCEs (R.S.D.>10%). The glucose biosensor fabricated from Pd-modified electrodes could be stored for up to 108 days without loosing significant activity. The Pd(CV)-SPCE also showed very reliable signal characteristics upon 50 consecutively repeated measurements of ascorbic acid. The electrocatalytic detection of the Pd-SPCE was combined with additional advantages of resistance to surface fouling and hence good stability. In conclusion, this study demonstrated that deposition of Pd thin film on SPCEs by electrodeposition or sputtering provided superior enhancement of electrochemical properties compared to Nafion/CNT-SPCEs. Despite their high electrochemical response, Pd(S)-SPCEs required an activation process to improve stability and Pd(CV)-SPCEs suffered from poor between electrode reproducibility.