Amperometric detection of glucose in fruit juices with polypyrrole-based biosensor with an integrated permselective layer for exclusion of interferences

Formation of MnO2-coated ITO electrodes with high catalytic activity for enzymatic glucose detection

We present the formation of a cheap and environmentally friendly working electrode material for glucose biosensors with good catalytic properties. The classic electrode in such devices consists of a conductive material modified with the enzyme glucose oxidase. The working principle is the electrochemical detection of hydrogen peroxide as a product of the enzymatic transformation of glucose. As a base material, we offer manganese dioxide; it is a natural highly selective catalyst for the decomposition of H2O2 and is electrochemically deposited onto the surface of ITO. We approached the formation of MnO2 films systematically. By changing parameters such as the deposition method, pH of the electrolyte, and the drying temperature of the precipitate, a series of electrodes were formed. These electrodes were characterized by SEM, electrochemical impedance spectroscopy, and XPS and their electrocatalytic activity was studied. Significant differences in the sensitivity of the electrodes were detected. The manganese dioxide film with the best catalytic characteristics is formed in the electrolyte with pH 1 by cyclic voltammetry and then drying at 60 °C. The surface of the electrode was then modified with a solution of GOx enzyme with a concentration of 2 mg ml-1 (100-250 units per mg solid). The sensitivity of such an electrode is 117.8 μA mmol-1 cm-2. The range of determined concentrations of glucose is from 0.1 mM to 3 mM. The sensitivity is comparable to that of electrodes based on expensive materials such as graphene and noble metals.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Chemical antifouling strategies in sensors for food analysis: A review

Surface biofouling induced by the undesired nonspecific adsorption of foulants (e.g., coexisting proteins and cells) in food matrices is a major issue of sensors for food analysis, hindering their reliability and accuracy of sensing. This issue can be addressed by developing antifouling strategies to prevent or alleviate nonspecific binding. Chemical antifouling strategies involve the use of chemical modifiers (i.e., antifouling materials) to strongly hydrate the surface and reduce surface biofouling. Through appropriate immobilization approaches, antifouling materials can be tethered onto sensors to form antifouling surfaces with well-ordered structures, balanced surface charges, and appropriate surface density and thickness. A rational antifouling surface can reduce the matrix effect, simplify sample pretreatment, and improve analytical performance. This review summarizes recent developments in chemical antifouling strategies in sensing. Surface antifouling mechanisms and common antifouling materials are described, and factors that may influence the antifouling effects of antifouling surfaces and approaches incorporating antifouling materials onto sensing surfaces are highlighted. Moreover, the specific applications of antifouling sensors in food analysis are introduced. Finally, we provide an outlook on future developments in antifouling sensors for food analysis.

Stimulus-Responsive DNA Hydrogel Biosensors for Food Safety Detection

Food safety has always been a major global challenge to human health and the effective detection of harmful substances in food can reduce the risk to human health. However, the food industry has been plagued by a lack of effective and sensitive safety monitoring methods due to the tension between the cost and effectiveness of monitoring. DNA-based hydrogels combine the advantages of biocompatibility, programmability, the molecular recognition of DNA molecules, and the hydrophilicity of hydrogels, making them a hotspot in the research field of new nanomaterials. The stimulus response property greatly broadens the function and application range of DNA hydrogel. In recent years, DNA hydrogels based on stimulus-responsive mechanisms have been widely applied in the field of biosensing for the detection of a variety of target substances, including various food contaminants. In this review, we describe the recent advances in the preparation of stimuli-responsive DNA hydrogels, highlighting the progress of its application in food safety detection. Finally, we also discuss the challenges and future application of stimulus-responsive DNA hydrogels.

Application of Polypyrrole-Based Electrochemical Biosensor for the Early Diagnosis of Colorectal Cancer

Although colorectal cancer (CRC) is easy to treat surgically and can be combined with postoperative chemotherapy, its five-year survival rate is still not optimistic. Therefore, developing sensitive, efficient, and compliant detection technology is essential to diagnose CRC at an early stage, providing more opportunities for effective treatment and intervention. Currently, the widely used clinical CRC detection methods include endoscopy, stool examination, imaging modalities, and tumor biomarker detection; among them, blood biomarkers, a noninvasive strategy for CRC screening, have shown significant potential for early diagnosis, prediction, prognosis, and staging of cancer. As shown by recent studies, electrochemical biosensors have attracted extensive attention for the detection of blood biomarkers because of their advantages of being cost-effective and having sound sensitivity, good versatility, high selectivity, and a fast response. Among these, nano-conductive polymer materials, especially the conductive polymer polypyrrole (PPy), have been broadly applied to improve sensing performance due to their excellent electrical properties and the flexibility of their surface properties, as well as their easy preparation and functionalization and good biocompatibility. This review mainly discusses the characteristics of PPy-based biosensors, their synthetic methods, and their application for the detection of CRC biomarkers. Finally, the opportunities and challenges related to the use of PPy-based sensors for diagnosing CRC are also discussed.

Poly(Thiophene)/Graphene Oxide-Modified Electrodes for Amperometric Glucose Biosensing

The availability of fast and non-expensive analytical methods for the determination of widespread interest analytes such as glucose is an object of large relevance; this is so not only in the field of analytical chemistry, but also in medicinal and in food chemistry. In this context, electrochemical biosensors have been proposed in different arrangements, according to the mode of electron transfer between the bioreceptor and the electrode. An efficient immobilization of an enzyme on the electrode surface is essential to assure satisfactory analytical performances of the biosensor in terms of sensitivity, limit of detection, selectivity, and linear range of employment. Here, we report the use of a thiophene monomer, (2,5-di(2-thienyl)thieno [3,2-b]thiophene (dTT-bT), as a precursor of an electrogenerated conducting film to immobilize the glucose oxidase (GOx) enzyme on Pt, glassy carbon (GC), and Au electrode surfaces. In addition, the polymer film electrochemically synthetized on a glassy carbon electrode was modified with graphene oxide before the deposition of GOx; the analytical performances of both the arrangements (without and with graphene oxide) in the glucose detection were compared. The biosensor containing graphene oxide showed satisfactory values of linear dynamic range (1.0-10 mM), limit of detection (0.036 mM), and sensitivity (9.4 µA mM^-1 cm^-2). Finally, it was tested in the determination of glucose in fruit juices; the interference from fructose, saccharose, and ascorbic acid was evaluated.

Ultrasensitive glucose detection from tears and saliva through integrating a glucose oxidase-coupled DNAzyme and CRISPR-Cas12a

The accurate and sensitive detection of glucose from secretory clinical samples, such as tears and saliva, remains a great challenge. In this research, a novel ultrasensitive glucose detection method consisting of a glucose oxidase (GOx), pistol-like DNAzyme (PLDz), and CRISPR-Cas12a system is proposed. First, the oxidation of glucose catalyzed by GOx leads to the production of H₂O₂; the self-cleavage activity of PLDz is activated after recognition of the produced H₂O₂. The two procedures triggered by COx and PLDz play an important role in accurately identifying glucose and converting glucose signals to nucleic acids. The obtained PLDz fragments can be recognized by the Cas12 enzyme and thus activate the trans-cleavage activity of the Cas12a enzyme. Finally, the surrounding reporter probes are cut by the Cas12a enzyme to produce fluorescence signals. In summary, an ultra-sensitive and specific fluorescence method has been developed for glucose detection from secretory clinical samples, which could potentially contribute to the noninvasive diagnosis of diabetes mellitus.

Silicon Carbide Nanoparticles based Nanofibrous Membrane in Comparison with Thin-Film Enzymatic Glucose Sensor

This work presents, silicon carbide nanoparticles (SiCNPs) embedded in a conductive polymer (CP) to be electrospun to fabricate a nanofibrous membrane and a thin-film. Electrochemical enzymatic glucose sensing mechanism of an electrospun nanofibrous membrane (ENFM) of SiCNPs in a CP compared to a spin-coated-thin-film (SCTF) of SiCNPs in a CP. Fiber alignment in the form of a matrix is a key factor that determines the physical properties of nanofiber membrane compared to thin-film. It is found that glucose sensing electrodes formed by a SiCNPs-ENFM has enhanced binding of the glucose oxidase (GOx) enzyme within the fibrous membrane as compared to a SiCNPs-SCTF. The SiCNPs-ENFM and SiCNPs-SCTF glucose sensing electrodes were characterized for morphology by using scanning electron microscopy (SEM) and for electrochemical activity by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) methods. SiCNPs-ENFM based glucose electrodes shown a detection range from a 0.5 mM to 20 mM concentration with a better sensitivity of 387.57 μA/gmMcm2, and low limit of detection (LOD) 552.89 nM compared to SiCNPs-SCTF with sensitivity of 6.477 μA/gmMcm2 and LOD of 60.87 μM. The change in current level with SiCNPs-ENFM was ~14% contrast to ~75% with the SiCNPs-SCTF based glucose sensor over 50 days. The electrochemical analysis results demonstrated that the SiCNPs-ENFM electrode provides enhanced sensitivity, better limit of detection (LOD), and durability compared to SiCNPs-SCTF based glucose sensing electrode.

E-Tongues/Noses Based on Conducting Polymers and Composite Materials: Expanding the Possibilities in Complex Analytical Sensing

Conducting polymers (CPs) are extensively studied due to their high versatility and electrical properties, as well as their high environmental stability. Based on the above, their applications as electronic devices are promoted and constitute an interesting matter of research. This review summarizes their application in common electronic devices and their implementation in electronic tongues and noses systems (E-tongues and E-noses, respectively). The monitoring of diverse factors with these devices by multivariate calibration methods for different applications is also included. Lastly, a critical discussion about the enclosed analytical potential of several conducting polymer-based devices in electronic systems reported in literature will be offered.

Silicon carbide nanoparticles electrospun nanofibrous enzymatic glucose sensor

This paper presents an electrospun-nanofibrous-membrane (ENFM) of silicon carbide nanoparticles (SiCNPs) with a conductive polymer (CP) for an electrochemical enzymatic glucose sensor. The surface area of a fiber matrix is a key physical property of a nanofiber membrane for enzyme binding. It is found that glucose sensing electrodes, having a SiCNPs-ENFM nanostructure, show enhanced binding of glucose oxidase (GO_x) enzyme within the fibrous membrane. Morphological characterization of SiCNPs based ENFM was performed by using scanning electron microscopy (SEM) and using transmission electron microscopy (TEM) for SiC nanoparticles. The electrochemical analysis of SiCNPs-ENFM electrode was conducted by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) methods. Glucose concentration was detected at +0.6 V in a 5 mM potassium ferricyanide electrolyte. SiCNPs-ENFM based glucose electrodes show a detection range from 0.5 mM to 20 mM concentration with the sensitivity of 30.75 μA/mM cm² and the detection limit was 0.56 μM. The lower change in current response for SiCNPs-ENFM based glucose sensing electrodes was observed for a 50 day period.

Cultivation of Saccharomyces cerevisiae with Feedback Regulation of Glucose Concentration Controlled by Optical Fiber Glucose Sensor

Glucose belongs among the most important substances in both physiology and industry. Current food and biotechnology praxis emphasizes its on-line continuous monitoring and regulation. These provoke increasing demand for systems, which enable fast detection and regulation of deviations from desired glucose concentration. We demonstrated control of glucose concentration by feedback regulation equipped with in situ optical fiber glucose sensor. The sensitive layer of the sensor comprises oxygen-dependent ruthenium complex and preimmobilized glucose oxidase both entrapped in organic–inorganic polymer ORMOCER^®. The sensor was placed in the laboratory bioreactor (volume 5 L) to demonstrate both regulations: the control of low levels of glucose concentrations (0.4 and 0.1 mM) and maintenance of the glucose concentration (between 2 and 3.5 mM) during stationary phase of cultivation of Saccharomyces cerevisiae. Response times did not exceed 6 min (average 4 min) with average deviation of 4%. Due to these regulation characteristics together with durable and long-lasting (≥2 month) sensitive layer, this feedback regulation system might find applications in various biotechnological processes such as production of low glucose content beverages.

DFT Prediction of Factors Affecting the Structural Characteristics, the Transition Temperature and the Electronic Density of Some New Conjugated Polymers

Conjugated polymers are promising materials for various cutting-edge technologies, especially for organic conducting materials and in the energy field. In this work, we have synthesized a new conjugated polymer and investigated the effect of distance between bond layers, side-chain functional groups (H, Br, OH, OCH3 and OC2H5) on structural characteristics, phase transition temperature (T), and electrical structure of C13H8OS using Density Functional Theory (DFT). The structural characteristics were determined by the shape, network constant (a, b and c), bond length (C-C, C-H, C-O, C-S, C-Br and O-H), phase transition temperatures, and the total energy (Etot) on a base cell. Our finding shows that the increase of layer thickness (h) of C13H8OS-H has a negligible effect on the transition temperature, while the energy bandgap (Eg) increases from 1.646 eV to 1.675 eV. The calculation of bond length with different side chain groups was carried out for which C13H8OS-H has C-H = 1.09 Å; C13H8OS-Br has C-Br = 1.93 Å; C13H8OS-OH has C-O = 1.36 Å, O-H = 0.78 Å; C13H8OS-OCH3 has C-O = 1.44 Å, O-H =1.10 Å; C13H8OS-OC2H5 has C-O = 1.45 Å, C-C = 1.51Å, C-H = 1.10 Å. The transition temperature (T) for C13H8OS-H was 500 K < T < 562 K; C13H8OS-Br was 442 K < T < 512 K; C13H8OS-OH was 487 K < T < 543 K; C13H8OS-OCH3 was 492 K < T < 558 K; and C13H8OS-OC2H5 was 492 K < T < 572 K. The energy bandgap (Eg) of Br is of Eg = 1.621 eV, the doping of side chain groups H, OH, OCH3, and OC2H5, leads to an increase of Eg from 1.621 eV to 1.646, 1.697, 1.920, and 2.04 eV, respectively.

Advances in nanomaterial application in enzyme-based electrochemical biosensors: a review

Electrochemical enzyme-based biosensors are one of the largest and commercially successful groups of biosensors. Integration of nanomaterials in the biosensors results in significant improvement of biosensor sensitivity, limit of detection, stability, response rate and other analytical characteristics. Thus, new functional nanomaterials are key components of numerous biosensors. However, due to the great variety of available nanomaterials, they should be carefully selected according to the desired effects. The present review covers the recent applications of various types of nanomaterials in electrochemical enzyme-based biosensors for the detection of small biomolecules, environmental pollutants, food contaminants, and clinical biomarkers. Benefits and limitations of using nanomaterials for analytical purposes are discussed. Furthermore, we highlight specific properties of different nanomaterials, which are relevant to electrochemical biosensors. The review is structured according to the types of nanomaterials. We describe the application of inorganic nanomaterials, such as gold nanoparticles (AuNPs), platinum nanoparticles (PtNPs), silver nanoparticles (AgNPs), and palladium nanoparticles (PdNPs), zeolites, inorganic quantum dots, and organic nanomaterials, such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), carbon and graphene quantum dots, graphene, fullerenes, and calixarenes. Usage of composite nanomaterials is also presented.

Stability and Stabilization of Enzyme Biosensors: The Key to Successful Application and Commercialization

Fifty-five years have passed and more than 100,000 articles have been published since the first report of an electrochemical enzyme biosensor. However, very few biosensors have reached practical application and commercialization. The bulk of the research effort has been on increasing sensitivity and selectivity. In contrast, the number of publications dealing with stability or stabilization of enzyme biosensors is very small. Here, we critically review enzyme stabilization strategies as well as the progress that has been done in the past 20 years with respect to enzyme biosensor stabilization. Glucose oxidase, lactate oxidase, alcohol oxidase, and xanthine oxidase are the focus of this review because of their potential applications in food. The inconsistency in reporting biosensor stability was identified as a critical hurdle to research progress in this area. Fundamental questions that remain unanswered are outlined.

Conducting Polymers, Hydrogels and Their Composites: Preparation, Properties and Bioapplications

This review is focused on current state-of-the-art research on electroactive-based materials and their synthesis, as well as their physicochemical and biological properties. Special attention is paid to pristine intrinsically conducting polymers (ICPs) and their composites with other organic and inorganic components, well-defined micro- and nanostructures, and enhanced surface areas compared with those of conventionally prepared ICPs. Hydrogels, due to their defined porous structures and being filled with aqueous solution, offer the ability to increase the amount of immobilized chemical, biological or biochemical molecules. When other components are incorporated into ICPs, the materials form composites; in this particular case, they form conductive composites. The design and synthesis of conductive composites result in the inheritance of the advantages of each component and offer new features because of the synergistic effects between the components. The resulting structures of ICPs, conducting polymer hydrogels and their composites, as well as the unusual physicochemical properties, biocompatibility and multi-functionality of these materials, facilitate their bioapplications. The synergistic effects between constituents have made these materials particularly attractive as sensing elements for biological agents, and they also enable the immobilization of bioreceptors such as enzymes, antigen-antibodies, and nucleic acids onto their surfaces for the detection of an array of biological agents. Currently, these materials have unlimited applicability in biomedicine. In this review, we have limited discussion to three areas in which it seems that the use of ICPs and materials, including their different forms, are particularly interesting, namely, biosensors, delivery of drugs and tissue engineering.

Electronic properties of the polypyrrole-dopant anions ClO4- and MoO42-: a density functional theory study

The conductive properties of polypyrrole chains doped with ClO₄^- or MoO₄^2- anions and the existence of polarons and bipolarons in these doped polypyrrole chains were investigated by performing computational calculations based on density functional theory (DFT). Doping with these anions was found to decrease the band gap of the polypyrrole. Theoretical calculations revealed that changing the type of oxidative agent applied does not affect the conversion of polypyrrole into a conducting polymer, but the conductivity of the doped polypyrrole does depend on the ratio of oxidant to polypyrrole.

In situ gold-nanoparticle electrogeneration on gold films deposited on paper for non-enzymatic electrochemical determination of glucose

This work describes the development and evaluation of a new electrochemical platform based on the sustainable generation of gold-nanoparticles on paper-based gold-sputtered electrodes. The disposable porous paper electrode is combined with screen-printed electrodes for ensuring a precise electrogeneration of nanoparticles and also for the evaluation of these simple, versatile and low-cost microfluidic devices. Two types of chromatographic paper with different thicknesses have been evaluated. Paper gold working electrodes modified with gold nanoparticles were characterized by scanning electron microscopy and cyclic voltammetry using potassium ferrocyanide as a common redox probe, showing an improved electrochemical performance when compared to bare gold electrodes. The platform has been applied to the non-enzymatic determination of glucose, molecule of enormous interest. The porous gold structure made by sputtering on paper, modified with electrogenerated nanoparticles allowed precise and accurate determination of the analyte in beverages at low potential.