Polypyrrole based next generation electrochemical sensors and biosensors: A review

Investigation of spectroscopic and electrical properties of doped poly(pyrrole-3-carboxylic acid)

The spectroscopic and electrical properties of poly(pyrrole-3-carboxylic acid) doped with p-TSA- (p-toluenesulfonate) and AQS- (anthraquinone sulfonate) were investigated. The variation in electrical conductivity as a function of temperature shows that the systems have semiconductor-like electrical characteristics. The investigated polymers exhibit 3D conductivity and less than 0.6 eV energy gaps. The IR and Raman spectra show that the charge carriers are polarons and bipolarons. Doping the poly(pyrrole-3-carboxylic acid) increases the number of charge carriers. Electron paramagnetic resonance has shown that localized polarons and bipolarons are formed within these polymers.

Synthesis and characterization of polysaccharide-cryogel and its application to the electrochemical detection of DNA

The main goal of our study is to demonstrate the applicability of the PPy-cryogel-modified electrodes for electrochemical detection of DNA. First, a polysaccharide-based cryogel was synthesized. This cryogel was then used as a template for chemical polypyrrole synthesis. This prepared polysaccharide-based conductive cryogel was used for electrochemical biosensing on DNA. Carrageenan (CG) and sodium alginate (SA) polysaccharides, which stand out as biocompatible materials, were used in cryogel synthesis. Electron transfer was accelerated by polypyrrole (PPy) synthesized in cryogel networks. A 2B pencil graphite electrode with a diameter of 2.00 mm was used as a working electrode. The prepared polysaccharide solution was dropped onto a working electrode as a support material to improve the immobilization capacity of biomolecules and frozen to complete the cryogelation step. PPy synthesis was performed on the electrodes whose cryogelation process was completed. In addition, the structures of cryogels synthesized on the electrode surface were characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Surface characterization of the modified electrodes was performed by energy-dispersive X-ray spectroscopy (EDX) analysis. Electrochemical determination of fish sperm DNA (fsDNA) was performed using a PPy-cryogel-modified electrode. The use of a porous 3D cryogel intermediate material enhanced the signal by providing a large surface area for the synthesis of PPy and increasing the biomolecule immobilization capacity. The detection limit was 0.98 µg mL-1 in the fsDNA concentration range 2.5-20 µg mL-1. The sensitivity of the DNA biosensor was estimated to 14.8 µA mM-1 cm-2. The stability of the biosensor under certain storage conditions was examined and observed to remain 66.95% up to 45 days.

Monitoring of Specific Phytoestrogens by Dedicated Electrochemical Sensors: A Review

Phytoestrogens are non-steroidal estrogens produced from plants that can bind with the human body's estrogenic receptor site and be used as a substitute for maintaining hormonal balance. They are mainly classified as flavonoids, phenolic acids, lignans, stilbenes, and coumestans; some are resocyclic acids of lactones, which are mycotoxins and not natural phytoestrogen. Phytoestrogens have many beneficial medicinal properties, making them an important part of the daily diet. Electrochemical sensors are widely used analytical tools for analysing various pharmaceuticals, chemicals, pollutants and food items. Electrochemical sensors provide an extensive platform for highly sensitive and rapid analysis. Several reviews have been published on the importance of the biological and medicinal properties of phytoestrogens. However, this review provides an overview of recent work performed through electrochemical measurements with electrochemical sensors and biosensors for all the classes of phytoestrogens done so far since 2019.

Insights into properties, synthesis and emerging applications of polypyrrole-based composites, and future prospective: A review

Recent advancements in polymer science and engineering underscore the importance of creating sophisticated soft materials characterized by well-defined structures and adaptable properties to meet the demands of emerging applications. The primary objective of polymeric composite technology is to enhance the functional utility of materials for high-end purposes. Both the inherent qualities of the materials and the intricacies of the synthesis process play pivotal roles in advancing their properties and expanding their potential applications. Polypyrrole (PPy)-based composites, owing to their distinctive properties, hold great appeal for a variety of applications. Despite the limitations of PPy in its pure form, these constraints can be effectively overcome through hybridization with other materials. This comprehensive review thoroughly explores the existing literature on PPy and PPy-based composites, providing in-depth insights into their synthesis, properties, and applications. Special attention is given to the advantages of intrinsically conducting polymers (ICPs) and PPy in comparison to other ICPs. The impact of doping anions, additives, and oxidants on the properties of PPy is also thoroughly examined. By delving into these aspects, this overview aims to inspire researchers to delve into the realm of PPy-based composites, encouraging them to explore new avenues for flexible technology applications.

Effect of hydrostatic pressure on charge carriers in a conducting pyrrole-co-poly(pyrrole-3-carboxylic) copolymer

The charge carriers in conducting pyrrole-co-poly(pyrrole-3-carboxylic) were examined using high-pressure Raman spectroscopy. The molecular structure of the new copolymer was investigated using high-resolution 13C ssNMR, 1H-13C 2D NMR correlation spectroscopy, and density functional theory (DFT) calculations. Bands in Raman spectra that showed the presence of polarons and bipolarons were studied. It was observed that the quantity of polarons and bipolarons correlated with the hydrostatic pressure. At a pressure of 4 GPa, an anomaly in the correlation between pressure and the position of the Raman band was identified.

Selective determination of an ovarian cancer biomarker at low concentrations with surface imprinted nanotube based chemosensor

In this study, an electrochemical chemosensor that utilizes a conductive polymer-based molecularly imprinted polymer (MIP) surface for rapid and reliable determination of CA125 was devised. A novel method has been applied to fabricate CA125 imprinted polypyrrole nanotubes (MI-PPy NT) via vapor deposition polymerization (VDP) as a recognition element for highly selective and sensitive determination of CA125. The chemosensor was prepared by immobilizing MI-PPy NT onto screen-printed gold electrodes (Au-SPE) and the performance of the sensor was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in terms of selectivity, sensitivity, linear dynamic concentration range (LDR) and limit of detection (LOD). The MI-PPy NT@Au-SPE sensor exhibited high sensitivity (68.57 μA per decade) to the CA125 concentration ranging from 0.1 U mL-1 to 100 U mL-1 at an LOD of 0.4 U mL-1 with a correlation coefficient of 0.9922. The developed chemosensors with their novel design combined with a facile fabrication method, prove to be promising as future state-of-the-art biosensors.

Design and synthesis of polypyrrole conductive ink based on sulfated chitosan for bactericide carbendazim detection

Conductive polymers (CPs) are typically insoluble in solvents, and devising biocompatible hydrophilic CPs is challenging and imperative to expand the applications of CPs. Herein, sulfated chitosan (SCS) is used as a green dopant instead of toxic poly(styrene sulfonate) (PSS), and SCS:polypyrrole (SCS:PPy) conductive ink is prepared by in situ polymerization. Due to the complex structure between PPy and SCS polyanion, the synthesized SCS:PPy dispersion forms a well-connected electric pathway and confers superior conductivity, dispersion stability, good film-forming ability, and high electrical stability. As proof of our concept, electrochemical sensing utilizing an SCS:PPy-modified screen-printed carbon electrode (SPCE) was performed towards carbendazim (CBZ). The SCS:PPy on the SPCE surface displayed greater sensitivity to CBZ because the conductive complex structure eased the electrocatalytic action of SCS:PPy by dramatically increasing the current intensity of CBZ oxidation and notably ameliorating stability. The sensor unveils the lowest detection value of 1.02 nM with a linear range of 0.05 to 906 μM for sensing trace CBZ by utilizing the pulse voltammetry technique. Interestingly, this senor shows excellent selectivity towards CBZ due to the formation of substantial interactions between SCS:PPy and CBZ, as demonstrated by molecular simulation studies. Furthermore, this sensor can precisely monitor CBZ in actual fruit and river water samples with satisfactory results. This study sheds light on the design and synthesis of sustainable hydrophilic CPs in the fabrication of sensors.

Rewritable printing of ionic liquid nanofilm utilizing focused ion beam induced film wetting

Manipulating liquid flow over open solid substrate at nanoscale is important for printing, sensing, and energy devices. The predominant methods of liquid maneuvering usually involve complicated surface fabrications, while recent attempts employing external stimuli face difficulties in attaining nanoscale flow control. Here we report a largely unexplored ion beam induced film wetting (IBFW) technology for open surface nanofluidics. Local electrostatic forces, which are generated by the unique charging effect of Helium focused ion beam (HFIB), induce precursor film of ionic liquid and the disjoining pressure propels and stabilizes the nanofilm with desired patterns. The IBFW technique eliminates the complicated surface fabrication procedures to achieve nanoscale flow in a controllable and rewritable manner. By combining with electrochemical deposition, various solid materials with desired patterns can be produced.

Toward Biomass-Based Organic Electronics: Continuous Flow Synthesis and Electropolymerization of N-Substituted Pyrroles

Pyrroles are foundational building blocks in a wide array of disciplines, including chemistry, pharmaceuticals, and materials science. Currently sourced from nonrenewable fossil sources, there is a strive to explore alternative and sustainable synthetic pathways to pyrroles utilizing renewable feedstocks. The utilization of biomass resources presents a compelling solution, particularly given that several key bulk and fine chemicals already originate from biomass. For instance, 2,5-dimethoxytetrahydrofuran and aniline are promising candidates for biomass-based chemical production. In this study, we present an innovative approach for synthesizing N-substituted pyrroles by modifying the Clauson-Kaas protocol, starting from 2,5-dimethoxytetrahydrofuran as the precursor. The developed methodology offers the advantage of producing pyrroles under mild reaction conditions with the potential for catalyst-free reactions depending upon the structural features of the substrate. We devised protocols suitable for both continuous flow and batch reactions, enabling the conversion of a wide range of anilines and sulfonamides into their respective N-substituted pyrroles with good to excellent yields. Moreover, we demonstrate the feasibility of depositing thin films of the corresponding polymers onto electrodes through in situ electropolymerization. This innovative application showcases the potential for sustainable, biomass-based organic electronics, thus, paving the way for environmentally friendly advancements in this field.

Multifunctional Polypyrrole-Based Textile Sensors for Integration into Personal Protection Equipment

Integrated safety sensors for personal protection equipment increasingly attract research activities as there is a high need for workers in delicate situations to be physically monitored in order to avoid accidents. In this work, we present a simple approach to generate thin, homogeneous polypyrrole (PPy) layers on flexible textile polyamide fabrics. PPy layers of 0.5-1 µm were deposited on the fabric, which thus kept its flexibility. The conductive layers are multifunctional and can act as temperature and gas sensors for the detection of corrosive gases such as HCl and NH3. Using three examples of life-threatening environments, we were able to monitor temperature, atmospheric NH3 and HCl within critical ranges, i.e., 100 to 400 ppm for ammonia and 20 to 100 ppm for HCl. In the presence of HCl, a decrease in resistance was observed, while gaseous NH3 led to an increase in resistance. The sensor signal thus allows for distinguishing between these two gases and indicating critical concentrations. The simple and cheap manufacturing of such PPy sensors is of substantial interest for the future design of multifunction functional sensors in protective clothing.

A simple synthesis of a core-shell structure PPy-Au nanocomposite for immunosensing of C-reactive protein

High-sensitivity C-reactive protein (hs-CRP) is an inflammatory biomarker and can accurately predict the development of cardiovascular disease (CVD). We synthesized a core-shell structure PPy-Au nanocomposite in situ by chemically oxidizing pyrrole (Py) with HAuCl4 and the produced Au nanoparticles realized the doping in the polymerization. Analysis of morphology and energy spectrum as well as electrochemical characterization confirmed the successful one-pot synthesis. The conductive polymers with porous structure provide abundant sites for anti-CRP binding and effectively enhanced the sensitivity of the label-free BSA/anti-CRP/PPy-Au/GCE immunosensor. Its analytical performance was observed using differential pulse voltammetry (DPV), with a linear range from 0.0005 to 60 μg mL-1 and a detection limit of 0.17 ng mL-1. The platform demonstrated satisfactory selectivity, stability, and reproducibility. To validate its clinical application, we detected CRP in human serum samples with a recovery rate of 101.00-105.95% and investigated the consistency of the developed method and immunoturbidimetry with a deviation between -1.2% and +3.2%, suggesting great potential for use in point-of-care testing (POCT).

Recent progress in optical and electrochemical aptasensor technologies for detection of aflatoxin B1

AFB1 (Aflatoxin B1) contamination is becoming a global concern issue due to its extraordinary occurrence, severe toxicity, as well as the great influence on the economic losses, food safety and environment. Therefore, it is desirable to develop novel analytical techniques for simple, rapid, accurate, and even point-of-care testing of AFB1. Fortunately, aptamer, considered as a new generation bioreceptor and even superior to classic antibody and enzyme, has been emerged remarkable application in food hazards detection. Correspondingly, aptasensors have been well-established toward AFB1 determination with outstanding performance. In this article, we first discuss and summarize the recent progress in optical and electrochemical aptasensors to monitor AFB1 over the past three years. In particular, the embedding of advanced nanomaterials for their improved analytical performance is highlighted. Furthermore, the critical analysis on various signal transduction strategies for aptasensors construction is discussed. Finally, we reveal the challenges and provide our opinion in future opportunities for aptasensor development.

Synthesis and application of polypyrrole nanofibers: a review

State-of-the-art polypyrrole nanofiber-based nanoarchitectonics can be generally fabricated by electrospinning, interfacial polymerization and reactive template methods. Even though analogous nanofiber morphologies and nanofibrous network architectures can be obtained by these methods, the structural details and structural complexities may alter significantly as different synthesis methods are applied. For the electrospinning technique, on one hand, nanofibers can be directly obtained by spinning polypyrrole-containing dope solutions; on the other, the electrospun nanofiber mats can be used as templates to direct the nanofiber formation; a two-step fabrication process, including the electrospinning of polymer nanofiber mats and deposition of polypyrrole on the polymer nanofibers' surface, is generally employed. By tuning the electrospinning parameters, the composition, diameter, morphology, and alignment of the as-obtained electrospun nanofiber mat can be effectively controlled, which may allow the fabrication of polypyrrole nanofibers with sophisticated nanostructures and nanoarchitectures. Interfacial polymerization is capable of generating polypyrrole nanofibers without templates. It is speculated that the protonation and re-orientation of polypyrrole at the oil-water interface may decoil the polymer chains and transform them into more extended conformations, while the charged polymer chains more easily diffuse into the water phase and form a stable dispersion. Different from electrospinning, the reactive templates may drive the formation of polypyrrole nanofibers through either redox or protonation mechanisms. Nanofibers with different curvatures, compositions, and architectures can be obtained by using different types of reactive template in a simple, fast, environment-friendly and one-step manner. A wide range of applications have been demonstrated by the polypyrrole nanofiber-based nanoarchitectonics, including cell culture, tissue engineering, neural stimulation, energy storage, and organic electronics.

COVID-19 impedimetric biosensor based on polypyrrole nanotubes, nickel hydroxide and VHH antibody fragment: specific, sensitive, and rapid viral detection in saliva samples

SARS-CoV-2 rapid spread required urgent, accurate, and prompt diagnosis to control the virus dissemination and pandemic management. Several sensors were developed using different biorecognition elements to obtain high specificity and sensitivity. However, the task to achieve these parameters in combination with fast detection, simplicity, and portability to identify the biorecognition element even in low concentration remains a challenge. Therefore, we developed an electrochemical biosensor based on polypyrrole nanotubes coupled via Ni(OH)₂ ligation to an engineered antigen-binding fragment of heavy chain-only antibodies (VHH) termed Sb#15. Herein we report Sb#15-His6 expression, purification, and characterization of its interaction with the receptor-binding domain (RBD) of SARS-CoV-2 in addition to the construction and validation of a biosensor. The recombinant Sb#15 is correctly folded and interacts with the RBD with a dissociation constant (K_D) of 27.1 ± 6.4 nmol/L. The biosensing platform was developed using polypyrrole nanotubes and Ni(OH)₂, which can properly orientate the immobilization of Sb#15-His6 at the electrode surface through His-tag interaction for the sensitive SARS-CoV-2 antigen detection. The quantification limit was determined as 0.01 pg/mL using recombinant RBD, which was expressively lower than commercial monoclonal antibodies. In pre-characterized saliva, both Omicron and Delta SARS-CoV-2 were accurately detected only in positive samples, meeting all the requirements recommended by the World Health Organization for in vitro diagnostics. A low sample volume of saliva is needed to perform the detection, providing results within 15 min without further sample preparations. In summary, a new perspective allying recombinant VHHs with biosensor development and real sample detection was explored, addressing the need for accurate, rapid, and sensitive biosensors.

Recent Progress in Biomedical Sensors Based on Conducting Polymer Hydrogels

Biosensors are increasingly taking a more active role in health science. The current needs for the constant monitoring of biomedical signals, as well as the growing spending on public health, make it necessary to search for materials with a combination of properties such as biocompatibility, electroactivity, resorption, and high selectivity to certain bioanalytes. Conducting polymer hydrogels seem to be a very promising materials, since they present many of the necessary properties to be used as biosensors. Furthermore, their properties can be shaped and enhanced by designing conductive polymer hydrogel-based composites with more specific functionalities depending on the end application. This work will review the recent state of the art of different biological hydrogels for biosensor applications, discuss the properties of the different components alone and in combination, and reveal their high potential as candidate materials in the fabrication of all-organic diagnostic, wearable, and implantable sensor devices.

Highly Stretchable, Self-Adhesive, Antidrying Ionic Conductive Organohydrogels for Strain Sensors

As flexible wearable devices, hydrogel sensors have attracted extensive attention in the field of soft electronics. However, the application or long-term stability of conventional hydrogels at extreme temperatures remains a challenge due to the presence of water. Antifreezing and antidrying ionic conductive organohydrogels were prepared using cellulose nanocrystals and gelatin as raw materials, and the hydrogels were prepared in a water/glycerol binary solvent by a one-pot method. The prepared hydrogels were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The mechanical properties, electrical conductivity, and sensing properties of the hydrogels were studied by means of a universal material testing machine and LCR digital bridge. The results show that the ionic conductive hydrogel exhibits high stretchability (elongation at break, 584.35%) and firmness (up to 0.16 MPa). As the binary solvent easily forms strong hydrogen bonds with water molecules, experiments show that the organohydrogels exhibit excellent freezing and drying (7 days). The organohydrogels maintain conductivity and stable sensitivity at a temperature range (-50 °C-50 °C) and after long-term storage (7 days). Moreover, the organohydrogel-based wearable sensors with a gauge factor of 6.47 (strain, 0-400%) could detect human motions. Therefore, multifunctional organohydrogel wearable sensors with antifreezing and antidrying properties have promising potential for human body monitoring under a broad range of environmental conditions.

Conductive bacterial cellulose: From drug delivery to flexible electronics

Bacterial cellulose (BC) is a chemically pure, non-toxic, and non-pyrogenic natural polymer with high mechanical strength and a complex fibrillar porous structure. Due to these unique biological and physical properties, BC has been amply used in the food industry and, to a somewhat lesser extent, in medicine and cosmetology. To expand its application the BC structure can be modified. This review presented some recent developments in electrically conductive BC-based composites. The as-synthesized BC is an excellent dielectric. Conductive polymers, graphene oxide, nanoparticles and other materials are used to provide it with conductive properties. Conductive bacterial cellulose (CBC) is currently investigated in numerous areas including electrically conductive scaffolds for tissue regeneration, implantable and wearable biointerfaces, flexible batteries, sensors, EMI shielding composites. However, there are several issues to be addressed before CBC composites can enter the market, namely, composite mechanical strength reduction, porosity decrease, change in chemical characteristics. Some of them can be addressed both at the stage of synthesis, biologically, or by adding (nano)materials with the required properties to the BC structure. We propose several solutions to meet the challenges and suggest some promising BC applications.

Highly sensitive detection of glucose via glucose oxidase immobilization onto conducting polymer-coated composite polyacrylonitrile nanofibers

Current study introduces composite polyacrylonitrile - multiwall carbon nanotubes nanofibers (PAN-MWCNTs NFs) coated with conducting polymers (polypyrrole (PPy) or poly(3,4-ethylenedioxythiophene) (PEDOT)) by chemical vapor deposition for efficient glucose detection. The potential of nanofibrous assemblies and nano-conducting elements in biosensing was explored as pre-processing of NFs with MWCNTs and post-processing with CPs were both employed. These 'core-shell' conducting NFs were further employed as platforms for glucose oxidase immobilization for enzymatic detection of glucose. The performance of the biosensors was closely correlated with the concentration of immobilized enzyme and with the type of conducting polymer. The biosensors showed high sensitivities of 92.94 and 81.72 µA/mM.cm^-2 for (PAN-MWCNTs)/ PEDOT and (PAN-MWCNTs)/ PPy accompanied by low limit of detection values of 2.30 and 2.38 µM, respectively. Good operational stability was observed throughout twenty-five consecutive measurements, over 90% activity was maintained for both sensors. This study represents proof of concept for the methodology, showcasing the advantages of nanomaterial synthesis for bio-applications. The work was compared thoroughly with previously reported biosensors showing some of the best results reported to date in terms of analytical characteristics.

Recent advances of polypyrrole conducting polymer film for biomedical application: Toward a viable platform for cell-microbial interactions

Polypyrrole (PPy) is one of the most studied conductive polymers due to its electrical conductivity and biological properties, which drive the possibility of numerous applications in the biomedical area. The physical-chemical features of PPy allow the manufacture of biocompatible devices, enhancing cell adhesion and proliferation. Furthermore, owing to the electrostatic interactions between the negatively charged bacterial cell wall and the positive charges in the polymer structure, PPy films can perform an effective antimicrobial activity. PPy is also frequently associated with biocompatible agents and antimicrobial compounds to improve the biological response. Thus, this comprehensive review appraised the available evidence regarding the PPy-based films deposited on metallic implanted devices for biomedical applications. We focus on understanding key concepts that could influence PPy attributes regarding antimicrobial effect and cell behavior under in vitro and in vivo settings. Furthermore, we unravel the several agents incorporated into the PPy film and strategies to improve its functionality. Our findings suggest that incorporating other elements into the PPy films, such as antimicrobial agents, biomolecules, and other biocompatible polymers, may improve the biological responses. Overall, the basic properties of PPy, when combined with other composites, electrostimulation techniques, or surface treatment methods, offer great potential in biocompatibility and/or antimicrobial activities. However, challenges in synthesis standardization and potential limitations such as low adhesion and mechanical strength of the film must be overcome to improve and broaden the application of PPy film in biomedical devices.

Carbon Inks-Based Screen-Printed Electrodes for Qualitative Analysis of Amino Acids

Due to the great significance of amino acids, a substantial number of research studies has been directed toward the development of effective and reliable platforms for their evaluation, detection, and identification. In order to support these studies, a new electrochemical platform based on PANI/ZnO nanowires' modified carbon inks screen-printed electrodes was developed for qualitative analysis of electroactive amino acids, with emphasis on tyrosine (Tyr) and tryptophan (Trp). A comparative investigation of the carbon ink before and after modification with the PANI/ZnO was performed by scanning electron microscopy and by Raman spectroscopy, confirming the presence of PANI and ZnO nanowires. Electrochemical investigations by cyclic voltammetry and electrochemical impedance spectroscopy have shown a higher charge-transfer rate constant, which is reflected into lower charge-transfer resistance and higher capacitance values for the PANI/ZnO modified ink when compared to the simple carbon screen-printed electrode. In order to demonstrate the electrochemical performances of the PANI/ZnO nanowires' modified carbon inks screen-printed electrodes for amino acids analysis, differential pulse voltammograms were obtained in individual and mixed solutions of electroactive amino acids. It has been shown that the PANI/ZnO nanowires' modified carbon inks screen-printed electrodes allowed for tyrosine and tryptophan a peak separation of more than 100 mV, enabling their screening and identification in mixed solutions, which is essential for the electrochemical analysis of proteins within the proteomics research field.

Study on the Electrochemiluminescence of Pentaphenylpyrrole in the Aqueous Phase Based on Structure-Regulated Strategy

Heterocyclic nitrogen compounds play a vital role in luminescent materials, but most of them face the challenges of aggregation-caused quenching (ACQ) and poor water solubility. In this work, we present the nitrogen heterocyclic pentaphenylpyrrole (PentaPP) with an excellent aggregation-induced electrochemiluminescence (AIE-ECL) performance in the aqueous phase through the comparison of the elegant ECL luminophore 5,10,15,20-tetraphenylporphyrin (TPP). Further studies suggest that such unique AIE-ECL arises from its propeller-like noncoplanar structure and the large conjugation from the phenyl groups on the ring. In addition, the new ECL analysis could feature some advantages of AIE characteristic, water compatibility, and strong signal and finally achieve the ultrasensitive detection toward the explosive 2,4,6-trinitrophenol (TNP) with a lower detection limit (1.1 nM). This study does not only benefit to solve the two key problems mentioned before but also enriches the fundamentals and applications for ECL and pyrrole research.

Recent Advances in Graphene-Based Nanocomposites for Ammonia Detection

The increasing demand to mitigate the alarming effects of the emission of ammonia (NH3) on human health and the environment has highlighted the growing attention to the design of reliable and effective sensing technologies using novel materials and unique nanocomposites with tunable functionalities. Among the state-of-the-art ammonia detection materials, graphene-based polymeric nanocomposites have gained significant attention. Despite the ever-increasing number of publications on graphene-based polymeric nanocomposites for ammonia detection, various understandings and information regarding the process, mechanisms, and new material components have not been fully explored. Therefore, this review summarises the recent progress of graphene-based polymeric nanocomposites for ammonia detection. A comprehensive discussion is provided on the various gas sensor designs, including chemiresistive, Quartz Crystal Microbalance (QCM), and Field-Effect Transistor (FET), as well as gas sensors utilising the graphene-based polymer nanocomposites, in addition to highlighting the pros and cons of graphene to enhance the performance of gas sensors. Moreover, the various techniques used to fabricate graphene-based nanocomposites and the numerous polymer electrolytes (e.g., conductive polymeric electrolytes), the ion transport models, and the fabrication and detection mechanisms of ammonia are critically addressed. Finally, a brief outlook on the significant progress, future opportunities, and challenges of graphene-based polymer nanocomposites for the application of ammonia detection are presented.

Electrochemical assay of acetamiprid in vegetables based on nitrogen-doped graphene/polypyrrole nanocomposites

Dual-mode electrochemical aptasensor based on nitrogen-doped graphene (NG) doped with the conducting polymer polypyrrole (PPy) nanocomposite is proposed for the determination of acetamiprid. NG/PPy was electrodeposited onto the glassy carbon electrode (GCE) using cyclic voltammetry technique. NG/PPy/GCE showed outstanding electrocatalytic activity for the oxidation of nitrite due to "active region" induced by the charge redistribution of carbon atoms. The ultrasensitive dual-mode biosensor for acetamiprid could be easily developed by coupling acetamiprid aptamers with the NG/PPy hybrid. The specific binding between acetamiprid and the aptamers resulted in the increase of differential pulse voltammetry (DPV) signal change and the decrease of chronoamperometry (CA) signal, and the concentration of acetamiprid could be measured. The working potentials of DPV and CA were - 0.2 ~ 0.4 V and - 0.4 ~ 0.4 V (vs. SCE), respectively. The dual-mode acetamiprid biosensor showed a wide linear range from 10^-12 to 10^-7 g mL^-1, with low detection limits of 1.15 × 10^-13 g mL^-1 and 7.32 × 10^-13 g mL^-1 through DPV and CA modes, respectively. Moreover, owing to high active area and superior conductivity, as well as good electrocatalytic ability, the dual-sensing platform based on NG/PPy nanocomposite supported the quantification of acetamiprid in complex samples. A dual-mode electrochemical aptasensor based on NG/PPy nanocomposite for acetamiprid detection was proposed through both the increase of differential pulse voltammetry (DPV) signal change and the decrease of chronoamperometry (CA) signal of the nitrite oxidation electrocatalyzed by NG/PPyn in sensors and biosensors.

Electrochemical DNA sensors for drug determination

In this review, recent achievements in the development of the DNA biosensors developed for the drug determination have been presented with particular emphasis to the main principles of their assembling and signal measurement approaches. The design of the DNA sensors is considered with characterization of auxiliary components and their necessity for the biosensor operation. Carbon nanomaterials, metals and their complexes as well as electropolymerized polymers are briefly described in the assembly of DNA sensors. The performance of the DNA sensors is summarized within 2017-2022 for various drugs and factors influencing the sensitivity and selectivity of the response are discussed. Special attention is paid to the mechanism of the signal generation and possible drawbacks in the analysis of real samples.

Synthesis and applications of TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes

In recent years, TiO2/ZnO hybrid nanostructures have been attracting the interest of the scientific community due to their excellent photoelectrochemical properties. The main advantage of TiO2/ZnO hybrid nanostructures over other photocatalysts based on semiconductor materials lies in their ability to form heterojunctions in which the valence and conduction bands of both semiconductors are intercalated. This factor produces a decrease in the band gap and the recombination rate and an increase in the light absorption range. The aim of this review is to perform a revision of the main methods to synthesise TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes. Electrochemical synthesis methods provide an easy, fast, and highly efficient route to carry out the synthesis of nanostructures such as nanowires, nanorods, nanotubes, etc. They allow us to control the stoichiometry, thickness and structure mainly by controlling the voltage, time, temperature, composition of the electrolyte, and concentration of monomers. In addition, a study of the most promising applications for TiO2/ZnO hybrid nanostructures has been carried out. In this review, the applications of dye-sensitised solar cell, photoelectrocatalytic degradation of organic compounds, photoelectrochemical water splitting, gas sensors, and lithium-ion batteries have been highlighted.

Label-free, ultrasensitive and rapid detection of FDA-approved TBI specific UCHL1 biomarker in plasma using MWCNT-PPY nanocomposite as bio-electrical transducer: A step closer to point-of-care diagnosis of TBI

Traumatic Brain Injury (TBI), a major cause of mortality and neurological disability affecting people of all ages worldwide, remains a diagnostic and therapeutic challenge to date. Rapid, ultra-sensitive, selective, and wide-range detection of TBI biomarkers in easily accessible body fluids is an unmet clinical need. Considering this, in this work, we report the design and development of a facile, label-free, highly stable and sensitive, chemi-impedance-based sensing platform for rapid and wide range detection of Ubiquitin-carboxy terminal hydrolase L1 (UCHL1: FDA-approved TBI specific plasma biomarker), using carboxylic functionalized MWCNTs embedded polypyrrole (PPY) nanocomposites (PPY/f-MWCNT). The said nanocomposites were synthesized using chemical oxidative polymerization method. Herein, the functionalized MWCNTs are used as conducting fillers so as to increase the polymer's dielectric constant according to the micro-capacitor model, thereby augmenting both DC electrical conductivity and AC dielectric property of the nanocomposite. The proposed immunosensing platform comprises of PPY/f-MWCNT modified interdigitated microelectrode (IDμEs) array, on which anti-UCHL1-antibodies are immobilized using suitable covalent chemistry. The AC electrical characterization of the nanocomposite modified IDμEs, with and without the antibodies, was performed through generic capacitance vs. frequency (C-F, 1 KHz - 1 MHz) and capacitance vs. applied bias (C-V, 0.1 V-1 V) measurements, using an Agilent B1500A parametric analyzer. The binding event of UCHL1 peptides to anti-UCHL1-antibodies was transduced in terms of normalised changes in parallel capacitance, via the C-F analysis. Further, we have tested the detection efficiency of the said immunoassay against UCHL1 spiked human plasma samples in the concentration range 10 fg/mL - 1 μg/mL. The proposed sensing platform detected UCHL1 in spiked-plasma samples linearly in the range of 10 fg/mL - 1 ng/mL with a sensitivity and LoD of 4.22 ((ΔC/C₀)/ng.mL^-1)/cm² and 0.363 fg/mL, respectively. Further, it showed excellent stability (30 weeks), repeatability, reproducibility, selectivity and interference-resistance. The proposed approach is label-free, and if desired, can be used in conjunction with DC measurements, for biosensing applications.

Electrodeposition and Characterization of Conducting Polymer Films Obtained from Carbazole and 2-(9H-carbazol-9-yl)acetic Acid

Electrochemical oxidation of electrolyte solutions containing carbazole (Cz) and 2-(9H-carbazol-9-yl)acetic acid (CzA) monomers was performed in acetonitrile solutions. Different Cz and CzA feed ratios were used to electrodeposit solid polymer films of various compositions, and to study the influence of the monomer ratio on the physicochemical properties (electroactivity, topography, adhesion, stiffness, wettability) of the polymer films. Thus, electrochemical oxidation led to the deposition of a solid film of micrometric thickness, but only for the solutions containing at least 30% of Cz. The proportion of Cz and CzA in the electrodeposited polymer films has little impact on the adhesion strength values measured by AFM. On the contrary, this proportion significantly modifies the stiffness of the films. Indeed, the stiffness of the polymer films varies from 9 to 24 GPa depending on the monomer ratio, which is much lower than the value obtained for unmodified polycarbazole (64 GPa). This leads to the absence of cracks in the films, which all have a fairly homogeneous globular structure. Moreover, among the different polymer films obtained, those prepared from 70:30 and 50:50 ratios in Cz:CzA monomer solutions seem to be the most interesting because these green films are conductive, thick, low in stiffness, do not show cracks and are resistant to prolonged immersion in water.

Electrochemical Biosensor Using Nitrogen-Doped Graphene/Au Nanoparticles/DNAzyme for Ca2+ Determination

An electrochemical biosensor for detecting Ca²⁺ concentration was proposed using glass carbon electrodes (GCEs) modified with nitrogen-doped graphene (NGR), gold nanoparticles (AuNPs) and DNAzyme. The resistance signal was amplified through two methods: electrochemical reduction of AuNPs on the NGR surface to increase the specific surface area of the electrode and strengthen the adsorption of DNAzyme; and increasement of the DNAzyme base sequence. The process of electrode modification was characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Experimental parameters’ influence, such as the deposition time of gold nanoparticles and the detection time, were assessed by electrochemical methods. The linear ranges of the electrochemical biosensor were in the range from 5 × 10⁻⁶ to 5 × 10⁻⁵ and 5 × 10⁻⁵ to 4 × 10⁻⁴ M, with a detection limit of 3.8 × 10⁻⁶ M. The concentration of Ca²⁺ in the serum of dairy cows was determined by the biosensor with satisfactory results, which could be potentially used to diagnose subclinical hypocalcemia.

Integration of Different Graphene Nanostructures with PDMS to Form Wearable Sensors

This paper presents a substantial review of the fabrication and implementation of graphene-PDMS-based composites for wearable sensing applications. Graphene is a pivotal nanomaterial which is increasingly being used to develop multifunctional sensors due to their enhanced electrical, mechanical, and thermal characteristics. It has been able to generate devices with excellent performances in terms of sensitivity and longevity. Among the polymers, polydimethylsiloxane (PDMS) has been one of the most common ones that has been used in biomedical applications. Certain attributes, such as biocompatibility and the hydrophobic nature of PDMS, have led the researchers to conjugate it in graphene sensors as substrates or a polymer matrix. The use of these graphene/PDMS-based sensors for wearable sensing applications has been highlighted here. Different kinds of electrochemical and strain-sensing applications have been carried out to detect the physiological signals and parameters of the human body. These prototypes have been classified based on the physical nature of graphene used to formulate the sensors. Finally, the current challenges and future perspectives of these graphene/PDMS-based wearable sensors are explained in the final part of the paper.

Sol-Gel Synthesis and Characterization of Highly Selective Poly(N-methyl pyrrole) Stannous(II)Tungstate Nano Composite for Mercury (Hg(II)) Detection

The sol-gel process was used to create a new type of polypyrrole-Stannous(II)tungstate nanocomposite by poly(N-methyl pyrrole (PNMPy) sol in Stannous(II)tungstate gel, produced separately using sodium silicotungstic acid and Tn(II)chloride. Tin(II)tungstate (SnWO3) was made by changing the mixing volume ratios of SnWO3 and with a constant amount of an organic polymer. The composite was characterized by TGA, XRD, FTIR, and SEM measurements. A commercially available glassy carbon electrode (GCE) was modified with PNMPy/nano-Stannous(II)WO3 nanocomposites to create a chemical sensor for selective detection of Hg2+ ions using an effective electrochemical methodology. In the I-V technique, selectively toxic Hg2+ ion was targeted selectively, which shows a rapid reaction toward PNMPy/nano-Stannous(II)WO3/Nafion/GCE sensor. It also demonstrates long-term stability, an ultra-low detection limit, exceptional sensitivity, and excellent reproducibility and repeatability. For 0.1 mM to 1.0 nM aqueous Hg2+ ion solution, a linear calibration plot (r2: 0.9993) was achieved, with a suitable sensitivity value of 2.8241 AM−1 cm−2 and an extraordinarily low detection limit (LOD) of 3.40.1 pM (S/N = 3). As a result, the cationic sensor modified by PNMPy/nano-Stannous(II)WO3/GCE could be a promising electrode.

Double Trigonal Pyramidal {SeO3} Groups Bridged 2-Picolinic Acid Modified Cerium-Inlaid Polyoxometalate Including Mixed Selenotungstate Subunits for Electrochemically Sensing Ochratoxin A

An organic-inorganic hybrid trigonal pyramidal {SeO3} group, bridged cerium-inlaid polyoxometalate (POM) Na16[Se2Ce4(H2O)8W4(HPIC)4O10][B-β-SeW8O30]2[Se2W12O46]2·60H2O (1) (HPIC = 2-picolinic acid), containing two disparate selenotungstate (ST) building blocks was synthesized by a one-step assembly strategy, which is established by two asymmetric sandwich-type {[Ce2(H2O)4W2(HPIC)2O4][B-β-SeW8O30][Se2W12O46]}10- moieties joined by double trigonal pyramidal {SeO3} groups. Its outstanding structural trait is that it contains two types of ST building blocks, Keggin-type [B-β-SeW8O30]8- and Dawson-like [Se2W12O46]12-, which are extremely rare in ST chemistry. Remarkably, [Se2W12O46]12- is first obtained in lanthanide-inlaid STs. Furthermore, 1@PPy conductive film (PPy = polypyrrole) was prepared by electrochemical polymerization and served as the electrode material, and then nano-gold particles (NGPs) were deposited on the surface of 1@PPy conductive film by an electrochemical deposition method in order to immobilize the aptamer of ochratoxin A. With the help of exonuclease I (EN I), the oxidation peak of the metalized Ag works as the detection signal to achieve the detection of ochratoxin A (OTXA). This study offers an available approach for creating organic-inorganic hybrid heteroatom-bridged lanthanide-inlaid POMs and reveals the likelihood of extending heteroatom-bridged lanthanide-inlaid POMs into electrochemical biosensing applications.

Irreversible and Self-Healing Electrically Conductive Hydrogels Made of Bio-Based Polymers

Electrically conductive materials that are fabricated based on natural polymers have seen significant interest in numerous applications, especially when advanced properties such as self-healing are introduced. In this article review, the hydrogels that are based on natural polymers containing electrically conductive medium were covered, while both irreversible and reversible cross-links are presented. Among the conductive media, a special focus was put on conductive polymers, such as polyaniline, polypyrrole, polyacetylene, and polythiophenes, which can be potentially synthesized from renewable resources. Preparation methods of the conductive irreversible hydrogels that are based on these conductive polymers were reported observing their electrical conductivity values by Siemens per centimeter (S/cm). Additionally, the self-healing systems that were already applied or applicable in electrically conductive hydrogels that are based on natural polymers were presented and classified based on non-covalent or covalent cross-links. The real-time healing, mechanical stability, and electrically conductive values were highlighted.

Unconventional Conjugation in macromonomers and polymers

Multiple reviews have been written concerning conjugated macromonomers and polymers both as general descriptions and for specific applications. In most examples, conjugation occurs via elec-tronic communication via continuous overlap of...

Electrochemical DNA Sensor Based on Acridine Yellow Adsorbed on Glassy Carbon Electrode

Electrochemical DNA sensors offer unique opportunities for the sensitive detection of specific DNA interactions. In this work, a voltametric DNA sensor is proposed on the base of glassy carbon electrode modified with carbon black, adsorbed acridine yellow and DNA for highly sensitive determination of doxorubicin antitumor drug. The signal recorded by cyclic voltammetry was attributed to irreversible oxidation of the dye. Its value was altered by aggregation of the hydrophobic dye molecules on the carbon black particles. DNA molecules promote disaggregation of the dye and increased the signal. This effect was partially suppressed by doxorubicin compensate for the charge of DNA in the intercalation. Sensitivity of the signal toward DNA and doxorubicin was additionally increased by treatment of the layer with dimethylformamide. In optimal conditions, the linear range of doxorubicin concentrations determined was 0.1 pM–1.0 nM, and the detection limit was 0.07 pM. No influence of sulfonamide medicines and plasma electrolytes on the doxorubicin determination was shown. The DNA sensor was tested on two medications (doxorubicin-TEVA and doxorubicin-LANS) and showed recoveries of 102–105%. The DNA sensor developed can find applications in the determination of drug residues in blood and for the pharmacokinetics studies.

Challenges in the design of electrochemical sensor for glyphosate-based on new materials and biological recognition

Glyphosate (GLY) is the main ingredient in the weed killer Roundup and the most widely used pesticide in the world. Studies of the harmful effects of GLY on human health began to become more wide-ranging after 2015. GLY is listed by the International Agency for Research on Cancer (IARC) as a carcinogenic hazard to humans. Moreover, GLY has the property to complex with transition metals and are stable for long periods, being considered a high-risk element for different matrices, such as environmental (soil and water) and food (usually genetically modified crops). Since that, it was noticed an increment in the development of new analytical methods for its determination in different matrices like food, environmental and biological fluids. Noteworthy, the application of electrochemical techniques for downstream detection sparked interest due to the ability to minimize or eliminate the use of polluting chemicals, using simple and affordable equipment. This work aims to review the contribution of the electroanalytical methods for the determination of GLY in different food and environmental matrices. Parameters such as the electrochemical transduction techniques based on the electrical measurement signals, receptor materials for electrodes preparation, and the detection mechanisms are described in this review. The literature review shows that the electrochemical sensors are powerful detection system that can be improved by their design and by their portability to fulfil the needs of the GLY determination in laboratory benches, or even in situ analysis.

Innovative Integration of Phase-Change Microcapsules with Metal-Organic Frameworks into an Intelligent Biosensing System for Enhancing Dopamine Detection

This work focuses on an interdisciplinary issue in energy management and biosensing techniques. Aiming at enhancing the biosensing detection of dopamine at high ambient temperatures, we developed an innovative integration of phase-change microcapsules with a metal-organic framework (MOF) based on zeolitic imidazolate framework-8 to develop an intelligent electrochemical biosensing system with a thermal self-regulation function. We first fabricated a type of electroactive microcapsules containing a MOF-anchored polypyrrole/SiO₂ double-layered shell and a phase-change material (PCM) core. The resultant microcapsules not only exhibit a regular spherical morphology with a layer-by-layer core-shell microstructure but also display an effective temperature-regulation capability to enhance enzymatic bioactivity under phase-change enthalpies of around 124.0 J·g^-1 along with good thermal impact resistance and excellent thermal cycling stability for long-term use in thermal energy management. These electroactive microcapsules were then used to modify a working electrode together with laccase as a biocatalyst to construct a thermal self-regulatory biosensor. With a high sensitivity of 3.541 μA·L·μmol^-1·cm^-2 and a low detection limit of 0.0069 μmol·L^-1 at 50 °C, this biosensor exhibits much better determination effectiveness toward dopamine at higher temperatures than conventional biosensors thanks to in situ thermal management derived from its PCM core in the electroactive microcapsules. This study offers a promising approach for development of intelligent thermal self-regulatory biosensors with an enhanced detection capability to identify various chemicals accurately in a wide range of applicable temperatures.

Towards point-of-care diagnosis of Alzheimer's disease: Multi-analyte based portable chemiresistive platform for simultaneous detection of β-amyloid (1-40) and (1-42) in plasma

Label-free simultaneous detection of Alzheimer's disease (AD) specific biomarkers Aβ40 and Aβ42 peptides on a single platform using polypyrrole nanoparticle-based chemiresistive biosensors is reported here. The proposed interdigitated-microelectrode based inexpensive multisensor-platform can concurrently detect Aβ40 and Aβ42 in spiked-plasma in the range of 10-14 - 10-6 g/mL (with LoDs being 5.71 and 9.09 fg/mL, respectively), enabling the estimation of diagnostically significant Aβ42/Aβ40 ratio. A detailed study has been undertaken here to record the individual sensor responses against spiked-plasma samples with varying amounts and proportions of the two target peptides, towards enabling disease-progression monitoring using the Aβ-ratio. As compared to the existing cost-ineffective brain-imaging techniques such as PET and MRI, and the high-risk CSF based invasive AD biomarkers detecting procedures, the proposed approach offers a viable alternative for affordable point-of-care AD diagnostics, with possible usage in performance evaluation of therapeutic drugs. Towards point-of-care applications, the portable readout used in this work was conjugated with an android-based mobile app for data-acquisition and analysis.