Progress in the Development of Intrinsically Conducting Polymer Composites as Biosensors

MXenes-polymer nanocomposites for biomedical applications: fundamentals and future perspectives

The article discusses the promising synergy between MXenes and polymers in developing advanced nanocomposites with diverse applications in biomedicine domains. MXenes, possessing exceptional properties, are integrated into polymer matrices through various synthesis and fabrication methods. These nanocomposites find applications in drug delivery, imaging, diagnostics, and environmental remediation. They offer improved therapeutic efficacy and reduced side effects in drug delivery, enhanced sensitivity and specificity in imaging and diagnostics, and effectiveness in water purification and pollutant removal. The perspective also addresses challenges like biocompatibility and toxicity, while suggesting future research directions. In totality, it highlights the transformative potential of MXenes-polymer nanocomposites in addressing critical issues across various fields.

Amine functionalised graphene embedded polyvinyl alcohol (PVA) and PVA-chitosan hydrogel composites

A novel amine-functionalized graphene oxide (AFG) doped polyvinyl alcohol (PVA)/chitosan (PVA-Ch) composite film was developed using an eco-synthesis approach, eliminating the need for halogenated compounds. The resulting AFG-doped PVA/Chitosan (PVA-Ch/AFG) polymer film exhibited promising properties for controlled delivery and biosensing applications. The investigation included assessing the swelling behaviour, dissolution percent, gel fraction, and mechanical properties of the polymer film. The swelling characteristics of PVA-Ch and PVA-Ch/AFG were found to be pH and temperature-dependent across various pH ranges (3, 5, 7, and 9). Interestingly, PVA-Ch/AFG demonstrated a stable swelling pattern at pH 5 and 7, unaffected by changes in chitosan concentration, indicating enhanced stability compared to PVA-Ch. The study also explored the use of PVA-Ch/AFG in a drug delivery system, revealing controlled release of the model antibiotic amphicillin, emphasizing its potential in medical applications. Furthermore, the eco-friendly synthesis route underscored the safety of PVA-Ch/AFG for use in food and medical applications. Biocompatibility assessments, including biodegradability studies and cytotoxicity tests on fibroblasts (3T3 cells), confirmed the safety profile of PVA-Ch/AFG. In conclusion, the study suggests that PVA-Ch/AFG holds promise for bio-sensing applications, offering a flexible and colorimetric platform capable of encapsulating, adsorbing, and desorbing biomolecules such as drugs and sensing compounds.

Fillers and methods to improve the effective (out-plane) thermal conductivity of polymeric thermal interface materials - A review

The internet of things and growing demand for smaller and more advanced devices has created the problem of high heat production in electronic equipment, which greatly reduces the work performance and life of the electronic instruments. Thermal interface material (TIM) is placed in between heat generating micro-chip and the heat dissipater to conduct all the produced heat to the heat sink. The development of suitable TIM with excellent thermal conductivity (TC) in both in-plane and through-plane directions is a very important need at present. For efficient thermal management, polymer composites are potential candidates. But in general, their thermal conductivity is low compared to that of metals. The filler integration into the polymer matrix is one of the two approaches used to increase the thermal conductivity of polymer composites and is also easy to scale up for industrial production. Another way to achieve this is to change the structure of polymer chains, which fall out of the scope of this work. In this review, considering the first approach, the authors have summarized recent developments in many types of fillers with different scenarios by providing multiple cases with successful strategies to improve through-plane thermal conductivity (TPTC) (k⊥). For a better understanding of TC, a comprehensive background is presented. Several methods to improve the effective (out-plane) thermal conductivity of polymer composites and different theoretical models for the calculation of TC are also discussed. In the end, it is given a detailed conclusion that provides drawbacks of some fillers, multiple significant routes recommended by other researchers to build thermally conductive polymer composites, future aspects along with direction so that the researchers can get a guideline to design an effective polymer-based thermal interface material.

Flexible Electrodes for Brain-Computer Interface System

Brain-computer interface (BCI) has been the subject of extensive research recently. Governments and companies have substantially invested in relevant research and applications. The restoration of communication and motor function, the treatment of psychological disorders, gaming, and other daily and therapeutic applications all benefit from BCI. The electrodes hold the key to the essential, fundamental BCI precondition of electrical brain activity detection and delivery. However, the traditional rigid electrodes are limited due to their mismatch in Young's modulus, potential damages to the human body, and a decline in signal quality with time. These factors make the development of flexible electrodes vital and urgent. Flexible electrodes made of soft materials have grown in popularity in recent years as an alternative to conventional rigid electrodes because they offer greater conformance, the potential for higher signal-to-noise ratio (SNR) signals, and a wider range of applications. Therefore, the latest classifications and future developmental directions of fabricating these flexible electrodes are explored in this paper to further encourage the speedy advent of flexible electrodes for BCI. In summary, the perspectives and future outlook for this developing discipline are provided.

A review of the thermal storage of phase change material, morphology, synthesis methods, characterization, and applications of microencapsulated phase change material

In the thermal energy storage area, microencapsulated phase change material (MPCM) is getting more popular among researchers. When phase change materials (PCMs) shift from one phase to another at a specific temperature, a significant quantity of thermal energy is stored. The PCM application focuses on upgrading worldwide energy conservation efforts in light of the rapidly dwindling fossil fuels. The thermal energy supplied by PCM is significantly influenced by the choice of supporting materials and encapsulation methods. A solution to the volume change issues of PCM, phase separation, and leakage is the PCM microencapsulation technique. One of the most common methods to increase the effectiveness of thermal storage material is attained by using PCM with microencapsulation. The preparation processes and thermal characteristics of the MPCM are summarized in this paper. This paper gives information about MPCM with its types, properties, testing, and characterizations. Tables describe specific examples of PCM with thermal properties. Applications in various fields are defined. This review gives as much information to help and be useful for new researchers in the field of thermal management systems to guide their future research.

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.

Conducting Polymers as Versatile Tools for the Electrochemical Detection of Cancer Biomarkers

The detection of cancer biomarkers has recently become an established method for the early diagnosis of cancer. The sensitive analysis of specific biomarkers can also be clinically applied for the determination of response to treatment and monitoring of disease progression. Because of the ultra-low concentration of cancer biomarkers in body fluids, diagnostic tools need to be highly sensitive and specific. Conducting polymers (CPs) are particularly known to exhibit numerous features that enable them to serve as excellent materials for the immobilization of biomolecules and the facilitation of electron transfer. Their large surface area, porosity, and the presence of functional groups provide CPs with binding sites suitable for capturing biomarkers, in addition to their sensitive and easy detection. The aim of this review is to present a comprehensive summary of the available electrochemical biosensors based on CPs and their composites for the ultrasensitive detection of selected cancer biomarkers. We have categorized the study based on different types of targeted biomarkers such as DNAs, miRNAs, proteins, enzymes, neurotransmitters and whole cancer cells. The sensitivity of their detection is enhanced by the presence of CPs, providing a limit of detection as low as 0.5 fM (for miRNA) and 10 cells (for the detection of cancer cells). The methods of multiplex biomarker detection and cell capture are indicated as the most promising category, since they furnish more accurate and reliable results. Ultimately, we discuss the available CP-based electrochemical sensors and promising approaches for facilitating cancer diagnosis and treatment.

Nanosphere Structures Using Various Materials: A Strategy for Signal Amplification for Virus Sensing

Nanomaterials have been explored in the sensing research field in the last decades. Mainly, 3D nanomaterials have played a vital role in advancing biomedical applications, and less attention was given to their application in the field of biosensors for pathogenic virus detection. The versatility and tunability of a wide range of nanomaterials contributed to the development of a rapid, portable biosensor platform. In this review, we discuss 3D nanospheres, one of the classes of nanostructured materials with a homogeneous and dense matrix wherein a guest substance is carried within the matrix or on its surface. This review is segmented based on the type of nanosphere and their elaborative application in various sensing techniques. We emphasize the concept of signal amplification strategies using different nanosphere structures constructed from a polymer, carbon, silica, and metal-organic framework (MOF) for rendering high-level sensitivity of virus detection. We also briefly elaborate on some challenges related to the further development of nanosphere-based biosensors, including the toxicity issue of the used nanomaterial and the commercialization hurdle.

Graphene Incorporated Electrospun Nanofiber for Electrochemical Sensing and Biomedical Applications: A Critical Review

The extraordinary material graphene arrived in the fields of engineering and science to instigate a material revolution in 2004. Graphene has promptly risen as the super star due to its outstanding properties. Graphene is an allotrope of carbon and is made up of sp²-bonded carbon atoms placed in a two-dimensional honeycomb lattice. Graphite consists of stacked layers of graphene. Due to the distinctive structural features as well as excellent physico-chemical and electrical conductivity, graphene allows remarkable improvement in the performance of electrospun nanofibers (NFs), which results in the enhancement of promising applications in NF-based sensor and biomedical technologies. Electrospinning is an easy, economical, and versatile technology depending on electrostatic repulsion between the surface charges to generate fibers from the extensive list of polymeric and ceramic materials with diameters down to a few nanometers. NFs have emerged as important and attractive platform with outstanding properties for biosensing and biomedical applications, because of their excellent functional features, that include high porosity, high surface area to volume ratio, high catalytic and charge transfer, much better electrical conductivity, controllable nanofiber mat configuration, biocompatibility, and bioresorbability. The inclusion of graphene nanomaterials (GNMs) into NFs is highly desirable. Pre-processing techniques and post-processing techniques to incorporate GNMs into electrospun polymer NFs are precisely discussed. The accomplishment and the utilization of NFs containing GNMs in the electrochemical biosensing pathway for the detection of a broad range biological analytes are discussed. Graphene oxide (GO) has great importance and potential in the biomedical field and can imitate the composition of the extracellular matrix. The oxygen-rich GO is hydrophilic in nature and easily disperses in water, and assists in cell growth, drug delivery, and antimicrobial properties of electrospun nanofiber matrices. NFs containing GO for tissue engineering, drug and gene delivery, wound healing applications, and medical equipment are discussed. NFs containing GO have importance in biomedical applications, which include engineered cardiac patches, instrument coatings, and triboelectric nanogenerators (TENGs) for motion sensing applications. This review deals with graphene-based nanomaterials (GNMs) such as GO incorporated electrospun polymeric NFs for biosensing and biomedical applications, that can bridge the gap between the laboratory facility and industry.

Plasmon-Enhanced Electrocatalysis of Conductive Polymer-Based Nano-Heterojunction for Small Molecule Metabolites Diagnostics

Conductive polymers are promising electrode candidates in the nonenzymatic catalytic detection of small molecule metabolites, due to the tunable electronic conductivity and versatile modifiability. However, the complex catalytic reaction pathway of conductive polymers results in lower detection sensitivity and a narrower linear range compared with clinical metal-based and carbon-based electrodes. Localized surface plasmon resonance (LSPR), characterized by deep strong light-matter coupling, has great potential in driving surface catalytic reactions at an ultrafast rate. Here, we constructed a salix argyracea-like polypyrrole nanowires/silver nanoparticles (PPy/AgNPs) heterojunction electrode using polydopamine as a dopant and chelator. Through cyclic voltammetry, the Mott-Schottky curve, and COMSOL simulation, we demonstrated that the LSPR-excited photocarriers enhanced PPy/AgNPs electrode electrocatalysis. Thus, the detection current response and linear range were significantly improved under the LSPR excitation when taking glucose and hydrogen peroxide as models of small molecule metabolites. Furthermore, we discussed the LSPR-enhanced detection mechanism of PPy/AgNPs electrode from the aspects of the Tafel slope, the apparent electron diffusion coefficient, and the charge transfer resistance. This strategy opens a new avenue toward the design of LSPR-enhanced conductive polymer electrodes.

C. D, Karki B, Samatha K, Kim AA, Park M, Pant B. Advancements in MXene-Polymer Nanocomposites in Energy Storage and Biomedical Applications

MXenes are 2D ceramic materials, especially carbides, nitrides, and carbonitrides derived from their parent ‘MAX’ phases by the etching out of ‘A’ and are famous due to their conducting, hydrophilic, biocompatible, and tunable properties. However, they are hardly stable in the outer environment, have low biodegradability, and have difficulty in drug release, etc., which are overcome by MXene/Polymer nanocomposites. The MXenes terminations on MXene transferred to the polymer after composite formation makes it more functional. With this, there is an increment in photothermal conversion efficiency for cancer therapy, higher antibacterial activity, biosensors, selectivity, bone regeneration, etc. The hydrophilic surfaces become conducting in the metallic range after the composite formation. MXenes can effectively be mixed with other materials like ceramics, metals, and polymers in the form of nanocomposites to get improved properties suitable for advanced applications. In this paper, we review different properties like electrical and mechanical, including capacitances, dielectric losses, etc., of nanocomposites more than those like Ti₃C₂T_x/polymer, Ti₃C₂/UHMWPE, MXene/PVA-KOH, Ti₃C₂T_x/PVA, etc. along with their applications mainly in energy storing and biomedical fields. Further, we have tried to enlist the MXene-based nanocomposites and compare them with conducting polymers and other nanocomposites. The performance under the NIR absorption seems more effective. The MXene-based nanocomposites are more significant in most cases than other nanocomposites for the antimicrobial agent, anticancer activity, drug delivery, bio-imaging, biosensors, micro-supercapacitors, etc. The limitations of the nanocomposites, along with possible solutions, are mentioned.

Optical Biosensor for the Detection of Infectious Diseases Using the Copolymer F8T2 with Application to COVID-19

The coronavirus pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has accelerated the development of biosensors based on new materials and techniques. Here, we present our effort to develop a fast and affordable optical biosensor using photoluminescence spectroscopy for anti-SARS-CoV-2 antibody detection. The biosensor was fabricated with a thin layer of the semiconductor polymer Poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-2,2′-bithiophene-5,5′-diyl)] (F8T2) as a signal transducer material. We mounted the biosensors by depositing a layer of F8T2 and an engineered version of RBD from the SARS-CoV-2 spike protein with a tag to promote hydrophobic interaction between the protein and the polymeric surface. We validated the biosensor sensitivity with decreasing anti-RBD polyclonal IgG concentrations and challenged the biosensor specificity with human serum samples from both COVID-19 negative and positive individuals. The antibody binding to the immobilized antigen shifted the F8T2 photoluminescence spectrum even at the low concentration of 0.0125 µg/mL. A volume as small as one drop of serum (100 µL) was sufficient to distinguish a positive from a negative sample without requiring multiple washing steps and secondary antibody reactions.

A sensitive and selective electrochemical sensor based on molecularly imprinted polymer for the assay of teriflunomide

In this work, pyrrole-histidine has been designed, synthesized and, used as a novel functional monomer to fabricate a molecularly imprinted electrochemical sensor for the selective and sensitive detection of teriflunomide (TER). The molecularly imprinted thin film of electrochemical sensor was constructed by directly electropolymerization of co-polymer of pyrrole-histidine (PyHis) with pyrrole in the presence of a template, TER, on a glassy carbon electrode (GCE). After electropolymerization, the structure and morphology of the fabricated MIP sensor were characterized by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and its electrochemical parameters such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). The poly (pyrrole-co-pyrrole-histidine) [Poly (Py-co-PyHis)]@MIP/GCE sensor have a linear TER concentration in the of 0.1-1.0 pM with a low detection limit of 11.38 fM. The present strategy for electrochemical sensor have been also showed excellent recovery in synthetic serum samples and tablet dosage form with the recoveries 97.56% and 100.35%, respectively. The developed [Poly (Py-co-PyHis)]@MIP/GCE sensor exhibited an excellent electrochemical response for TER due to the synergistic effect of conducting polymer and molecularly imprinting techniques.

Molecularly imprinted polymers via reversible addition-fragmentation chain-transfer synthesis in sensing and environmental applications

Molecularly imprinted polymers (MIP) have shown their potential as artificial and selective receptors for environmental monitoring. These materials can be tailor-made to achieve a specific binding event with a template through a chosen mechanism. They are capable of emulating the recognition capacity of biological receptors with superior stability and versatility of integration in sensing platforms. Commonly, these polymers are produced by traditional free radical bulk polymerization (FRP) which may not be the most suitable for enhancing the intended properties due to the poor imprinting performance. To improve the imprinting technique and the polymer capabilities, controlled/living radical polymerization (CRP) has been used to overcome the main drawbacks of FRP. Combining CRP techniques such as RAFT (reversible addition-fragmentation chain transfer) with MIP has achieved higher selectivity, sensitivity, and sorption capacity of these polymers when implemented as the transductor element in sensors. The present work focuses on RAFT-MIP design and synthesis strategies to enhance the binding affinities and their implementation in environmental contaminant sensing applications.

Conducting polymer-based sensors for food and drug analysis

Conducting polymers (CPs) are a category of polymeric materials with conjugated main chains. The characteristic electrical and optical properties of CPs can be fine-tuned through controlling the doping states of CPs. Because of their long-term stability in water, CPs have been demonstrated as electroactive biointerfaces and electrode materials especially in aqueous environments. Serving as multifunctional interfaces and organic electrodes for the integration bioelectronics and devices, CPs have been studied and applied in various biological applications. This paper provides a review of conducting polymer-based electrochemical sensors, particularly those used in biological fields. General conducting polymers and derivatives and their main electrochemical sensing platforms with different design of devices are introduced. Cyclic voltammetry, differential pulse voltammetry, chronoamperometry, electrochemical impedance spectroscopy, and quartz crystal microbalance methods and their features are then explored as detection methods for the analysis of drugs and food. To enhance the sensitivity and lower the detection limit of sensing platforms, various CP-based nanocomposites have been designed and developed. Although the electrodes made of CP-based nanocomposites usually outperform those made of pristine CPs, more systematic studies are required to provide insights into the design of nanocomposite-based electrodes. More applications of CP-based sensors for advanced food and drug analyses are expected.

PDMS-Parylene Hybrid, Flexible Micro-ECoG Electrode Array for Spatiotemporal Mapping of Epileptic Electrophysiological Activity from Multicortical Brain Regions

Epilepsy detection and focus location are urgent issues that need to be solved in epilepsy research. A cortex conformable and fine spatial accuracy electrocorticogram (ECoG) sensor array, especially for real-time detection of multicortical functional regions and delineating epileptic focus remains a challenge. Here, we fabricated a polydimethylsiloxane (PDMS)-parylene hybrid, flexible micro-ECoG electrode array. The multiwalled carbon nanotubes (MWCNTs)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) nanocomposite-modified electrode interface significantly improved the sensing performance with low impedance (20.68 ± 6.65 kΩ), stable phase offset, and high sensitivity. The electrophysiological activities of multicortical brain regions (somatosensory cortex, parietal association cortex, and visual cortex) were simultaneously monitored during normal and epileptic statuses. The epileptic ECoG activities spread spatiotemporally from the starting point toward the adjacent cortex. Significant variations of the waveform, power, and frequency band were observed. The ECoG potential (123 ± 23 μV) at normal status was prominently up to 417 ± 87 μV at the spike wave stage. Besides, the power for epileptic activity (11.049 ± 4.513 μW) was 10 times higher than that (1.092 ± 0.369 μW) for normal activity. In addition, the theta frequency band was found to be a characteristic frequency band of epileptic signals. These joint analysis results of multicortical regions indicated that the active micron-scale region on the parietal association cortex was more likely to be the epileptogenic focus. Cortical mapping with high spatial detail provides the accurate delineation of lesions. The flexible micro-ECoG electrode array is a powerful tool for constructing a spatiotemporal map of the cortex. It provides a technical platform for epileptic focus location, biomedical diagnosis, and brain-computer interaction.

Silk Fibroin As an Immobilization Matrix for Sensing Applications

The development of flexible, biocompatible, and environment-friendly sensors has attracted a significant amount of scientific interest for the past few decades. Among all the natural materials, silk fibroin (SF), due to its tunable biodegradability, biocompatibility, ease of processing, presence of functional groups, and controllable dimensions, has opened up opportunities for immobilizing multitudinous biomolecules and conformability to the skin, among other attractive opportunities. The silk fibroins also offer good physical properties, such as superior toughness and tensile strength. The sensors made of SF as an immobilization matrix have demonstrated excellent analytical performance, sensing even at low concentrations. The significant advantage of silk fibroins is the presence of functional groups along with a controllable conformation transition that enables immobilization of receptor molecules using silk fibroins as an immobilization matrix enables us to entrap the receptor molecules without using any chemical reagents. This review encompasses a detailed discussion on sensors, the advantages of using silk fibroins as an immobilization matrix for various receptors, their applications, and the future research scope in this state-of-the-art technology based upon the explorable applications for silk fibroin-based sensors.

Graphene impregnated electrospun nanofiber sensing materials: a comprehensive overview on bridging laboratory set-up to industry

Owing to the unique structural characteristics as well as outstanding physio-chemical and electrical properties, graphene enables significant enhancement with the performance of electrospun nanofibers, leading to the generation of promising applications in electrospun-mediated sensor technologies. Electrospinning is a simple, cost-effective, and versatile technique relying on electrostatic repulsion between the surface charges to continuously synthesize various scalable assemblies from a wide array of raw materials with diameters down to few nanometers. Recently, electrospun nanocomposites have emerged as promising substrates with a great potential for constructing nanoscale biosensors due to their exceptional functional characteristics such as complex pore structures, high surface area, high catalytic and electron transfer, controllable surface conformation and modification, superior electric conductivity and unique mat structure. This review comprehends graphene-based nanomaterials (GNMs) (graphene, graphene oxide (GO), reduced GO and graphene quantum dots) impregnated electrospun polymer composites for the electro-device developments, which bridges the laboratory set-up to the industry. Different techniques in the base polymers (pre-processing methods) and surface modification methods (post-processing methods) to impregnate GNMs within electrospun polymer nanofibers are critically discussed. The performance and the usage as the electrochemical biosensors for the detection of wide range analytes are further elaborated. This overview catches a great interest and inspires various new opportunities across a wide range of disciplines and designs of miniaturized point-of-care devices.

Electrochemical DNA Sensor Based on the Copolymer of Proflavine and Azure B for Doxorubicin Determination

A DNA sensor has been developed for the determination of doxorubicin by consecutive electropolymerization of an equimolar mixture of Azure B and proflavine and adsorption of native DNA from salmon sperm on a polymer film. Electrochemical investigation showed a difference in the behavior of individual drugs polymerized and their mixture. The use of the copolymer offered some advantages, i.e., a higher roughness of the surface, a wider range of the pH sensitivity of the response, a denser and more robust film, etc. The formation of the polymer film and its redox properties were studied using scanning electron microscopy and electrochemical impedance spectroscopy. For the doxorubicin determination, its solution was mixed with DNA and applied on the polymer surface. After that, charge transfer resistance was assessed in the presence of [Fe(CN)₆]^3-/4- as the redox probe. Its value regularly grew with the doxorubicin concentration in the range from 0.03 to 10 nM (limit of detection 0.01 nM). The DNA sensor was tested on the doxorubicin preparations and spiked samples mimicking blood serum. The recovery was found to be 98-106%. The DNA sensor developed can find application for the determination of drug residues in blood and for the pharmacokinetics studies.

Polymeric immunosensors for tumor detection

Cancer is a broad-spectrum disease which is spread globally, having high mortality rates. This results from genetic, epigenetic and molecular abnormalities caused by various mutations. The main reason behind this critical problem lies in its diagnostics, the late detection of the disease is the root cause of all this. This can be managed well by the timely diagnosis of cancer by means of the tumor biomarkers present in the body fluids such as serum, blood, and urine. These tumor biomarkers are present in normal conditions as well, but their concentrations are altered in the presence of a malignant tumor. Prolonged studies have reported that immunosensors can be used to detect the minimal amount of biomarkers present in the sample and also provides point-of-care detection. The recent investigations demonstrated the use of polymers along with immunosensors for enhancing their selectivity and sensitivity towards the biomarkers and making them even more efficient. This review focuses on the variety of tumor biomarkers, different types of immunosensors and polymeric immunosensors using different polymers like polypyrrole, polyaniline, PHEMA, etc.

Electrochemical Biosensors for Determination of Colorectal Tumor Biomarkers

The accurate determination of specific tumor markers associated with cancer with non-invasive or minimally invasive procedures is the most promising approach to improve the long-term survival of cancer patients and fight against the high incidence and mortality of this disease. Quantification of biomarkers at different stages of the disease can lead to an appropriate and instantaneous therapeutic action. In this context, the determination of biomarkers by electrochemical biosensors is at the forefront of cancer diagnosis research because of their unique features such as their versatility, fast response, accurate quantification, and amenability for multiplexing and miniaturization. In this review, after briefly discussing the relevant aspects and current challenges in the determination of colorectal tumor markers, it will critically summarize the development of electrochemical biosensors to date to this aim, highlighting the enormous potential of these devices to be incorporated into the clinical practice. Finally, it will focus on the remaining challenges and opportunities to bring electrochemical biosensors to the point-of-care testing.

Advancements in Hydrogel-Functionalized Immunosensing Platforms

Explicit antigen-antibody binding has accelerated the development of immunosensors for the detection of various analytes in biomedical and environmental domains. Being a subclass of biosensors, immunosensors have been a significant area of research in attaining high sensitivity and an ultralow sensing limit to detect biological analytes present in trace levels. The highly porous structure, large surface area, and excellent biocompatibility of hydrogels enabling the retainability of the activity and innate framework of the attached biomolecules make them a suitable candidate for immunosensor fabrication. Hydrogels based on polycarboxylate, cellulose, polyaniline, polypyrrole, sodium alginate, chitosan, and agarose are exploited in conjunction with other nanomaterials such as AuNPs, GO, and MWCNTs to augment the electron transfer during the immunosensing mechanism. Surface plasmon resonance, electrochemiluminescence, colorimetric, and electrochemical assays are different strategies utilized for the signal transduction in hydrogel-based immunosensors during the formation of the antigen-antibody complex. These hydrogel-based immunosensors exhibit rapid response, excellent stability, reproducibility, high selectivity and high sensitivity, a broad range of detection, an ultralow limit of detection, and display results similar to those for the ELISA test. This review propounds different hydrogel-functionalized immunosensing platforms classified on the basis of their signal transduction for the detection of disparate cancer biomarkers (tumor necrosis factor, α-fetoprotein, prostate-specific antigen, carbohydrate antigen 24-2, carcinoembryonic antigen, neuron-specific enolase, and cytokeratin antigen 21-1), hormones (cortisol, cortisone, and human chorionic gonadotropin), human IgG, and ractopamine in animal feeds.

Recent developments in conducting polymers: applications for electrochemistry

Scientists have categorized conductive polymers as materials having strongly reversible redox behavior and uncommon combined features of plastics and metal. Because of their multifunctional characteristics, e.g., simplistic synthesis, acceptable environmental stability, beneficial optical, electronic, and mechanical features, researchers have largely considered them for diverse applications. Therefore, their capability of catalyzing several electrode reactions has been introduced as one of their significant features. A thin layer of the conducting polymer deposited on the substrate electrode surface can augment the electrode process kinetics of several solution species. Such electrocatalytic procedures with modified conducting polymer electrodes can create beneficial utilization in diverse fields of applied electrochemistry. This review article explores typical recent applications of conductive polymers (2016–2020) as active electrode materials for energy storage applications, electrochemical sensing, and conversion fields such as electrochemical supercapacitors, lithium-ion batteries, fuel cells, and solar cells.

Scientists have categorized conductive polymers as materials having strongly reversible redox behavior and uncommon combined features of plastics and metal.