Conducting Polymer Based Nanobiosensors

Electronic Tongues and Noses: A General Overview

As technology advances, electronic tongues and noses are becoming increasingly important in various industries. These devices can accurately detect and identify different substances and gases based on their chemical composition. This can be incredibly useful in fields such as environmental monitoring and industrial food applications, where the quality and safety of products or ecosystems should be ensured through a precise analysis. Traditionally, this task is performed by an expert panel or by using laboratory tests but sometimes becomes a bottleneck because of time and other human factors that can be solved with technologies such as the provided by electronic tongue and nose devices. Additionally, these devices can be used in medical diagnosis, quality monitoring, and even in the automotive industry to detect gas leaks. The possibilities are endless, and as these technologies continue to improve, they will undoubtedly play an increasingly important role in improving our lives and ensuring our safety. Because of the multiple applications and developments in this field in the last years, this work will present an overview of the electronic tongues and noses from the point of view of the approaches developed and the methodologies used in the data analysis and steps to this aim. In the same manner, this work shows some of the applications that can be found in the use of these devices and ends with some conclusions about the current state of these technologies.

Development of Paper-Based Fluorescent Molecularly Imprinted Polymer Sensor for Rapid Detection of Lumpy Skin Disease Virus

Lumpy Skin Disease (LSD) is a notifiable viral disease caused by Lumpy Skin Disease virus (LSDV). It is usually associated with high economic losses, including a loss of productivity, infertility, and death. LSDV shares genetic and antigenic similarities with Sheep pox virus (SPV) and Goat pox (GPV) virus. Hence, the LSDV traditional diagnostic tools faced many limitations regarding sensitivity, specificity, and cross-reactivity. Herein, we fabricated a paper-based turn-on fluorescent Molecularly Imprinted Polymer (MIP) sensor for the rapid detection of LSDV. The LSDV-MIPs sensor showed strong fluorescent intensity signal enhancement in response to the presence of the virus within minutes. Our sensor showed a limit of detection of 101 log10 TCID50/mL. Moreover, it showed significantly higher specificity to LSDV relative to other viruses, especially SPV. To our knowledge, this is the first record of a paper-based rapid detection test for LSDV depending on fluorescent turn-on behavior.

Bode Phase Angle Signaling of a TB Disease Biomarker

Tuberculosis (TB) is a worldwide burden whose total control and eradication remains a challenge due to factors including false positive/negative diagnoses associated with the poor sensitivity of the current diagnostics in immune-compromised and post-vaccinated individuals. As these factors complicate both diagnosis and treatment, the early diagnosis of TB is of pivotal importance towards reaching the universal vision of a TB-free world. Here, an aptasensor for signaling an interferon gamma (IFN-γ) TB biomarker at low levels is reported. The aptasensor was assembled through gold-thiol interactions between poly(3,4-propylenedioxythiophene), gold nanoparticles, and a thiol-modified DNA aptamer specific to IFN-γ. The aptasensor sensitively detected IFN-γ in spiked pleural fluid samples with a detection limit of 0.09 pg/mL within a linear range from 0.2 pg/mL to 1.2 pg/mL. The good performance of the reported aptasensor indicates that it holds the potential for application in the early diagnosis of, in addition to TB, various diseases associated with IFN-γ release in clinical samples.

Advancements in tailoring PEDOT: PSS properties for bioelectronic applications: A comprehensive review

In the field of bioelectronics, the demand for biocompatible, stable, and electroactive materials for functional biological interfaces, sensors, and stimulators, is drastically increasing. Conductive polymers (CPs) are synthetic materials, which are gaining increasing interest mainly due to their outstanding electrical, chemical, mechanical, and optical properties. Since its discovery in the late 1980s, the CP Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) has become extremely attractive, being considered as one of the most capable organic electrode materials for several bioelectronic applications in the field of tissue engineering and regenerative medicine. Main examples refer to thin, flexible films, electrodes, hydrogels, scaffolds, and biosensors. Within this context, the authors contend that PEDOT:PSS properties should be customized to encompass: i) biocompatibility, ii) conductivity, iii) stability in wet environment, iv) adhesion to the substrate, and, when necessary, v) (bio-)degradability. However, consolidating all these properties into a single functional solution is not always straightforward. Therefore, the objective of this review paper is to present various methods for acquiring and improving PEDOT:PSS properties, with the primary focus on ensuring its biocompatibility, and simultaneously addressing the other functional features. The last section highlights a collection of designated studies, with a particular emphasis on PEDOT:PSS/carbon filler composites due to their exceptional characteristics.

Nanoparticle Synthesis and Their Integration into Polymer-Based Fibers for Biomedical Applications

The potential of nanoparticles as effective drug delivery systems combined with the versatility of fibers has led to the development of new and improved strategies to help in the diagnosis and treatment of diseases. Nanoparticles have extraordinary characteristics that are helpful in several applications, including wound dressings, microbial balance approaches, tissue regeneration, and cancer treatment. Owing to their large surface area, tailor-ability, and persistent diameter, fibers are also used for wound dressings, tissue engineering, controlled drug delivery, and protective clothing. The combination of nanoparticles with fibers has the power to generate delivery systems that have enhanced performance over the individual architectures. This review aims at illustrating the main possibilities and trends of fibers functionalized with nanoparticles, focusing on inorganic and organic nanoparticles and polymer-based fibers. Emphasis on the recent progress in the fabrication procedures of several types of nanoparticles and in the description of the most used polymers to produce fibers has been undertaken, along with the bioactivity of such alliances in several biomedical applications. To finish, future perspectives of nanoparticles incorporated within polymer-based fibers for clinical use are presented and discussed, thus showcasing relevant paths to follow for enhanced success in the field.

Rapid-format recombinant antibody-based methods for the diagnosis of Clostridioides difficile infection: Recent advances and perspectives

Clostridioides difficile, the most common cause of nosocomial diarrhea, has been continuously reported as a worldwide problem in healthcare settings. Additionally, the emergence of hypervirulent strains of C. difficile has always been a critical concern and led to continuous efforts to develop more accurate diagnostic methods for detection of this recalcitrant pathogen. Currently, the diagnosis of C. difficile infection (CDI) is based on clinical manifestations and laboratory tests for detecting the bacterium and/or its toxins, which exhibit varied sensitivity and specificity. In this regard, development of rapid diagnostic techniques based on antibodies has demonstrated promising results in both research and clinical environments. Recently, application of recombinant antibody (rAb) technologies like phage display has provided a faster and more cost-effective approach for antibody production. The application of rAbs for developing ultrasensitive diagnostic tools ranging from immunoassays to immunosensors, has allowed the researchers to introduce new platforms with high sensitivity and specificity. Additionally, DNA encoding antibodies are directly accessible in these approaches, which enables the application of antibody engineering to increase their sensitivity and specificity. Here, we review the latest studies about the antibody-based ultrasensitive diagnostic platforms for detection of C. difficile bacteria, with an emphasis on rAb technologies.

Poly(1-Napthylamine) Nanoparticles as Potential Scaffold for Supercapacitor and Photocatalytic Applications

Herein, we explore the supercapacitor and photocatalytic applications of poly(1-naphthylamine) (PNA) nanoparticles. The PNA nanoparticles were synthesized by using polymerization of 1-naphthylamine and characterized with several techniques in order to understand the morphological, structural, optical and compositional properties. The structural and morphological properties confirmed the formation of crystalline nanoparticles of PNA. The Fourier-transform infrared (FTIR) spectrum revealed the successful polymerization of 1-naphthylamine monomer to PNA. The absorption peaks that appeared at 236 and 309 nm in the UV−Vis spectrum for PNA nanoparticles represented the π−π* transition. The supercapacitor properties of the prepared PNA nanoparticles were evaluated with cyclic voltammetry (CV) and galvanostatic charge−discharge (GCD) methods at different scan rates and current densities, respectively. The effective series resistance was calculated using electrochemical impedance spectroscopy (EIS), resulting in a minimum resistance value of 1.5 Ω. The highest specific capacitance value of PNA was found to be 255 Fg−1. This electrode also exhibited excellent stability with >93% capacitance retention for 1000 cycles, as measured at 1A g−1. Further, the prepared PNA nanoparticles were used as an effective photocatalyst for the photocatalytic degradation of methylene blue (MB) dye, which exhibited ~61% degradation under UV light irradiation. The observed results revealed that PNA nanoparticles are not only a potential electrode material for supercapacitor applications but also an efficient photocatalyst for the photocatalytic degradation of hazardous and toxic organic dyes.

Conducting Polymer-Coated Carbon Cloth Captures and Releases Extracellular Vesicles by a Rapid and Controlled Redox Process

Electrochemical techniques offer great opportunities for the capture of chemical and biological entities from complex mixtures and their subsequent release into clean buffers for analysis. Such methods are clean, robust, rapid, and compatible with a wide range of biological fluids. Here, we designed an electrochemically addressable system, based on a conducting terpolymer [P(EDOT-co-EDOTSAc-co-EDOTEG)] coated onto a carbon cloth substrate, to selectively capture and release biological entities using a simple electrochemical redox process. The conducting terpolymer composition was optimized and the terpolymer-coated carbon cloth was extensively characterized using electrochemical analysis, Raman and Fourier transform-infrared spectroscopy, water contact angle analysis, and scanning electron microscopy. The conductive terpolymer possesses a derivative of EDOT with an acetylthiomethyl moiety (EDOTSAc), which is converted into a "free" thiol that then undergoes reversible oxidation/reduction cycles at +1.0 V and -0.8 V (vs Ag/AgCl), respectively. That redox process enables electrochemical capture and on-demand release. We first demonstrated the successful electrochemical capture/release of a fluorescently labeled IgG antibody. The same capture/release procedure was then applied to release extracellular vesicles (EVs), originating from both MCF7 and SKBR3 breast cancer cell line bioreactors. EVs were captured using the substrate-conjugated HER2 antibody which was purified from commercially available trastuzumab. Capture and release of breast cancer EVs using a trastuzumab-derived HER2 antibody has not been reported before (to the best of our knowledge). A rapid (2 min) release at a low potential (-0.8 V) achieved a high release efficiency (>70%) of the captured, HER2+ve, SKBR3 EVs. The developed system and the electrochemical method are efficient and straightforward and have vast potential for the isolation and concentration of various biological targets from large volumes of biological and other (e.g., environmental) samples.

Advances and emerging challenges in MXenes and their nanocomposites for biosensing applications

Two-dimensional materials have unique properties and their better functionality has created new paradigms in the field of sensing. Over the past decade, a new family of 2D materials known as MXenes has emerged as a promising material for numerous applications, including biosensing. Their metallic conductivity, rich surface chemistry, hydrophilicity, good biocompatibility, and high anchoring capacity for biomaterials make them an attractive candidate to detect a variety of analytes. Despite such notable properties, there are certain limitations associated with them. This review aims to present a detailed survey of MXene's synthesis; in particular, their superiority in the field of biosensing as compared to other 2D materials is addressed. Their low oxidative stability is still an open challenge, and recent investigations on MXene's oxidation are summarized. The hexagonal stacking network of MXenes acts as a distinctive matrix to load nanoparticles, and the embedded nanoparticles can bind an excess number of biomolecules (e.g., antibodies) thereby improving biosensor performance. We will also discuss the synthesis and corresponding performance of MXenes nanocomposites with noble metal nanoparticles and magnetic nanoparticles. Furthermore, Nb and Ti2C-based MXenes, and Ti3C2-MXene sandwich immunoassays are also reviewed in view of their importance. Different aspects and challenges associated with MXenes (from their synthesis to final applications) and the future perspectives described give new directions to fabricate novel biosensors.

Recent Progress on Nanomaterials for NO2 Surface Acoustic Wave Sensors

NO₂ gas surface acoustic wave (SAW)sensors are under continuous development due to their high sensitivity, reliability, low cost and room temperature operation. Their integration ability with different receptor nanomaterials assures a boost in the performance of the sensors. Among the most exploited nano-materials for sensitive detection of NO₂ gas molecules are carbon-based nanomaterials, metal oxide semiconductors, quantum dots, and conducting polymers. All these nanomaterials aim to create pores for NO₂ gas adsorption or to enlarge the specific surface area with ultra-small nanoparticles that increase the active sites where NO₂ gas molecules can diffuse. This review provides a general overview of NO₂ gas SAW sensors, with a focus on the different sensors’ configurations and their fabrication technology, on the nanomaterials used as sensitive NO₂ layers and on the test methods for gas detection. The synthesis methods of sensing nanomaterials, their functionalization techniques, the mechanism of interaction between NO₂ molecules and the sensing nanomaterials are presented and discussed.

An Overview of Hierarchical Design of Textile-Based Sensor in Wearable Electronics

Smart textiles have recently aroused tremendous interests over the world because of their broad applications in wearable electronics, such as human healthcare, human motion detection, and intelligent robotics. Sensors are the primary components of wearable and flexible electronics, which convert various signals and external stimuli into electrical signals. While traditional electronic sensors based on rigid silicon wafers can hardly conformably attach on the human body, textile materials including fabrics, yarns, and fibers afford promising alternatives due to their characteristics including light weight, flexibility, and breathability. Of fundamental importance are the needs for fabrics simultaneously having high electrical and mechanical performance. This article focused on the hierarchical design of the textile-based flexible sensor from a structure point of view. We first reviewed the selection of newly developed functional materials for textile-based sensors, including metals, conductive polymers, carbon nanomaterials, and other two-dimensional (2D) materials. Then, the hierarchical structure design principles on different levels from microscale to macroscale were discussed in detail. Special emphasis was placed on the microstructure control of fibers, configurational engineering of yarn, and pattern design of fabrics. Finally, the remaining challenges toward industrialization and commercialization that exist to date were presented.

Nano-biosupercapacitors enable autarkic sensor operation in blood

Today's smallest energy storage devices for in-vivo applications are larger than 3 mm³ and lack the ability to continuously drive the complex functions of smart dust electronic and microrobotic systems. Here, we create a tubular biosupercapacitor occupying a mere volume of 1/1000 mm³ (=1 nanoliter), yet delivering up to 1.6 V in blood. The tubular geometry of this nano-biosupercapacitor provides efficient self-protection against external forces from pulsating blood or muscle contraction. Redox enzymes and living cells, naturally present in blood boost the performance of the device by 40% and help to solve the self-discharging problem persistently encountered by miniaturized supercapacitors. At full capacity, the nano-biosupercapacitors drive a complex integrated sensor system to measure the pH-value in blood. This demonstration opens up opportunities for next generation intravascular implants and microrobotic systems operating in hard-to-reach small spaces deep inside the human body.

Preparations, Properties, and Applications of Polyaniline and Polyaniline Thin Films-A Review

Polyaniline (PANI) is a famous conductive polymer, and it has received tremendous consideration from researchers in the field of nanotechnology for the improvement of sensors, optoelectronic devices, and photonic devices. PANI is doped easily by different acids and dopants because of its easy synthesis and remarkable environmental stability. This review focuses on different preparation processes of PANI thin film by chemical and physical methods. Several features of PANI thin films, such as their magnetic, redox, and antioxidant, anti-corrosion, and electrical and sensing properties, are discussed in this review. PANI is a highly conductive polymer. Given its unique properties, easy synthesis, low cost, and high environmental stability in various applications such as electronics, drugs, and anti-corrosion materials, it has attracted extensive attention. The most important PANI applications are briefly reviewed at the end of this review.

Recent Advances in the Fabrication and Functionalization of Flexible Optical Biosensors: Toward Smart Life-Sciences Applications

Over the last 30 years, optical biosensors based on nanostructured materials have obtained increasing interest since they allow the screening of a wide variety of biomolecules with high specificity, low limits of detection, and great sensitivity. Among them, flexible optical platforms have the advantage of adapting to non-planar surfaces, suitable for in vivo and real-time monitoring of diseases and assessment of food safety. In this review, we summarize the newest and most advanced platforms coupling optically active materials (noble metal nanoparticles) and flexible substrates giving rise to hybrid nanomaterials and/or nanocomposites, whose performances are comparable to the ones obtained with hard substrates (e.g., glass and semiconductors). We focus on localized surface plasmon resonance (LSPR)-based and surface-enhanced Raman spectroscopy (SERS)-based biosensors. We show that large-scale, cost-effective plasmonic platforms can be realized with the currently available techniques and we emphasize the open issues associated with this topic.

Recent Advances of Field-Effect Transistor Technology for Infectious Diseases

Field-effect transistor (FET) biosensors have been intensively researched toward label-free biomolecule sensing for different disease screening applications. High sensitivity, incredible miniaturization capability, promising extremely low minimum limit of detection (LoD) at the molecular level, integration with complementary metal oxide semiconductor (CMOS) technology and last but not least label-free operation were amongst the predominant motives for highlighting these sensors in the biosensor community. Although there are various diseases targeted by FET sensors for detection, infectious diseases are still the most demanding sector that needs higher precision in detection and integration for the realization of the diagnosis at the point of care (PoC). The COVID-19 pandemic, nevertheless, was an example of the escalated situation in terms of worldwide desperate need for fast, specific and reliable home test PoC devices for the timely screening of huge numbers of people to restrict the disease from further spread. This need spawned a wave of innovative approaches for early detection of COVID-19 antibodies in human swab or blood amongst which the FET biosensing gained much more attention due to their extraordinary LoD down to femtomolar (fM) with the comparatively faster response time. As the FET sensors are promising novel PoC devices with application in early diagnosis of various diseases and especially infectious diseases, in this research, we have reviewed the recent progress on developing FET sensors for infectious diseases diagnosis accompanied with a thorough discussion on the structure of Chem/BioFET sensors and the readout circuitry for output signal processing. This approach would help engineers and biologists to gain enough knowledge to initiate their design for accelerated innovations in response to the need for more efficient management of infectious diseases like COVID-19.

Development strategies of conducting polymer-based electrochemical biosensors for virus biomarkers: Potential for rapid COVID-19 detection

Rapid, accurate, portable, and large-scale diagnostic technologies for the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) are crucial for controlling the coronavirus disease (COVID-19). The current standard technologies, i.e., reverse-transcription polymerase chain reaction, serological assays, and computed tomography (CT) exhibit practical limitations and challenges in case of massive and rapid testing. Biosensors, particularly electrochemical conducting polymer (CP)-based biosensors, are considered as potential alternatives owing to their large advantages such as high selectivity and sensitivity, rapid detection, low cost, simplicity, flexibility, long self-life, and ease of use. Therefore, CP-based biosensors can serve as multisensors, mobile biosensors, and wearable biosensors, facilitating the development of point-of-care (POC) systems and home-use biosensors for COVID-19 detection. However, the application of these biosensors for COVID-19 entails several challenges related to their degradation, low crystallinity, charge transport properties, and weak interaction with biomarkers. To overcome these problems, this study provides scientific evidence for the potential applications of CP-based electrochemical biosensors in COVID-19 detection based on their applications for the detection of various biomarkers such as DNA/RNA, proteins, whole viruses, and antigens. We then propose promising strategies for the development of CP-based electrochemical biosensors for COVID-19 detection.

Development of nano-immunosensor with magnetic separation and electrical detection of Escherichia coli using antibody conjugated Fe3O4@Ppy

Detection of bacterial pathogens is the need of the hour due to the increase in antibiotic resistance and the infusion of multi-drug-resistant parasites. The conventional strategies such as ELISA, PCR, and MNP based tests for the detection are efficient but they are cost, time, lab, and manpower intensive. Thus, warranting a simple and effective technique for rapid detection of bacterial pathogens. Magnetic nanoparticles (NPs) have proved to be better alternatives for separation of bacterial pathogens from a variety of sample sources. However, the use of magnetic NPs has not been successful in the detection of these parasites. The current work involves the coating of magnetic NPs (Fe₃O₄) with a conducting polymer (polypyrrole; Ppy) to facilitate simultaneous separation and detection. Electrical (conductivity) measurement was the mode of choice due to the sensitivity, accuracy, and ease it offers. To enhance the conductivity, carboxylic groups were expressed on the Fe₃O₄@Ppy complex and to ensure specificity, E. coli specific antibodies were conjugated. The resulting complex at various process parameters was characterized using FTIR, VSM, and SEM. SEM images were recorded to ensure bacterial separation at optimal process parameters. The impedance analysis and conductivity measurements were carried out for the sample volume of 15 μl. The bacterial suspension from 10¹-10⁶ CFU ml^-1 was successfully detected with a limit of detection of 10 CFU ml^-1 within 10 min using a simplistic detection method.

Charge Transfer and Biocompatibility Aspects in Conducting Polymer-Based Enzymatic Biosensors and Biofuel Cells

Charge transfer (CT) is a very important issue in the design of biosensors and biofuel cells. Some nanomaterials can be applied to facilitate the CT in these bioelectronics-based devices. In this review, we overview some CT mechanisms and/or pathways that are the most frequently established between redox enzymes and electrodes. Facilitation of indirect CT by the application of some nanomaterials is frequently applied in electrochemical enzymatic biosensors and biofuel cells. More sophisticated and still rather rarely observed is direct charge transfer (DCT), which is often addressed as direct electron transfer (DET), therefore, DCT/DET is also targeted and discussed in this review. The application of conducting polymers (CPs) for the immobilization of enzymes and facilitation of charge transfer during the design of biosensors and biofuel cells are overviewed. Significant attention is paid to various ways of synthesis and application of conducting polymers such as polyaniline, polypyrrole, polythiophene poly(3,4-ethylenedioxythiophene). Some DCT/DET mechanisms in CP-based sensors and biosensors are discussed, taking into account that not only charge transfer via electrons, but also charge transfer via holes can play a crucial role in the design of bioelectronics-based devices. Biocompatibility aspects of CPs, which provides important advantages essential for implantable bioelectronics, are discussed.

Electrochemical Sensors Based on Conducting Polymers for the Aqueous Detection of Biologically Relevant Molecules

Electrochemical sensors appear as low-cost, rapid, easy to use, and in situ devices for determination of diverse analytes in a liquid solution. In that context, conducting polymers are much-explored sensor building materials because of their semiconductivity, structural versatility, multiple synthetic pathways, and stability in environmental conditions. In this state-of-the-art review, synthetic processes, morphological characterization, and nanostructure formation are analyzed for relevant literature about electrochemical sensors based on conducting polymers for the determination of molecules that (i) have a fundamental role in the human body function regulation, and (ii) are considered as water emergent pollutants. Special focus is put on the different types of micro- and nanostructures generated for the polymer itself or the combination with different materials in a composite, and how the rough morphology of the conducting polymers based electrochemical sensors affect their limit of detection. Polypyrroles, polyanilines, and polythiophenes appear as the most recurrent conducting polymers for the construction of electrochemical sensors. These conducting polymers are usually built starting from bifunctional precursor monomers resulting in linear and branched polymer structures; however, opportunities for sensitivity enhancement in electrochemical sensors have been recently reported by using conjugated microporous polymers synthesized from multifunctional monomers.

Conducting Polymers in the Design of Biosensors and Biofuel Cells

Fast and sensitive determination of biologically active compounds is very important in biomedical diagnostics, the food and beverage industry, and environmental analysis. In this review, the most promising directions in analytical application of conducting polymers (CPs) are outlined. Up to now polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene) are the most frequently used CPs in the design of sensors and biosensors; therefore, in this review, main attention is paid to these conducting polymers. The most popular polymerization methods applied for the formation of conducting polymer layers are discussed. The applicability of polypyrrole-based functional layers in the design of electrochemical biosensors and biofuel cells is highlighted. Some signal transduction mechanisms in CP-based sensors and biosensors are discussed. Biocompatibility-related aspects of some conducting polymers are overviewed and some insights into the application of CP-based coatings for the design of implantable sensors and biofuel cells are addressed. New trends and perspectives in the development of sensors based on CPs and their composites with other materials are discussed.

Biosensors for the Detection of Bacterial and Viral Clinical Pathogens

Biosensors are measurement devices that can sense several biomolecules, and are widely used for the detection of relevant clinical pathogens such as bacteria and viruses, showing outstanding results. Because of the latent existing risk of facing another pandemic like the one we are living through due to COVID-19, researchers are constantly looking forward to developing new technologies for diagnosis and treatment of infections caused by different bacteria and viruses. Regarding that, nanotechnology has improved biosensors' design and performance through the development of materials and nanoparticles that enhance their affinity, selectivity, and efficacy in detecting these pathogens, such as employing nanoparticles, graphene quantum dots, and electrospun nanofibers. Therefore, this work aims to present a comprehensive review that exposes how biosensors work in terms of bacterial and viral detection, and the nanotechnological features that are contributing to achieving a faster yet still efficient COVID-19 diagnosis at the point-of-care.

Advancements in Microfabricated Gas Sensors and Microanalytical Tools for the Sensitive and Selective Detection of Odors

In recent years, advancements in micromachining techniques and nanomaterials have enabled the fabrication of highly sensitive devices for the detection of odorous species. Recent efforts done in the miniaturization of gas sensors have contributed to obtain increasingly compact and portable devices. Besides, the implementation of new nanomaterials in the active layer of these devices is helping to optimize their performance and increase their sensitivity close to humans' olfactory system. Nonetheless, a common concern of general-purpose gas sensors is their lack of selectivity towards multiple analytes. In recent years, advancements in microfabrication techniques and microfluidics have contributed to create new microanalytical tools, which represent a very good alternative to conventional analytical devices and sensor-array systems for the selective detection of odors. Hence, this paper presents a general overview of the recent advancements in microfabricated gas sensors and microanalytical devices for the sensitive and selective detection of volatile organic compounds (VOCs). The working principle of these devices, design requirements, implementation techniques, and the key parameters to optimize their performance are evaluated in this paper. The authors of this work intend to show the potential of combining both solutions in the creation of highly compact, low-cost, and easy-to-deploy platforms for odor monitoring.

Light-Induced Nanowetting: Erasable and Rewritable Polymer Nanoarrays via Solid-to-Liquid Transitions

Template wetting methods have been widely applied in the preparation of one-dimensional (1D) polymer nanomaterials. The pattern control using the template wetting methods, however, still remains a great challenge, mainly due to the nonselectivity of the polymers toward the environmental triggering. In this work, we present a facile light-induced nanowetting (LIN) method to fabricate patterned nanoarrays using anodic aluminum oxide (AAO) templates. Photoresponsive azobenzene-containing polymers (azopolymers) that exhibit light-induced reversible solid-to-liquid transitions are used. Upon exposure to ultraviolet lights, the azopolymer chains can wet the nanopores of the AAO templates in a liquid state via capillary force. The azopolymer chains are then solidified by illuminating them with visible lights, resulting in the formation of azopolymer nanoarrays. Notably, using designed photomasks, the patterns of the nanoarrays can be ingeniously controlled with the characteristic of erasable and rewritable nanostructures.

Combining Electrospinning and Vapor-Phase Polymerization for the Production of Polyacrylonitrile/ Polypyrrole Core-Shell Nanofibers and Glucose Biosensor Application

In this work, polyacrylonitrile (PAN) nanofiber mats coated with conductive polypyrrole layers were produced at the surface of gold electrodes by a two-step approach combining electrospinning and vapor phase polymerization. In the first step, smooth and uniform PAN fibers exhibiting an average diameter of 650 ± 10 nm were generated through electrospinning of 12 wt% PAN solutions. The electrospun PAN fibers were impregnated with iron(III)tosylate (FeTos), annealed at 70°C and used as a robust and stable template for the growth of a thin layer of conductive polymer by co-polymerizing pyrrole (Py) and pyrrole-3-carboyxylic acid (Py3COOH) vapors under nitrogen atmosphere. The carboxyl groups introduced in polypyrrole coatings enabled further covalent binding of a model enzyme, glucose oxidase. The effect of different parameters (concentration of FeTos into the immersion solution, time of polymerization, Py/Py3COOH molar ratio) on the PAN/PPy/PPy3COOH/GOx impedimetric biosensor response was investigated. In the best conditions tested (immersion of the PAN fibers into 20 wt% FeTos solution, polymerization time: 30 min, 1:2 Py/Py3COOH ratio), the biosensor response was linear in a wide range of glucose concentration (20 nM−2μM) and selective toward ascorbic and uric acids. A very low limit of detection (2 nM) compared to those already reported in the literature was achieved. This value enables the determination of glucose in human serum after a large dilution of the sample (normal concentrations: 3.6 mM−6.1 mM range).

Biosensors on the road to early diagnostic and surveillance of Alzheimer's disease

Alzheimer's disease is a debilitating and largely untreatable condition with subtle onset and slow progression over an extensive period of time, which culminate in increasing levels of disability. As Alzheimer's disease prevalence is expected to grow exponentially in the upcoming decades, there is an urgency to develop analytical technologies for the sensitive, reliable and cost-effective detection of Alzheimer's disease biomarkers. Biosensors are powerful analytical devices that translate events of biological recognition on physical or chemical transducers into electrical, thermal or optical signals. The high sensitivity and selectivity of biosensors associated with easy, rapid and low-cost determination of analytes have made this discipline one of the most intensively studied in the past decades. This review centers on recent advances, challenges and trends of Alzheimer's disease biosensing particularly in the effort to combine the unique properties of nanomaterials with biorecognition elements. In the last decade, impressive progresses have been made towards the development of biosensors, mainly electrochemical and optical, for detection of Alzheimer's disease biomarkers in the pico- and femto-molar range. Nonetheless, advances in multiplexed detection, robustness, stability and specificity are still necessary to ensure an accurate and differentiated diagnosis of this disease.

Nanomaterials towards Biosensing of Alzheimer's Disease Biomarkers

Alzheimer's disease (AD) is an incurable and highly debilitating condition characterized by the progressive degeneration and/or death of nerve cells, which leads to manifestation of disabilities in cognitive functioning. In recent years, the development of biosensors for determination of AD's main biomarkers has made remarkable progress, particularly based on the tremendous advances in nanoscience and nanotechnology. The unique and outstanding properties of nanomaterials (such as graphene, carbon nanotubes, gold, silver and magnetic nanoparticles, polymers and quantum dots) have been contributing to enhance the electrochemical and optical behavior of transducers while offering a suitable matrix for the immobilization of biological recognition elements. Therefore, optical and electrochemical immuno- and DNA-biosensors with higher sensitivity, selectivity and longer stability have been reported. Nevertheless, strategies based on the detection of multiple analytes still need to be improved, as they will play a crucial role in minimizing misdiagnosis. This review aims to provide insights into the conjugation of nanomaterials with different transducers highlighting their crucial role in the construction of biosensors for detection of AD main biomarkers.

Development of Fast E-nose System for Early-Stage Diagnosis of Aphid-Stressed Tomato Plants

An electronic nose (E-nose) system equipped with a sensitive sensor array was developed for fast diagnosis of aphid infestation on greenhouse tomato plants at early stages. Volatile organic compounds (VOCs) emitted by tomato plants with and without aphid attacks were detected using both the developed E-nose system and gas chromatography mass spectrometry (GC-MS), respectively. Sensor performance, with fast sensor responses and high sensitivity, were observed using the E-nose system. A principle component analysis (PCA) indicated accurate diagnosis of aphid-stressed plants compared to healthy ones, with the first two PCs accounting for 86.7% of the classification. The changes in VOCs profiles of the healthy and infested tomato plants were quantitatively determined by GC-MS. Results indicated that a group of new VOCs biomarkers (linalool, carveol, and nonane (2,2,4,4,6,8,8-heptamethyl-)) played a role in providing information on the infestation on the tomato plants. More importantly, the variation in the concentration of sesquiterpene VOCs (e.g., caryophyllene) and new terpene alcohol compounds was closely associated with the sensor responses during E-nose testing, which verified the reliability and accuracy of the developed E-nose system. Tomato plants growing in spring had similar VOCs profiles as those of winter plants, except several terpenes released from spring plants that had a slightly higher intensity.

Electrochemical sensors and biosensors based on the use of polyaniline and its nanocomposites: a review on recent advances

Polyaniline and its composites with nanoparticles have been widely used in electrochemical sensor and biosensors due to their attractive properties and the option of tuning them by proper choice of materials. The review (with 191 references) describes the progress made in the recent years in polyaniline-based biosensors and their applications in clinical sensing, food quality control, and environmental monitoring. A first section summarizes the features of using polyaniline in biosensing systems. A subsequent section covers sensors for clinical applications (with subsections on the detection of cancer cells and bacteria, and sensing of glucose, uric acid, and cholesterol). Further sections discuss sensors for use in the food industry (such as for sulfite, phenolic compounds, acrylamide), and in environmental monitoring (mainly pesticides and heavy metal ions). A concluding section summarizes the current state, highlights some of the challenges currently compromising performance in biosensors and nanobiosensors, and discusses potential future directions. Graphical abstract Schematic presentation of electrochemical sensor and biosensors applications based on polyaniline/nanoparticles in various fields of human life including medicine, food industry, and environmental monitoring. The simultaneous use of suitable properties polyaniline and nanoparticles can provide the fabrication of sensing systems with high sensitivity, short response time, high signal/noise ratio, low detection limit, and wide linear range by improving conductivity and the large surface area for biomolecules immobilization.

Applications of PEDOT in bioelectronic medicine

The widespread use of conducting polymers, especially poly(3,4-ethylene dioxythiophene) (PEDOT), within the space of bioelectronics has enabled improvements, both in terms of electrochemistry and functional versatility, of conventional metallic electrodes. This short review aims to provide an overview of how PEDOT coatings have contributed to functionalizing existing bioelectronics, the challenges which meet conducting polymer coatings from a regulatory and stability point of view and the possibilities to bring PEDOT-based coatings into large-scale clinical applications. Finally, their potential use for enabling new technologies for the field of bioelectronics as biodegradable, stretchable and slow-stimulation materials will be discussed.

Evolution of Self-Organized Microcapsules with Variable Conductivities from Self-Assembled Nanoparticles at Interfaces

Self-organization dramatically affects the surface properties of materials on a macroscopic scale, such as wettability and adhesion. Fundamentally, it is equally interesting when self-organization at the nanoscale affects the bulk properties and thus provides a means to engineer the optoelectronic properties of the materials on larger scales. In this work, we report the evolution of conductive self-organized polymer microcapsules from a monomer emulsion droplet stabilized by a monolayer of conductive Janus nanoparticles (JNPs) via a mechanism resembling morphogenesis. The wall of the resulting conductive microcapsule has a honeycomb-like structure with highly oriented JNPs occupying each hollow cell. The JNPs consist of an electrically conductive lobe and an insulating lobe; because of their orientation and presence in the honeycomb, the conductivity of the microcapsule is greatly enhanced as compared to that of each of the constituting materials. This method can be universally applied to induce self-organization in conductive polymers forming by oxidative addition.

Facile and controllable electrochemical fabrication of cell-adhesive polypyrrole electrodes using pyrrole-RGD peptides

Electrically conductive polymers, such as polypyrrole (PPy), have been widely used for the fabrication of various biosensors and tissue engineering scaffolds. For their biologically relevant applications, conductive biomaterials capable of intimate cellular interactions are highly desired. However, conventional methods to incorporate biomolecules into conductive polymers do not offer fine and easy control over the surface density of the biomolecules and/or their stability. We present a novel method to electrochemically immobilize cell-adhesive Arg-Gly-Asp (RGD) ligands on PPy electrode surfaces with a simple control over the peptide surface density by varying the electrodeposition time. Synthesized pyrrole-GGGRGDS conjugates were electrochemically incorporated onto the surfaces of PPy-coated electrodes. The electrochemical impedances of the RGD-grafted PPy electrodes were not significantly different from the unmodified PPy films. Time-of-flight secondary-ion mass spectroscopy confirmed the presence of the RGD motif on the surface of the modified electrodes. In vitro studies with human mesenchymal stem cells (hMSCs) showed higher adhesion and faster proliferation of hMSCs on the PPy with a higher RGD density. This facile electrochemical modification of electrode surfaces allowed for a good control over the peptide surface density and cellular interactions and will benefit the fabrication of cell-interactive scaffolds or bio-electrodes.