Nanocomposite and Nanoporous Polyaniline Conducting Polymers Exhibit Enhanced Catalysis of Nitrite Reduction

An ultrasensitive biosensor for prostate specific antigen detection in complex serum based on functional signal amplifier and designed peptides with both antifouling and recognizing capabilities

The development of biosensors capable of averting biofouling and detecting biomarkers in complex biological media remains a challenge. Herein, an ultralow fouling and highly sensitive biosensor based on specifically designed antifouling peptides and a signal amplification strategy was designed for prostate specific antigen (PSA) detection in human serum. A low fouling layer of poly(ethylene glycol) (PEG) doped the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was electrodeposited on the electrode surface, followed by the immobilization of streptavidin and further attachment of biotin-labelled peptides. The peptide was designed to include PSA specific recognition domain (HSSKLQK) and antifouling domain (PPPPEKEKEKE), and the terminal of the peptide was functionalized with -SH group. DNA functionalized gold nanorods (DNA/AuNRs) were then attached to the electrode, and methylene blue (MB) molecules were adsorbed to the DNA to form the signal amplifier. In the presence of PSA, the peptide was specifically cleaved and resulted in the loss of AuNRs together with DNA and MB, and thus significant decrease of the current signal. The biosensor exhibited a low limit of detection (LOD) of 0.035 pg mL^-1 (S/N = 3), with a wide linear range from 0.10 pg mL^-1 to 10.0 ng mL^-1, and it was able to detect PSA in real human serum owing to the presence of the antifouling peptides, indicating great potential of the constructed biosensor for practical application.

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.

Phytic acid doped poly(3,4-ethylenedioxythiophene) modified with copper nanoparticles for enzymeless amperometric sensing of glucose

A nanocomposite consisting of phytic acid (PA) that was doped with poly(3,4-ethylenedioxy-thiophene) (PEDOT) and modified with copper nanoparticles (CuNPs) was placed on a glassy carbon electrode and then applied in an enzymeless glucose sensor. The undulating PEDOT/PA composite has good conductivity and a large surface area, which was suitable as substrate for the uniform growth of CuNPs. The modified electrode typically operated at a potential near 0.55 V (vs. Ag/AgCl) demonstrated remarkable catalytic activity towards direct oxidation of glucose in NaOH solution (the major limitation of this sensor). Figures of merit include (a) a wide analytical range (5 to 403 μM); (b) high sensitivity (79.27 μA·μM^-1·cm^-2), (c) a low detection limit (0.28 μM at a signal to noise ratio of 3), and (d) fast response (< 4 s). Graphical abstractA nanocomposite of phytic acid (PA) doped poly(3,4-ethylenedioxy-thiophene) (PEDOT) modified with copper nanoparticles (CuNPs) onto a glassy carbon electrode was prepared by electrochemical strategy. The CuNPs/PEDOT/PA-modified electrodes were applied in enzymeless glucose sensors with high performance.

A polyaniline inverse opal/nanofiber network film fabricated at an air–water interface

An air–water interface polymerization method for producing Janus polyaniline films with inverse opal and nanofiber network at its two sides.

Nitrite-Enhanced Charge Transfer to and from Single Polyaniline Nanotubes

As Liu et al. reported previously (Appl. Mater. Today 2017, 7, 239-245), the charge transfer to partially oxidized polyaniline (PANI) nanotubes in electrochemical reactions is heavily limited due to the non-conductivity of the reduction/oxidation products. In this paper, the doping level of individual PANI nanotubes was substantially enhanced using nitrite as an electron acceptor in sulfuric acid aqueous solution as recorded by the nano-impact method. The charge transferred to one single tube during reduction process is close to the theoretical value of 170±112 pC per tube (assuming 2-electron reduction for the PANI tubes studied), while the charge during PANI oxidation is dramatically decreased. Reaction processes are proposed based on the oxidative properties of nitrite in acid solution. UV-visible spectroscopy analysis further confirms an oxidation-reduction reaction between PANI and nitrite. In contrast the electrochemical reaction of ensembles (21 μg cm^-1 ) of PANI tubes on glassy carbon electrodes simply show limited electrocatalytic activity.

PEGylated Polyaniline Nanofibers: Antifouling and Conducting Biomaterial for Electrochemical DNA Sensing

Biofouling arising from nonspecific adsorption is a substantial outstanding challenge in diagnostics and disease monitoring, and antifouling sensing interfaces capable of reducing the nonspecific adsorption of proteins from biological complex samples are highly desirable. We present herein the preparation of novel composite nanofibers through the grafting of polyethylene glycol (PEG) polymer onto polyaniline (PANI) nanofibers and their application in the development of antifouling electrochemical biosensors. The PEGylated PANI (PANI/PEG) nanofibers possessed large surface area and remained conductive and at the same time demonstrated excellent antifouling performances in single protein solutions as well as complex human serum samples. Sensitive and low fouling electrochemical biosensors for the breast cancer susceptibility gene (BRCA1) can be easily fabricated through the attachment of DNA probes to the PANI/PEG nanofibers. The biosensor showed a very high sensitivity to target BRCA1 with a linear range from 0.01 pM to 1 nM and was also efficient enough to detect DNA mismatches with satisfactory selectivity. Moreover, the DNA biosensor based on the PEGylated PANI nanofibers supported the quantification of BRCA1 in complex human serum, indicating great potential of this novel biomaterial for application in biosensors and bioelectronics.

A non-covalent interaction of Schiff base copper alanine complex with green synthesized reduced graphene oxide for highly selective electrochemical detection of nitrite

A novel and selective nitrite sensor based on non-covalent interaction of Schiff base copper complex [Cu(sal-ala)(phen)] with reduced graphene oxide (RGO) was developed by simple eco-friendly approach.

Nitrite Oxidation with Copper-Cobalt Nanoparticles on Carbon Nanotubes Doped Conducting Polymer PEDOT Composite

Copper-cobalt bimetal nanoparticles (Cu-Co) have been electrochemically prepared on glassy carbon electrodes (GCEs), which were electrodeposited with conducting polymer nanocomposites of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes (CNTs). Owing to their good conductivity, high mechanical strength, and large surface area, the PEDOT/CNTs composites offered excellent substrates for the electrochemical deposition of Cu-Co nanoparticles. As a result of their nanostructure and the synergic effect between Cu and Co, the Cu-Co/PEDOT/CNTs composites exhibited significantly enhanced catalytic activity towards the electrochemical oxidation of nitrite. Under optimized conditions, the nanocomposite-modified electrodes had a fast response time within 2 s and a linear range from 0.5 to 430 μm for the detection of nitrite, with a detection limit of 60 nm. Moreover, the Cu-Co/PEDOT/CNTs composites were highly stable, and the prepared nitrite sensors could retain more than 96 % of their initial response after 30 days.

Cost-effective preparation and sensing application of conducting polymer PEDOT/ionic liquid nanocomposite with excellent electrochemical properties

A stable and porous nanocomposite of PEDOT/IL with excellent electrocatalytic activity was prepared through a cost-effective electrochemical strategy.

A novel electrochemical sensor based on zirconia/ordered macroporous polyaniline for ultrasensitive detection of pesticides

A simple and mild strategy was proposed to develop a novel electrochemical sensor based on zirconia/ordered macroporous polyaniline (ZrO₂/OMP) and further used for the detection of methyl parathion (MP), one of the organophosphate pesticides (OPPs).

Graphene oxide doped poly(3,4-ethylenedioxythiophene) modified with copper nanoparticles for high performance nonenzymatic sensing of glucose

A highly sensitive and stable nonenzymatic glucose sensor was developed through the electrochemical deposition of Cu nanoparticles onto an electrodeposited nanocomposite of conducting polymer PEDOT doped with graphene oxide.

Sandwich approach toward inverse opals with linear and nonlinear optical functionalities

Three-dimensionally ordered macroporous materials have unique structural and optical properties, making them useful for numerous applications in catalysis, membrane science, and optics. Accessible and economic fabrication of these materials is essential to fully explore the many possibilities that these materials present. A new templating method to fabricate three-dimensionally ordered macroporous materials without overlayers is presented. The resulting structures are freestanding inverse opals with large-area uniformity. The versatility and power of our fabrication method is demonstrated by synthesizing inverse opals displaying fluorescence, chirality, upconversion, second harmonic generation, and third harmonic generation. This economical and versatile fabrication method will facilitate research on inverse opals in general and on linear and nonlinear optical effects in 3D photonic crystals specifically. The relative ease of synthesis and wide variety of resulting materials will help the characterization and improvement of existing anomalous dispersion effects in these structures, while providing a platform for the discovery and demonstration of novel effects.

Enhanced catalytic and dopamine sensing properties of electrochemically reduced conducting polymer nanocomposite doped with pure graphene oxide

Significantly enhanced catalytic activity of a nanocomposite composed of conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) doped with graphene oxide (GO) was achieved through a simple electrochemical reduction process. The nanocomposite (PEDOT/GO) was electrodeposited on an electrode and followed by electrochemical reduction, and the obtained reduced nanocomposite (PEDOT/RGO) modified electrode exhibited lowered electrochemical impedance and excellent electrocatalytic activity towards the oxidation of dopamine. Based on the excellent catalytic property of PEDOT/RGO, an electrochemical sensor capable of sensitive and selective detection of DA was developed. The fabricated sensor can detect DA in a wide linear range from 0.1 to 175μM, with a detection limit of 39nM, and it is free from common interferences such as uric acid and ascorbic acid.

Enhanced electrochemical performance of highly porous supercapacitor electrodes based on solution processed polyaniline thin films

Enhancement to the electrochemical performance of supercapacitor electrodes were realized by incorporating highly porous conductive polymer films prepared with solution-processed polyaniline. The resultant nanostructures contained characteristic pores measuring 30-150 nm. Such electrodes generated from a solution of polyaniline-camphorsulfonic acid (PANI/CSA) exhibited higher porosity and electro-catalytic activity than those generated from conventional PANI nanomaterials. These improvements were attributed to faster ion diffusion at the PANI electrode/electrolyte interface. The highest specific capacitance observed for a supercapacitor fabricated with a porous PANI electrode obtained was 361 F g(-1) at 0.25 A g(-1), which is more than twice that of an equivalent electrode made with pristine PANI. Furthermore, supercapacitors made with highly porous PANI electrodes exhibited high electrochemical stability and rate performances.

Novel amperometric aptasensor based on analyte-induced suppression of enzyme catalysis in polymeric bionanocomposites

We report on a novel label-free biosensing interface based on multifunctional polymeric bionanocomposites (PBNCs) and its application for sensitive detection of protein based on the analyte-induced suppression of enzymatic catalysis in PBNCs. Thrombin and its aptamer are adopted as a model system to construct an amperometric aptasensor. First, polydopamine-based PBNCs with glucose oxidase (GOx) entrapped at high load/activity and Au nanoparticles (AuNPs) dispersed in high abundance on the surface were prepared through a chemical/biochemical synthesis method, as proven by UV-vis spectrophotometry, digital imaging, and transmission electron microscopy. Then, the PBNCs were cast-coated onto an Au electrode. The PBNC-modified Au electrode presented a high chronoamperometric sensitivity of 113 ± 2 μA cm(-2) mM(-1) to glucose, as well as a high capability of immobilizing the aptamer through the surficial AuNPs to fabricate a label-free aptasensing interface. The binding of thrombin to the aptasensor surface significantly hindered the mass-transfer of the enzymatic substrates/products and thus suppressed the enzymatic catalysis efficiency, which produced obvious signal change through measuring the electrooxidation of enzymatically generated H(2)O(2). The thus-prepared aptasensor could detect thrombin with a broad detection range (1-100 nM), a detection limit down to 0.1 nM, and satisfactory specificity. The developed aptasensing method may find broad applications in the fields of clinical diagnosis, environmental protection, and food safety.

Detection of gliadin in foods using a quartz crystal microbalance biosensor that incorporates gold nanoparticles

This work develops a label-free gliadin immunosensor that is based on changes in the frequency of a quartz crystal microbalance (QCM) chip. A higher sensitivity was obtained by applying 25 nm gold nanoparticles (AuNPs) to the surface of a bare QCM electrode. Subsequently, chicken anti-gliadin antibodies (IgY) were immobilized directly on the AuNP-modified surface by cross-linking amine groups in IgY with glutaraldehyde. Experimental results revealed that the change in frequency exhibited when 2 ppm gliadin was bound to the AuNP-modified electrode was 35 Hz (48%) greater than that of the bare gold electrode. The linear dynamic range in 60% ethanol was from 1 × 10(1) to 2 × 10(5) ppb gliadin, and the calculated limit of detection (LOD) was 8 ppb. The entire detection process was completed in 40 min and was highly repeatable. Additionally, the AuNP-modified QCM system generated results in the detection of gliadin in 10 commercial food products that were consistent with those obtained using an AOAC-approved gliadin kit. In conclusion, the QCM platform provides a potential alternative means of ensuring that people with wheat allergies and celiac patients have access to gliadin-free food.

Aligned/unaligned conducting polymer cryogels with three-dimensional macroporous architectures from ice-segregation-induced self-assembly of PEDOT-PSS

Porous conducting polymers are of great interest because of the huge potential to combine high surface areas in the dry state with physical properties relevant to organic electronics. Aligned or unaligned conducting polymer cryogels with 3D macroporous architectures have been prepared using the ice-segregation-induced self-assembly (ISISA) of different poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) freezing precursors as a dispersion or a formed hydrogel. The chemical composition and molecular structure of the resulting conducting polymer cryogels have been investigated by X-ray photoelectron spectroscopy and Raman spectroscopy, respectively. The morphologies of the PEDOT-PSS cryogels, together with their textural structures, have been revealed by scanning electron microscopy, mercury porosimetry, and nitrogen sorption tests. Processing PEDOT-PSS via ISISA endows the conducting polymers with novel properties, as demonstrated by a series of X-ray diffraction, differential scanning calorimetry, and electrical conductivity tests. These conducting polymer cryogels with aligned/unaligned macroporous architectures suggest the potential in the development of electronic components, tissue engineering, and next-generation catalytic and separation supports.

Quantum-dot-modified electrode in combination with NADH-dependent dehydrogenase reactions for substrate analysis

A quantum dot-electrode system was developed which allows the sensitive detection of NADH (nicotinamide adenine dinucleotide). The colloidal semiconductive CdSe/ZnS nanocrystals (quantum dots) are attached to gold by chemisorption via a dithiol compound. The current signal can be triggered by illumination of the quantum-dot-modified electrode surface. Because of photoexcitation, electron-hole pairs are generated in the quantum dots, which can be detected as anodic or cathodic photocurrent. The immobilization of the nanocrystals is verified by amperometric photocurrent and quartz crystal microbalance (QCM) measurements. This study shows that CdSe/ZnS quantum dot-modified electrodes allow concentration dependent NADH detection in the range of 20 microM to 2 mM already at rather low potentials (around 0 V vs. Ag/AgCl, 1 M KCl). Therefore such electrodes can be used in combination with NADH-producing enzyme reactions for the light-triggered analysis of the respective substrates of the biocatalyst. It can be shown that glucose detection is feasible with such an electrode system and photocurrent measurements.

Synergistically improved sensitivity for the detection of specific DNA sequences using polyaniline nanofibers and multi-walled carbon nanotubes composites

A sensitive electrochemical DNA biosensor was successfully realized on polyaniline nanofibers (PANI), multi-walled carbon nanotubes (MWNT) and chitosan (CHIT) modified carbon paste electrode (CPE) based on the synergistic effect between PANI and MWNT nanoparticles in chitosan film. PANI and MWNT nanocomposites resulted in highly enhanced electron conductive and biocompatible nanostructured film, which was examined by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The immobilization of the probe DNA on the surface of electrode was largely improved due to the unique synergistic effect of PANI and MWNT. The DNA hybridization events were monitored with an EIS label-free detection strategy. Under the optimal conditions, the dynamic detection range of this DNA electrochemical biosensor was from 1.0 x 10(-13) to 1.0 x 10(-7)mol/L and a detection limit of 2.7 x 10(-14)mol/L for the detection of DNA specific sequence of the phosphinothricin acetyltransferase gene (PAT, one of the important screening detection genes for the transgenic plants). Simultaneously, the polymerase chain reaction (PCR) amplification of the terminator of nopaline synthase gene (NOS) from the sample of one kind of genetically modified soybean was also detected satisfactorily.