Electric-field-assisted growth of functionalized poly(3,4-ethylenedioxythiophene) nanowires for label-free protein detection

Aptamer-functionalized field-effect transistor biosensors for disease diagnosis and environmental monitoring

Nano-biosensors that are composed of recognition molecules and nanomaterials have been extensively utilized in disease diagnosis, health management, and environmental monitoring. As a type of nano-biosensors, molecular specificity field-effect transistor (FET) biosensors with signal amplification capability exhibit prominent advantages including fast response speed, ease of miniaturization, and integration, promising their high sensitivity for molecules detection and identification. With intrinsic characteristics of high stability and structural tunability, aptamer has become one of the most commonly applied biological recognition units in the FET sensing fields. This review summarizes the recent progress of FET biosensors based on aptamer functionalized nanomaterials in medical diagnosis and environmental monitoring. The structure, sensing principles, preparation methods, and functionalization strategies of aptamer modified FET biosensors were comprehensively summarized. The relationship between structure and sensing performance of FET biosensors was reviewed. Furthermore, the challenges and future perspectives of FET biosensors were also discussed, so as to provide support for the future development of efficient healthcare management and environmental monitoring devices.

Advances in the Translation of Electrochemical Hydrogel-Based Sensors

Novel biomaterials for bio- and chemical sensing applications have gained considerable traction in the diagnostic community with rising trends of using biocompatible and lowly cytotoxic material. Hydrogel-based electrochemical sensors have become a promising candidate for their swellable, nano-/microporous, and aqueous 3D structures capable of immobilizing catalytic enzymes, electroactive species, whole cells, and complex tissue models, while maintaining tunable mechanical properties in wearable and implantable applications. With advances in highly controllable fabrication and processability of these novel biomaterials, the possibility of bio-nanocomposite hydrogel-based electrochemical sensing presents a paradigm shift in the development of biocompatible, "smart," and sensitive health monitoring point-of-care devices. Here, recent advances in electrochemical hydrogels for the detection of biomarkers in vitro, in situ, and in vivo are briefly reviewed to demonstrate their applicability in ideal conditions, in complex cellular environments, and in live animal models, respectively, to provide a comprehensive assessment of whether these biomaterials are ready for point-of-care translation and biointegration. Sensors based on conductive and nonconductive polymers are presented, with highlights of nano-/microstructured electrodes that provide enhanced sensitivity and selectivity in biocompatible matrices. An outlook on current challenges that shall be addressed for the realization of truly continuous real-time sensing platforms is also presented.

Nanowire-based sensor electronics for chemical and biological applications

Detection and recognition of chemical and biological species via sensor electronics are important not only for various sensing applications but also for fundamental scientific understanding. In the past two decades, sensor devices using one-dimensional (1D) nanowires have emerged as promising and powerful platforms for electrical detection of chemical species and biologically relevant molecules due to their superior sensing performance, long-term stability, and ultra-low power consumption. This paper presents a comprehensive overview of the recent progress and achievements in 1D nanowire synthesis, working principles of nanowire-based sensors, and the applications of nanowire-based sensor electronics in chemical and biological analytes detection and recognition. In addition, some critical issues that hinder the practical applications of 1D nanowire-based sensor electronics, including device reproducibility and selectivity, stability, and power consumption, will be highlighted. Finally, challenges, perspectives, and opportunities for developing advanced and innovative nanowire-based sensor electronics in chemical and biological applications are featured.

Multifunctional one-dimensional polymeric nanostructures for drug delivery and biosensor applications

Advances in nanotechnology in the last decades have paved the way for significant achievements in diagnosis and treatment of various diseases. Different types of functional nanostructures have been explored and utilized as tools for addressing the challenges in detection or treatment of diseases. In particular, one-dimensional nanostructures hold great promise in theranostic applications due to their increased surface area-to-volume ratios, which allow better targeting, increased loading capacity and improved sensitivity to biomolecules. Stable polymeric nanostructures that are stimuli-responsive, biocompatible and biodegradable are especially preferred for bioapplications. In this review, different synthesis techniques of polymeric one-dimensional nanostructures are explored and functionalization methods of these nanostructures for specific applications are explained. Biosensing and drug delibiovery applications of these nanostructures are presented in detail.

Soft and flexible material-based affinity sensors

Recent advances in biosensors and point-of-care (PoC) devices are poised to change and expand the delivery of diagnostics from conventional lateral-flow assays and test strips that dominate the market currently, to newly emerging wearable and implantable devices that can provide continuous monitoring. Soft and flexible materials are playing a key role in propelling these trends towards real-time and remote health monitoring. Affinity biosensors have the capability to provide for diagnosis and monitoring of cancerous, cardiovascular, infectious and genetic diseases by the detection of biomarkers using affinity interactions. This review tracks the evolution of affinity sensors from conventional lateral-flow test strips to wearable/implantable devices enabled by soft and flexible materials. Initially, we highlight conventional affinity sensors exploiting membrane and paper materials which have been so successfully applied in point-of-care tests, such as lateral-flow immunoassay strips and emerging microfluidic paper-based devices. We then turn our attention to the multifarious polymer designs that provide both the base materials for sensor designs, such as PDMS, and more advanced functionalised materials that are capable of both recognition and transduction, such as conducting and molecularly imprinted polymers. The subsequent content discusses wearable soft and flexible material-based affinity sensors, classified as flexible and skin-mountable, textile materials-based and contact lens-based affinity sensors. In the final sections, we explore the possibilities for implantable/injectable soft and flexible material-based affinity sensors, including hydrogels, microencapsulated sensors and optical fibers. This area is truly a work in progress and we trust that this review will help pull together the many technological streams that are contributing to the field.

Deprotonation-Induced Conductivity Shift of Polyethylenedioxythiophenes in Aqueous Solutions: The Effects of Side-Chain Length and Polymer Composition

Deprotonation-induced conductivity shift of poly(3,4-ethylenedixoythiophene)s (PEDOTs) in aqueous solutions is a promising platform for chemical or biological sensor due to its large signal output and minimum effect from material morphology. Carboxylic acid group functionalized poly(Cn-EDOT-COOH)s are synthesized and electrodeposited on microelectrodes. The microelectrodes are utilized to study the effect of carboxylic acid side-chain length on the conductivity curve profiles in aqueous buffer with different pH. The conductivity shifts due to the buffer pH are effected by the length of the carboxylic acid side-chains. The shifts can be explained by the carboxylic acid dissociation property (pKa) at the solid-liquid interface, self-doping effect, and effective conjugation length. Conductivity profiles of poly(EDOT-OH-co-C₂-EDOT-COOH) copolymers are also studied. The shifts show linear relationship with the feed monomer composition used in electrochemical polymerization.

Multidimensional Conductive Nanofilm-Based Flexible Aptasensor for Ultrasensitive and Selective HBsAg Detection

Hepatitis B virus (HBV) infection is a major worldwide health issue causing serious liver diseases, including liver cirrhosis and hepatocellular carcinoma. Monitoring the serum hepatitis B surface antigen (HBsAg) level is pivotal to the diagnosis of HBV infection. In this study, we describe multidimensional conductive nanofilm (MCNF)-based field-effect transistor (FET) aptasensor for HBsAg detection. The MCNF, composed of vertically oriented carboxylic polypyrrole nanowires (CPPyNW) and graphene layer, is formed using electropolymerization of pyrrole on the graphene surface and following acid treatment. The amine-functionalized HBsAg-binding aptamers are then immobilized on the CPPyNW surface through covalent bonding formation (i.e., amide group). The prepared aptasensor presents highly sensitive to HBsAg as low as 10 aM among interfering biomolecules with various deformations. Moreover, the MCNF-based aptasensor has great potential for practical application in the noninvasive real-time diagnosis because of its improved sensing ability to the human serum and artificial saliva.

Glycan Stimulation Enables Purification of Prostate Cancer Circulating Tumor Cells on PEDOT NanoVelcro Chips for RNA Biomarker Detection

A glycan-stimulated and poly(3,4-ethylene-dioxythiophene)s (PEDOT)-based nanomaterial platform is fabricated to purify circulating tumor cells (CTCs) from blood samples of prostate cancer (PCa) patients. This new platform, phenylboronic acid (PBA)-grafted PEDOT NanoVelcro, combines the 3D PEDOT nanosubstrate, which greatly enhances CTC capturing efficiency, with a poly(EDOT-PBA-co-EDOT-EG3) interfacial layer, which not only provides high specificity for CTC capture upon antibody conjugation but also enables competitive binding of sorbitol to gently release the captured cells. CTCs purified by this PEDOT NanoVelcro chip provide well-preserved RNA transcripts for the analysis of the expression level of several PCa-specific RNA biomarkers, which may provide clinical insights into the disease.

PNA versus DNA in electrochemical gene sensing based on conducting polymers: study of charge and surface blocking effects on the sensor signal

In this communication, we present an in-depth study of DNA/DNA, DNA/PNA and PNA/PNA hybridisation on a conducting polymer-modified electrode, measured by means of electrochemical impedance spectroscopy (EIS). DNA or PNA nucleic base sequence probes (where DNA stands for deoxyribonucleic acid and PNA for peptide nucleic acid) were covalently attached onto the sensor surface. As PNA is a non-charged variant of DNA, we investigate the effects of the surface charge and surface blocking by the surface confined probe/target nucleic bases complexes onto the kinetics of redox reaction of Fe(CN)₆^3-/4- couple occurring at the electrode/solution interface that provides electrochemical readout for hybridisation. A range of hybridisation detection experiments were performed, where the surface charge and surface charge density were varied, through varying the charged nature of the probe and the target (i.e. PNA or DNA) and the density of surface-bound PNA and DNA probes. To further the understanding of these effects on the measured electrochemical signal, kinetic studies of the hybridisation reactions were undertaken, and the equilibrium binding constants and binding rate constants for the hybridisation reactions were obtained. The study provides valuable insights to guide future designs of biosensors.

Electroconductive Hydrogel Based on Functional Poly(Ethylenedioxy Thiophene)

Poly(ethylene dioxythiophene) with functional pendant groups bearing double bonds is synthesized and employed for the fabrication of electroactive hydrogels with advantageous characteristics: covalently cross-linked porous 3D scaffolds with notable swelling ratio, appropriate mechanical properties, electroactivity in physiological conditions, and suitability for proliferation and differentiation of C2C12 cells. This is a new approach for the fabrication of conductive engineered constructs.

Multidimensional hybrid conductive nanoplate-based aptasensor for platelet-derived growth factor detection

In the development of disease diagnoses, rapid responses to and accurate selectivity for target analytes are critical aspects. As one diagnostic approach, biosensors with high sensitivity and selectivity are investigated to detect disorder factors (e.g., endocrine disruptors and cancer oncoproteins). In this report, we demonstrate an aptamer-functionalized multidimensional hybrid conducting-polymer (3-carboxylated polypyrrole) plate (A_MHCPP) based field-effect transistor (FET) sensor to detect a platelet-derived growth factor (PDGF-BB). The multidimensional hybrid conducting-polymer plates (MHCPPs) are formed on the graphene surface by using electrodeposition and vapor deposition polymerization (VDP) steps. The amine-functionalized PDGF-B binding aptamers are then immobilized on the carboxylated polypyrrole surface by means of covalent bond formation (-CONH). The prepared FET sensors present high sensing ability toward PDGF-BB - as low as 1.78 fM among interfering biomolecules at room temperature.

Poly(3,4-ethylenedioxythiophene) Bearing Phosphorylcholine Groups for Metal-Free, Antibody-Free, and Low-Impedance Biosensors Specific for C-Reactive Protein

Conducting polymers possessing biorecognition elements are essential for developing electrical biosensors sensitive and specific to clinically relevant biomolecules. We developed a new 3,4-ethylenedioxythiophene (EDOT) derivative bearing a zwitterionic phosphorylcholine group via a facile synthesis through the Michael-type addition thiol-ene "click" reaction for the detection of an acute-phase biomarker human C-reactive protein (CRP). The phosphorylcholine group, a major headgroup in phospholipid, which is the main constituent of plasma membrane, was also expected to resist nonspecific adsorption of other proteins at the electrode/solution interface. The biomimetic EDOT derivative was randomly copolymerized with EDOT, via an electropolymerization technique with a dopant sodium perchlorate, onto a glassy carbon electrode to make the synthesized polymer film both conductive and target-responsive. The conducting copolymer films were characterized by cyclic voltammetry, scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The specific interaction of CRP with phosphorylcholine in a calcium-containing buffer solution was determined by differential pulse voltammetry, which measures the altered redox reaction between the indicators ferricyanide/ferrocyanide as a result of the binding event. The conducting polymer-based protein sensor achieved a limit of detection of 37 nM with a dynamic range of 10-160 nM, covering the dynamically changing CRP levels in circulation during the acute phase. The results will enable the development of metal-free, antibody-free, and low-impedance electrochemical biosensors for the screening of nonspecific biomarkers of inflammation and infection.

Direct ultrasensitive electrical detection of prostate cancer biomarkers with CMOS-compatible n- and p-type silicon nanowire sensor arrays

Sensitive and quantitative analysis of proteins is central to disease diagnosis, drug screening, and proteomic studies. Here, a label-free, real-time, simultaneous and ultrasensitive prostate-specific antigen (PSA) sensor was developed using CMOS-compatible silicon nanowire field effect transistors (SiNW FET). Highly responsive n- and p-type SiNW arrays were fabricated and integrated on a single chip with a complementary metal oxide semiconductor (CMOS) compatible anisotropic self-stop etching technique which eliminated the need for a hybrid method. The incorporated n- and p-type nanowires revealed complementary electrical response upon PSA binding, providing a unique means of internal control for sensing signal verification. The highly selective, simultaneous and multiplexed detection of PSA marker at attomolar concentrations, a level useful for clinical diagnosis of prostate cancer, was demonstrated. The detection ability was corroborated to be effective by comparing the detection results at different pH values. Furthermore, the real-time measurement was also carried out in a clinically relevant sample of blood serum, indicating the practicable development of rapid, robust, high-performance, and low-cost diagnostic systems.

Aptamer-functionalized hybrid carbon nanofiber FET-type electrode for a highly sensitive and selective platelet-derived growth factor biosensor

Precise selectivity and rapid responses to target biomolecules are important in the development of biosensors. In particular, highly sensitive and selective biosensors have been used in clinical treatment to detect factors such as cancer oncoproteins and endocrine disruptors. Herein, highly sensitive liquid electrolyte field-effect transistor (FET) system biosensors were fabricated to detect platelet-derived growth factor (PDGF) using a PDGF-B binding aptamer conjugated with carboxylic polypyrrole-coated metal oxide-decorated carbon nanofibers (CPMCNFs) as the signal transducer. First, CPMCNFs were fabricated using vapor deposition polymerization (VDP) of the carboxylic pryrrole monomer (CPy) on metal oxide-decorated carbon nanofiber (MCNF) surfaces with no treatment for carbon surface functionalization. Furthermore, a 3 nm thick uniformly coated carboxylic polypyrrole (CPPy) layer was formed without aggregation. The CPMCNFs were integrated with the PDGF-B binding aptamer and immobilized on the interdigitated array substrate by covalent anchoring to produce a FET-type biosensor transducer. The PDGF-B binding aptamer conjugated CPMCNF (CPB-Apt) FET sensor was highly sensitive (5 fM) and extremely selective for isoforms of PDGFs. Additionally, the CPB-Apt FET sensor could be reused over a few weeks.

Intrinsically conducting polymer nanowires for biosensing

The fabrication of conductive polymer nanowires and their sensing of nucleic acids, proteins and pathogens is reviewed in this feature article.

Controlling the morphology of conductive PEDOT by in situ electropolymerization: from thin films to nanowires with variable electrical properties

The controlled electrochemical synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) as a model conjugated polymer is described here. We show that the morphology of electrochemically synthesized PEDOT can be finely tuned directly in a device, by carefully guiding the nucleation and growth processes as well as electromigration phenomena, resulting in structures with variable electrical properties.

Synergizing nucleic acid aptamers with 1-dimensional nanostructures as label-free field-effect transistor biosensors

Since the introduction by Gold et al. in 1990, nucleic acid aptamers had evolved to become a true contender in biosensors for protein and cell detections. Aptamers are short strands of synthetically designed DNA or RNA oligonucleotides that can be self-assembled into unique 3-dimensional structures and can bind to different proteins, cells or even small molecules at a high level of specificity and affinity. In recent years, there had been many reports in literature in using aptamers in place of conventional antibodies as capture biomolecules on the surface. This is mainly due to the better thermal stability properties and ease in production. Consequently, also these characteristics allowed the aptamers to find use in field effect transistors (FETs) based upon 1D nanostructured (1D-NS) as label-free biosensing. In terms of designing label-free platforms for biosensors applications, 1D-NS FET had been an attractive option due to reported high sensitivities toward protein targets arising from the large surface area for detection as well as to their label-free nature. Since the first aptamer-based 1D-NS FET biosensor had surfaced in 2005, there had been many more improvements in the overall design and sensitivity in recent years. In this review, the latest developments in synergizing these two interesting areas of research (aptamers and 1D-NS FET) will be discussed for a range of different nanowire types as well as for the detection results.

Investigation of protein detection parameters using nanofunctionalized organic field-effect transistors

Biodetection using organic field-effect transistors (OFETs) is gaining increasing interest for applications as diverse as food security, environmental monitoring, and medical diagnostics. However, there still lacks a comprehensive, empirical study on the fundamental limits of OFET sensors. In this paper, we present a thorough study of the various parameters affecting biosensing using an OFET decorated with gold nanoparticle (AuNP) binding sites. These parameters include the spacing between receptors, pH of the buffer, and ionic strength of the buffer. To this end, we employed the thrombin protein and its corresponding DNA binding aptamer to form our model detection system. We demonstrate a detection limit of 100 pM for this protein with high selectivity over other proteases in situ. We describe herein a feasible approach for protein detection with OFETs and a thorough investigation of parameters governing biodetection events using OFETs. Our obtained results should provide important guidelines to tailor the sensor's dynamic range to suit other desired OFET-based biodetection applications.

Pure Graphene Oxide Doped Conducting Polymer Nanocomposite for Bio-interfacing

Advanced materials that are highly biocompatible and easily modifiable with biomolecules are of great importance for bio-interfacing and the development of biodevices. Here, a biocompatible conducting polymer based nanocomposite was electrochemically synthesized through the electropolymerization of poly(3, 4-ethylene dioxythiophene) (PEDOT) in the presence of graphene oxide (GO) as the only dopant. GO contains many negatively charged carboxyl functional groups and is highly dispersible in aqueous solutions, enabling its facile incorporation and even distribution throughout the conducting polymer. PEDOT/GO films exhibited minimal cytotoxicity after 24 h and supported neuron growth with significantly longer neurites than a control PEDOT/PSS film, indicating that the PEDOT/GO film provides a positive growth signal to developing neurons. While some of the negatively charged functional carboxyl groups of GO "dope" the PEDOT, others are exposed freely on the surface of the nanocomposite allowing easy functionalization of the PEDOT/GO composite with biomolecules. Functional laminin peptide, RNIAEIIKDI (p20), was covalently bound to the surface of the PEDOT/GO film and maintained its bioactivity, as evidenced by an increased neurite outgrowth from neurons cultured on the functionalized composite surface. The ease of biomolecule functionalization of the PEDOT/GO nanocomposite, along with its low electrochemical impedance, minimal toxicity and permissiveness to neuron growth, underlines its potential as a material for widespread biosensing, neural interfacing and tissue engineering applications.

Comparative study on aptamers as recognition elements for antibiotics in a label-free all-polymer biosensor

We present an all-polymer electrochemical microfluidic biosensor using Topas(®) as substrate and a conductive polymer bilayer as electrode material. The conductive bilayer consists of tosylate doped poly(3,4-ethylenedioxythiophene) (PEDOT:TsO) and the hydroxymethyl derivative PEDOT-OH:TsO, which was covalently functionalized with two aptamer probes with affinity to ampicillin or kanamycin A, respectively. Using electrochemical impedance spectroscopy (EIS) we were able to detect ampicillin in a concentration range from 100pM to 1μM and kanamycin A from 10nM to 1mM. The obtained EIS spectra were fitted with an equivalent circuit model successfully explaining the impedance signal. Real samples from regular ultra-high temperature treated low-fat milk spiked with ampicillin were successfully tested to assess the functionality of the sensor with real samples. In conclusion, we have demonstrated the applicability of the newly developed platform for real time, label-free and selective impedimetric detection of commonly used antibiotics. Additionally it was possible to detect ampicillin in a milk sample at a concentration below the allowed maximum residue limit (MRL) in the European Union.

Virus-poly(3,4-ethylenedioxythiophene) biocomposite films

Virus-poly(3,4-ethylenedioxythiophene) (virus-PEDOT) biocomposite films are prepared by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) in aqueous electrolytes containing 12 mM LiClO(4) and the bacteriophage M13. The concentration of virus in these solutions, [virus](soln), is varied from 3 to 15 nM. A quartz crystal microbalance is used to directly measure the total mass of the biocomposite film during its electrodeposition. In combination with a measurement of the electrodeposition charge, the mass of the virus incorporated into the film is calculated. These data show that the concentration of the M13 within the electropolymerized film, [virus](film), increases linearly with [virus](soln). The incorporation of virus particles into the PEDOT film from solution is efficient, resulting in a concentration ratio of [virus](film):[virus](soln) ≈ 450. Virus incorporation into the PEDOT causes roughening of the film topography that is observed using scanning electron microscopy and atomic force microscopy (AFM). The electrical conductivity of the virus-PEDOT film, measured perpendicular to the plane of the film using conductive tip AFM, decreases linearly with virus loading, from 270 μS/cm for pure PEDOT films to 50 μS/cm for films containing 100 μM virus. The presence on the virus surface of displayed affinity peptides did not significantly influence the efficiency of incorporation into virus-PEDOT biocomposite films.

Electropolymerized conjugated polyelectrolytes with tunable work function and hydrophobicity as an anode buffer in organic optoelectronics

A new class of conductive polyelectrolyte films with tunable work function and hydrophobicity has been developed for the anode buffer layer in organic electronic devices. The work function of these films featuring a copolymer of ethylenedioxythiophene (EDOT), and its functionalized analogues were found to be easily tunable over a range of almost 1 eV and reach values as high as those of PEDOT:PSS. The new buffer material does not need the addition of any insulating or acidic material that might limit the film conductivity or device lifetime. Organic photovoltaic devices built with these films showed improved open-circuit voltage over those of the known PSS-free conductive EDOT-based polymers with values as high as that obtained for PEDOT:PSS. Furthermore, the surface hydrophobicity of these new copolymer films was found to be sensitive to the chemical groups attached to the polymer backbone, offering an attractive method for surface energy tuning.

Functional polymers in protein detection platforms: optical, electrochemical, electrical, mass-sensitive, and magnetic biosensors

The rapidly growing field of proteomics and related applied sectors in the life sciences demands convenient methodologies for detecting and measuring the levels of specific proteins as well as for screening and analyzing for interacting protein systems. Materials utilized for such protein detection and measurement platforms should meet particular specifications which include ease-of-mass manufacture, biological stability, chemical functionality, cost effectiveness, and portability. Polymers can satisfy many of these requirements and are often considered as choice materials in various biological detection platforms. Therefore, tremendous research efforts have been made for developing new polymers both in macroscopic and nanoscopic length scales as well as applying existing polymeric materials for protein measurements. In this review article, both conventional and alternative techniques for protein detection are overviewed while focusing on the use of various polymeric materials in different protein sensing technologies. Among many available detection mechanisms, most common approaches such as optical, electrochemical, electrical, mass-sensitive, and magnetic methods are comprehensively discussed in this article. Desired properties of polymers exploited for each type of protein detection approach are summarized. Current challenges associated with the application of polymeric materials are examined in each protein detection category. Difficulties facing both quantitative and qualitative protein measurements are also identified. The latest efforts on the development and evaluation of nanoscale polymeric systems for improved protein detection are also discussed from the standpoint of quantitative and qualitative measurements. Finally, future research directions towards further advancements in the field are considered.

Graphene and other nanomaterial-based electrochemical aptasensors

Electrochemical aptasensors, which are based on the specificity of aptamer-target recognition, with electrochemical transduction for analytical purposes have received particular attention due to their high sensitivity and selectivity, simple instrumentation, as well as low production cost. Aptamers are functional nucleic acids with specific and high affinity to their targets, similar to antibodies. However, they are completely selected in vitro in contrast to antibodies. Due to their stability, easy chemical modifications and proneness to nanostructured device construction, aptamer-based sensors have been incorporated in a variety of applications including electrochemical sensing devices. In recent years, the performance of aptasensors has been augmented by incorporating novel nanomaterials in the preparation of better electrochemical sensors. In this review, we summarize the recent trends in the use of nanomaterials for developing electrochemical aptasensors.

Ultrasensitive protein detection using an aptamer-functionalized single polyaniline nanowire

A highly sensitive, conductometric and label-free biosensor for the detection of immunoglobulin E (IgE) is developed based on the immobilzation of the IgE aptamer onto a single polyaniline nanowire electrochemically synthesized in a facile and controllable way.

Surface polymerization of (3,4-ethylenedioxythiophene) probed by in situ scanning tunneling microscopy on Au(111) in ionic liquids

The electropolymerization of 3,4-ethylenedioxythiophene (EDOT) to poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in the air and water-stable ionic liquids 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate [HMIm]FAP and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]TFSA. In situ scanning tunnelling microscopy (STM) results show that the electropolymerization of EDOT in the ionic liquid can be probed on the nanoscale. In contrast to present understanding, it was observed that the EDOT can be oxidised in ionic liquids well below its oxidation potential and the under potential growth of polymer was visualized by in situ STM. These results serve as the first study to confirm the under potential growth of conducting polymers in ionic liquids. Furthermore, ex situ microscopy measurements were performed. Quite a high current of 670 nA was observed on the nanoscale by conductive scanning force microscopy (CSFM).