Polypyrrole-Au Nanoparticles Composite as Suitable Platform for DNA Biosensor with Electrochemical Impedance Spectroscopy Detection

Nano-Scaled Materials and Polymer Integration in Biosensing Tools

The evolution of biosensors and diagnostic devices has been thriving in its ability to provide reliable tools with simplified operation steps. These evolutions have paved the way for further advances in sensing materials, strategies, and device structures. Polymeric composite materials can be formed into nanostructures and networks of different types, including hydrogels, vesicles, dendrimers, molecularly imprinted polymers (MIP), etc. Due to their biocompatibility, flexibility, and low prices, they are promising tools for future lab-on-chip devices as both manufacturing materials and immobilization surfaces. Polymers can also allow the construction of scaffold materials and 3D structures that further elevate the sensing capabilities of traditional 2D biosensors. This review discusses the latest developments in nano-scaled materials and synthesis techniques for polymer structures and their integration into sensing applications by highlighting their various structural advantages in producing highly sensitive tools that rival bench-top instruments. The developments in material design open a new door for decentralized medicine and public protection that allows effective onsite and point-of-care diagnostics.

Ultrasensitive early detection of insulin antibody employing novel electrochemical nano-biosensor based on controllable electro-fabrication process

An ultrasensitive novel electrochemical nano-biosensor for rapid detection of insulin antibodies against diabetes antigens was developed in this research. The presence of insulin antibodies has been demonstrated to be a strong predictor for the development of type 1 diabetes in individuals who do not have diabetes but are genetically predisposed. The proposed nano-biosensor fabrication process was based on the optimized sequential electropolymerization of polyaniline and electrodeposition of gold nanoparticles on the surface of the functionalized gold electrode. The morphological and chemical characterization of the modified electrode was studied by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and micro Raman spectroscopy. Moreover, the role of each component in the modification of the electrode was studied by electrochemical methods systematically. After immobilizing insulin antigen and blocking with bovine serum albumin, the nano-biosensor was used for determining different concentrations of insulin antibody under the optimal conditions. This nano-biosensor could respond to insulin antibody with a linear calibration range from 0.001 ng ml^-1 to 1000 ng ml^-1 with the detection limit of 0.017 pg ml^-1 and 0.034 pg ml^-1 and selectivity of 18.544 μA ng^-1 ml.cm^-2 and 31.808 μA ng^-1 ml.cm^-2 via differential pulse voltammetry and square wave voltammetry, respectively. This novel nano-biosensor exhibited a short response time, high sensitivity, and good reproducibility. It was successfully used in determining the insulin antibody in human samples with a standard error of less than 0.178. Therefore, the nano-biosensor has the potential for the application of early detection of type 1 diabetes. To our best knowledge, label-free electrochemical detection of insulin antibody based on immunosensor is developed for the first time.

Nanostructured sensor platform based on organic polymer conjugated to metallic nanoparticle for the impedimetric detection of SARS-CoV-2 at various stages of viral infection

The projection of new biosensing technologies for genetic identification of SARS-COV-2 is essential in the face of a pandemic scenario. For this reason, the current research aims to develop a label-free flexible biodevice applicable to COVID-19. A nanostructured platform made of polypyrrole (PPy) and gold nanoparticles (GNP) was designed for interfacing the electrochemical signal in miniaturized electrodes of tin-doped indium oxide (ITO). Oligonucleotide primer was chemically immobilized on the flexible transducers for the biorecognition of the nucleocapsid protein (N) gene. Methodological protocols based on cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM) were used to characterize the nanotechnological apparatus. The biosensor’s electrochemical performance was evaluated using the SARS-CoV-2 genome and biological samples of cDNA from patients infected with retrovirus at various disease stages. It is inferred that the analytical tool was able to distinguish the expression of SARS-CoV-2 in patients diagnosed with COVID-19 in the early, intermediate and late stages. The biosensor exhibited high selectivity by not recognizing the biological target in samples from patients not infected with SARS-CoV-2. The proposed sensor obtained a linear response range estimated from 800 to 4000 copies µL⁻¹ with a regression coefficient of 0.99, and a detection limit of 258.01 copies µL⁻¹. Therefore, the electrochemical biosensor based on flexible electrode technology represents a promising trend for sensitive molecular analysis of etiologic agent with fast and simple operationalization. In addition to early genetic diagnosis, the biomolecular assay may help to monitor the progression of COVID-19 infection in a novel manner.

Evolution of nucleic acids biosensors detection limit III

This review is an update of two previous ones focusing on the limit of detection of electrochemical nucleic acid biosensors allowing direct detection of nucleic acid target (miRNA, mRNA, DNA) after hybridization event. A classification founded on the nature of the electrochemical transduction pathway is established. It provides an overall picture of the detection limit evolution of the various sensor architectures developed during the last three decades and a critical report of recent strategies.

Electrochromic Self-Electrostabilized Polypyrrole Films Doped with Surfactant and Azo Dye

Two azo dyes, acid red 1 (AR1) and acid red 18 (AR18), were used alone or in combination with sodium dodecyl sulfate (SDS) for the electropolymerization of a pyrrole monomer. Polypyrrole (PPy) showed higher redox capacity when SDS and AR18 were used simultaneously as dopant agents (PPy/AR18-SDS) than when the conducting polymer was produced in the presence of SDS, AR18, AR1, or an AR1/SDS mixture. Moreover, PPy/AR18-SDS is a self-stabilizing material that exhibits increasing electrochemical activity with the number of oxidation–reduction cycles. A mechanism supported by scanning electron microscopy and X-ray diffraction structural observations was proposed to explain the synergy between the SDS surfactant and the AR18 dye. On the other hand, the Bordeaux red color of PPy/AR18-SDS, which exhibits an optical band gap of 1.9 eV, rapidly changed to orange-yellow and blue colors when films were reduced and oxidized, respectively, by applying linear or step potential ramps. Overall, the results indicate that the synergistic utilization of AR18 and SDS as dopant agents in the same polymerization reaction is a very successful and advantageous strategy for the preparation of PPy films with cutting-edge electrochemical and electrochromic properties.

Progress in the Development of Intrinsically Conducting Polymer Composites as Biosensors

Biosensors are analytical devices which find extensive applications in fields such as the food industry, defense sector, environmental monitoring, and in clinical diagnosis. Similarly, intrinsically conducting polymers (ICPs) and their composites have lured immense interest in bio-sensing due to their various attributes like compatibility with biological molecules, efficient electron transfer upon biochemical reactions, loading of bio-reagent, and immobilization of biomolecules. Further, they are proficient in sensing diverse biological species and compounds like glucose (detection limit ≈0.18 nm), DNA (≈10 pm), cholesterol (≈1 µm), aptamer (≈0.8 pm), and also cancer cells (≈5 pm mL-1) making them a potential candidate for biological sensing functions. ICPs and their composites have been extensively exploited by researchers in the field of biosensors owing to these peculiarities; however, no consolidated literature on the usage of conducting polymer composites for biosensing functions is available. This review extensively elucidates on ICP composites and doped conjugated polymers for biosensing functions of copious biological species. In addition, a brief overview is provided on various forms of biosensors, their sensing mechanisms, and various methods of immobilizing biological species along with the life cycle assessment of biosensors for various biosensing applications, and their cost analysis.

Electrodeposition⁻Assisted Assembled Multilayer Films of Gold Nanoparticles and Glucose Oxidase onto Polypyrrole-Reduced Graphene Oxide Matrix and Their Electrocatalytic Activity toward Glucose

The study reports a facile and eco-friendly approach for nanomaterial synthesis and enzyme immobilization. A corresponding glucose biosensor was fabricated by immobilizing the gold nanoparticles (AuNPs) and glucose oxidase (GOD) multilayer films onto the polypyrrole (PPy)/reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) via the electrodeposition and self-assembly. PPy and graphene oxide were first coated on the surface of a bare GCE by the electrodeposition. Then, AuNPs and GOD were alternately immobilized onto PPy-RGO/GCE electrode using the electrodeposition of AuNPs and self-assembly of GOD to obtain AuNPs-GOD multilayer films. The resulting PPy-RGO-(AuNPs-GOD)_n/GCE biosensors were used to characterize and assess their electrocatalytic activity toward glucose using cyclic voltammetry and amperometry. The response current increased with the increased number of AuNPs-GOD layers, and the biosensor based on four layers of AuNPs-GOD showed the best performance. The PPy-RGO-(AuNPs-GOD)₄/GCE electrode can detect glucose in a linear range from 0.2 mM to 8 mM with a good sensitivity of 0.89 μA/mM, and a detection limit of 5.6 μM (S/N = 3). This study presents a promising eco-friendly biosensor platform with advantages of electrodeposition and self-assembly, and would be helpful for the future design of more complex electrochemical detection systems.

A Comparative Study of Poly(Azure A) Film-Modified Disposable Electrodes for Electrocatalytic Oxidation of H₂O₂: Effect of Doping Anion

In the present paper, poly(azure A) (PAA) films were electrosynthetized in the presence of different doping anions on disposable screen-printed carbon electrodes (SPCEs). The anions used included inorganic monoatomic (chloride and fluoride), inorganic polyatomic (nitrate and sulfate) and organic polyatomic (dodecyl sulfate, DS) species. The coated electrodes thus obtained were characterized by electrochemical techniques and SEM. They showed improved electrocatalytic activities towards hydrogen peroxide oxidation compared to that of a bare SPCE. In particular, the insertion of DS anions inside PAA films provided a special sensitivity to the electrocatalysis of H₂O₂, which endowed these electrodes with promising analytical features for H₂O₂ quantification. We obtained a wide linear response for H₂O₂ within a range of 5 µM to 3 mM and a limit of detection of 1.43 ± 0.10 µM (signal-to-noise ratio of 3). Furthermore, sensitivity was 72.4 ± 0.49 nA·µM⁻¹∙cm⁻² at a relatively low electrocatalytic oxidation overpotential of 0.5 V vs. Ag. The applicability of this boosted system was tested by the analysis of H₂O₂ in commercial samples of a hair lightener and an antiseptic and was corroborated by spectrophotometric methods.

Nanomaterial-doped conducting polymers for electrochemical sensors and biosensors

This review summarizes recent advances in the development of electrochemical sensors and biosensors based on nanomaterial doped conducting polymers.

Electrochemical preparation and characterization of polypyrrole/stainless steel electrodes decorated with gold nanoparticles

The electrosynthesis and characterization of polypyrrole(PPy)/stainless steel electrodes decorated with gold nanoparticles and the performance of the composite electrode for sensing applications is described. PPy films were grown in potassium perchlorate and sodium salicylate solutions under comparable electropolymerization conditions. Polymer films prepared in the presence of perchlorate ions exhibited worm-like structures, whereas columnar structures were obtained in salicylate-containing solutions. Voltammetric response of PPy films prepared in salicylate solutions was more reversible. PPy films were decorated with gold nanoparticles obtained by a double step potentiostatic electrodeposition routine that allowed fine control of deposit characteristics. Analysis of deposits was performed by means of SEM and confocal Raman spectroscopy. The electrocatalytic activity of the Au/PPy electrodes was assessed for the electro-oxidation of hydrazine and hydroxylamine. Results showed a successful optimization of the route of synthesis that rendered nanocomposite electrode materials with promising applications in electrochemical sensing.