Adsorption of catechol onto PEDOT films doped with gold nanoparticles: Electrochemical and spectroscopic studies

Synthesis and characterization of enhanced azo-azomethine doped PANI/HCl conducting polymers for electrochemical applications

In this study, conducting polymers composed of polyaniline hydrochloric acid (PANI/HCl) with varying concentrations of a newly synthesized azo-azomethine dye (4-(((Z)-2-hydroxy-5-((Z)-(4-hydroxyphenyl)diazenyl)-3-methoxybenzylidene)amino)benzoic acid) were synthesized using a chemical oxidative polymerization technique. The synthesized azo-azomethine was characterized by FTIR, 1H-NMR, 13C-NMR, and HRMS. The effects of varying the concentration of the dopant azo-azomethine in PANI/HCl on its optical, structural, thermal, and electrical properties were examined using FTIR, UV-Vis, XRD, FESEM, TEM, cyclic voltammetry, and electrical impedance spectra. The results indicate that the optical, direct, and indirect band gaps of the doped polymers decreased from 4.48 and 3.96 eV to 3.91 and 2.49 eV, respectively. The crystalline structure and phase transitions in the doped polymers were examined using X-ray diffraction. Cyclic voltammetry demonstrated that the doped polymers exhibited higher electrochemical conductivity compared to the pure polymer, with the specific capacitance increasing from 161.17 to 816.9 F/g. The electrical impedance spectra revealed the bulk resistance and conductivity of the material. Among all the doped polymers, PANI/HCl with an azo-azomethine concentration of 5 × 10-5 M exhibited lower bulk resistance (10 Ω) and higher electrical conductivity (σ = 50.09 × 10-3 S cm-1).

Graphene oxide-alginate hydrogel-based indicator displacement assay integrated with diaper for non-invasive Alzheimer's disease screening

Pyrocatechol violet/copper ion-graphene oxide/alginate (PV/Cu2+-GO/Alg) hydrogel was fabricated and applied as a colorimetric sensor for monitoring urinary cysteine via an indicator-displacement assay (IDA) and Cu2+-cysteine affinity pair. The hydrogel-based sensor was formed by Ca2+ cations cross-linked PV/Cu2+-GO/Alg. The morphologies of hydrogel were characterized by field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy and Fourier-transform Raman spectroscopy. Incorporating GO into the hydrogel improved its uniformity of porosity, large surface area, and compressive strength, leading to amplified colorimetric signals of the hydrogel sensor. Under optimal conditions, this sensor offered a linear range of 0.0-0.5 g/L with a detection limit of 0.05 g/L for cysteine without interfering effects in urine. Furthermore, this hydrogel-based sensor was applied for urinary cysteine detection and validated with laser desorption ionization mass spectrometry. This platform could be used to determine cysteine at its cutoff (0.25 g/L) in human urine, which was distinguishable between normal and abnormal individuals, to evaluate an early stage of Alzheimer's disease. Eventually, this system was integrated with diapers for a wearable cysteine sensor.

COVID-19 impedimetric biosensor based on polypyrrole nanotubes, nickel hydroxide and VHH antibody fragment: specific, sensitive, and rapid viral detection in saliva samples

SARS-CoV-2 rapid spread required urgent, accurate, and prompt diagnosis to control the virus dissemination and pandemic management. Several sensors were developed using different biorecognition elements to obtain high specificity and sensitivity. However, the task to achieve these parameters in combination with fast detection, simplicity, and portability to identify the biorecognition element even in low concentration remains a challenge. Therefore, we developed an electrochemical biosensor based on polypyrrole nanotubes coupled via Ni(OH)₂ ligation to an engineered antigen-binding fragment of heavy chain-only antibodies (VHH) termed Sb#15. Herein we report Sb#15-His6 expression, purification, and characterization of its interaction with the receptor-binding domain (RBD) of SARS-CoV-2 in addition to the construction and validation of a biosensor. The recombinant Sb#15 is correctly folded and interacts with the RBD with a dissociation constant (K_D) of 27.1 ± 6.4 nmol/L. The biosensing platform was developed using polypyrrole nanotubes and Ni(OH)₂, which can properly orientate the immobilization of Sb#15-His6 at the electrode surface through His-tag interaction for the sensitive SARS-CoV-2 antigen detection. The quantification limit was determined as 0.01 pg/mL using recombinant RBD, which was expressively lower than commercial monoclonal antibodies. In pre-characterized saliva, both Omicron and Delta SARS-CoV-2 were accurately detected only in positive samples, meeting all the requirements recommended by the World Health Organization for in vitro diagnostics. A low sample volume of saliva is needed to perform the detection, providing results within 15 min without further sample preparations. In summary, a new perspective allying recombinant VHHs with biosensor development and real sample detection was explored, addressing the need for accurate, rapid, and sensitive biosensors.

PEDOT: PSS/AuNPs-Based Composite as Voltammetric Sensor for the Detection of Pirimicarb

An electrochemical sensor for the pesticide Pirimicarb (PMC) has been developed. A screen-printed electrode (SPCE) was used and modified with the conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) and gold nanoparticles (AuNPs) to enhance electrochemical proprieties. Electrode characterizations were performed using scattering electron microscopy (SEM) and cyclic voltammetry (CV). With the SPCE/PEDOT:PSS/AuNPs modified electrode, a new peak at 1.0 V appeared in the presence of PMC related to the PMC oxidation. To elucidate the mechanism of PMC oxidation, Gas Chromatography-Mass Spectrometry (GC-MS), where two major peaks were identified, evidencing that the device can both detect and degrade PMC by an electro-oxidation process. Exploring this peak signal, it was possible the sensor development, performing detection from 93.81-750 µmol L^-1, limits of quantification (LOQ) and detection (LOD) of 93.91 µmol L^-1 and 28.34 µmol L^-1, respectively. Thus, it was possible to study and optimization of PMC degradation, moreover, to perform detection at low concentrations and with good selectivity against different interferents using a low-cost printed electrode based on graphite modified with conductive polymer and AuNPs.

Effect of strontium doping on the electrochemical pseudocapacitance of Y1-xSrxMnO3-δ perovskites

Grid-scale bulk energy storage solutions are needed to utilize the full potential of renewable energy technologies. Pseudocapacitive electrochemical energy storage can play a vital role in developing efficient energy storage solutions. The use of perovskites as anion intercalation-type pseudocapacitor electrodes has received significant attention in recent years. In this study, Sr-doped YMnO₃i.e. Y_1-xSr_xMnO_3-δ perovskite was prepared by the solid-state ceramic route and studied for electrochemical pseudocapacitance in aqueous KOH electrolyte. Microstructures, morphologies, and electrochemical properties of these materials were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance method. The formation of the mostly cubic phase, with 50% strontium doped YMnO₃ (YSMO-50) provides an equivalent three-dimensional network and superior conductivity due to Mn³⁺-O^2--Mn⁴⁺ hopping conduction. YSMO-50 exhibited low intrinsic resistance, 1.45 Ω cm^-2, and the highest specific capacity, 259.83 F g^-1 at a current density of 1 A g^-1 in 2 M KOH aqueous electrolyte. Redox-mediated interconversion of oxide to hydroxide (M²⁺O^2- + H₂O + e^- ↔ M⁺OH^- + OH^-) in aqueous media is shown to be the reason behind the high capacitance of YSMO-50. The excellent electrochemical performance of YSMOs was attributed to the reversible interconversion of oxide-ion into hydroxide ion coupled with surface redox reaction of Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ occurring during the charge-discharge process. The maximum energy density of 65.13 W h kg^-1 was achieved at a power density of 0.45 kW kg^-1 for an asymmetric mode, in which YSMO serves as a negative electrode and Activated carbon (AC) as a positive electrode in the PVA-KOH gel electrolyte. Our study reveals that the doping of low valence atom (Sr) at the A-site in perovskite manganites (YMnO₃) may be an effective tool to enhance the pseudocapacitive performance of perovskite-based electrodes.

Development of Folate-Group Impedimetric Biosensor Based on Polypyrrole Nanotubes Decorated with Gold Nanoparticles

In this study, polypyrrole nanotubes (PPy-NT) and gold nanoparticles (AuNPs) were electrochemically synthesized to form a hybrid material and used as an electroactive layer for the attachment of proteins for the construction of a high-performance biosensor. Besides the enhancement of intrinsic conductivity of the PPy-NT, the AuNPs act as an anchor group for the formation of self-assembly monolayers (SAMs) from the gold-sulfur covalent interaction between gold and Mercaptopropionic acid (MPA). This material was used to evaluate the viability and performance of the platform developed for biosensing, and three different biological approaches were tested: first, the Avidin-HRP/Biotin couple and characterizations were made by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), wherein we detected Biotin in a linear range of 100-900 fmol L^-1. The studies continued with folate group biomolecules, using the folate receptor α (FR-α) as a bioreceptor. Tests with anti-FR antibody detection were performed, and the results obtained indicate a linear range of detection from 0.001 to 6.70 pmol L^-1. The same FR-α receptor was used for Folic Acid detection, and the results showed a limit of detection of 0.030 nmol L^-1 and a limit of quantification of 90 pmol L^-1. The results indicate that the proposed biosensor is sensitive and capable of operating in a range of clinical interests.

Interfacial Characterization of Polypyrrole/AuNP Composites towards Electrocatalysis of Ascorbic Acid Oxidation

Polypyrrole (PPy) is an interesting conducting polymer due to its good environmental stability, high conductivity, and biocompatibility. The association between PPy and metallic nanoparticles has been widely studied since it enhances electrochemical properties. In this context, gold ions are reduced to gold nanoparticles (AuNPs) directly on the polymer surface as PPy can be oxidized to an overoxidized state. This work proposes the PPy electrochemical synthesis followed by the direct reduction of gold on its surface in a fast reaction. The modified electrodes were characterized by electronic microscopic and infrared spectroscopy. The effect of reduction time on the electrochemical properties was evaluated by the electrocatalytic properties of the obtained material from the oxidation of ascorbic acid (AA) and electrochemical impedance spectroscopy studies. The presence of AuNPs improved the AA electrocatalysis by reducing oxidation potential and lowering charge transfer resistance. EIS data were fitted using a transmission line model. The results indicated an increase in the electronic transport of the polymeric film in the presence of AuNPs. However, PPy overoxidation occurs when the AuNPs’ deposition is higher than 30 s. In PPy/AuNPs 15 s, smaller and less agglomerated particles were formed with fewer PPy overoxidized, confirming the observed electrocatalytic behavior.

Development of polypyrrole (nano)structures decorated with gold nanoparticles toward immunosensing for COVID-19 serological diagnosis

The rapid and reliable detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroconversion in humans is crucial for suitable infection control. In this sense, many studies have focused on increasing the sensibility, lowering the detection limits and minimizing false negative/positive results. Thus, biosensors based on nanoarchitectures of conducting polymers are promising alternatives to more traditional materials since they can hold improved surface area, higher electrical conductivity and electrochemical activity. In this work, we reported the analytical comparison of two different conducting polymers morphologies for the development of an impedimetric biosensor to monitor SARS-CoV-2 seroconversion in humans. Biosensors based on polypyrrole (PPy), synthesized in both globular and nanotubular (NT) morphology, and gold nanoparticles are reported, using a self-assembly monolayer of 3-mercaptopropionic acid and covalently linked SARS-CoV-2 Nucleocapsid protein. First, the novel hybrid materials were characterized by electron microscopy and electrochemical measurements, and the biosensor step-by-step construction was characterized by electrochemical and spectroscopic techniques. As a proof of concept, the biosensor was used for the impedimetric detection of anti-SARS-CoV-2 Nucleocapsid protein monoclonal antibodies. The results showed a linear response for different antibody concentrations, good sensibility and possibility to quantify 7.442 and 0.4 ng/mL of monoclonal antibody for PPy in the globular and NT morphology, respectively. The PPy-NTs biosensor was able to discriminate serum obtained from COVID-19 positive versus negative clinical samples and is a promising tool for COVID-19 immunodiagnostic, which can contribute to further studies concerning rapid, efficient, and reliable detections.

PEDOT-AuNPs-based impedimetric immunosensor for the detection of SARS-CoV-2 antibodies

Electrochemical sensors and biosensors are useful techniques for fast, inexpensive, sensitive, and easy detection of innumerous specimen. In face of COVID-19 pandemic, it became evident the necessity of a rapid and accurate diagnostic test, so the impedimetric immunosensor approach can be a good alternative to replace the conventional tests due to the specific antibody-antigen binding interaction and the fast response in comparison to traditional methods. In this work, a modified electrode with electrosynthesized PEDOT and gold nanoparticles followed by the immobilization of truncated nucleoprotein (N aa160-406aa) was used for a fast and reliable detection of antibodies against COVID-19 in human serum sample. The method consists in analyzing the charge-transfer resistance (R_CT) variation before and after the modified electrode comes into contact with the positive and negative serum sample for COVID-19, using [Fe(CN)₆]^3-/4- as a probe. The results show a linear and selective response for serum samples diluted in a range of 2.5 × 10³ to 20 × 10³. Also, the electrode material was fully characterized by Raman spectroscopy, transmission electron microscopy and scanning electron microscopy coupled with EDS, indicating that the gold nanoparticles were well distributed around the polymer matrix and the presence of the biological sample was confirmed by EDS analysis. EIS measurements allowed to differentiate the negative and positive samples by the difference in the R_CT magnitude, proving that the material developed here has potential properties to be applied in impedimetric immunosensors for the detection of SARS-CoV-2 antibodies in about 30 min.

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.

A novel signal amplification strategy electrochemical immunosensor for ultra-sensitive determination of p53 protein

In this work, we fabricated a novel sandwich-type electrochemical immunosensor for quantitative and ultra-sensitive determination of tumor suppressor protein p53 by signal amplification strategy. Conductive polymers poly (3, 4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) has significantly effect on enhancing charge transfer and markedly increases the sensitivity of electrochemical immunosensing. Gold nanoparticles (AuNPs) as high conductivity nanocarriers were also used to capture monoclonal antibodies (Ab₁) due to their large specific surface areas. In addition, pH responsive zeolitic imidazolate framework (ZIF-8) was used to load the redox probe 2, 3-diaminophenazine (DAP) and the secondary antibodies (Ab₂) to form a sensitive-type ZIF-8-DAP-Ab₂ immunoprobe. After the sandwich-type immunoassay with the free p53 protein, with the release of probe DAP after the electrochemical signal amplificated by PEDOT:PSS and AuNPs, the ultra-sensitive and quantitative determination of p53 protein was realized with working range of 1-120 ng mL^-1 and low detection limit of 0.09 ng mL^-1. Besides, the fabricated electrochemical immunosensor exhibited good recovery, high sensitivity, reliability, and selectivity.