Conductive imprinted electrochemical sensor for epinephrine sensitive detection and double recognition

Detection of epinephrine using a K2Fe4O7 modified glassy carbon electrode

Iron-based electrochemical catalysts used to modify electrodes for biosensing have received more attention from biosensor manufacturers because of their excellent biocompatibility and low cost. In this work, a fast-ion conductor potassium ferrite (K2Fe4O7) modified glassy carbon electrode (GCE) was prepared for detecting epinephrine (EP) by electrochemical techniques. The obtained K2Fe4O7/GCE electrode exhibited not only a wide linear range over EP concentration from 2 μM to 260 μM with a detection limit of 0.27 μM (S/N = 3) but also high selectivity toward EP in the presence of common interferents ascorbic acid (AA) and uric acid (UA), as well as good reproducibility and stability.

Smart green CQD@SiO2 hybrid coated optical fiber manifesting dual versatile absorptive and MIP features towards epinephrine detection

For the first time, in this study, a novel optical fiber biosensor is proposed and developed via coating only one smart functional layer of silica-supported carbon dots realizing the concepts of both lossy mode resonance (LMR) and molecularly imprinted polymer (MIP) for epinephrine detection. The carbon quantum dots (CQDs) are prepared using a green synthesis method and then treated with a molecularly imprinted polymer (MIP) strategy. Under ultrasonic irradiation, a SiO₂ shell was stabilized on the surface of the CQDs to graft and to provide the LMR/MIP functional layer onto the curved optical fiber surface. Accurate structural and morphological characterization confirmed the carbon quantum dot agents and also the SiO₂ supporting shells on the optical fiber, while spectroscopic analysis confirms the formation of the imprinted polymer and desirable absorbance characteristics. The experimental and numerical sensing studies revealed that the proposed sensing probe allows the rapid adsorption/desorption of epinephrine to the sensing films and highly permeable coating for studying the influence of effective parameters. Under the optimal experimental conditions, the sensitivity of the proposed LMR-based optical fiber sensor is reported to be 0.37 nm μM^-1 with a correlation coefficient of 0.99. So, sensitive detection of epinephrine at a low concentration can be guaranteed with a 0.72 mM LOD.

Electrochemical sensor for the detection of adrenaline at poly(crystal violet) modified electrode: optimization and voltammetric studies

Herein, we report the electropolymerization of crystal violet (CRV) on a bare glassy carbon electrode (GCE) for the detection of adrenaline (AD). Electropolymerization parameters such as electrolyte pH, scan rate and monomer concentrations were optimized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The characterization of CRV and poly(crystal violet) (PCV) was done using FT-IR, UV-visible spectroscopy and EIS. More importantly, the charge transfer resistance (R_ct) and other EIS data recorded from the EIS of various forms of the poly(crystal violet) (PCV) modified glassy carbon electrode (GCE) in AD were used for identifying the best PCV modified electrode. Subsequent application of the electrode prepared at optimum conditions (PGCE) for AD detection using the square wave voltammetry (SWV) gave a limit of detection (LOD) of 2.86 μM over a linear range of 10.3-102.7 μM. This sensor also showed considerable stability, good AD recovery from the real sample (98.9%), and excellent reproducibility, making it a suitable analytical tool for AD detection at the micromolar level.

Bio-Inspired Imprinting Materials for Biomedical Applications

Inspired by the recognition mechanism of biological molecules, molecular imprinting techniques (MITs) are imparted with numerous merits like excellent stability, recognition specificity, adsorption properties, and easy synthesis processes, and thus broaden the avenues for convenient fabrication protocol of bio-inspired molecularly imprinted polymers (MIPs) with desirable functions to satisfy the extensive demands of biomedical applications. Herein, the recent research progress made with respect to bio-inspired imprinting materials is discussed in this review. First, the underlying mechanism and basic components of a typical molecular imprinting procedure are briefly explored. Then, emphasis is put on the introduction of diverse MITs and novel bio-inspired imprinting materials. Following these two sections, practical applications of MIPs in the field of biomedical science are focused on. Last but not least, perspectives on the remaining challenges and future development of bio-inspired imprinting materials are presented.

Detection of chlorpyrifos based on molecular imprinting with a conducting polythiophene copolymer loaded on multi-walled carbon nanotubes

Molecular imprinting technique (MIT) with electrochemical sensing provides an attractive tool for the fabrication of sensors. Incorporation of conducting copolymer and surface imprinting strategies in the sensing device improves the conducting properties and poor template accessibility, slow binding kinetics at the same time. Here, this technique was employed with conducting polymers with multi-walled carbon nanotubes (MWCNT) to build an electrochemical sensor for detecting Chlorpyrifos (CPF) in vegetable sample solutions. In this work, we aimed at synthesizing a copolymer of 3-thiophene acetic acid and 3,4-ethylene dioxythiophene on the surface of MWCNT. We further constructed a polymer drop-casted glassy carbon electrode sensor for ultrasensitive detection CPF. Under optimal conditions, the sensor exhibited a very low limit of detection (LOD) of 4.0 × 10^-12 M for CPF. Due to the excellent repeatability and reusability of the materials, this study and findings have potential applications in the monitoring of pesticides from vegetable samples.

Modern and Dedicated Methods for Producing Molecularly Imprinted Polymer Layers in Sensing Applications

Molecular imprinting (MI) is the most available and known method to produce artificial recognition sites, similar to antibodies, inside or at the surface of a polymeric material. For this reason, scholars all over the world have found MI appealing, thus developing, in this past period, various types of molecularly imprinted polymers (MIPs) that can be applied to a wide range of applications, including catalysis, separation sciences and monitoring/diagnostic devices for chemicals, biochemicals and pharmaceuticals. For instance, the advantages brought by the use of MIPs in the sensing and analytics field refer to higher selectivity, sensitivity and low detection limits, but also to higher chemical and thermal stability as well as reusability. In light of recent literature findings, this review presents both modern and dedicated methods applied to produce MIP layers that can be integrated with existent detection systems. In this respect, the following MI methods to produce sensing layers are presented and discussed: surface polymerization, electropolymerization, sol–gel derived techniques, phase inversionand deposition of electroactive pastes/inks that include MIP particles.

MXene/carbon nanohorns decorated with conductive molecularly imprinted poly(hydroxymethyl-3,4-ethylenedioxythiophene) for voltammetric detection of adrenaline

A novel molecularly imprinted sensor was developed for the voltammetric determination of adrenaline (AD). MXene/carbon nanohorn (MXene/CNH) composite with good electric conductivity and enormous accessible active sites was firstly introduced as catalytic substrate. Subsequently, molecularly imprinted polymer (MIP) film was fabricated in mixed solutions containing hydroxymethyl-3,4-ethylenedioxythiophene (functional monomer) and AD (template) through electro-polymerization process. A molecularly imprinted sensor was formed after removing the template. The morphology and elemental composition of the prepared composites were studied by scanning electron microscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical performance of the molecularly imprinted sensors. Under optimized conditions, the designed sensor displays a wide linear range from 1.0 nM to 60.0 μM and a low limit of detection of 0.3 nM. The developed sensor also presents good selectivity, reproducibility and long-term stability, and satisfactory feasibility in practical sample analysis. MXene/carbon nanohorns decorated with conductive molecularly imprinted poly(hydroxymethyl-3,4-ethylenedioxythiophene) was proposed for highly sensitive and selective detection of adrenaline.

Selective determination of epinephrine using electrochemical sensor based on ordered mesoporous carbon / nickel oxide nanocomposite

A nanocomposite of ordered mesoporous carbon/nickel oxide (OMC-NiO) was synthesized by hard-templating method. The nanocomposite remained ordered mesostructure and high surface area with the NiO nanocrystals embedded in the wall of the OMC. A sensitive sensor for electrochemical detection of epinephrine (EP) was developed with GCE modified by OMC-NiO nanocomposite. Cyclic voltammogram (CV) and differential pulse voltammetry (DPV) were used as the techniques to explore the electrochemical behavior of EP on OMC-NiO/GCE surface. The result showed that the electrode demonstrated better electrocatalytic performance to EP compared to that seen at OMC/GCE. Under the optimum condition, DPV measurements of the electrode response displayed a linear detection range for 8.0 × 10^-7 to 5.0 × 10^-5 M with a detection limit of 8.5 × 10^-8 M (S/N = 3). It is worth noting that the electrocatalytic redox mechanism of EP on the electrode have studied through experiments and calculations (cyclic voltammetry and molecular electrostatic potential distribution). Moreover, the electrocatalytic behavior for the oxidation of EP and uric acid (UA) on OMC-NiO/GCE surface was investigated. The result showed that the sensor can be used to selectively determinate EP in the presence of an excesses of UA. Finally, the developed sensor was successfully applied to the determination of EP in spiked human blood serum and EP injection with satisfactory results.

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.

Glucose-Responsive Gene Delivery at Physiological pH through Tertiary-Amine Stabilized Boronate-PVA Particles Synthesized by One-Pot Reaction

We report a physiologically stable and cytocompatible glucose-responsive nonviral gene delivery system made up of boronate functionalized polymeric material. Herein, we utilize boronate cis-diol interactions to develop a glucose-responsive submicron particle (SMP) system. The stability of the boronate interaction at a physiological pH was achieved by copolymerization of dimethyl aminoethyl methacrylate (DMAEMA) with acrylamidophenylboronic acid (AAPBA) and the formation of a complex with polyvinylalcohol (PVA) which is governed by cis-diol interactions. The shift in hydrodynamic diameter of SMPs was observed and correlated with increasing glucose concentrations at a physiological pH. Optimal transfection was observed for a 5 µg dose of the gaussia luciferase reporter gene in NIH3T3 cells without any adverse effect on cellular viability. The destabilization of the AAPBA–PVA complex by interacting with glucose allowed the release of encapsulated bovine serum albumin (BSA) in a glucose-responsive manner. In total, 95% of BSA was released from SMPs at a 50 mM glucose concentration after 72 h. A two-fold increase in transfection was observed in 50 mM glucose compared to that of 10 mM glucose.

Construction of a selective non-enzymatic electrochemical sensor based on hollow nickel nanospheres/carbon dots–chitosan and molecularly imprinted polymer film for the detection of glucose

A non-enzymatic glucose electrochemical sensor platform was fabricated by assembling hollow nickel nanospheres/carbon dots–chitosan and molecularly imprinted polymer film modified a glass carbon electrode.

Tramadol sensing in non-invasive biological fluids using a voltammetric electronic tongue and an electrochemical sensor based on biomimetic recognition

Tramadol (TRA) is a weak opioid analgesic, prescribed to relieve mild to moderately severe pain. However, side effects of TRA overdoses, including vomiting, depression, tachycardia, convulsions, morbidity and mortality are often reported. In this study, an electrochemical sensor based on molecularly imprinted conductive polymer was firstly developed for the quantitative and non-invasive detection of TRA. Secondly, a voltammetric electronic tongue (VE-Tongue) combined with chemometric methods was used for the qualitative analysis. The MIP sensor was constructed by self-assembling a poly-aniline layer coated with silver nanoparticles (PANI-AgNPs) on a screen-printed gold electrode (Au-SPE). Then, 2-amino-thiophenol was polymerised in the presence of TRA. The electronic device exhibits, under optimal conditions, responses proportional to TRA concentrations (0.01-100 µg/mL) with detection and quantification limits of 9.42 µg/mL and 28.55 µg/mL, respectively. Moreover, its selectivity was proven by insignificant interferences of substances (paracetamol and citric acid). Spiked saliva and urine samples were used for the sensor practical application with a significant recovery above 90% and standard deviations below 4.5%. Besides, urine samples' analyses using VE-Tongue and pattern recognition methods show good discrimination, classification, and prediction results with scores above 95%. Correspondingly, both electro-analytical devices could be viable for monitoring drugs in biological matrices.

A Nonenzymatic Glucose Sensor Platform Based on Specific Recognition and Conductive Polymer-Decorated CuCo2O4 Carbon Nanofibers

CuCo₂O₄ decoration carbon nanofibers (CNFs) as an enzyme-free glucose sensor were fabricated via electrospinning technology and carbonization treatment. The CNFs with advantages of abundant nitrogen amounts, porosity, large surface area, and superior electrical conductivity were used as an ideal matrix for CuCo₂O₄ decoration. The resultant CuCo₂O₄–CNF hybrids possessed favorable properties of unique three-dimensional architecture and good crystallinity, accompanied by the CuCo₂O₄ nanoparticles uniformly growing on the CNF skeleton. To further enhance the selective molecular recognition capacity of the developed sensor, a conductive film was synthesized through the electropolymerization of thiophene and thiophene-3-boronic acid (TBA). Based on the synergistic effects of the performances of CNFs, CuCo₂O₄ nanoparticles, and boronic acid-decorated polythiophene layer, the obtained poly(thiophene-3-boronic acid) (PTBA)/CuCo₂O₄–CNF-modified electrodes (PTBA/CuCo₂O₄–CNFs/glassy carbon electrode (GCE)) displayed prominent electrocatalytic activity toward electro-oxidation of glucose. The fabricated sensor presented an outstanding performance in the two linear ranges of 0.01–0.5 mM and 0.5–1.5 mM, with high selectivity of 2932 and 708 μA·mM⁻¹·cm⁻², respectively. The composite nanofibers also possessed good stability, repeatability, and excellent anti-interference selectivity toward the common interferences. All these results demonstrate that the proposed composite nanofibers hold great potential in the application of constructing an enzyme-free glucose sensing platform.

Molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon: fabrication, characterization and electrochemical detection of uric acid

An electrochemical sensor is described for determination of uric acid (UA). Carbon-enwrapped nickel nanoparticles (Ni@BC) were coated with polydopamine (PDA) that was molecularly imprinted with UA. The biomass carbon (BC) was synthesized by one-step solid-state pyrolysis from leaves of Firmiana platanifolia. The imprinted polymer was obtained by electrodeposition of DA as the monomer. The amount of monomer, the scan cycles, pH value and adsorption time were optimized. Furthermore, the selectivity of the MIP for UA on a glassy carbon electrode (GCE) was evaluated by selectivity tests. The differential pulse voltammetric responses to UA with and without interferents were consistent. The modified GCE has a linear response in the 0.01-30 μM UA concentration range, and the limit of detection is 8 nM. The MIP electrode was applied to the analysis of UA in urine for which the initial concentrations were determined by the phosphotungstic acid kit. Recoveries ranged from 91.3 to 113.4%, with relative standard deviations between 1.3 and 9.7% (n = 3). Graphical abstract Schematic presentation of electrochemical detection of uric acid by molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon (Ni@BC-MIP).