Electrochemical Sensors Based on Metal Nanoparticles with Biocatalytic Activity

Biosensors have attracted a great deal of attention, as they allow for the translation of the standard laboratory-based methods into small, portable devices. The field of biosensors has been growing, introducing innovations into their design to improve their sensing characteristics and reduce sample volume and user intervention. Enzymes are commonly used for determination purposes providing a high selectivity and sensitivity; however, their poor shelf-life is a limiting factor. Researchers have been studying the possibility of substituting enzymes with other materials with an enzyme-like activity and improved long-term stability and suitability for point-of-care biosensors. Extra attention is paid to metal and metal oxide nanoparticles, which are essential components of numerous enzyme-less catalytic sensors. The bottleneck of utilising metal-containing nanoparticles in sensing devices is achieving high selectivity and sensitivity. This review demonstrates similarities and differences between numerous metal nanoparticle-based sensors described in the literature to pinpoint the crucial factors determining their catalytic performance. Unlike other reviews, sensors are categorised by the type of metal to study their catalytic activity dependency on the environmental conditions. The results are based on studies on nanoparticle properties to narrow the gap between fundamental and applied research. The analysis shows that the catalytic activity of nanozymes is strongly dependent on their intrinsic properties (e.g. composition, size, shape) and external conditions (e.g. pH, type of electrolyte, and its chemical composition). Understanding the mechanisms behind the metal catalytic activity and how it can be improved helps designing a nanozyme-based sensor with the performance matching those of an enzyme-based device. GRAPHICAL ABSTRACT: [Image: see text

Synthesis of organic-inorganic hybrids for the electrocatalytic detection of biologically active molecules

Abstract: Biomedical diagnosis and testing are often accompanied by inefficiencies, including high-priced tests, high detection limits, and interference from other biologically relevant molecules. To overcome such inefficiencies, the construction of electrochemical sensors has attracted interest due to their promising nature. They are simple to fabricate, and they offer high sensitivity and selectivity and low detection limits. In this research work, aniline and some transition metals were used to form complex materials as tools in electrochemical biosensor fabrication. In general, cyclic voltammetric (CV), square wave voltammetric (SWV), and chronoamperometric techniques were employed to model the aniline metal complexes electrochemical reactivities on working glassy carbon electrodes. Fourier transformed infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Nuclear magnetic resonance (NMR), and Elemental analyzer (EA) were used for further characterization. Furthermore, the materials were employed for electrocatalytic detection of biologically active molecules. In this regard, aniline-based metal complexes of bismuth, nickel, and cobalt were synthesized, characterized, and applied for the electrocatalytic detection of biologically active molecules. The complexes were synthesized by a simple complexation method using aniline as a ligand. The as-prepared complexes were deposited on the glassy carbon electrode (GCE) using the drop and dry method and investigated as an electrocatalyst for the efficient and sensitive detection of dopamine, iodine, uric acid, and cysteine. The hybrid materials showed good voltammetric sensor application for the detection of biologically active molecules. The results indicated that the electrodes modified with the complex materials could detect micromolar concentrations of dopamine, iodine, uric acid, and cysteine. The bismuth aniline complex (BAC) indicated 12.3 μM and 23.17 μM low detection limits for dopamine and iodine, respectively. The nickel aniline complex (NAC) revealed a 2.09 μM limit of detection and a wide linear range of 2.5 μM-220 μM for cysteine detection. The cobalt-aniline complex (COAC) indicated 9.26 μM and 9.52 μM limit of detection for uric acid and dopamine respectively, with linear ranges of 20 – 280 μM and 10 – 200 μM. The developed sensors could eliminate the interference of other biomolecules such as ascorbic acid, glucose, and histamine, to mention a few. The sensors were only selective to the analytes of interest. The electrochemical sensors developed in this work demonstrate good potential for the molecular diagnosis of neurological disorders such as Parkinson’s disease.Ph.D. (Chemistry

Synthesis of organic-inorganic hybrids for the electrocatalytic detection of biologically active molecules

Abstract: Biomedical diagnosis and testing are often accompanied by inefficiencies, including high-priced tests, high detection limits, and interference from other biologically relevant molecules. To overcome such inefficiencies, the construction of electrochemical sensors has attracted interest due to their promising nature. They are simple to fabricate, and they offer high sensitivity and selectivity and low detection limits. In this research work, aniline and some transition metals were used to form complex materials as tools in electrochemical biosensor fabrication. In general, cyclic voltammetric (CV), square wave voltammetric (SWV), and chronoamperometric techniques were employed to model the aniline metal complexes electrochemical reactivities on working glassy carbon electrodes. Fourier transformed infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Nuclear magnetic resonance (NMR), and Elemental analyzer (EA) were used for further characterization. Furthermore, the materials were employed for electrocatalytic detection of biologically active molecules. In this regard, aniline-based metal complexes of bismuth, nickel, and cobalt were synthesized, characterized, and applied for the electrocatalytic detection of biologically active molecules. The complexes were synthesized by a simple complexation method using aniline as a ligand. The as-prepared complexes were deposited on the glassy carbon electrode (GCE) using the drop and dry method and investigated as an electrocatalyst for the efficient and sensitive detection of dopamine, iodine, uric acid, and cysteine. The hybrid materials showed good voltammetric sensor application for the detection of biologically active molecules. The results indicated that the electrodes modified with the complex materials could detect micromolar concentrations of dopamine, iodine, uric acid, and cysteine. The bismuth aniline complex (BAC) indicated 12.3 μM and 23.17 μM low detection limits for dopamine and iodine, respectively. The nickel aniline complex (NAC) revealed a 2.09 μM limit of detection and a wide linear range of 2.5 μM-220 μM for cysteine detection. The cobalt-aniline complex (COAC) indicated 9.26 μM and 9.52 μM limit of detection for uric acid and dopamine respectively, with linear ranges of 20 – 280 μM and 10 – 200 μM. The developed sensors could eliminate the interference of other biomolecules such as ascorbic acid, glucose, and histamine, to mention a few. The sensors were only selective to the analytes of interest. The electrochemical sensors developed in this work demonstrate good potential for the molecular diagnosis of neurological disorders such as Parkinson’s disease.D.Phil. (Chemistry

Polymers and plastics modified electrodes for biosensors: a review

Polymer materials offer several advantages as supports of biosensing platforms in terms of flexibility, weight, conformability, portability, cost, disposability and scope for integration. The present study reviews the field of electrochemical biosensors fabricated on modified plastics and polymers, focusing the attention, in the first part, on modified conducting polymers to improve sensitivity, selectivity, biocompatibility and mechanical properties, whereas the second part is dedicated to modified “environmentally friendly” polymers to improve the electrical properties. These ecofriendly polymers are divided into three main classes: bioplastics made from natural sources, biodegradable plastics made from traditional petrochemicals and eco/recycled plastics, which are made from recycled plastic materials rather than from raw petrochemicals. Finally, flexible and wearable lab-on-a-chip (LOC) biosensing devices, based on plastic supports, are also discussed. This review is timely due to the significant advances achieved over the last few years in the area of electrochemical biosensors based on modified polymers and aims to direct the readers to emerging trends in this field.Peer ReviewedPostprint (published version

E-Tongues/Noses Based on Conducting Polymers and Composite Materials: Expanding the Possibilities in Complex Analytical Sensing

Conducting polymers (CPs) are extensively studied due to their high versatility and electrical properties, as well as their high environmental stability. Based on the above, their applications as electronic devices are promoted and constitute an interesting matter of research. This review summa- rizes their application in common electronic devices and their implementation in electronic tongues and noses systems (E-tongues and E-noses, respectively). The monitoring of diverse factors with these devices by multivariate calibration methods for different applications is also included. Lastly, a critical discussion about the enclosed analytical potential of several conducting polymer-based devices in electronic systems reported in literature will be offered

Recent advances in non-enzymatic electrochemical detection of hydrophobic metabolites in biofluids

This review focuses on recent advances in non-enzymatic electrochemical biosensors for detection of hydrophobic metabolites. Electrochemical approaches have been widely applied in many established and emerging technologies and a large range of electrochemical biosensors have been used for detection of various hydrophobic metabolites. Despite the progress made in this field, some problems still exist, specifically, electrochemical detection of hydrophobic biomarkers can be challenging in complex biological fluids. In this review, we have highlighted some of the most representative surface modification technologies that have been employed in electrochemical biosensors to counter the problems of poor sensitivity and selectivity towards hydrophobic metabolites. The hydrophobic metabolites discussed in this review include uric acid, epinephrine, cortisol, cholesterol, tyrosine, adenine, guanine, cytosine, and thymine. This is followed by discussion on future research directions for electrochemical sensing of hydrophobic biomarkers

Electrochemical Aptasensor for Detection of Dopamine

This work presents a proof of concept of a novel, simple, and sensitive method of detection of dopamine, a neurotransmitter within the human brain. We propose a simple electrochemical method for the detection of dopamine using a dopamine-specific aptamer labeled with an electrochemically active ferrocene tag. Aptamers immobilized on the surface of gold screen-printed gold electrodes via thiol groups can change their secondary structure by wrapping around the target molecule. As a result, the ferrocene labels move closer to the electrode surface and subsequently increase the electron transfer. The cyclic voltammograms and impedance spectra recorded on electrodes in buffer solutions containing different concentration of dopamine showed, respectively, the increase in both the anodic and cathodic currents and decrease in the double layer resistance upon increasing the concentration of dopamine from 0.1 to 10 nM L-1. The high affinity of aptamer-dopamine binding (KD ≈ 5 nM) was found by the analysis of the binding kinetics. The occurrence of aptamer-dopamine binding was directly confirmed with spectroscopic ellipsometry measurements

Electrochemical Sensors Based on Carbon Nanotubes

This review focuses on recent contributions in the development of the electrochemical sensors based on carbon nanotubes (CNTs). CNTs have unique mechanical and electronic properties, combined with chemical stability, and behave electrically as a metal or semiconductor, depending on their structure. For sensing applications, CNTs have many advantages such as small size with larger surface area, excellent electron transfer promoting ability when used as electrodes modifier in electrochemical reactions, and easy protein immobilization with retention of its activity for potential biosensors. CNTs play an important role in the performance of electrochemical biosensors, immunosensors, and DNA biosensors. Various methods have been developed for the design of sensors using CNTs in recent years. Herein we summarize the applications of CNTs in the construction of electrochemical sensors and biosensors along with other nanomaterials and conducting polymers

Recent advances in the fabrication and application of screen-printed electrochemical (bio)sensors based on carbon materials for biomedical, agri-food and environmental analyses

This review describes recent advances in the fabrication of electrochemical (bio)sensors based on screen-printing technology involving carbon materials and their application in biomedical, agri-food and environmental analyses. It will focus on the various strategies employed in the fabrication of screen-printed (bio)sensors, together with their performance characteristics; the application of these devices for the measurement of selected naturally occurring biomolecules, environmental pollutants and toxins will be discussed