Electrochemical immunosensor for ethinylestradiol using diazonium salt grafting onto silver nanoparticles-silica–graphene oxide hybrids

Fabrication of an innovative electrochemical sensor based on graphene-coated silver nanoparticles decorated over graphitic carbon nitride for efficient determination of estradiol

Monitoring small amount of endocrine disrupting chemical, estradiol (E2) residue in environmental and biological samples is extremely important because of its possible connections to breast and prostate malignancies and gastrointestinal disorders. The newly synthesized graphene-coated silver nanoparticles (GN@Ag) decorated on graphitic carbon nitride (g-C3N4)-based hybrid nanomaterial (GN@Ag/g-C3N4) was used to modify glassy carbon electrode (GCE) for electroanalytical measurement of E2. The GN@Ag/g-C3N4 nanocomposite prepared through ultrasonic-assisted reflux methodology was characterized using various physicochemical methods. The scanning electron microscopy and transmission electron microscopy have shown that GN@Ag nanoparticles were decorated and randomly dispersed over g-C3N4 sheets. The exceptional electrochemical response towards the oxidation of E2 was observed through cyclic voltammetry due to the quick electron transfer ability and superior conductivity of GN@Ag/g-C3N4/GCE. The detection limit was found to be 0.002 μM with wide linear range of E2 concentration (0.005-8.0 μM) along with remarkable stability of the fabricated electrode for 21 days showing 91% retention in initial current. The kinetic parameters such as catalytic rate constant and diffusion coefficient for E2 were estimated to be 1.1 × 105 M-1 s-1 and 1.9 × 10-4 cm2 s-1, respectively, by employing chronoamperometry. The proposed sensor also demonstrated its practical applicability for E2 determination in environmental and biological samples with a recovery range of 95-104%. Furthermore, the developed sensing platform is much better compared to reported methods in terms of simplicity, accuracy, detection limit, linearity range, and usefulness in real sample for E2 sensing.

Strategies and Applications of Graphene and Its Derivatives-Based Electrochemical Sensors in Cancer Diagnosis

Graphene is an emerging nanomaterial increasingly being used in electrochemical biosensing applications owing to its high surface area, excellent conductivity, ease of functionalization, and superior electrocatalytic properties compared to other carbon-based electrodes and nanomaterials, enabling faster electron transfer kinetics and higher sensitivity. Graphene electrochemical biosensors may have the potential to enable the rapid, sensitive, and low-cost detection of cancer biomarkers. This paper reviews early-stage research and proof-of-concept studies on the development of graphene electrochemical biosensors for potential future cancer diagnostic applications. Various graphene synthesis methods are outlined along with common functionalization approaches using polymers, biomolecules, nanomaterials, and synthetic chemistry to facilitate the immobilization of recognition elements and improve performance. Major sensor configurations including graphene field-effect transistors, graphene modified electrodes and nanocomposites, and 3D graphene networks are highlighted along with their principles of operation, advantages, and biosensing capabilities. Strategies for the immobilization of biorecognition elements like antibodies, aptamers, peptides, and DNA/RNA probes onto graphene platforms to impart target specificity are summarized. The use of nanomaterial labels, hybrid nanocomposites with graphene, and chemical modification for signal enhancement are also discussed. Examples are provided to illustrate applications for the sensitive electrochemical detection of a broad range of cancer biomarkers including proteins, circulating tumor cells, DNA mutations, non-coding RNAs like miRNA, metabolites, and glycoproteins. Current challenges and future opportunities are elucidated to guide ongoing efforts towards transitioning graphene biosensors from promising research lab tools into mainstream clinical practice. Continued research addressing issues with reproducibility, stability, selectivity, integration, clinical validation, and regulatory approval could enable wider adoption. Overall, graphene electrochemical biosensors present powerful and versatile platforms for cancer diagnosis at the point of care.

Advances on Hormones and Steroids Determination: A Review of Voltammetric Methods since 2000

This article presents advances in the electrochemical determination of hormones and steroids since 2000. A wide spectrum of techniques and working electrodes have been involved in the reported measurements in order to obtain the lowest possible limits of detection. The voltammetric and polarographic techniques, due to their sensitivity and easiness, could be used as alternatives to other, more complicated, analytical assays. Still, growing interest in designing a new construction of the working electrodes enables us to prepare new measurement procedures and obtain lower limits of detection. A brief description of the measured compounds has been presented, along with a comparison of the obtained results.

Tailoring the performance of electrochemical biosensors based on carbon nanomaterials via aryldiazonium electrografting

Carbon nanomaterials (CNs) offer some of the most valuable properties for electrochemical biosensing applications, such as good electrical conductivity, wide electrochemical stability, high specific surface area, and biocompatibility. Regardless the envisioned sensing application, endowing CNs with specific functions through controlled chemical functionalization is fundamental for promoting the specific binding of the analyte. As a versatile and straightforward method of surface functionalization, aryldiazonium chemistry have been successfully used to accommodate in a stable and reproducible way different functionalities, while the electrochemical route has become the favourite choice since the deposition conditions can be readily controlled and adapted to the substrate. In particular, the modification of CNs by electrochemical reduction of aryl diazonium salts is established as a powerful tool which allows tailoring the chemical and electronic properties of the sensing platform. By outlining the stimulating results disclosed in the last years, this article provides not only a comprehensively review, but also a rational assessment on contribution of aryldiazonium electrografting in developing CNs-based electrochemical biosensors. Furthermore, some of the emerging challenges to be surpassed to effectively implement this methodology for in vivo and point of care analysis are also highlighted.

Porphyran-capped silver nanoparticles as a promising antibacterial agent and electrode modifier for 5-fluorouracil electroanalysis

In the present work, the green synthesis of silver nanoparticles (AgNPs) using the sulfated polysaccharide porphyran (PFR) as capping agent and d-glucose as reducing agent is described. PFR was extracted from red seaweed and characterized by employing ¹³C NMR and determination of total sugar, protein, and sulfate contents. The obtained AgNPs-PFR were characterized by using UV-VIS spectroscopy, zeta potential determination, FESEM, and TEM, which demonstrated that PFR was effective at capping the AgNPs, yielding stable suspensions. The AgNPs-PFR presented good antimicrobial properties against Gram-positive and Gram-negative bacterial strains (Staphylococcus aureus and Escherichia coli, respectively). The AgNPs-PFR were also employed as the modifier of carbon paste electrodes, which were efficiently applied as electrochemical sensors for the determination of 5-fluorouracil (5-FU), an important anticancer drug, through square wave voltammetry (SWV). The AgNPs-PFR improved the electrochemical properties of the electrodes, and enhanced their electroanalytical performance. The developed sensing device presented detection and quantification limits equal to 10.7 and 35.8 μmol L-1, respectively, towards 5-FU determination. The proposed electrochemical sensor successfully quantified 5-FU in a real pharmaceutical formulation, confirming its potential as a new promising analytical detection tool for 5-FU quality control purposes.

Electrochemical study and simultaneous voltammetric determination of contraceptives ethinylestradiol and cyproterone acetate using silver nanoparticles solid amalgam electrode and cationic surfactant

In this work we propose the voltammetric analysis of contraceptive hormones ethinylestradiol (EE) and cyproterone acetate (CPA) using solid amalgam electrode fabricated with silver nanoparticles. To the best of our knowledge, this is the first report describing the simultaneous determination of these two compounds and also the first report of the use of amalgam electrode for analysis of EE and CPA. The voltammetric behavior of both substances was investigated by their reduction. An irreversible electrochemical process involving two protons and two electrons was found for each compound. The analytical assays were carried out using staircase voltammetry (SCV). Due to this, aiming to improve the analytical sensitivity, the cationic surfactant cetyltrimethylammonium bromide was also used. The instrumental and experimental parameters were studied and optimized to achieve the best conditions for the analysis. Under the optimum conditions, the voltammetric signals of EE and CPA showed dependence on the concentration range from 6.4 × 10^-7 to 7.8 × 10^-6 mol L^-1 and from 1.0 × 10^-6 to 1.0 × 10^-5 mol L^-1, respectively. The limits of detection obtained were 1.03 × 10^-7 mol L^-1 for EE and 2.99 × 10^-7 mol L^-1 for CPA. The analytical usefulness of the method was evaluated through its application on the simultaneous determination of EE and CPA in pharmaceutical formulations and urine samples. The two analytes were successfully quantified in these samples with good precision and the values found presented satisfactory concordance with the reference values, suggesting acceptable analytical efficiency for the approach described here.

Development of Electrochemical Sensor Based on Carbonaceal and Metal Phthalocyanines Materials for Determination of Ethinyl Estradiol

This work describes the development of an electrochemical sensor that was used in the determination of ethinyl estradiol (EE) in pharmaceutical formulations, river water, and milk using the square wave voltammetry technique. Studies were carried out using different carbonaceous materials (multiwalled carbon nanotubes, reduced graphene oxide Reduced graphene oxide, graphite) and different metallic phthalocyanines (cobalt, iron and manganese). Based on these studies it was possible to obtain the best system for the construction of the sensor. The device was obtained by the chemical modification of a glassy carbon electrode (GCE) with multiwalled carbon nanotubes (MWCNTs) and cobalt phthalocyanine (CoPc). The materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Under conditions previously optimized for the proposed method, an analytical curve was constructed, presenting linearity in a range of 2.50–90.0 μmol L−1 (R = 0.990), with detection limit of 2.20 μmol L−1 and quantification of 2.50 μmol L−1. The validation of the methodology for the determination of EE using GCE-MWCNTs-CoPc was performed, being accurate, precise, stable and sensitive. The recovery of ethinyl estradiol in the sample of pharmaceutical formulation was 103.93%, in the samples of river water ranged from 92.75% to 96.47%, and in the milk sample was from 88.00% to 96.20%. Thus, the proposed method presented a viable alternative for the determination of ethinyl estradiol in the quality control of pharmaceutical and food formulations as well as in environmental control.

Electrochemical immunosensors - A powerful tool for analytical applications

Immunosensors are biosensors based on interactions between an antibody and antigen on a transducer surface. Either antibody or antigen can be the species immobilized on the transducer to detect antigen or antibody, respectively. Because of the strong binding forces between these biomolecules, immunosensors present high selectivity and very high sensitivity, making them very attractive for many applications in different science fields. Electrochemical immunosensors explore measurements of an electrical signal produced on an electrochemical transductor. This signal can be voltammetric, potentiometric, conductometric or impedimetric. Immunosensors utilizing electrochemical detection have been explored in several analyses since they are specific, simple, portable, and generally disposable and can carry out in situ or automated detection. This review addresses the potential of immunosensors destined for application in food and environmental analysis, and cancer biomarker diagnosis. Emphasis is given to the approaches that have been used for construction of electrochemical immunosensors. Additionally, the fundamentals of immunosensors, technology of transducers and nanomaterials and a general overview of the possible applications of electrochemical immunosensors to the food, environmental and diseases analysis fields are described.

A sensitive label-free electrochemical immunosensor for detection of cytokeratin 19 fragment antigen 21-1 based on 3D graphene with gold nanopaticle modified electrode

Previous studies have confirmed that cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) serves as a powerful biomarker in non-small cell lung cancer (NSCLC). Herein, we report for the first time a label-free electrochemical immunosensor for sensitive and selective detection of tumor marker CYFRA21-1. In this work, three-dimensional graphene @ gold nanoparticles (3D-G@Au) nanocomposite was modified on the glassy carbon electrode (GCE) surface to enhance the conductivity of immunosensor. The anti-CYFRA21-1 captured and fixed on the modified GCE through the cross-linking of chitosan (CS), glutaraldehyde (GA) and anti-CYFRA21-1. The differential pulse voltammetry (DPV) peak current change due to the specific interaction between anti-CYFRA21-1 and CYFRA21-1 on the modified electrode surface was utilized to detect CYFRA21-1. Under optimized conditions, the proposed electrochemical immunosensor was employed to detect CYFRA21-1 and exhibited a wide linear range of 0.25-800ngmL^-1 and low detection limit of 100pgmL^-1 (S/N = 3). Moreover, the recovery rates of serum samples were in the range from 95.2% to 108.7% and the developed immunosensor also shows a good correlation (less than 6.6%) with enzyme-linked immunosorbent assay (ELISA) in the detection of clinical serum samples. Therefore, it is expected that the proposed immunosensor based on a 3D-G@Au has great potential in clinical medical diagnosis of CYFRA21-1.

Recent Advances in Electrochemical Immunosensors

Immunosensors have experienced a very significant growth in recent years, driven by the need for fast, sensitive, portable and easy-to-use devices to detect biomarkers for clinical diagnosis or to monitor organic pollutants in natural or industrial environments. Advances in the field of signal amplification using enzymatic reactions, nanomaterials such as carbon nanotubes, graphene and graphene derivatives, metallic nanoparticles (gold, silver, various oxides or metal complexes), or magnetic beads show how it is possible to improve collection, binding or transduction performances and reach the requirements for realistic clinical diagnostic or environmental control. This review presents these most recent advances; it focuses first on classical electrode substrates, then moves to carbon-based nanostructured ones including carbon nanotubes, graphene and other carbon materials, metal or metal-oxide nanoparticles, magnetic nanoparticles, dendrimers and, to finish, explore the use of ionic liquids. Analytical performances are systematically covered and compared, depending on the detection principle, but also from a chronological perspective, from 2012 to 2016 and early 2017.

Hybrid 2D-nanomaterials-based electrochemical immunosensing strategies for clinical biomarkers determination

Owing to the outstanding conductivity and biocompatibility as well as numerous other fascinating properties of two-dimensional (2D)-nanomaterials, 2D-based nanohybrids have shown unparalleled superiorities in the field of electrochemical biosensors. This review highlights latest advances in electrochemical immunosensors for clinical biomarkers based on different hybrid 2D-nanomaterials. Particular attention will be given to hybrid nanostructures involving graphene and other graphene-like 2D-layered nanomaterials (GLNs). Several recent strategies for using such 2D-nanomaterial heterostructures in the development of modern immunosensors, both for tagging or modifying electrode transducers, are summarized and discussed. These hybrid nanocomposites, quite superior than their rival materials, will undoubtedly have an important impact within the near future and not only in clinical areas. Current challenges and future perspectives in this rapidly growing field are also outlined.

Improved Electrochemical Detection of Zinc Ions Using Electrode Modified with Electrochemically Reduced Graphene Oxide

Increasing urbanization and industrialization lead to the release of metals into the biosphere, which has become a serious issue for public health. In this paper, the direct electrochemical reduction of zinc ions is studied using electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE). The graphene oxide (GO) was fabricated using modified Hummers method and was electrochemically reduced on the surface of GCE by performing cyclic voltammograms from 0 to −1.5 V. The modification was optimized and properties of electrodes were determined using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The determination of Zn(II) was performed using differential pulse voltammetry technique, platinum wire as a counter electrode, and Ag/AgCl/3 M KCl reference electrode. Compared to the bare GCE the modified GCE/ERGO shows three times better electrocatalytic activity towards zinc ions, with an increase of reduction current along with a negative shift of reduction potential. Using GCE/ERGO detection limit 5 ng·mL⁻¹ was obtained.