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This work describes the development of a simple and ultrasensitive electroanalytical methodology for the determination of microribonucleic acids (miRNAs) making use of nanostructured disposable electrodes. The strategy involves direct hybridization of the target miRNA (miRNA–21) with a specific thiolated RNA probe self-assembled together with mercaptohexanol (MCH) onto gold nanoparticles (AuNP)-modified screen-printed electrodes (SH-RNA/MCH-AuNP-SPCEs). In addition, the resulting RNA/miRNA homoduplexes are recognized with the viral protein p19 and labeled with a HRP-conjugated anti-Maltose Binding Protein (MBP) monoclonal antibody. Amperometric detection was carried out at −0.20 V ( vs . the Ag pseudoreference electrode) using the H 2 O 2 /hydroquinone (HQ) system. The prepared biosensors showed a linear dependence between the measured cathodic current and the concentration of the target miRNA over the 0.5–50 pmol L −1 range with a calculated detection limit (LOD) of 142 fmol L −1 without any target miRNA amplification. The assay lasted 60 min once the SH-RNA/MCH-AuNP-SPCEs were prepared. The SH-RNA/MCH-AuNP-SPCEs bioplatforms exhibit at least 2 months-storage stability and possess attractive practical advantages compared with other methods involving either p19 protein or amplification techniques. The usefulness of the method was demonstrated by determining the endogenous level of the target miRNA in total RNA (RNA t ) extracted from healthy and cancerous breast cells. [ABSTRACT FROM AUTHOR]

A new method for the detection of miRNAs making use of a competitive RNA/RNA hybridization configuration is described in this work. A biotinylated miRNA (biotin-miRNA) of identical sequence to that of the target miRNA is mixed with the samples to be analyzed allowing competition to be accomplished with the target miRNA for a thiolated RNA probe assembled onto a gold nanoparticles (AuNPs) modified screen-printed electrode. After labeling the hybridized biotin-miRNA with streptavidin-HRP conjugates, amperometric detection at −0.20 V was carried out using the H 2 O 2 /hydroquinone (HQ) system. The decrease in the amperometric response was proportional to the concentration of model target miRNA-21 in the 100 fM to 25.0 pM range. The integrated sensor provided a very low detection limit (25 fM, 0.25 attomol in 10 μL sample) for miRNA-21 without any amplification step, a complete discrimination against single nucleotide mismatched sequences under practical conditions and high storage stability. The usefulness of the developed method was demonstrated by determining the endogenous levels of the mature target miRNA in total RNA (RNA t ) extracted from cancerous and non-cancerous cells. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented which discusses various papers published within the issue, including one on the development of electrochemical immunosensing scaffolds, one on the use of screen-printed electrodes, and another on control of electron transfer.

Proper functionalization of electrode surfaces and/or nanomaterials plays a crucial role in the preparation of electrochemical (bio)sensors and their resulting performance. In this context, copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has been demonstrated to be a powerful strategy due to the high yields achieved, absence of by-products and moderate conditions required both in aqueous medium and under physiological conditions. This particular chemistry offers great potential to functionalize a wide variety of electrode surfaces, nanomaterials, metallophthalocyanines (MPcs) and polymers, thus providing electrochemical platforms with improved electrocatalytic ability and allowing the stable, reproducible and functional integration of a wide range of nanomaterials and/or different biomolecules (enzymes, antibodies, nucleic acids and peptides). Considering the rapid progress in the field, and the potential of this technology, this review paper outlines the unique features imparted by this particular reaction in the development of electrochemical sensors through the discussion of representative examples of the methods mainly reported over the last five years. Special attention has been paid to electrochemical (bio)sensors prepared using nanomaterials and applied to the determination of relevant analytes at different molecular levels. Current challenges and future directions in this field are also briefly pointed out. [ABSTRACT FROM AUTHOR]

Abstract An amperometric immunosensor for the determination of the biomarker endoglin (CD105) to comply with the requirements of sensitivity and accuracy demanded in clinical practice is reported in this work. The immunosensing platform is implemented onto disposable electrodes modified with poly(pyrrolepropionic) acid (pPPA). The methodology involves a sandwich configuration and labeling of the biotinylated detector antibody with poly-HRP-streptavidin for signal amplification. Amperometric detection of hydrogen peroxide reduction in the presence of HQ was employed as analytical readout. The different steps involved in the immunosensor preparation were monitored by electrochemical impedance spectroscopy. The resulting immunosensor provided a linear range between 0.18 and 20 ng mL−1, adequate for the determination of CD105 in serum, with a detection limit (LOD) of 140 pg mL−1. These analytical characteristics improve those reported previously for other electrochemical immunosensors. A good reproducibility of the measurements, an excellent storage stability of the anti-CD105-pPPA/SPCE bioplatforms and an excellent selectivity of the resulting immunosensors were found. The usefulness of the immunosensors was tested by analyzing human serum samples collected from healthy individuals and patients of colorectal, breast and lung cancer and epidermolysis bullosa. The results were successfully validated against those provided by an ELISA kit. Graphical abstract Amperometric immunosensing platform, implemented onto a disposable electrode modified with pPPA and involving a sandwich configuration for sensitive and accurate determination of CD105 in serum samples from cancer or epidermolysis bullosa patients with minimal sample treatment. Image 1 [ABSTRACT FROM AUTHOR]