Electrochemical Affinity Biosensors: Pervasive Devices with Exciting Alliances and Horizons Ahead.

Electrochemical affinity biosensors are evolving at breakneck speed, strengthening and colonizing more and more niches and drawing unimaginable roadmaps that increasingly make them protagonists of our daily lives. They achieve this by combining their intrinsic attributes with those acquired by leveraging the significant advances that occurred in (nano)materials technology, bio(nano)materials and nature-inspired receptors, gene editing and amplification technologies, and signal detection and processing techniques. The aim of this Perspective is to provide, with the support of recent representative and illustrative literature, an updated and critical view of the repertoire of opportunities, innovations, and applications offered by electrochemical affinity biosensors fueled by the key alliances indicated. In addition, the imminent challenges that these biodevices must face and the new directions in which they are envisioned as key players are discussed.

Functionalized Ag/Fe-MOFs nanocomposite as a novel endogenous redox mediator for determination of α2,6-sialylated glycans in serum.

The development of a novel signal amplification system is described for sensitive determination of α2,6-sialylated glycans (α2,6-sial-Gs), an important prognostic tumor biomarker. First, Fe-based metal-organic frameworks (Fe-MOFs) with silver nanoparticles (AgNPs) decorated onto the outer surface were designed and synthesized with controlled octahedron structures. The new Ag/Fe-MOFs nanocomposite possessed strong conductivity and a large surface area to carry more nanoprobes. To connect the Ag/Fe-MOFs nanocomposite with more groups, the nanocomposite was functionalized by -COOH with SH-PEG-COOH to bind with an α2,6-sial-Gs catcher, M-APBA, via -CONH- bonds. More importantly, the Ag/Fe-MOFs also exhibited an excellent endogenous redox mediator property to produce electrons, which is the fundamental mechanism underlying amplification of an electronic signal. A gold electrode was used to accelerate electron transfer and immobilize the α2,6-sial-Gs lectin (SNA). After the sandwich-type catcher recognition (SNA/α2,6-sial-Gs/M-APBA), the current peak response was provoked in the process of oxidizing AgNPs to Ag+ in the forward anodic potential sweep, while Cl- in a PBS solution was transferred into Ag+ to maintain charge neutrality. Optimized particles were employed for direct fabrication of the sandwich-type affinity biosensor, which was found to show a linear detection range from 1 fg mL-1 to 1 ng mL-1 with a detection limit of 0.09 fg mL-1. Furthermore, the biosensor exhibited excellent specificity and stability, indicating that such a novel nanobiotechnology platform can be used to initiate potential utility for monitoring biomarkers in serum. (A)Schematic presentation of synthesis and surface modification of Ag/Fe-MOFs. The new Ag/Fe-MOFs nanocomposite possessed commendable conductivity and large surface area to carry more nanoprobe; after functionalizing the Ag/MOFs with SH-PEG-COOH, the functionalized endogenous redox mediator (c-Ag/MOFs) realized the possibility that can connect with the biological catcher. (B) Schematic diagram of electrode construction for detecting α2,6-sialylated glycans (α2,6-sial-Gs). By using the c-Ag/Fe-MOFs functional endogenous redox mediator, we successfully implemented the electrochemical detection of α2,6-sial-Gs.

Nanozymes in electrochemical affinity biosensing.

Over the past decade, artificial nanomaterials that exhibit properties similar to those of enzymes are gaining attraction in electrochemical biosensing as highly stable and low-cost alternatives to enzymes. This review article discusses the main features of the various nanomaterials (metal oxide, metal, and carbon-based materials) explored so far to mimic different kinds of enzymes. The unprecedented opportunities imparted by these functional nanomaterials or their nanohybrids, mostly providing peroxidase-like activity, in electrochemical affinity biosensing are critically discussed mainly in connection with their use as catalytic labels or electrode surface modifiers by highlighting representative strategies reported in the past 5 years with application in the food, environmental, and biomedical fields. Apart from outlining the pros and cons of nanomaterial-based enzyme mimetics arising from the impressive development they have experienced over the last few years, current challenges and future directions for achieving their widespread use and exploiting their full potential in the development of electrochemical biosensors are discussed. Graphical abstract.

Cutting-Edge Advances in Electrochemical Affinity Biosensing at Different Molecular Level of Emerging Food Allergens and Adulterants.

The presence of allergens and adulterants in food, which represents a real threat to sensitized people and a loss of consumer confidence, is one of the main current problems facing society. The detection of allergens and adulterants in food, mainly at the genetic level (characteristic fragments of genes that encode their expression) or at functional level (protein biomarkers) is a complex task due to the natural interference of the matrix and the low concentration at which they are present. Methods for the analysis of allergens are mainly divided into immunological and deoxyribonucleic acid (DNA)-based assays. In recent years, electrochemical affinity biosensors, including immunosensors and biosensors based on synthetic sequences of DNA or ribonucleic acid (RNA), linear, aptameric, peptide or switch-based probes, are gaining special importance in this field because they have proved to be competitive with the methods commonly used in terms of simplicity, test time and applicability in different environments. These unique features make them highly promising analytical tools for routine determination of allergens and food adulterations at the point of care. This review article discusses the most significant trends and developments in electrochemical affinity biosensing in this field over the past two years as well as the challenges and future prospects for this technology.

Contribution of inorganic and organic components to sorption of neutral and ionizable pharmaceuticals by sediment/soil.

Our previous study showed that the sorption coefficient of certain polar pharmaceuticals to river sediment, especially particular amines, was unexpectedly high. Thus, we conducted sorption experiments of selected polar pharmaceuticals and pyrene derivatives, including amines, carboxylic acids, and neutral compounds, to model clay minerals, i.e., montmorillonite and kaolin, in addition to silica sands and humic substances. The contribution of each component was roughly estimated by simple fractionation of the individual sorption coefficients. Relatively high sorption coefficients (K d values) were found, especially for amines on clay minerals, which suggest that electrochemical affinity may play an important role. The estimated contribution percentage suggests a relatively large contribution from inorganic constituents, such as clay minerals, for silt loam soil; in contrast, organic components predominantly contribute for sandy river sediments. These findings could be the key to understanding not only the fate and transport but also bioavailability and environmental risks of pharmaceuticals, which are mostly polar and/or ionizable.

Molecular Biosensors for Electrochemical Detection of Infectious Pathogens in Liquid Biopsies: Current Trends and Challenges.

Rapid and reliable diagnosis of infectious diseases caused by pathogens, and timely initiation of appropriate treatment are critical determinants to promote optimal clinical outcomes and general public health. Conventional in vitro diagnostics for infectious diseases are time-consuming and require centralized laboratories, experienced personnel and bulky equipment. Recent advances in electrochemical affinity biosensors have demonstrated to surpass conventional standards in regards to time, simplicity, accuracy and cost in this field. The tremendous potential offered by electrochemical affinity biosensors to detect on-site infectious pathogens at clinically relevant levels in scarcely treated body fluids is clearly stated in this review. The development and application of selected examples using different specific receptors, assay formats and electrochemical approaches focusing on the determination of specific circulating biomarkers of different molecular (genetic, regulatory and functional) levels associated with bacterial and viral pathogens are critically discussed. Existing challenges still to be addressed and future directions in this rapidly advancing and highly interesting field are also briefly pointed out.

Non-Invasive Breast Cancer Diagnosis through Electrochemical Biosensing at Different Molecular Levels.

The rapid and accurate determination of specific circulating biomarkers at different molecular levels with non- or minimally invasive methods constitutes a major challenge to improve the breast cancer outcomes and life quality of patients. In this field, electrochemical biosensors have demonstrated to be promising alternatives against more complex conventional strategies to perform fast, accurate and on-site determination of circulating biomarkers at low concentrations in minimally treated body fluids. In this article, after discussing briefly the relevance and current challenges associated with the determination of breast cancer circulating biomarkers, an updated overview of the electrochemical affinity biosensing strategies emerged in the last 5 years for this purpose is provided highlighting the great potentiality of these methodologies. After critically discussing the most interesting features of the electrochemical strategies reported so far for the single or multiplexed determination of such biomarkers with demonstrated applicability in liquid biopsy analysis, existing challenges still to be addressed and future directions in this field will be pointed out.

Diagnostics Strategies with Electrochemical Affinity Biosensors Using Carbon Nanomaterials as Electrode Modifiers.

Early diagnosis is often the key to successful patient treatment and survival. The identification of various disease signaling biomarkers which reliably reflect normal and disease states in humans in biological fluids explain the burgeoning research field in developing new methodologies able to determine the target biomarkers in complex biological samples with the required sensitivity and selectivity and in a simple and rapid way. The unique advantages offered by electrochemical sensors together with the availability of high affinity and specific bioreceptors and their great capabilities in terms of sensitivity and stability imparted by nanostructuring the electrode surface with different carbon nanomaterials have led to the development of new electrochemical biosensing strategies that have flourished as interesting alternatives to conventional methodologies for clinical diagnostics. This paper briefly reviews the advantages of using carbon nanostructures and their hybrid nanocomposites as electrode modifiers to construct efficient electrochemical sensing platforms for diagnosis. The review provides an updated overview of some selected examples involving attractive amplification and biosensing approaches which have been applied to the determination of relevant genetic and protein diagnostics biomarkers.

Magnetic Particles Coupled to Disposable Screen Printed Transducers for Electrochemical Biosensing.

Ultrasensitive biosensing is currently a growing demand that has led to the development of numerous strategies for signal amplification. In this context, the unique properties of magnetic particles; both of nano- and micro-size dimensions; have proved to be promising materials to be coupled with disposable electrodes for the design of cost-effective electrochemical affinity biosensing platforms. This review addresses, through discussion of selected examples, the way that nano- and micro-magnetic particles (MNPs and MMPs; respectively) have contributed significantly to the development of electrochemical affinity biosensors, including immuno-, DNA, aptamer and other affinity modes. Different aspects such as type of magnetic particles, assay formats, detection techniques, sensitivity, applicability and other relevant characteristics are discussed. Research opportunities and future development trends in this field are also considered.

Electrochemical affinity biosensors for detection of mycotoxins: A review.

This review discusses the current state of electrochemical biosensors in the determination of mycotoxins in foods. Mycotoxins are highly toxic secondary metabolites produced by molds. The acute toxicity of these results in serious human and animal health problems, although it has been only since early 1960s when the first studied aflatoxins were found to be carcinogenic. Mycotoxins affect a broad range of agricultural products, most important cereals and cereal-based foods. A majority of countries, mentioning especially the European Union, have established preventive programs to control contamination and strict laws of the permitted levels in foods. Official methods of analysis of mycotoxins normally requires sophisticated instrumentation, e.g. liquid chromatography with fluorescence or mass detectors, combined with extraction procedures for sample preparation. For about sixteen years, the use of simpler and faster analytical procedures based on affinity biosensors has emerged in scientific literature as a very promising alternative, particularly electrochemical (i.e., amperometric, impedance, potentiometric or conductimetric) affinity biosensors due to their simplicity and sensitivity. Typically, electrochemical biosensors for mycotoxins use specific antibodies or aptamers as affinity ligands, although recombinant antibodies, artificial receptors and molecular imprinted polymers show potential utility. This article deals with recent advances in electrochemical affinity biosensors for mycotoxins and covers complete literature from the first reports about sixteen years ago.