Highly sensitive electrochemical aptasensor for immunoglobulin E detection based on sandwich assay using enzyme-linked aptamer

Electrochemical Biosensors for Whole Blood Analysis: Recent Progress, Challenges, and Future Perspectives

Whole blood, as one of the most significant biological fluids, provides critical information for health management and disease monitoring. Over the past 10 years, advances in nanotechnology, microfluidics, and biomarker research have spurred the development of powerful miniaturized diagnostic systems for whole blood testing toward the goal of disease monitoring and treatment. Among the techniques employed for whole-blood diagnostics, electrochemical biosensors, as known to be rapid, sensitive, capable of miniaturization, reagentless and washing free, become a class of emerging technology to achieve the target detection specifically and directly in complex media, e.g., whole blood or even in the living body. Here we are aiming to provide a comprehensive review to summarize advances over the past decade in the development of electrochemical sensors for whole blood analysis. Further, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms.

Biomedical applications of aptamer-modified chitosan nanomaterials: An updated review

Among polysaccharides of environmental and economic interest, chitosan (CS) is receiving much attention, particularly in the food and biotechnology industries to encapsulate active food ingredients and immobilize enzymes. CS nanoparticles (CS NPs) combine the intrinsic beneficial properties of both natural polymers and nanoscale particles such as quantum size effect, biocompatibility, biodegradability, and ease of modification, and have great potential for bioimaging, drug delivery, and biosensing applications. Aptamers are single-stranded oligonucleotides that can fold into predetermined structures and bind to the corresponding biomolecules. They are mainly used as targeting ligands in biosensors, disease diagnostic kits and treatment strategies. They can deliver contrast agents and drugs into cancer cells and tissues, control microorganism growth and precisely target pathogens. Aptamer-conjugated CS NPs can significantly improve the efficacy of conventional therapies, minimize their side effects on normal tissues, and overcome the enhanced permeability retention (EPR) effect. Further, aptamer-conjugated carbohydrate-based nanobiopolymers have shown excellent antibacterial and antiviral properties and can be used to develop novel biosensors for the efficient detection of antibiotics, toxins, and other biomolecules. This updated review aims to provide a comprehensive overview of the bioapplications of aptamer-conjugated CS NPs used as innovative diagnostic and therapeutic platforms, their limitations, and potential future directions.

Fabrication of a label-free electrochemical aptasensor to detect cytochrome c in the early stage of cell apoptosis

A label-free direct electrochemical aptasensor is presented for the identification of cytochrome c (Cyt c) at the nM concentration level. Carbon nanofibers (CNF), as a highly conductive material, were used to modify a glassy carbon electrode (GCE) and thus increase its conductivity. Moreover, to enhance the immobilization of aptamers (Apt) on the electrode surface, graphene oxide functionalized with aspartic acid (GOAsp) was added to the surface. Aspartic acid with countless carboxyl groups (-COOH) on its surface caused more aptamers to be immobilized on the electrode surface. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were used to monitor the step-by-step fabrication of the label-free direct electrochemical aptasensor. The label-free quantification of Cyt c was also done by the direct electron transfer between the Fe(III)/Fe(II)-heme redox-active sites which were selectively bound to the aptamers on the GCE and the surface of the electrode. Under optimum conditions, the peak currents of differential pulse voltammograms at 0.26 V (vs. Ag/AgCl) were used for calibration. The proposed aptasensor performs in a wide dynamic range from 10 nM to 100 µM with a low detection limit of 0.74 nM for cytochrome c. It also has high selectivity as well as acceptable stability. These advantages make the biosensor capable of detecting early-stage apoptotic cells that contribute to early cancer diagnosis.

Multienzymes activity of metals and metal oxide nanomaterials: applications from biotechnology to medicine and environmental engineering

With the rapid advancement and progress of nanotechnology, nanomaterials with enzyme-like catalytic activity have fascinated the remarkable attention of researchers, due to their low cost, high operational stability, adjustable catalytic activity, and ease of recycling and reuse. Nanozymes can catalyze the same reactions as performed by enzymes in nature. In contrast the intrinsic shortcomings of natural enzymes such as high manufacturing cost, low operational stability, production complexity, harsh catalytic conditions and difficulties of recycling, did not limit their wide applications. The broad interest in enzymatic nanomaterial relies on their outstanding properties such as stability, high activity, and rigidity to harsh environments, long-term storage and easy preparation, which make them a convenient substitute instead of the native enzyme. These abilities make the nanozymes suitable for multiple applications in sensing and imaging, tissue engineering, environmental protection, satisfactory tumor diagnostic and therapeutic, because of distinguished properties compared with other artificial enzymes such as high biocompatibility, low toxicity, size dependent catalytic activities, large surface area for further bioconjugation or modification and also smart response to external stimuli. This review summarizes and highlights latest progress in applications of metal and metal oxide nanomaterials with enzyme/multienzyme mimicking activities. We cover the applications of sensing, cancer therapy, water treatment and anti-bacterial efficacy. We also put forward the current challenges and prospects in this research area, hoping to extension of this emerging field. In addition to therapeutic potential of nanozymes for disease prevention, their practical effects in diagnostics, to monitor the presence of SARS-CoV-2 and related biomarkers for future pandemics will be predicted.

Biosensors for Detecting Lymphocytes and Immunoglobulins

Lymphocytes (B, T and natural killer cells) and immunoglobulins are essential for the adaptive immune response against external pathogens. Flow cytometry and enzyme-linked immunosorbent (ELISA) kits are the gold standards to detect immunoglobulins, B cells and T cells, whereas the impedance measurement is the most used technique for natural killer cells. For point-of-care, fast and low-cost devices, biosensors could be suitable for the reliable, stable and reproducible detection of immunoglobulins and lymphocytes. In the literature, such biosensors are commonly fabricated using antibodies, aptamers, proteins and nanomaterials, whereas electrochemical, optical and piezoelectric techniques are used for detection. This review describes how these measurement techniques and transducers can be used to fabricate biosensors for detecting lymphocytes and the total content of immunoglobulins. The various methods and configurations are reported, along with the advantages and current limitations.

Ratiometric fluorescence resonance energy transfer aptasensor for highly sensitive and selective detection of Acinetobacter baumannii bacteria in urine sample using carbon dots as optical nanoprobes

Development of sensitive and selective analytical method for accurate diagnosis of Acinetobacter baumannii (Ab) bacteria in biological samples is a challenge. Herein, we developed an ingenious ratiometric fluorescent aptasensor for sensitive and selective detection of (Ab) bacteria based on fluorescence resonance energy transfer (FRET) between ortho-phenylenediamines carbon dot (o-CD), nitrogen-doped carbon nanodots (NCND) as donor's species and graphene oxide (GO) as acceptor. NCND that assembled onto the edge of graphene oxide (GO) exhibited quenched photoluminescence emission, and with the absorption of the modified o-CD with aptamer (o-CD-ssDNA) onto the graphene oxide surface the fluorescence of o-CD was efficiently quenched. The aptamer (ssDNA) as a biorecognition element is bound with A. baumannii specifically which releases the o-CD-ssDNA from GO and the recovery of the fluorescence signal of o-CD, while the fluorescence intensity of NCND only slightly altered and acted as the reference signal in ratiometric fluorescence assay. The fluorescence intensity ratio (I₅₅₀ nm/I₄₄₀nm) varied from 2.0 to 10.0 with the concentration of bacteria changing from 2.0 × 10³ to 4.5 × 10⁷ cfu/mL and the low detection limit of 3.0 × 10² cfu/mL (S/N = 3). The feasibility of the developed aptasensor for selective detection of A. baumannii in urine sample with satisfactory results was also demonstrated.

A Review: New Trends in Electrode Systems for Sensitive Drug and Biomolecule Analysis

Drug and biomolecule analysis with high precision, fast response, not expensive, and user-friendly methods have been very important for developing technology and clinical applications. Electrochemical methods are highly capable for assaying the concentration of electroactive drug or biomolecule and supply excellent knowledge concerning its physical and chemical properties such as electron transfer rates, diffusion coefficients, electron transfer number, and oxidation potential. Electrochemical methods have been widely applied because of their accuracy, sensitivity, cheapness, and can applied on-site determinations of various substances. The progress on electronics has allowed developing reliable, more sensitive and less expensive instrumentations, which have significant contribution in the area of drug development, drug and biomolecule analysis. The developing new sensors for electrochemical analysis of these compounds have growing interest in recent years. Screen-printed based electrodes have a great interest in electrochemical analysis of various drugs and biomolecules due to their easy manufacturing procedure of the electrode allow the transfer of electrochemical laboratory experiments for disposable on-site analysis of some compounds. Paper based electrodes are also fabricated by new technology. They can be preferred due to their easy, cheap, portable, disposable, and offering high sensitivity properties for many application field such as environmental monitoring, food quality control, clinical diagnosis, drug, and biomolecules analysis. In this review, the recent electrochemical drug and biomolecule (DNA, RNA, µRNA, Biomarkers, etc.) studies will be presented that involve new trend disposable electrodes.

Self-Assembly of Functional Nucleic Acid-Based Colorimetric Competition Assay for the Detection of Immunoglobulin E

In this work, we have developed a simple and rapid colorimetric assay for the detection of immunoglobulin E (IgE) using functional nucleic acids (FNAs) and a solid-phase competition enzyme-linked immunosorbent assay (ELISA). The FNAs including aptamer of recombinant IgE, G-quadruplex and its complementary fragments were immobilized on 96-well microplates to achieve recognition and detection of IgE in biological samples. The G-quadruplex DNAzyme catalyzed 2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS)-hemin-H2O2 system was used to improve the sensitivity of colorimetric assay. In the presence of IgE, the hairpin structure and G-quadruplex would be destroyed, resulting in the inactivation of DNAzyme and subsequent reduction of its absorbance. This cost-effective approach detected IgE in the linear range from 5.0 pg/mL to 500 ng/mL, with the limit of detection (LOD) of 2.0 pg/mL, under optimal conditions. Moreover, the developed method was successfully applied to the rapid detection of IgE in human urine, indicating a great potentiality of this approach in clinical diagnosis and other biomedical applications.

Hybrid synthetic receptor composed of molecularly imprinted polydopamine and aptamers for impedimetric biosensing of urea

An electrochemical aptamer-based method is described for highly specific sensing of urea. Urea-imprinted polydopamine was obtained by electropolymerization of dopamine (DA). The molecularly imprinted polymer (MIP) also contains DNA aptamers on gold nanoparticles decorated with a carbon nanotube network (AuNP/CNT). The material was placed on a glassy carbon electrode (GCE). After removal of urea from the MIP cavities, the GCE display double recognition capability which makes it superior to conventional MIP-only or aptamer-only based assays. On exposure of the modified electrode to urea, the interfacial charge transfer of the redox probe hexacyanoferrate is traced, typically measured at a peak voltage of 0.22 V vs. Ag/AgCl. The change in charge transfer resistance depends on the urea concentration. The assay has a 900 fM detection limit, and response is the linear up to 500 nM urea concentrations. Graphical abstract ᅟ.

An aptamer embedded in a molecularly imprinted polymer for impedimetric determination of tetracycline

The authors introduce a new kind of aptameric imprinted polymer for sensing tetracycline (TET), thereby combining the unique features of aptamer-based and molecularly imprinted polymer based recognition. The dual recognition scheme results in sensing capabilities that are superior to those of the aptamer alone, or of a conventional molecularly imprinted polymer alone. In the first step, the aptamer-TET complex was immobilized on the surface of a glassy carbon electrode (GCE) decorated with gold nanoparticles. Dopamine was then electropolymerized on the surface of the modified GCE to entrap the aptamer-TET complex. TET was then extracted with an ethanol-acetic acid mixture (95:5) in order to create void cavities. On exposure to TET, the cavities are filled with TET again, and this leads to a retardment of the interfacial charge transfer of the redox probe hexacyanoferrate, typically measured at a peak voltage of 0.22 V vs. Ag/AgCl. The assay detects TET in the concentration ranges from 0.5-100 pM and from 1-1000 nM with a very low limit of detection of 144 fM. Its superior selectivity and affinity make this assay a viable tool as demonstrated for the successful analysis of TET in spiked milk samples. Graphical abstract Schematic representation of a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNPs) and coated with an aptamer-imprinted polymer (MIP).

A novel electrochemical aptasensor for highly sensitive and quantitative detection of the streptomycin antibiotic

In the present study, we report a facile approach to employ gold nanoparticle (AuNPs) and thiol graphene quantum dots (GQD-SH) as the nanomaterial for ultrasensitive detection of streptomycin (STR). Based on this strategy, a GQD-SH was immobilized onto the surface of a glassy carbon electrode (GCE). AuNPs have been immobilized on SH groups of GQDs through bonding formation of AuS and Apt have been loaded on the electrode surface through the interaction between thiol group of aptamer. By incubating STR as a target onto the surface of the prepared Apt/AuNPs/GQD-SH/GCE as a proposed nanoaptasensor, the Apt/STR complex was formed and the changes of the electrochemical signal were evaluated with the EIS technique. The proposed nanoaptasensor showed wide linear range from 0.1 to 700pgml^-1. Finally, the proposed nanoaptasensor was successfully applied for the determination of STR in real samples and satisfactory results were obtained.

Competitive horseradish peroxidase-linked aptamer assay for sensitive detection of Aflatoxin B1

Aflatoxin B1 (AFB1) is one of highly toxic mycotoxins and a known human carcinogen. The frequent contamination of AFB1 in food products and large health risk of AFB1 have raised global concerns. Sensitive detection of AFB1 is of vital importance and highly demanded. Herein, we reported a competitive horseradish peroxidase (HRP)-linked aptamer assay for AFB1, combining the advantages of aptamer for affinity binding and enzyme label for signal amplification. In this assay, free AFB1 in solution competed with a covalent conjugate of bovine serum albumin-AFB1 (BSA-AFB1) coated on the wells of microplate in binding to the HRP-labeled aptamer probe. HRP attached on BSA-AFB1 in the wells catalyzed the conversion of substrates into products, allowing the final detection of AFB1 through measurement of the generated products. When TMB (3,3',5,5'-tetramethylbenzidine dihydrochloride) was used as substrate, absorbance analysis of the product of enzyme reaction enabled the detection of AFB1 at 0.2nM. We further lowered the detection limit of AFB1 to 0.01nM through chemiluminescence analysis by using chemiluminescence substrate of HRP. This assay enabled the detection of AFB1 in complex sample matrix, such as diluted white wine and maize flour. This assay provides a simple, sensitive and rapid method for AFB1 determination.

Ultra-sensitive aptasensor based on a GQD nanocomposite for detection of hepatitis C virus core antigen

In the present study, by using the aptamer proximity binding assay strategy, a novel electrochemical aptasensor is described for ultrasensitive detection of hepatitis C virus (HCV) core antigen. The immobilization surface is prepared by the modification of a glassy carbon electrode (GCE) with a graphene quantum dots (GQD). GQD were introduced as a novel and suitable substrate for aptamers through π-π stacking interactions, the richness of hydrophilic edges as well as hydrophobic plane in GQD which enhances the aptamer absorption on the electrode surface. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed at each stage of the chemical modification process to confirm the resulting surface changes. EIS technique was used as an efficient alternative detection system for HCV core antigen measurement with detection limit 3.3 pg mL^-1 and two linear concentration range 10-70 pg mL^-1 and 70-400 pg mL^-1. Moreover, the fabricated aptasensor could accurately detect HCV core antigen concentration in human serum samples. Such an aptasensor opens a rapid, selective and sensitive route for HCV core antigen detection and provides a promising strategy for potential applications in clinical diagnostics.

Comparison of two fabricated aptasensors based on modified carbon paste/oleic acid and magnetic bar carbon paste/Fe3O4@oleic acid nanoparticle electrodes for tetracycline detection

In this research, we have improved two aptasensors based on a modified carbon paste electrode (CPE) with oleic acid (OA), and a magnetic bar carbon paste electrode (MBCPE) with Fe3O4 magnetic nanoparticles and oleic acid (OA). After the immobilization process of anti-TET at the electrode surfaces, the aptasensors were named CPE/OA/anti-TET and MBCPE/Fe3O4NPs/OA/anti-TET respectively. In this paper, the detection of tetracycline is compared using CPE/OA/anti-TET and MBCPE/Fe3O4NPs/OA/anti-TET aptasensors. These modified electrodes were characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), UV-vis spectroscopy, and voltammetric methods. The linear range and the detection limit for TET with the CPE/OA/anti-TET aptasensor were found to be 1.0×10(-12)-1.0×10(-7)M and 3.0×10(-13)M respectively by EIS method. The linear range and the detection limit for TET with the CPE/OA/anti-TET aptasensor were found to be 1.0×10(-10)-1.0×10(-7)M with a limit of detection of 2.9×10(-11)M using differential pulse voltammetry (DPV) technique. The MBCPE/Fe3O4NPs/OA/anti-TET aptasensor was used for determination of TET, and a liner range of 1.0×10(-14)-1.0×10(-6)M with a detection limit of 3.8×10(-15)M was obtained by EIS method. Also, the linear range and detection limit of 1.0×10(-12)-1.0×10(-6)M and 3.1×10(-13)M respectively, were obtained for MBCPE/Fe3O4NPs/OA/anti-TET aptasensor using DPV. The proposed aptasensors were applied for determination of tetracycline in some real samples such as drug, milk, honey and blood serum samples.

Bioanalytical methods for food allergy diagnosis, allergen detection and new allergen discovery

For effective monitoring and prevention of the food allergy, one of the emerging health problems nowadays, existing diagnostic procedures and allergen detection techniques are constantly improved. Meanwhile, new methods are also developed, and more and more putative allergens are discovered. This review describes traditional methods and summarizes recent advances in the fast evolving field of the in vitro food allergy diagnosis, allergen detection in food products and discovery of the new allergenic molecules. A special attention is paid to the new diagnostic methods under laboratory development like various immuno- and aptamer-based assays, including immunoaffinity capillary electrophoresis. The latter technique shows the importance of MS application not only for the allergen detection but also for the allergy diagnosis.

ELAKCA: Enzyme-Linked Aptamer Kissing Complex Assay as a Small Molecule Sensing Platform

We report herein a novel sandwich-type enzyme-linked assay for the "signal-on" colorimetric detection of small molecules. The approach (referred to as enzyme-linked aptamer kissing complex assay (ELAKCA)) relied on the kissing complex-based recognition of the target-bound hairpin aptamer conformational state by a specific RNA hairpin probe. The aptamer was covalently immobilized on a microplate well surface to act as target capture element. Upon small analyte addition, the folded aptamer was able to bind to the biotinylated RNA hairpin module through loop-loop interaction. The formed ternary complex was then revealed by the introduction of the streptavidin-horseradish peroxidase conjugate that catalytically converted the 3,3',5,5'-tetramethylbenzidine substrate into a colorimetric product. ELAKCA was successfully designed for two different systems allowing detecting the adenosine and theophylline molecules. The potential practical applicability in terms of biological sample analysis (human plasma), temporal stability, and reusability was also reported. Owing to the variety of both hairpin functional nucleic acids, kissing motifs, and enzyme-based signaling systems, ELAKCA opens up new prospects for developing small molecule sensing platforms of wide applications.

An electrochemical aptasensor based on a TiO2/three-dimensional reduced graphene oxide/PPy nanocomposite for the sensitive detection of lysozyme

A sensitive aptasensor based on a nanocomposite of hollow titanium dioxide nanoball, three-dimensional reduced graphene oxide, and polypyrrole (TiO2/3D-rGO/PPy) was developed for lysozyme detection. A lysozyme aptamer was easily immobilized onto the TiO2/3D-rGO/PPy nanocomposite matrix by assembling the aptamer onto graphene through simple π-stacking interactions and electrostatic interactions between PPy molecular chains and aptamer strands. In the presence of lysozyme, the aptamer on the adsorbent layer catches the target on the electrode interface, which generates a barrier for electrons and inhibits electron transfer, subsequently resulting in decreased electrochemically differential pulse voltammetric signals of a gold electrode modified with TiO2/3D-rGO/PPy. Using this strategy, a low limit of detection of 0.085 ng mL(-1) (5.5 pM) for detecting lysozyme was observed within the detection range of 0.1-50 ng mL(-1) (0.007-3.5 nM). The aptasensor also presents high specificity for lysozyme, which is unaffected by the coexistence of other proteins. Such an aptasensor opens a rapid, selective, and sensitive route to lysozyme detection. This finding indicates that the TiO2/3D-rGO/PPy nanocomposite could be used as an electrochemical biosensor for detecting proteins in the biomedical field.

Electrochemical immunosensor for interferon-γ based on disposable ITO detector and HRP-antibody-conjugated nano gold as signal tag

Tuberculosis is the most frequent cause of infection-related death worldwide. A new disposable electrochemical immunosensor with low cost and simple fabrication was proposed to detect interferon-γ (IFN-γ). Diallyldimethylammonium chloride (PDDA) and Au nanoparticle (AuNP) composite were used to provide an efficient biointerface, horseradish peroxidase (HRP)-labeled antibody-conjugated AuNP (HRP-Ab2-AuNP) bioconjugates were used as a novel signal tag. The large amounts of HRP on the signal tag can catalyze the oxidation of Hydroquinone (HQ) by H2O2, which can induce an amplified reductive current. The catalytic reduction current was related to the amount of HRP immobilized on the surface, which itself was related to the concentration of IFN-γ. Under optimized conditions, the proposed immunosensor showed a high sensitivity and a linear range of 0.1-10,000pg/mL with a detection limit of 0.048pg/mL. The assay results of clinical serum samples obtained by the immunosensor were in acceptable agreement with the reference values. Therefore, the immunosensor possessed excellent clinical value in early diagnosis and control of tuberculosis.

Ultrasensitive electrochemical immunosensor for PSA biomarker detection in prostate cancer cells using gold nanoparticles/PAMAM dendrimer loaded with enzyme linked aptamer as integrated triple signal amplification strategy

In the present study, a triple signal amplification strategy was developed for ultrasensitive immunosensing of prostate-specific antigen (PSA) tumor marker. The proposed system was achieved by modification of glassy carbon electrode with graphene oxide/chitosan film and covalently attached of monoclonal PSA antibody and thionine as redox probe onto the modified electrode surface. Then, immunosensing was completed using sandwich-type immunoreaction of the PSA-antigen between anti-PSA immobilized on the graphene/chitosan interface and PSA-aptamer. For improve the sensitivity, polyamidoamine dendrimer-encapsulated gold nanoparticles (AuNPs-PAMAM) was used for covalent attachment of PSA-aptamer and HRP linked aptamer (Au-PAMA/aptamer-HRP) as electrochemical label in the sandwich format and electrocatalytic reduction of H2O2 in the presence of enzymatically oxidized thionine was measured. Under optimized condition, the obtained detection limit and linear concentration range were 10 fg ml(-1)(S/N=3) and 0.1 pg ml(-1) to 90 ngml(-1) respectively, using differential pulse voltammetry as measuring technique. In addition, electrochemical impedance spectroscopy (EIS) was used as simple, rapid, low cost label free analytical technique for PSA measurement with detection limit of 5 pg ml(-1) at concentration range up to 35 ng ml(-1). Finally, the immunosensor is used to PSA detection in human serum and prostate tissue samples and the obtained result is well agreed with the values obtained by the standard ELISA method. The obtained results indicate the proposed immunosensor can be used for monitor the differences in PSA concentration in cancer tissue samples which holds great promise in clinical screening of cancer biomarkers.