The strategies of DNA immobilization and hybridization detection mechanism in the construction of electrochemical DNA sensor: A review

Advanced materials-integrated electrochemical sensors as promising medical diagnostics tools: A review

Electrochemical sensors have increasingly been linked with terms as modern biomedically effective highly selective and sensitive devices, wearable and wireless technology, portable electronics, smart textiles, energy storage, communication and user-friendly operating systems. The work brings the overview of the current advanced materials and their application strategies for improving performance, miniaturization and portability of sensing devices. It provides the extensive information on recently developed (bio)sensing platforms based on voltammetric, amperometric, potentiometric and impedimetric detection modes including portable, non-invasive, wireless, and self-driven miniaturized devices for monitoring human and animal health. Diagnostics of selected free radical precursors, low molecular biomarkers, nucleic acids and protein-based biomarkers, bacteria and viruses of today's interest is demonstrated.

Ultrasensitive Electrochemical Impedance Detection of Mycoplasma agalactiae DNA by Low-Cost and Disposable Au-Decorated NiO Nanowall Electrodes

Nanostructured electrodes detecting bacteria or viruses through DNA hybridization represent a promising method, which may be useful in on-field applications where PCR-based methods are very expensive, time-consuming, and require trained personnel. Indeed, electrochemical sensors combine disposability, fast response, high sensitivity, and portability. Here, a low-cost and high-surface-area electrode, based on Au-decorated NiO nanowalls, demonstrates a highly sensitive PCR-free detection of a real sample of Mycoplasma agalactiae (Ma) DNA. NiO nanowalls, synthesized by aqueous methods, thermal annealing, and Au decoration, by electroless deposition, ensure a high-surface-area platform for successful immobilization of Ma thiolated probe DNA. The morphological, chemical, and electrochemical properties of the electrode were characterized, and a reproducible detection of synthetic Ma DNA was observed and investigated by impedance measurements. Electrochemical impedance spectroscopy (EIS) ascribed the origin of impedance signal to the Ma DNA hybridization with its probe immobilized onto the electrode. The electrode successfully discriminates between DNA extracted from healthy and infected sheep milk, showing the ability to detect Ma DNA in concentrations as low as 53 ± 2 copy number μL^-1. The Au-decorated NiO nanowall electrode represents a promising route toward PCR-free, disposable, rapid, and molecular detection.

The potential of electrochemistry for the detection of coronavirus-induced infections

Human coronaviruses (HCoV) are no stranger to the global environment. The etiology of previous outbreaks with reported symptoms of respiratory tract infections was attributed to different coronavirus strains, with the latest global pandemic in 2019 also belonging to the coronavirus family. Timely detection, effective therapeutics and future prevention are stake key holders in the management of coronavirus-induced infections. Apart from the gold standard clinical diagnostics, electrochemical techniques have also demonstrated their great potentials in the detection of different viruses and their correlated antibodies and antigens, showing high sensitivities and selectivities, and faster times for the analysis. This article aims to critically review the multifaceted electrochemical approaches, not only in the development of point-of-care portable devices but also as alternative detection strategies that can be coupled with traditional methods for the detection of various strains of coronaviruses.

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Electrochemical biosensing detection methods for coronavirus-induced infections.

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Potential rapid and cost-effective point-of-care diagnostics for mass testing.

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Electrochemistry helps to overcome limitations faced by gold standard diagnostics.

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Experimental schemes, strengths, and drawbacks of various electrochemical strategies.

Bright fluorescent nucleic acid detection with CRISPR-Cas12a and poly(thymine) templated copper nanoparticles

Fluorescence-based diagnostic tools are attractive and versatile tests with multiple advantages: ease of use, sensitivity and rapid results. The advent of CRISPR-Cas technology has created new avenues for the development of diagnostic testing tools. In this study, by effectively combining the specific functions of two enzymes, CRISPR-Cas12a and terminal deoxynucleotidyl transferase (TdT), we developed a DNA detection assay that generates copper nanoparticles (CuNPs) that are easily visible to the naked eye under UV-light; we named this detection assay Cas12a Activated Nuclease poly-T Reporter Illuminating Particles (CANTRIP). Upon specific target DNA recognition by Cas12a, single-stranded DNA (ssDNA) reporter oligos with blocked 3'-ends are cut into smaller ssDNA fragments, thereby generating neo 3'-hydroxyl moieties. TdT subsequently elongates these newly formed ssDNA fragments, incorporating only dTTP nucleotides, and these poly(thymine)-tails subsequently function as scaffolds for the formation of CuNPs. These CuNPs produce a bright fluorescent signal upon UV excitation, and thus, this bright orange signal indicates the presence of target DNA, which in this proof-of-concept study consisted of anthrax lethal factor plasmid DNA. CANTRIP, which combines two detection platforms consisting of CRISPR-Cas12a and fluorescent CuNPs into a single reaction, appears to be a robust, low-cost and simple diagnostic tool.

AuNPs/CNF-modified DNA biosensor for early and quick detection of O. tsutsugamushi in patients suffering from scrub typhus

A novel approach has been developed for the detection of 56 kDa tissue-specific antigen (TSA) gene of Orientia tsutsugamushi a causative agent of scrub typhus disease. The approach was developed by immobilization of 5' NH2 labeled ssDNA probe selective to 56 kDa TSA gene, to the surface of AuNPs/CNF modified screen-printed electrode. An electrochemical response was recorded with single stranded genomic DNA (ssDNA) of O. tsutsugamushi isolated from patient sample, using cyclic voltammetry and electrochemical impedance spectroscopy. The electrode surface was characterized by Field-Emission Scanning electron microscope (FE-SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy at each step of fabrication. The DNA biosensor shows optimum response within 50-60 s at room temperature (25 ± 3 °C). The sensor shows higher sensitivity [7849 (µA/cm²)/ng DNA], fast response time (60 s), wider linear range (0.04-2.6 ng) with limit of detection of 0.02 ng/µl of ssDNA sample.

How Nanophotonic Label-Free Biosensors Can Contribute to Rapid and Massive Diagnostics of Respiratory Virus Infections: COVID-19 Case

The global sanitary crisis caused by the emergence of the respiratory virus SARS-CoV-2 and the COVID-19 outbreak has revealed the urgent need for rapid, accurate, and affordable diagnostic tests to broadly and massively monitor the population in order to properly manage and control the spread of the pandemic. Current diagnostic techniques essentially rely on polymerase chain reaction (PCR) tests, which provide the required sensitivity and specificity. However, its relatively long time-to-result, including sample transport to a specialized laboratory, delays massive detection. Rapid lateral flow tests (both antigen and serological tests) are a remarkable alternative for rapid point-of-care diagnostics, but they exhibit critical limitations as they do not always achieve the required sensitivity for reliable diagnostics and surveillance. Next-generation diagnostic tools capable of overcoming all the above limitations are in demand, and optical biosensors are an excellent option to surpass such critical issues. Label-free nanophotonic biosensors offer high sensitivity and operational robustness with an enormous potential for integration in compact autonomous devices to be delivered out-of-the-lab at the point-of-care (POC). Taking the current COVID-19 pandemic as a critical case scenario, we provide an overview of the diagnostic techniques for respiratory viruses and analyze how nanophotonic biosensors can contribute to improving such diagnostics. We review the ongoing published work using this biosensor technology for intact virus detection, nucleic acid detection or serological tests, and the key factors for bringing nanophotonic POC biosensors to accurate and effective COVID-19 diagnosis on the short term.

Modified Enzyme Substrates for the Detection of Bacteria: A Review

The ability to detect, identify and quantify bacteria is crucial in clinical diagnostics, environmental testing, food security settings and in microbiology research. Recently, the threat of multidrug-resistant bacterial pathogens pushed the global scientific community to develop fast, reliable, specific and affordable methods to detect bacterial species. The use of synthetically modified enzyme substrates is a convenient approach to detect bacteria in a specific, economic and rapid manner. The method is based on the use of specific enzyme substrates for a given bacterial marker enzyme, conjugated to a signalogenic moiety. Following enzymatic reaction, the signalophor is released from the synthetic substrate, generating a specific and measurable signal. Several types of signalophors have been described and are defined by the type of signal they generate, such as chromogenic, fluorogenic, luminogenic, electrogenic and redox. Signalophors are further subdivided into groups based on their solubility in water, which is key in defining their application on solid or liquid media for bacterial culturing. This comprehensive review describes synthetic enzyme substrates and their applications for bacterial detection, showing their mechanism of action and their synthetic routes.

DNA Electrochemical Biosensor Based on Iron Oxide/Nanocellulose Crystalline Composite Modified Screen-Printed Carbon Electrode for Detection of Mycobacterium tuberculosis

Death from tuberculosis has resulted in an increased need for early detection to prevent a tuberculosis (TB) epidemic, especially in closed and crowded populations. Herein, a sensitive electrochemical DNA biosensor based on functionalized iron oxide with mercaptopropionic acid (MPA-Fe3O4) nanoparticle and nanocellulose crystalline functionalized cetyl trimethyl ammonium bromide (NCC/CTAB) has been fabricated for the detection of Mycobacterium tuberculosis (MTB). In this study, a simple drop cast method was applied to deposit solution of MPA-Fe3O4/NCC/CTAB onto the surface of the screen-printed carbon electrode (SPCE). Then, a specific sequence of MTB DNA probe was immobilized onto a modified SPCE surface by using the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) coupling mechanism. For better signal amplification and electrochemical response, ruthenium bipyridyl Ru(bpy)32+ was assigned as labels of hybridization followed by the characteristic test using differential pulse voltammetry (DPV). The results of this biosensor enable the detection of target DNA until a concentration as low as 7.96 × 10-13 M with a wide detection range from 1.0 × 10-6 to 1.0 × 10-12 M. In addition, the developed biosensor has shown a differentiation between positive and negative MTB samples in real sampel analysis.

Interplay of Effective Surface Area, Mass Transport, and Electrochemical Features in Nanoporous Nucleic Acid Sensors

Electrochemical biosensors transduce biochemical events (e.g., DNA hybridization) to electrical signals and can be readily interfaced with electronic instrumentation for portability. Nanostructuring the working electrode enhances sensor performance via augmented effective surface area that increases the capture probability of an analyte. However, increasing the effective surface area via thicker nanostructured electrodes hinders the analyte's permeation into the nanostructured volume and limits its access to deeper electrode surfaces. Here, we use nanoporous gold (np-Au) with various thicknesses and pore morphologies coupled with a methylene blue (MB) reporter-tagged DNA probe for DNA target detection as a model system to study the influence of electrode features on electrochemical sensing performance. Independent of the DNA target concentration, the hybridization current (surrogate for detection sensitivity) increases with the surface enhancement factor (EF), until an EF of ∼5, after which the sensor performance deteriorates. Electrochemical and fluorometric quantification of a desorbed DNA probe suggest that DNA permeation is severely limited for higher EFs. In addition, undesirable capacitive currents disguise the faradaic currents from the MB reporter at larger EFs that require higher square wave voltammetry (SWV) frequencies. Finally, a real-time hybridization study reveals that expanding the effective surface area beyond EFs of ∼5 decreases sensor performance.

Rapid and label-free electrochemical DNA biosensor based on a facile one-step electrochemical synthesis of rGO-PPy-(L-Cys)-AuNPs nanocomposite for the HTLV-1 oligonucleotide detection

Human T cell leukemia virus type 1 (HTLV-1) as the first human retrovirus is currently a serious endemic health challenge. Despite the use of assorted molecular or serological assays for HTLV-1 detection, there are several limitations due to the lack of a confirmatory test that may affect the accuracy of the results. Herein, a novel label-free biosensor for the detection of HTLV-1 Tax gene has been reported. An electrochemical facile ecofriendly synthesis method has been demonstrated based on a synthesis of nanocomposite of reduced graphene oxide, polypyrrole, and gold nanoparticles (rGO-PPy-(l-Cys)-AuNPs) deposited on the surface of screen-printed carbon electrode. Electrochemical techniques were used to characterize and study the electrochemical behavior of the rGO-PPy-(l-Cys)-AuNPs, which exhibited a stable reference peak at 0.21 V associated with hybridization forms by applying the differential pulse voltammetry. The designed DNA biosensor presented a wide linear range from 0.1 fM to 100 µM and a low detection limit of 20 atto-molar. The proposed biosensor presented in this study provides outstanding selectivity, sensitivity, repeatability, and reproducibility.

Functional Molecular Interfaces for Impedance-Based Diagnostics

In seeking to develop and optimize reagentless electroanalytical assays, a consideration of the transducing interface features lies key to any subsequent sensitivity and selectivity. This review briefly summarizes some of the most commonly used receptive interfaces that have been employed within the development of impedimetric molecular sensors. We discuss the use of high surface area carbon, nanoparticles, and a range of bioreceptors that can subsequently be integrated. The review spans the most commonly utilized biorecognition elements, such as antibodies, antibody fragments, aptamers, and nucleic acids, and touches on some novel emerging alternatives such as nanofragments, molecularly imprinted polymers, and bacteriophages. Reference is made to the immobilization chemistries available along with a consideration of both optimal packing density and recognition probe orientation. We also discuss assay-relevant mechanistic details and applications in real sample analysis.

Lateral field excited quartz crystal microbalances for biosensing applications

The most common bulk acoustic wave device used in biosensing applications is the quartz crystal microbalance (QCM), in which a resonant pure shear acoustic wave is excited via electrodes on both major faces of a thin AT-cut quartz plate. For biosensing, the QCM is used to detect the capture of a target by a target-capture film. The sensitivity of the QCM is typically based solely on the detection of mechanical property changes, as electrical property change detection is limited by the electrode on its sensing surface. A modification of the QCM called the lateral field excited (LFE) QCM (LFE-QCM) has been developed with a bare sensing surface as both electrodes are now on a single face of the quartz plate. Compared to the QCM, the LFE-QCM exhibits significantly higher sensitivity to both electrical and mechanical property changes. This paper presents theoretical and experimental aspects of LFE-QCMs. In particular, the presence and strength of the usual and newfound LFE-QCM modes depend on the electrical properties of the film and/or sensing environment. This work also presents examples of experimental setups for measuring the response of an LFE-QCM, followed by results of LFE-QCMs used to detect liquid electrical and mechanical properties, chemical targets, and biological targets. Finally, details are given about the attachment of various target-capture films to the LFE-QCM surface to capture biomarkers associated with diseases such as cancer.

A homogeneous electrochemical DNA sensor on the basis of a self-assembled thiol layer on a gold support and by using tetraferrocene for signal amplification

An unmodified electrochemical biosensor has been constructed, which can directly detect DNA in homogeneous solution. The synthesized new compound tetraferrocene was used for signal amplification. The dual-hairpin probe DNA was tagged with a tetraferrocene at the 3' terminal and a thiol at the 5' terminal. Without being hybridized with target DNA, the loop of probe prevented the thiol from contacting the exposed gold electrode surface with an applied potential. After hybridization with the target DNA, the loop-stem structure of the probe was opened, which led to the formation of the hairpin DNA structure. Afterwards, the thiol easily contacted the electrode and accomplished potential-assisted Au-S self-assembly. Its current signal depends on the concentration of target DNA in the 1.8 × 10^-13 to 1.8 × 10^-9 M concentration range, and the detection limit is 0.14 pM. The technique is a meaningful study because of its high selectivity and sensitivity. Graphical abstract Schematic diagram of the electrochemical DNA sensor operation. Target DNA and probe DNA hybridization, resulting in the disappearance of the steric hindrance of the probe stem ring. A higher signal was generated when tetraferrocene reached the electrode. The electrochemical signals were determined by differential voltammetric pulses (DPV).

Real-time and label-free detection of VKORC1 genes based on a magnetoelastic biosensor for warfarin therapy

Various thrombotic disorders have been treated with the anticoagulant warfarin. However, a small change in warfarin concentration may lead to drug adverse reactions or therapeutic failure due to its narrow therapeutic index. Therefore, the dose of warfarin must be monitored for each patient during therapy in real-time and in a sensitive and stable manner. In this work, we designed a magnetoelastic (ME) biosensor using Metglas alloy 2826 to detect VKORC1 genotypes, which is one of the most important known genetic determinants of warfarin dosing. The sensor enabled both fast responses to DNA binding and wireless transmission of signals. Specifically in the target recognition layer, the sensor introduced an avidin-biotin interaction system for signal amplification by increasing the surface load mass. The resonance frequency shift of the signal was linear to the concentration of the target in the range of 0.1 fM to 10 pM, with a detection limit (LOD) of 0.00389 fM (S/N = 3) and a sensitivity of 45.7 Hz pM^-1. Importantly, this ME-based biosensor was small and portable without the use of any optical labels, which has high potential to be applied in advanced biomedical diagnosis of nucleic acids and proteins.

Graphitic Carbon Nitride as an Amplification Platform on an Electrochemical Paper-Based Device for the Detection of Norovirus-Specific DNA

Norovirus is one of the leading causes of gastroenteritis, acute vomiting, intense diarrhoea, acute pain in the stomach, high fever, headaches, and body pain. Conventional methods of detection gave us very promising results but had disadvantages such as low sensitivity, cost ineffectiveness, reduced specificity and selectivity, etc. Therefore, biosensors can be a viable alternative device which can overcome all setbacks associated with the conventional method. An electrochemical sensor based on oxidized graphitic carbon nitride (Ox-g-C₃N₄) modified electrochemical paper-based analytical device (ePAD) was fabricated for the detection of norovirus DNA. The synthesized Ox-g-C₃N₄ nanosheets were characterized by field emission scanning electron microscopy (FESEM), X-ray Diffraction (XRD), UV-Vis spectroscopy and X-Ray Photoelectron Spectroscopy. The capture probe DNA (PDNA) modified electrodes were characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). These two characterization techniques were also employed to find the optimal scan rate, response time and temperature of the fabricated sensor. The fabricated biosensor showed a limit of detection (LOD) of 100 fM. Furthermore, the specificity of the reported biosensor was affirmed by testing the response of capture probe DNA with oxidized graphitic carbon nitride (PDNA/Ox-g-C₃N₄) modified ePAD on the introduction of a non-complimentary DNA. The fabricated ePAD sensor is easy to fabricate, cost effective and specific, and requires a minimum analysis time of 5 s.

Advances in aptasensor technology

Aptasensors form a class of biosensors that function on the basis of a biological recognition. An aptasensor is advantageous because it incorporates a unique biologic recognition element, i.e., an aptamer, coupled to a transducer to convert a biological interaction to readable signals that can be easily processed and reported. In such biosensors, the specificity of aptamers is comparable to and sometimes even better than that of antibodies. Using the SELEX technique, aptamers with high specificity and affinity to various targets can be isolated from large pools of different oligonucleotides. Nowadays, new modifications of the SELEX technique and, as a result, easy generation and synthesis of aptamers have led to the wide application of these materials as biological receptors in biosensors. In this regard, aptamers promise a bright future. In the present research a brief account is initially provided of the recent developments in aptasensors for various targets. Then, immobilization methods, design strategies, current limitations and future directions are discussed for aptasensors.

One-Step Synthesis of Tunable Zinc-Based Nanohybrids as an Ultrasensitive DNA Signal Amplification Platform

Herein, we demonstrated a one-step route for the manufacturing of polypyrrole (PPy)/zinc nanohybrids with tunable elemental composition and nanoscale component mixing resolution by using an ultrafast (within tens of seconds) microwave approach for ultrasensitive DNA biosensors. The zinc-based nanoparticles (i.e., MWPPy/ZnO and MWPPy/ZnS) were produced by loading zinc acetate (ZnAc₂) on PPy under the electromagnetic environment of a microwave with or without sulfur powder in one pot. Then, the signal amplification platforms were fabricated by modifying the glassy carbon electrode (GCE) with the obtained nanohybrids. It was found that both of the resultant MWPPy/ZnO and MWPPy/ZnS were suitable for ultrasensitive DNA molecule detection of the gastric carcinoma related PIK3CA gene ascribing to their unique hybrid nanostructures and surface characteristics. Experimental results revealed that the proposed GCE/MWPPy/ZnO sensor showed a linear range of 1.0 × 10^-10 to 1.0 × 10^-13 M. Notably, the GCE/MWPPy/ZnS sensor was endowed with promising DNA hybrid selection with a minimum concentration response of 1.0 × 10^-18 M. The corresponding detection limit was, respectively, found to be 2.90 × 10^-11 and 7.73 × 10^-21 M for MWPPy/ZnO- and MWPPy/ZnS-based biosensors. Furthermore, reliable determination of single-base and two-base mismatched DNA are more attractive, which greatly supported the application of the constructed zinc-based nanohybrids for the detection of single nucleotide polymorphism in genetic diseases, biological infectious pathogens, or warning against bio-warfare agents.

Early-stage cervical cancer diagnosis based on an ultra-sensitive electrochemical DNA nanobiosensor for HPV-18 detection in real samples

BACKGROUND

In several years ago, infection with human papillomaviruses (HPVs), have been prevalent in the worlds especially HPV type 18, can lead to cervical cancer. Therefore, rapid, accurate, and early diagnosis of HPV for successful treatment is essential. The present study describes the development of a selective and sensitive electrochemical biosensor base on DNA, for early detection of HPV-18. For this purpose, a nanocomposite of reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) were electrodeposited on a screen-printed carbon electrode (SPCE). Then, Au nanoparticles (AuNPs) were dropped on a modified SPCE. Subsequently, single strand DNA (ssDNA) probe was immobilized on the modified electrode. The link attached between AuNPs and probe ssDNA provided by L-cysteine via functionalizing AuNPs (Cys-AuNPs). The differential pulse voltammetry (DPV) assay was also used to electrochemical measurement. The measurement was based on the oxidation signals of anthraquninone-2-sulfonic acid monohydrate sodium salt (AQMS) before and after hybridization between the probe and target DNA.

RESULTS

The calibration curve showed a linear range between 0.01 fM to 0.01 nM with a limit of detection 0.05 fM. The results showed that the optimum concentration for DNA probe was 5 µM. The good performance of the proposed biosensor was achieved through hybridization of DNA probe-modified SPCE with extracted DNA from clinical samples.

CONCLUSIONS

According to the investigated results, this biosensor can be introduced as a proprietary, accurate, sensitive, and rapid diagnostic method of HPV 18 in the polymerase chain reaction (PCR) of real samples.

The sweet detection of rolling circle amplification: Glucose-based electrochemical genosensor for the detection of viral nucleic acid

Herein, an isothermal padlock probe-based assay for the simple and portable detection of pathogens coupled with a glucose oxidase (GOx)-based electrochemical readout is reported. Infectious diseases remain a constant threat on a global scale, as in recurring pandemics. Rapid and portable diagnostics hold the promise to tackle the spreading of diseases and decentralising healthcare to point-of-care needs. Ebola, a hypervariable RNA virus causing fatalities of up to 90% for recent outbreaks in Africa, demands immediate attention for bedside diagnostics. The design of the demonstrated assay consists of a rolling circle amplification (RCA) technique, responsible for the generation of nucleic acid amplicons as RCA products (RCPs). The RCPs are generated on magnetic beads (MB) and subsequently, connected via streptavidin-biotin bonds to GOx. The enzymatic catalysis of glucose by the bound GOx allows for an indirect electrochemical measurement of the DNA target. The RCPs generated on the surface of the MB were confirmed by scanning electron microscopy, and among other experimental conditions such as the type of buffer, temperature, concentration of GOx, sampling and measurement time were evaluated for the optimum electrochemical detection. Accordingly, 125 μg mL^-1 of GOx with 5 mM glucose using phosphate buffer saline (PBS), monitored for 1 min were selected as the ideal conditions. Finally, we assessed the analytical performance of the biosensing strategy by using clinical samples of Ebola virus from patients. Overall, this work provides a proof-of-concept bioassay for simple and portable molecular diagnostics of emerging pathogens using electrochemical detection, especially in resource-limited settings.

Nano-Biosensing Platforms for Detection of Cow's Milk Allergens: An Overview

Among prevalent food allergies, cow milk allergy (CMA) is most common and may persist throughout the life. The allergic individuals are exposed to a constant threat due to milk proteins' presence in uncounted food products like yogurt, cheese, and bakery items. The problem can be more severe due to cross-reactivity of the milk allergens in the food products due to homologous milk proteins of diverse species. This problem can be overcome by proper and reliable food labeling in order to ensure the life quality of allergic persons. Therefore, highly sensitive and accurate analytical techniques should be developed to detect the food allergens. Here, significant research advances in biosensors (specifically immunosensors and aptasensors) are reviewed for detection of the milk allergens. Different allergic proteins of cow milk are described here along with the analytical standard methods for their detection. Additionally, the commercial status of biosensors is also discussed in comparison to conventional techniques like enzyme-linked immunosorbent assay (ELISA). The development of novel biosensing mechanisms/kits for milk allergens detection is imperative from the perspective of enforcement of labeling regulations and directives keeping in view the sensitive individuals.

An ultrasensitive electrochemical DNA sensing strategy free from pre-immobilization via G-quadruplex based homogenous proximity hybridization

Motivated by the desire for simple, rapid and highly sensitive DNA detection, we presented a signal-on electrochemical DNA (E-DNA) sensing strategy utilizing cooperative proximity hybridization based on a G-quadruplex (G4) probe labeled with the SH, which could specifically hybridize with its target DNA in homogenous solution. In the presence of target DNA, proximity hybridization was triggered to form a Y-shaped complex and the SH was released from G4 probe stem, companied by chemisorption on the electrode surface through Au-S binding when applied a positive potential, which brought Fc labeled on the signal probe close to the electrode surface. Thus, electrochemical signal dramatically increased, ensuring the highly sensitive "signal-on" assay. Such an E-DNA sensing strategy allows for ultrasensitive DNA detection with a detection limit as low as 2.82 × 10^-15 M and a wide linear response from 1.0 × 10^-9 to 1.0 × 10^-15 M. In addition, the powerful discriminating ability of the mismatched DNA from the perfect matched target DNA was also demonstrated. More importantly, this homogenous proximity hybridization strategy could expand to colorimetric assay by incorporating G4 probe with hemin to form DNAzyme, which could effectively catalyze ABTS to generate a visual color change. Taking the joint advantages of G4 stem-loop probe and homogenous proximity hybridization, this sensing strategy exhibits greatly enhanced sensitivity and excellent specificity, making it a promising strategy for point-of-care testing.

Review of Electrochemical DNA Biosensors for Detecting Food Borne Pathogens

The vital importance of rapid and accurate detection of food borne pathogens has driven the development of biosensor to prevent food borne illness outbreaks. Electrochemical DNA biosensors offer such merits as rapid response, high sensitivity, low cost, and ease of use. This review covers the following three aspects: food borne pathogens and conventional detection methods, the design and fabrication of electrochemical DNA biosensors and several techniques for improving sensitivity of biosensors. We highlight the main bioreceptors and immobilizing methods on sensing interface, electrochemical techniques, electrochemical indicators, nanotechnology, and nucleic acid-based amplification. Finally, in view of the existing shortcomings of electrochemical DNA biosensors in the field of food borne pathogen detection, we also predict and prospect future research focuses from the following five aspects: specific bioreceptors (improving specificity), nanomaterials (enhancing sensitivity), microfluidic chip technology (realizing automate operation), paper-based biosensors (reducing detection cost), and smartphones or other mobile devices (simplifying signal reading devices).

N-Doped Graphene Oxide Decorated with PtCo Nanoparticles for Immobilization of Double-Stranded Deoxyribonucleic Acid and Investigation of Clenbuterol-Induced DNA Damage

We demonstrate here a facile hydrothermal-assisted formation of PtCo alloy nanoparticles (NPs) and their simultaneous anchoring on the graphitic surface of N-doped graphene oxide (NGO). Doping induced nanopores in the carbon surface to facilitate the uniform and homogeneous anchoring of alloy nanoparticles. It was revealed that the formation of PtCo NPs on an NGO interface plodded excellent tendency toward double-stranded deoxyribonucleic acid (dsDNA). The dsDNA immobilization was enabled by the presence of several oxidation states of Pt and Co. The same property was further used to monitor the direct detection of dsDNA damage induced by clenbuterol via screen-printed carbon electrodes. Cyclic voltammetric and electrochemical impedance spectroscopic characterization traced well the dsDNA attachment on the modified electrode surface. Differential pulsed voltammetry was further used as a tool to monitor the characteristic guanine peak before and after incubating with clenbuterol used as a damage probe for the dsDNA. The findings can further be appurtenant in exploring dsDNA immobilization protocols and developing analytical methods for determination of various dsDNA damaging agents.

Electrochemical detection of DNA mismatches using a branch-shaped hierarchical SWNT-DNA nano-hybrid bioelectrode

Common approaches for DNA mutation detection are high cost and have difficult or complex procedure. We propose a fast quantitative method for recognition of DNA mutation based on SWNT/DNA self-assembled nanostructure. Covalent SWNT/DNA hybrid nanostructures are widely used in the fabrication of electrochemical biosensors. Interfacing carbon nanotubes with DNA in particular, is used as a detection method for the analysis of genetic disorders or the detection of mismatches in DNA hybridisation. We have designed a self-assembled, branch-shaped hybrid nanostructure by hybridisation of two sticky oligos that are attached to the ends of SWNTs via a linker oligo. These hybrid nanostructures showed a good conductivity that was greater than free SWNTs. Impedance spectroscopy studies illustrated that the conductivity of these hybrid nanostructures depended on the conformation and structure of the hybridised DNA. We demonstrated that the strategy of using SWNT/DNA self-assembled hybrid nanostructure fabrication yields sensitive and selective tools to discriminate mismatches in DNA. Cyclic voltammetry (CV) and impedance spectroscopy clearly revealed that the conductivity of the branch-shaped and hierarchical hybridised SWNT/DNA nanostructure is higher when matched, than when mismatched in a 1 and 1' hybridised SWNT/DNA nanostructure. Rapid biosensing of match and mismatch nanostructure based on carbon printed electrode showed similar results which can be used for rapid and fast detection of DNA mismatch.

Dynamics and molecular interactions of single-stranded DNA in nucleic acid biosensors with varied surface properties

Electrochemical DNA biosensors utilizing self-assembled monolayers (SAMs) with inserted DNA probes are promising biosensor designs because of their ease of preparation, miniaturization, and tunability. However, much is still unknown about the interactions between biomolecules such as DNA and various surfaces. A fundamental question regarding these sensors concerns the nature of diffusion of target molecules taking place on sensor surfaces and whether it speeds up the molecular recognition process. Lack of understanding of molecular interaction and surface diffusion in addition to questions regarding the behavior of DNA probes immobilized on these surfaces currently limits the rational design of nucleic acid biosensors. Using all-atom unbiased molecular dynamics (MD) simulations we found that single-stranded DNA (ssDNA) behavior on SAMs is drastically altered by different surface chemistries, with ssDNA adopting very different orientations upon adsorption and surface diffusivity varying over an order of magnitude. Probe behavior varies equally broadly as probes are considerably more stable in certain SAMs than others, which affects the accessibility of probes to the target molecules and likely changes DNA hybridization kinetics in multiple ways. We also found that nearby probes can alter each other's orientations substantially, which highlights the importance of surface density control. Our results elucidate nucleic acid biosensor dynamics vital to rational design and offer insights that can aid in the design of surface properties and patterning for specific applications.

Pressure-Modulated Selective Electrokinetic Trapping for Direct Enrichment, Purification, and Detection of Nucleic Acids in Human Serum

Micro total-analysis systems (μTAS) have been extensively developed for the detection of nucleic acids (NAs) in resource-limited settings in recent years, yet the sample-preparation steps that interface real-world samples with on-chip analytics remain as the technical bottleneck. We report pressure-modulated selective electrokinetic trapping (PM-SET) for the direct enrichment, purification, and detection of NAs in human serum in one step without involving tedious solid-phase extraction, chemical amplification, and surface-hybridization-based assays. Under appropriately modulated hydrostatic pressures, NAs in human serum were selectively enriched in an electrokinetic concentrator with the majority of background proteins removed, achieving an enrichment factor of >4800 in 15 min. A sequence-specific NA was detected simultaneously during the enrichment process using a complementary morpholino (MO) probe, realizing a limit of detection of 3 pM in 15 min. PM-SET greatly reduces the cost, time, and complexity of sample preparation for NA detection and could be easily interfaced with existing NA-detection devices to achieve true sample-to-answer biomolecular analytics.

Specific detection of stable single nucleobase mismatch using SU-8 coated silicon nanowires platform

Novel microarray platform for single nucleotide polymorphisms (SNPs) detection has been developed using silicon nanowires (SiNWs) as support and two different surface modification methods for attaining the necessary functional groups. Accordingly, we compared the detection specificity and stability over time of the probes printed on SiNWs modified with (3-aminopropyl)triethoxysilane (APTES) and glutaraldehyde (GAD), or coated with a simpler procedure using epoxy-based SU-8 photoresist. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used for comparative characterization of the unmodified and coated SiNWs. The hybridization efficiency was assessed by comprehensive statistical analysis of the acquired data from confocal fluorescence scanning of the manufactured biochips. The high detection specificity between the hybridized probes containing different mismatch types was demonstrated on SU-8 coating by one way ANOVA test (adjusted p value *** < .0001). The stability over time of the probes tethered on SiNWs coated with SU-8 was evaluated after 1, 4, 8 and 21 days of probe incubation, revealing values for coefficient of variation (CV) between 2.4% and 5.6%. The signal-to-both-standard-deviations ratio measured for SU-8 coated SiNWs platform was similar to the commercial support, while the APTES-GAD coated SiNWs exhibited the highest values.

Sensors Based on Bio and Biomimetic Receptors in Medical Diagnostic, Environment, and Food Analysis

Analytical chemistry is now developing mainly in two areas: automation and the creation of complexes that allow, on the one hand, for simultaneously analyzing a large number of samples without the participation of an operator, and on the other, the development of portable miniature devices for personalized medicine and the monitoring of a human habitat. The sensor devices, the great majority of which are biosensors and chemical sensors, perform the role of the latter. That last line is considered in the proposed review. Attention is paid to transducers, receptors, techniques of immobilization of the receptor layer on the transducer surface, processes of signal generation and detection, and methods for increasing sensitivity and accuracy. The features of sensors based on synthetic receptors and additional components (aptamers, molecular imprinted polymers, biomimetics) are discussed. Examples of bio- and chemical sensors' application are given. Miniaturization paths, new power supply means, and wearable and printed sensors are described. Progress in this area opens a revolutionary era in the development of methods of on-site and in-situ monitoring, that is, paving the way from the "test-tube to the smartphone".

Microbiological Sensing Technologies: A Review

Microorganisms have a significant influence on human activities and health, and consequently, there is high demand to develop automated, sensitive, and rapid methods for their detection. These methods might be applicable for clinical, industrial, and environmental applications. Although different techniques have been suggested and employed for the detection of microorganisms, and the majority of these methods are not cost effective and suffer from low sensitivity and low specificity, especially in mixed samples. This paper presents a comprehensive review of microbiological techniques and associated challenges for bioengineering researchers with an engineering background. Also, this paper reports on recent technological advances and their future prospects for a variety of microbiological applications.