Hybridization assay at a disposable electrochemical biosensor for the attomole detection of amplified human cytomegalovirus DNA

Development of quantitative detection methods for four Alzheimer's disease specific biomarker panels using electrochemical immunosensors based on enzyme immunoassay

Accurate and timely diagnosis of Alzheimer's disease (AD) is necessary to maximize the effectiveness of treatment and using biomarkers for diagnosis is attracting attention as a minimally invasive method with few side effects. Electrochemical immunosensor (EI) is a method that is in the spotlight in the medical and bioanalytical fields due to its portability and field usability. Here, we quantified four AD specific biomarkers using EIs based on enzyme immunoassay. We selected and developed quantitative methods for the biomarkers using screen-printed gold electrodes. For three biomarkers, quantification was performed using competition immunoassays in which antigen-antibody premix mixtures were applied to antigen-immobilized electrodes and the limit of detection (LOD) values were secured, 1.20 ng/ml, 1.30 ng/ml, and 1.74 ng/ml, respectively. For the other, a sandwich immunoassay using antibody pair was selected for quantification and LOD was also achieved as 0.077 ng/ml. All four biomarkers in buffer samples were successfully quantified and reliable R2 values were obtained, and reliable calibration curves were secured for three biomarkers in spiked human serum samples. The immunosensors developed and will be optimized are expected to be used in various fields, including detection of biomarkers for not only AD but also related diseases.

Development of a Novel Phagomagnetic-Assisted Isothermal DNA Amplification System for Endpoint Electrochemical Detection of Listeria monocytogenes

The hitherto implemented Listeria monocytogenes detection techniques are cumbersome or require expensive non-portable instrumentation, hindering their transposition into on-time surveillance systems. The current work proposes a novel integrated system resorting to loop-mediated isothermal amplification (LAMP), assisted by a bacteriophage P100-magnetic platform, coupled to an endpoint electrochemical technique, towards L. monocytogenes expeditious detection. Molybdophosphate-based optimization of the bacterial phagomagnetic separation protocol allowed the determination of the optimal parameters for its execution (pH 7, 25 °C, 32 µg of magnetic particles; 60.6% of specific capture efficiency). The novel LAMP method targeting prfA was highly specific, accomplishing 100% inclusivity (for 61 L. monocytogenes strains) and 100% exclusivity (towards 42 non-target Gram-positive and Gram-negative bacteria). As a proof-of-concept, the developed scheme was successfully validated in pasteurized milk spiked with L. monocytogenes. The phagomagnetic-based approach succeeded in the selective bacterial capture and ensuing lysis, triggering Listeria DNA leakage, which was efficiently LAMP amplified. Methylene blue-based electrochemical detection of LAMP amplicons was accomplished in 20 min with remarkable analytical sensitivity (1 CFU mL^-1). Hence, the combined system presented an outstanding performance and robustness, providing a 2.5 h-swift, portable, cost-efficient detection scheme for decentralized on-field application.

Recent Advancements in Electrochemical Biosensors for Monitoring the Water Quality

The release of chemicals and microorganisms from various sources, such as industry, agriculture, animal farming, wastewater treatment plants, and flooding, into water systems have caused water pollution in several parts of our world, endangering aquatic ecosystems and individual health. World Health Organization (WHO) has introduced strict standards for the maximum concentration limits for nutrients and chemicals in drinking water, surface water, and groundwater. It is crucial to have rapid, sensitive, and reliable analytical detection systems to monitor the pollution level regularly and meet the standard limit. Electrochemical biosensors are advantageous analytical devices or tools that convert a bio-signal by biorecognition elements into a significant electrical response. Thanks to the micro/nano fabrication techniques, electrochemical biosensors for sensitive, continuous, and real-time detection have attracted increasing attention among researchers and users worldwide. These devices take advantage of easy operation, portability, and rapid response. They can also be miniaturized, have a long-life span and a quick response time, and possess high sensitivity and selectivity and can be considered as portable biosensing assays. They are of special importance due to their great advantages such as affordability, simplicity, portability, and ability to detect at on-site. This review paper is concerned with the basic concepts of electrochemical biosensors and their applications in various water quality monitoring, such as inorganic chemicals, nutrients, microorganisms' pollution, and organic pollutants, especially for developing real-time/online detection systems. The basic concepts of electrochemical biosensors, different surface modification techniques, bio-recognition elements (BRE), detection methods, and specific real-time water quality monitoring applications are reviewed thoroughly in this article.

Genosensors as an alternative diagnostic sensing approaches for specific detection of various certain viruses: a review of common techniques and outcomes

Viral infections are responsible for the deaths of millions of people throughout the world. Since outbreak of highly contagious and mutant viruses such as contemporary sars-cov-2 pandemic, has challenged the conventional diagnostic methods, the entity of a thoroughly sensitive, specific, rapid and inexpensive detecting technique with minimum level of false-positivity or -negativity, is desperately needed more than any time in the past decades. Biosensors as minimized devices could detect viruses in simple formats. So far, various nucleic acid, immune- and protein-based biosensors were designed and tested for recognizing the genome, antigen, or protein level of viruses, respectively; however, nucleic acid-based sensing techniques, which is the foundation of constructing genosensors, are preferred not only because of their ultra-sensitivity and applicability in the early stages of infections but also for their ability to differentiate various strains of the same virus. To date, the review articles related to genosensors are just confined to particular pathogenic diseases; In this regard, the present review covers comprehensive information of the research progress of the electrochemical, optical, and surface plasmon resonance (SPR) genosensors that applied for human viruses' diseases detection and also provides a well description of viruses' clinical importance, the conventional diagnosis approaches of viruses and their disadvantages. This review would address the limitations in the current developments as well as the future challenges involved in the successful construction of sensing approaches with the functionalized nanomaterials and also allow exploring into core-research works regarding this area.

Enzyme-Assisted Nucleic Acid Detection for Infectious Disease Diagnostics: Moving toward the Point-of-Care

Driven by complex and interconnected factors, including population growth, climate change, and geopolitics, infectious diseases represent one of the greatest healthcare challenges of the 21st century. Diagnostic technologies are the first line of defense in the fight against infectious disease, providing critical information to inform epidemiological models, track diseases, decide treatment choices, and ultimately prevent epidemics. The diagnosis of infectious disease at the genomic level using nucleic acid disease biomarkers has proven to be the most effective approach to date. Such methods rely heavily on enzymes to specifically amplify or detect nucleic acids in complex samples, and significant effort has been exerted to harness the power of enzymes for in vitro nucleic acid diagnostics. Unfortunately, significant challenges limit the potential of enzyme-assisted nucleic acid diagnostics, particularly when translating diagnostic technologies from the lab toward the point-of-use or point-of-care. Herein, we discuss the current state of the field and highlight cross-disciplinary efforts to solve the challenges associated with the successful deployment of this important class of diagnostics at or near the point-of-care.

DNA/RNA Electrochemical Biosensing Devices a Future Replacement of PCR Methods for a Fast Epidemic Containment

Pandemics require a fast and immediate response to contain potential infectious carriers. In the recent 2020 Covid-19 worldwide pandemic, authorities all around the world have failed to identify potential carriers and contain it on time. Hence, a rapid and very sensitive testing method is required. Current diagnostic tools, reverse transcription PCR (RT-PCR) and real-time PCR (qPCR), have its pitfalls for quick pandemic containment such as the requirement for specialized professionals and instrumentation. Versatile electrochemical DNA/RNA sensors are a promising technological alternative for PCR based diagnosis. In an electrochemical DNA sensor, a nucleic acid hybridization event is converted into a quantifiable electrochemical signal. A critical challenge of electrochemical DNA sensors is sensitive detection of a low copy number of DNA/RNA in samples such as is the case for early onset of a disease. Signal amplification approaches are an important tool to overcome this sensitivity issue. In this review, the authors discuss the most recent signal amplification strategies employed in the electrochemical DNA/RNA diagnosis of pathogens.

A capacitive DNA sensor for sensitive detection ofEscherichia coliO157:H7 in potable water based on thez3276genetic marker: fabrication and analytical performance

We report a label-free biosensor for the detection ofEscherichia coliO157:H7 ATCC 43895 in potable water using a newly designed DNA sensing probe targeting thez3276genetic marker.

Atomic force microscopy study of EDTA induced desorption of metal ions immobilized DNA from mica surface

Adsorption of DNA molecules onto substrate, such as mica, is well documented. However, desorption of the immobilized DNA molecules from substrate, which is also an important aspect of DNA behavior on substrate, has not been paid much attention. Here, DNA molecules were first immobilized on mica surface by using divalent metal ions as the bridge agents. Desorption of the immobilized DNA from mica surface was realized via ethylenediamine tetraacetic acid disodium salt (EDTA) treatment. EDTA is a chelating agent; it can remove the bridging metal ions between DNA and mica, which leads to the release of DNA molecules from mica substrate. The divalent metal ions assisted DNA adsorption onto mica surface and the EDTA induced DNA desorption from mica surface were followed by atomic force microscopy (AFM). Randomly dispersed DNA strands and DNA networks are two distinct adsorption morphologies of DNA on mica surface and their desorption processes from mica surface induced by EDTA are also different. Other factors that influence the EDTA-induced DNA desorption, such as type of bridging metal ion and DNA molecule length, have also been systematically studied. Moreover, EDTA treatment has no effect on the integrity of DNA molecule. The EDTA induced desorption of metal ions immobilized DNA from mica surface is simple and effective, which has potential applications in DNA separation and purification, DNA biophysics, and DNA-based nanotechnology.

Electrochemical Enzyme-Linked Sandwich Assay with a Cellulase Label for Ultrasensitive Analysis of Synthetic DNA and Cell-Isolated RNA

Electrochemical enzyme-linked sandwich assays on magnetic beads (MBs) refer to one of the most sensitive approaches for analysis of nonamplified nucleic acid samples, with redox enzymes being routinely used as labels. Here, we report a sensitive and inexpensive electrochemical nucleic acid sandwich assay on MBs that exploits a hydrolytic enzyme cellulase as a label, while MBs are used for preconcentration and bioseparation of analyzed samples. Binding of target DNA or RNA to capture DNA-modified MB triggers sandwich assembly and its labeling with cellulase. Application of the assembled sandwich to the electrodes covered with insulating nitrocellulose films induces film digestion by the cellulase label and pronounced changes in the electrical properties of the electrodes, the extent of the changes being proportional to the concentration of the analyzed nucleic acids. Down to 1 amol of Lactobacillus brevis specific synthetic DNA and rRNA isolated from L. brevis cells could be detected in 1 mL samples in the overall from 2 to 3 h assay. The assay is universal and can be adapted for point-of-care-testing and for in-field environmental and microbiomic analysis of unamplified samples of any DNA/RNA sequences.

DNA Electrochemistry and Electrochemical Sensors for Nucleic Acids

Sensitive, specific, and fast analysis of nucleic acids (NAs) is strongly needed in medicine, environmental science, biodefence, and agriculture for the study of bacterial contamination of food and beverages and genetically modified organisms. Electrochemistry offers accurate, simple, inexpensive, and robust tools for the development of such analytical platforms that can successfully compete with other approaches for NA detection. Here, electrode reactions of DNA, basic principles of electrochemical NA analysis, and their relevance for practical applications are reviewed and critically discussed.

Integrated Affinity Biosensing Platforms on Screen-Printed Electrodes Electrografted with Diazonium Salts

Adequate selection of the electrode surface and the strategies for its modification to enable subsequent immobilization of biomolecules and/or nanomaterials integration play a major role in the performance of electrochemical affinity biosensors. Because of the simplicity, rapidity and versatility, electrografting using diazonium salt reduction is among the most currently used functionalization methods to provide the attachment of an organic layer to a conductive substrate. This particular chemistry has demonstrated to be a powerful tool to covalently immobilize in a stable and reproducible way a wide range of biomolecules or nanomaterials onto different electrode surfaces. Considering the great progress and interesting features arisen in the last years, this paper outlines the potential of diazonium chemistry to prepare single or multianalyte electrochemical affinity biosensors on screen-printed electrodes (SPEs) and points out the existing challenges and future directions in this field.

Biosensors for plant pathogen detection

Infectious plant diseases are caused by pathogenic microorganisms such as fungi, bacteria, viruses, viroids, phytoplasma and nematodes. Worldwide, plant pathogen infections are among main factors limiting crop productivity and increasing economic losses. Plant pathogen detection is important as first step to manage a plant disease in greenhouses, field conditions and at the country boarders. Current immunological techniques used to detect pathogens in plant include enzyme-linked immunosorbent assays (ELISA) and direct tissue blot immunoassays (DTBIA). DNA-based techniques such as polymerase chain reaction (PCR), real time PCR (RT-PCR) and dot blot hybridization have also been proposed for pathogen identification and detection. However these methodologies are time-consuming and require complex instruments, being not suitable for in-situ analysis. Consequently, there is strong interest for developing new biosensing systems for early detection of plant diseases with high sensitivity and specificity at the point-of-care. In this context, we revise here the recent advancement in the development of advantageous biosensing systems for plant pathogen detection based on both antibody and DNA receptors. The use of different nanomaterials such as nanochannels and metallic nanoparticles for the development of innovative and sensitive biosensing systems for the detection of pathogens (i.e. bacteria and viruses) at the point-of-care is also shown. Plastic and paper-based platforms have been used for this purpose, offering cheap and easy-to-use really integrated sensing systems for rapid on-site detection. Beside devices developed at research and development level a brief revision of commercially available kits is also included in this review.

A novel electrochemical DNA biosensor based on a modified magnetic bar carbon paste electrode with Fe3O4NPs-reduced graphene oxide/PANHS nanocomposite

In this study, we have designed a label free DNA biosensor based on a magnetic bar carbon paste electrode (MBCPE) modified with nanomaterial of Fe3O4/reduced graphene oxide (Fe3O4NP-RGO) as a composite and 1- pyrenebutyric acid-N- hydroxysuccinimide ester (PANHS) as a linker for detection of DNA sequences. Probe (BRCA1 5382 insC mutation detection) strands were immobilized on the MBCPE/Fe3O4-RGO/PANHS electrode for the exact incubation time. The characterization of the modified electrode was studied using different techniques such as scanning electron microscopy (SEM), infrared spectroscopy (IR), vibrating sample magnetometer (VSM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry methods. Some experimental parameters such as immobilization time of probe DNA, time and temperature of hybridization process were investigated. Under the optimum conditions, the immobilization of the probe and its hybridization with the target DNA (Complementary DNA) were tested. This DNA biosensor revealed a good linear relationship between ∆Rct and logarithm of the complementary target DNA concentration ranging from 1.0×10(-18)molL(-1) to 1.0×10(-8)molL(-1) with a correlation coefficient of 0.9935 and a detection limit of 2.8×10(-19)molL(-1). In addition, the mentioned biosensor was satisfactorily applied for discriminating of complementary sequences from non-complementary sequences. The constructed biosensor (MBCPE/Fe3O4-RGO/PANHS/ssDNA) with high sensitivity, selectivity, stability, reproducibility and low cost can be used for detection of BRCA1 5382 insC mutation.

A Label-Free Impedimetric DNA Sensor Based on a Nanoporous SnO₂ Film: Fabrication and Detection Performance

Nanoporous SnO₂ thin films were elaborated to serve as sensing electrodes for label-free DNA detection using electrochemical impedance spectroscopy (EIS). Films were deposited by an electrodeposition process (EDP). Then the non-Faradic EIS behaviour was thoroughly investigated during some different steps of functionalization up to DNA hybridization. The results have shown a systematic decrease of the impedance upon DNA hybridization. The impedance decrease is attributed to an enhanced penetration of ionic species within the film volume. Besides, the comparison of impedance variations upon DNA hybridization between the liquid and vapour phase processes for organosilane (APTES) grafting on the nanoporous SnO₂ films showed that vapour-phase method is more efficient. This is due to the fact that the vapour is more effective than the solution in penetrating the nanopores of the films. As a result, the DNA sensors built from vapour-treated silane layer exhibit a higher sensitivity than those produced from liquid-treated silane, in the range of tested target DNA concentration going to 10 nM. Finally, the impedance and fluorescence response signals strongly depend on the types of target DNA molecules, demonstrating a high selectivity of the process on nanoporous SnO₂ films.

Study of DNA adsorption on mica surfaces using a surface force apparatus

We report our studies on the adsorption properties of double-stranded DNA molecules on mica surfaces in a confined environment using a surface force apparatus. Specifically, we studied the influence of cation species and concentrations on DNA adsorption properties. Our results indicated that divalent cations (Mg²⁺ and Co²⁺) preferred to form uniform and moderately dense DNA layers on a mica substrate. By measuring the interactions between DNA-coated mica and bare mica in an aqueous solution, obvious adhesion was observed in a cobalt chloride solution, possibly due to the ion-correlation attraction between negatively charged DNA and the mica surface. Furthermore, the interaction differences that were observed with MgCl₂ and CoCl₂ solutions reveal that the specific adsorption behaviors of DNA molecules on a mica substrate were mediated by these two salts. Our results are helpful to elucidate the dynamics of DNA binding on a solid substrate.

Electrochemical DNA hybridization sensors based on conducting polymers

Conducting polymers (CPs) are a group of polymeric materials that have attracted considerable attention because of their unique electronic, chemical, and biochemical properties. This is reflected in their use in a wide range of potential applications, including light-emitting diodes, anti-static coating, electrochromic materials, solar cells, chemical sensors, biosensors, and drug-release systems. Electrochemical DNA sensors based on CPs can be used in numerous areas related to human health. This review summarizes the recent progress made in the development and use of CP-based electrochemical DNA hybridization sensors. We discuss the distinct properties of CPs with respect to their use in the immobilization of probe DNA on electrode surfaces, and we describe the immobilization techniques used for developing DNA hybridization sensors together with the various transduction methods employed. In the concluding part of this review, we present some of the challenges faced in the use of CP-based DNA hybridization sensors, as well as a future perspective.

Electrophoretic and field-effect graphene for all-electrical DNA array technology

Field-effect transistor biomolecular sensors based on low-dimensional nanomaterials boast sensitivity, label-free operation and chip-scale construction. Chemical vapour deposition graphene is especially well suited for multiplexed electronic DNA array applications, since its large two-dimensional morphology readily lends itself to top-down fabrication of transistor arrays. Nonetheless, graphene field-effect transistor DNA sensors have been studied mainly at single-device level. Here we create, from chemical vapour deposition graphene, field-effect transistor arrays with two features representing steps towards multiplexed DNA arrays. First, a robust array yield--seven out of eight transistors--is achieved with a 100-fM sensitivity, on par with optical DNA microarrays and at least 10 times higher than prior chemical vapour deposition graphene transistor DNA sensors. Second, each graphene acts as an electrophoretic electrode for site-specific probe DNA immobilization, and performs subsequent site-specific detection of target DNA as a field-effect transistor. The use of graphene as both electrode and transistor suggests a path towards all-electrical multiplexed graphene DNA arrays.

Reagents in microfluidics: an 'in' and 'out' challenge

Microfluidic devices are excellent at downscaling chemical and biochemical reactions and thereby can make reactions faster, better and more efficient. It is therefore understandable that we are seeing these devices being developed and used for many applications and research areas. However, microfluidic devices are more complex than test tubes or microtitre plates and the integration of reagents into them is a real challenge. This review looks at state-of-the-art methods and strategies for integrating various classes of reagents inside microfluidics and similarly surveys how reagents can be released inside microfluidics. The number of methods used for integrating and releasing reagents is surprisingly large and involves reagents in dry and liquid forms, directly-integrated reagents or reagents linked to carriers, as well as active, passive and hybrid release methods. We also made a brief excursion into the field of drug release and delivery. With this review, we hope to provide a large number of examples of integrating and releasing reagents that can be used by developers and users of microfluidics for their specific needs.

Magnetic nanoparticle-based immunosensor for electrochemical detection of hepatitis B surface antigen

An electrochemical immunosensor was developed for the detection of hepatitis B surface antigen (HBsAg). The biotinylated hepatitis B surface antibody was immobilized on streptavidin magnetic nanoparticles and used for targeting the HBsAg. By the addition of horseradish peroxidase conjugated with secondary antibody (HRP-HBsAb), a sandwich-type immunoassay format was formed. Aminophenol as substrate for conjugated HRP was enzymatically changed into 3-aminophenoxazone (3-APZ). This electroactive enzymatic production (3-APZ) was transferred into an electrochemical cell and monitored by cyclic voltammetry. Under optimal conditions, the cathodic current response of 3-APZ, which was proportional to the HBsAg concentration, was measured by a glassy carbon electrode. The immunosensor response was linear toward HBsAg in the concentration range from 0.001 to 0.015 ng/ml with a detection limit of 0.9 pg/ml at a signal/noise ratio of 3.

Sensitive point-of-care monitoring of HIV related DNA sequences with a personal glucometer

The hybridizations between the HIV target DNA and the capture probes as well as the signal probes conjugated to the multi-invertase/nanoparticle composites lead to the conversion of sucrose to glucose, which is monitored by the personal glucometer and provides quantitative digital readings for point-of-care diagnosis of HIV DNA fragments.

Electroanalysis of single-nucleotide polymorphism by hairpin DNA architectures

Genetic analysis of infectious and genetic diseases and cancer diagnostics require the development of efficient tools for fast and reliable analysis of single-nucleotide polymorphism (SNP) in targeted DNA and RNA sequences often responsible for signalling disease onset. Here, we highlight the main trends in the development of electrochemical genosensors for sensitive and selective detection of SNP that are based on hairpin DNA architectures exhibiting better SNP recognition properties compared with linear DNA probes. SNP detection by electrochemical hairpin DNA beacons is discussed, and comparative analysis of the existing SNP sensing strategies based on enzymatic and nanoparticle signal amplification schemes is presented.

A thin layer-based amperometric enzyme immunoassay for the rapid and sensitive diagnosis of respiratory syncytial virus infections

A simple electrochemical sandwich immunoassay involving a polystyrene microarray slide coated with monoclonal capture antibodies and carbon screen-printed sensors (SPS) was designed for the rapid diagnosis of respiratory syncytial virus (RSV). The detection of the antibody-antigen complex formation relied on the use of a horseradish peroxidase conjugate. Its chronoamperometric measurement detection was performed by confining a droplet of H(2)O(2)/3,3',5,5'-tetramethylbenzidine enzyme substrate/mediator solution within a thin layer between one spot of the microarray and the surface of one screen-printed electrochemical cell. The accumulation of the enzyme product in the thin film of liquid enhanced the electrochemical response which allowed the development of a rapid (25 min) and sensitive thin layer-based amperometric (TLA) enzyme immunoassay. The method was successfully compared to commercially-available immunofluorescent and real-time PCR assays for RSV testing in respiratory secretion clinical samples. This suggests that owing to its rapidity, convenience, low-cost, portability and ability to provide quantified results, the reported concept could be a promising point-of-care diagnostic tool to screen patients with suspected respiratory infection or other types of infectious diseases.

Electrochemical sandwich assay for attomole analysis of DNA and RNA from beer spoilage bacteria Lactobacillus brevis

Attomole (10(-18)mol) levels of RNA and DNA isolated from beer spoilage bacterial cells Lactobacillus brevis have been detected by the electrochemical sandwich DNA hybridization assay exploiting enzymatic activity of lipase. DNA sequences specific exclusively to L. brevis DNA and RNA were selected and used for probe and target DNA design. The assay employs magnetic beads (MB) modified with a capture DNA sequence and a reporter DNA probe labeled with the enzyme, both made to be highly specific for L. brevis DNA. Lipase-labeled DNAs captured on MBs in the sandwich assay were collected on gold electrodes modified with a ferrocene (Fc)-terminated SAM formed by aliphatic esters. Lipase hydrolysis of the ester bond released a fraction of the Fc redox active groups from the electrode surface, decreasing the electrochemical signal from the surface-confined Fc. The assay, shown to be efficient for analysis of short synthetic DNA sequences, was ineffective with genomic double stranded bacterial DNA, but it allowed down to 16 amole detection of 1563 nts long RNA, isolated from bacterial ribosomes without the need for PCR amplification, and single DNA strands produced from ribosomal RNA. No interference from E. coli RNA was registered. The assay allowed analysis of 400 L. brevis cells isolated from 1L of beer, which fits the "alarm signal" range (from 1 to 100 cells per 100mL).

STUDY OF NANOPOROUS MEMBRANES WITH APPLICATIONS IN THE ENHANCED DETECTION OF CADIOVASCULAR BIOMARKER PROTEINS

The goal of this work is to understand the role of nanoconfinement in designing molecular biosensors. We have been investigating microdevices incorporated with nanoporous membranes as molecular biosensor platforms. Detection of ultra low concentration of biomolecules is the key expectation from the new class of molecular biosensors utilizing nanomaterial. In this paper we have evaluated the role of the physical attributes of nanoporous aluminum oxide membranes in nanoconfinement and enhancing sensitivity of detection of protein biomolecules. In this biosensor configuration we have generated a sandwich assay in a high density array of nanoscale confined spaces generated by overlaying the nanoporous alumina membrane over metallic microscale sensing sites. The binding of the biomolecules results in the perturbation of the electrical double layer due to the binding of the test protein (C-reactive protein). Using electrical impedance spectroscopy (EIS), the capacitance changes in the electrical double layer associated with specific protein binding has been evaluated. The sensor performance metrics of sensitivity and dynamic range have been analyzed with changes in the pore diameter.

An integrated electrochemical device based on immunochromatographic test strip and enzyme labels for sensitive detection of disease-related biomarkers

A novel electrochemical biosensing device that integrates an immunochromatographic test strip and a screen-printed electrode (SPE) connected to a portable electrochemical analyzer was presented for rapid, sensitive, and quantitative detection of disease-related biomarker in human blood samples. The principle of the sensor is based on sandwich immunoreactions between a biomarker and a pair of its antibodies on the test strip, followed by highly sensitive square-wave voltammetry (SWV) detection. Horseradish peroxidase (HRP) was used as a signal reporter for electrochemical readout. Hepatitis B surface antigen (HBsAg) was employed as a model protein biomarker to demonstrate the analytical performance of the sensor in this study. Some critical parameters governing the performance of the sensor were investigated in detail. Under optimal conditions, this sensor was capable of detecting a minimum of 0.3 ng mL(-1) (S/N=3) HBsAg with a wide linear concentration range from 1 to 500 ng mL(-1). The sensor was further utilized to detect HBsAg spiked in human plasma with an average recovery of 91.3%. In comparison, a colorimetric immunochromatographic test strip assay (ITSA) was also conducted. The result shows that the SWV detection in the electrochemical sensor is much more sensitive for the quantitative determination of HBsAg than the colorimetric detection, indicating that such a sensor is a promising platform for rapid and sensitive point-of-care testing/screening of disease-related biomarkers in a large population.

"Off-on" electrochemical hairpin-DNA-based genosensor for cancer diagnostics

A simple and robust "off-on" signaling genosensor platform with improved selectivity for single-nucleotide polymorphism (SNP) detection based on the electronic DNA hairpin molecular beacons has been developed. The DNA beacons were immobilized onto gold electrodes in their folded states through the alkanethiol linker at the 3'-end, while the 5'-end was labeled with a methylene blue (MB) redox probe. A typical "on-off" change of the electrochemical signal was observed upon hybridization of the 27-33 nucleotide (nt) long hairpin DNA to the target DNA, in agreement with all the hitherto published data. Truncation of the DNA hairpin beacons down to 20 nts provided improved genosensor selectivity for SNP and allowed switching of the electrochemical genosensor response from the on-off to the off-on mode. Switching was consistent with the variation in the mechanism of the electron transfer reaction between the electrode and the MB redox label, for the folded beacon being characteristic of the electrochemistry of adsorbed species, while for the "open" duplex structure being formally controlled by the diffusion of the redox label within the adsorbate layer. The relative current intensities of both processes were governed by the length of the formed DNA duplex, potential scan rate, and apparent diffusion coefficient of the redox species. The off-on genosensor design used for detection of a cancer biomarker TP53 gene sequence favored discrimination between the healthy and SNP-containing DNA sequences, which was particularly pronounced at short hybridization times.

DNA diagnostics: nanotechnology-enhanced electrochemical detection of nucleic acids

The detection of mismatched base pairs in DNA plays a crucial role in the diagnosis of genetic-related diseases and conditions, especially for early stage treatment. Among the various biosensors that have been used for DNA detection, EC sensors show great promise because they are capable of precise DNA recognition and efficient signal transduction. Advancements in micro- and nanotechnologies, specifically fabrication techniques and new nanomaterials, have enabled for the development of highly sensitive, highly specific sensors making them attractive for the detection of small sequence variations. Furthermore, the integration of sensors with sample preparation and fluidic processes enables for rapid, multiplexed DNA detection essential for POC clinical diagnostics.

Detection of microarray-hybridized oligonucleotides with magnetic beads

The efficiency of hybridization analysis with oligonucleotide microarrays depends heavily on the method of detection. Conventional methods based on labeling nucleic acids with fluorescent, chemiluminescent, enzyme, or radioactive reporters suffer from a number of serious drawbacks which demand development of new detection techniques. Here, we report two new approaches for detection of hybridization with oligonucleotide microarrays employing magnetic beads as active labels. In the first method streptavidin-coated magnetic beads are used to discover biotin-labeled DNA molecules hybridized with arrayed oligonucleotide probes. In the second method biotin-labeled DNA molecules are bound first to the surface of magnetic beads and then hybridized with arrayed complementary strands on bead-array contacts. Using a simple low-power microscope with a dark-field illumination and a pair of complementary primers as a model hybridization system we evaluated sensitivity, speed, and cost of the new detection method and compared its performance with the detection techniques employing enzyme and fluorescent labels. It was shown that the detection of microarray-hybridized DNA with magnetic beads combines low cost with high speed and enhanced assay sensitivity, opening a new way to routine hybridization assays which do not require precise measurements of DNA concentration.

Electrochemical DNA sandwich assay with a lipase label for attomole detection of DNA

A fast and sensitive electrochemical lipase-based sandwich hybridization assay for detection of attomole levels of DNA has been developed. A combination of magnetic beads, used for pre-concentration and bioseparation of the analyte with a lipase catalyst label allowed detection of DNA with a limit of 20 amol.

Sensitive electrochemical detection of horseradish peroxidase at disposable screen-printed carbon electrode

A rapid, simple and sensitive electrochemical assay of horseradish peroxidase (HRP) performed on disposable screen-printed carbon electrode was developed. HRP activities were monitored by square-wave voltammetric (SWV) measuring the electroactive enzymatic product in the presence of o-aminophenol and hydrogen peroxide substrate solution. SWV analysis demonstrated a greater sensitivity and shorter analysis time than the widely used amperometric and differential-pulsed voltammetric methods. The voltammetric characteristics of substrate and enzymatic product as well as the parameters of SWV analysis were optimized. Under optimized conditions, a linear response for HRP from 0.003 - 0.1 U/mL and a detection limit of 0.002 U/mL (1.25×10(-15) mol in 25 μL) were obtained with a good precision (RSD = 8%; n = 6). This rapid and sensitive HRP assay with microliters-assay volume could be readily integrated to portable devices and point-of-care (POC) diagnosis applications.

Opto-electronic DNA chip-based integrated card for clinical diagnostics

Clinical diagnostics is one of the most promising applications for microfluidic lab-on-a-chip or lab-on-card systems. DNA chips, which provide multiparametric data, are privileged tools for genomic analysis. However, automation of molecular biology protocol and use of these DNA chips in fully integrated systems remains a great challenge. Simplicity of chip and/or card/instrument interfaces is amongst the most critical issues to be addressed. Indeed, current detection systems for DNA chip reading are often complex, expensive, bulky and even limited in terms of sensitivity or accuracy. Furthermore, for liquid handling in the lab-on-cards, many devices use complex and bulky systems, either to directly manipulate fluids, or to ensure pneumatic or mechanical control of integrated valves. All these drawbacks prevent or limit the use of DNA-chip-based integrated systems, for point-of-care testing or as a routine diagnostics tool. We present here a DNA-chip-based protocol integration on a plastic card for clinical diagnostics applications including: (1) an opto-electronic DNA-chip, (2) fluid handling using electrically activated embedded pyrotechnic microvalves with closing/opening functions. We demonstrate both fluidic and electric packaging of the optoelectronic DNA chip without major alteration of its electronical and biological functionalities, and fluid control using novel electrically activable pyrotechnic microvalves. Finally, we suggest a complete design of a card dedicated to automation of a complex biological protocol with a fully electrical fluid handling and DNA chip reading.

Enzyme-Linked Electrochemical Detection of PCR-Amplified Nucleotide Sequences Using Disposable Screen-Printed Sensors. Applications in Gene Expression Monitoring

Electrochemical enzyme-linked techniques for sequence-specific DNA sensing are presented. These techniques are based on attachment of streptavidin-alkaline phosphatase conjugate to biotin tags tethered to DNA immobilized at the surface of disposable screen-printed carbon electrodes (SPCE), followed by production and electrochemical determination of an electroactive indicator, 1-naphthol. Via hybridization of SPCE surface-confined target DNAs with end-biotinylated probes, highly specific discrimination between complementary and non-complementary nucleotide sequences was achieved. The enzyme-linked DNA hybridization assay has been successfully applied in analysis of PCR-amplified real genomic DNA sequences, as well as in monitoring of plant tissue-specific gene expression. In addition, we present an alternative approach involving sequence-specific incorporation of biotin-labeled nucleotides into DNA by primer extension. Introduction of multiple biotin tags per probe primer resulted in considerable enhancement of the signal intensity and improvement of the specificity of detection.