Electrochemical Cloth-Based DNA Sensors (ECDSs): A New Class of Electrochemical Gene Sensors

Combining WO3@AuNPs with Poly(amidoamine) Allows Sensitive Electrochemical Detection of DR1 Based on Dual Signal Amplification

Down-regulator of transcription 1 (DR1) is considered as a biomarker of hashimoto's thyroiditis (HT), which is a risk factor for thyroid cancer. Here, a label-free electrochemical biosensor for DR1 detection was constructed based on polyamidoamine (PAMAM) polymer and the nanocomposite (WO3@AuNPs) composed of tungsten trioxide (WO3) and gold nanoparticles (AuNPs). WO3@AuNPs was obtained by combining monolayer WO3 nanosheets, which has high conductivity, and AuNPs. The modification of WO3@AuNPs can not only increase the conductivity of the electrode but also provide more active sites for signaling units, thus greatly improve the sensitivity of the sensor. The polymer PAMAM is biocompatible and non-immunogenic, and its end functional group can bind to the target molecules, providing them with more binding sites and thus improving the sensitivity of the sensor. Under optimal conditions, the label-free biosensor showed a good linear relationship between the logarithm of DR1 concentration and the impedance in the range of 10 fg ⋅ mL-1 to 100 ng ⋅ mL-1, with a detection limit as low as 0.3 fg ⋅ mL-1. Besides, this label-free electrochemical platform exhibited satisfactory selectivity and anti-interference capability in human serum samples. Therefore, this method has considerable potential in clinical detection of DR1.

Wax screen-printable ink for massive fabrication of negligible-to-nil cost fabric-based microfluidic (bio)sensing devices for colorimetric analysis of sweat

Fabric-based microfluidic analytical devices (μADs) have emerged as a promising material for replacing paper μADs thanks to their superior properties in terms of stretchability, mechanical strength, and their wide scope of applicability in wearable devices or embedded in garments. The major obstacle in their widespread use is the lack of a technique enabling their massive fabrication at a negligible-to-nil cost. In response, we report the development of a wax ink with proper thixotropic and hydrophobic properties, fully compatible with automatic screen-printing that allows the one step massive fabrication of microfluidics on a cotton/elastane fabric, with a printing resolution 400 μm (hydrophilic channel) and 1000 μm (hydrophobic barrier), without being necessary any post curing. The cost of the ink (50 g) and of each microfluidic device is ca. 2.3 and 0.007 €, respectively. The active component of the ink was a refined beeswax in a matrix based on ethyl cellulose in 2-butoxy ethyl acetate. Screen-printed fabric μADs were used for the simultaneous colorimetric determination of pH and urea in untreated human sweat by using multivariate regression analysis. This method enabled the direct measurement of urea using urease, regardless of the sweat's pH, and shows strong agreement with a reference method.

Electrochemical nucleic acid sensors: Competent pathways for mobile molecular diagnostics

Electrochemical nucleic acid biosensor has demonstrated great promise in clinical diagnostic tests, mainly because of its flexibility, high efficiency, low cost, and easy integration for analytical applications. Numerous nucleic acid hybridization-based strategies have been developed for the design and construction of novel electrochemical biosensors for diagnosing genetic-related diseases. This review describes the advances, challenges, and prospects of electrochemical nucleic acid biosensors for mobile molecular diagnosis. Specifically, the basic principles, sensing elements, applications in diagnosis of cancer and infectious diseases, integration with microfluidic technology and commercialization are mainly included in this review, aiming to provide new insights and directions for the future development of electrochemical nucleic acid biosensors.

Electrochemical Biosensors as a Novel Platform in the Identification of Listeriosis Infection

Listeria monocytogenes (L.M.) is a gram-positive bacillus with wide distribution in the environment. This bacterium contaminates water sources and food products and can be transmitted to the human population. The infection caused by L.M. is called listeriosis and is common in pregnant women, immune-deficient patients, and older adults. Based on the released statistics, listeriosis has a high rate of hospitalization and mortality; thus, rapid and timely detection of food contamination and listeriosis cases is necessary. During the last few decades, biosensors have been used for the detection and monitoring of varied bacteria species. These devices are detection platforms with great sensitivity and low detection limits. Among different types of biosensors, electrochemical biosensors have a high capability to circumvent several drawbacks associated with the application of conventional laboratory techniques. In this review article, different electrochemical biosensor types used for the detection of listeriosis were discussed in terms of actuators, bioreceptors, specific working electrodes, and signal amplification. We hope that this review will facilitate researchers to access a complete and comprehensive template for pathogen detection based on the different formats of electrochemical biosensors.

Nucleotide detection mechanism and comparison based on low-dimensional materials: A review

The recent pandemic has led to the fabrication of new nucleic acid sensors that can detect infinitesimal limits immediately and effectively. Therefore, various techniques have been demonstrated using low-dimensional materials that exhibit ultrahigh detection and accuracy. Numerous detection approaches have been reported, and new methods for impulse sensing are being explored. All ongoing research converges at one unique point, that is, an impetus: the enhanced limit of detection of sensors. There are several reviews on the detection of viruses and other proteins related to disease control point of care; however, to the best of our knowledge, none summarizes the various nucleotide sensors and describes their limits of detection and mechanisms. To understand the far-reaching impact of this discipline, we briefly discussed conventional and nanomaterial-based sensors, and then proposed the feature prospects of these devices. Two types of sensing mechanisms were further divided into their sub-branches: polymerase chain reaction and photospectrometric-based sensors. The nanomaterial-based sensor was further subdivided into optical and electrical sensors. The optical sensors included fluorescence (FL), surface plasmon resonance (SPR), colorimetric, and surface-enhanced Raman scattering (SERS), while electrical sensors included electrochemical luminescence (ECL), microfluidic chip, and field-effect transistor (FET). A synopsis of sensing materials, mechanisms, detection limits, and ranges has been provided. The sensing mechanism and materials used were discussed for each category in terms of length, collectively forming a fusing platform to highlight the ultrahigh detection technique of nucleotide sensors. We discussed potential trends in improving the fabrication of nucleotide nanosensors based on low-dimensional materials. In this area, particular aspects, including sensitivity, detection mechanism, stability, and challenges, were addressed. The optimization of the sensing performance and selection of the best sensor were concluded. Recent trends in the atomic-scale simulation of the development of Deoxyribonucleic acid (DNA) sensors using 2D materials were highlighted. A critical overview of the challenges and opportunities of deoxyribonucleic acid sensors was explored, and progress made in deoxyribonucleic acid detection over the past decade with a family of deoxyribonucleic acid sensors was described. Areas in which further research is needed were included in the future scope.

Nucleic acid amplification-based strategy to detect foodborne pathogens in milk: a review

Milk contaminated with trace amounts of foodborne pathogens can considerably threaten food safety and public health. Therefore, rapid and accurate detection techniques for foodborne pathogens in milk are essential. Nucleic acid amplification (NAA)-based strategies are widely used to detect foodborne pathogens in milk. This review article covers the mechanisms of the NAA-based detection of foodborne pathogens in milk, including polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), rolling circle amplification (RCA), and enzyme-free amplification, among others. Key factors affecting detection efficiency and the advantages and disadvantages of the above techniques are analyzed. Potential on-site detection tools based on NAA are outlined. We found that NAA-based strategies were effective in detecting foodborne pathogens in milk. Among them, PCR was the most reliable. LAMP showed high specificity, whereas RPA and RCA were most suitable for on-site and in-situ detection, respectively, and enzyme-free amplification was more economical. However, factors such as sample separation, nucleic acid target conversion, and signal transduction affected efficiency of NAA-based strategies. The lack of simple and effective sample separation methods to reduce the effect of milk matrices on detection efficiency was noteworthy. Further research should focus on simplifying, integrating, and miniaturizing microfluidic on-site detection platforms.

A cloth-based electrochemiluminescence sensor for determination of salbutamol residues in pork samples

The fabrication of a cloth-based analytical device combined with electrochemiluminescence detection was established for the rapid determination of salbutamol in pork samples. A hand-coloring method to pattern the hydrophobic chamber was employed, and a three-carbon electrode system was subsequently screen printed onto the patterned cotton chamber. Further modifications of the working electrode surface were conducted using platinum nanoparticles and chitosan solution. The salbutamol enhanced the electrochemiluminescence signal of tris(2,2'-bipyridyl)ruthenium(II) complex in the Britton-Robinson buffer of pH 9.5 and the potential quantitative assay for SAL detection was exhibited. The proposed sensor illustrated a linear calibration curve of the logarithmic SAL concentration in the range of 5 × 10^-2 to 5 × 10⁴ µg L^-1 (r² > 0.996). A limit of detection of 6.8 ng L^-1 was observed. The CAD-ECL sensor was successfully applied for the determination of salbutamol residuals in pork samples. The method validation was performed using the LC-MS method.

Nucleic acid isothermal amplification-based soft nanoarchitectonics as an emerging electrochemical biosensing platform

The emergence of nucleic acid isothermal amplification strategies based on soft nanoarchitectonics offers a new dimension to the traditional electrochemical technique, particularly because of its flexibility, high efficiency, and increased sensitivity for analytical applications. Various DNA/RNA isothermal amplification strategies have been developed for the design and fabrication of new electrochemical biosensors for efficient and important biomolecular detection. Herein, we provide an overview of recent efforts in this research field and the strategies for signal-amplified sensing systems, with their biological applications, current challenges and prospects in this promising new area.

A rotary multi-positioned cloth/paper hybrid microfluidic device for simultaneous fluorescence sensing of mercury and lead ions by using ion imprinted technologies

A novel rotary cloth/paper hybrid microfluidic analytical device (μCPAD) was proposed via the synergy of the fluorescence sensing cloth-based component and rotary paper-based microfluidic analytical device (μPAD) for simultaneous detection of mercury (Hg²⁺) and lead (Pb²⁺) ions. Fluorescence sensing cloth-based component was prepared by grafting quantum dots onto cotton cloth and then modifying with ion imprinted polymers (IIP). Because the cloth has good ductility and durability, it can bear strong oscillation during the fabrication of grafting quantum dots and IIP, and brings a lot of convenience to the production process. At the same time, because rotary μCPAD was stacked by three-layer papers with designed hydrophilic channels and hydrophobic barriers, it could realize simultaneous detection of Hg²⁺ and Pb²⁺ ions by rotating top layer counterclockwise or clockwise. The fluorescence signals were obtained through quantum dots' electron transfer fluorescence quenching effect with the limits of detection were 0.18 and 0.07 μg/L, respectively. This method successfully realized the transference of specific and sensitive fluorescence sensing materials (quantum dots) onto the microfluidic device to improve the portability and expanded applications. Moreover, the novel microfluidic device may have great potential in point-of-care testing of heavy metal ions in environmental monitoring fields.

Textile-based electrochemical sensors and their applications

Textile and their composite-based functional sensors are extensively acknowledged and preferred detection platforms in recent times. Developing suitable methodologies for fabricating textile sensors can be achieved either by integration of conductive fibers and yarns into textiles using technologies such as weaving, knitting and embroidery; or by functionalization of textile materials with conductive nanomaterials/inks using printing or coating methods. Textile materials are gaining enormous attention for fabricating soft lab-on-fabric devices due to their unique features such as high flexibility, wear and wash resistance, mechanical strength and promising sensing performances. Owing to these collective properties, textile-based electrochemical transducers are now showcasing rapid and accurate electrical measurements towards real time point-of-care diagnostics and environmental monitoring applications. The present review provides a brief overview of key progress made in the field of developing textile materials and their composites-based electrochemical sensors and biosensors in recent years where electrode configurations are specifically based on either natural or synthetic fabrics. Different ways to fabricate and functionalize textiles for their application in electrochemical analysis are briefly discussed. The review ends with a conclusive note focusing on the current challenges in the fabrication of textile-based stable electrochemical sensors and biosensors.

A novel cloth-based supersandwich electrochemical aptasensor for direct, sensitive detection of pathogens

Traditional detection methods for food-borne pathogens are usually expensive and laborious, so there is an urgent need for an economical, facile and sensitive method. In this work, a novel cloth-based supersandwich electrochemical aptasensor (CSEA) is firstly developed for direct detection of pathogens. Carbon ink- and wax-based screen-printing is used to make cloth-based electrodes and hydrophilic/hydrophobic regions respectively to fabricate the sensing devices. Two well-designed, specific single-stranded DNA sequences arise a cascade hybridization reaction to form the DNA supersandwich (DSS) whose grooves can be inserted by methylene blue (MB), which effectively amplifies the current signal to greatly improve the detection sensitivity. Taking the detection of Salmonella typhimurium (S. typhimurium) as an example, the aptamers bind to S. typhimurium to form the target-aptamers complex, which can simultaneously bind to the capture probe and DSS, resulting in detection of S. typhimurium. Moreover, the addition of tail sequences of aptamer makes the proposed CSEA versatile. Under optimized conditions, the electrochemical signal increases linearly with the logarithm of S. typhimurium concentration over the range from 10² to 10⁸ CFU mL^-1, with a limit of detection of 16 CFU mL^-1. Additionally, the CSEA efficiently determined the levels of S. typhimurium in milk samples. Experimental results illustrate that the fabricated CSEA is sensitive, specific, reproducible and stable. Moreover, when Ru(bpy)₃²⁺ replaces MB, the electrochemiluminescence (ECL) can be performed. Thus, for the proposed sensing strategy, the dual-mode detection of electrochemistry and ECL is easily realized.

Progress of Wearable and Flexible Electrochemical Biosensors With the Aid of Conductive Nanomaterials

Conductive nanomaterials have recently gained a lot of interest due to their excellent physical, chemical, and electrical properties, as well as their numerous nanoscale morphologies, which enable them to be fabricated into a wide range of modern chemical and biological sensors. This study focuses mainly on current applications based on conductive nanostructured materials. They are the key elements in preparing wearable electrochemical Biosensors, including electrochemical immunosensors and DNA biosensors. Conductive nanomaterials such as carbon (Carbon Nanotubes, Graphene), metals and conductive polymers, which provide a large effective surface area, fast electron transfer rate and high electrical conductivity, are summarized in detail. Conductive polymer nanocomposites in combination with carbon and metal nanoparticles have also been addressed to increase sensor performance. In conclusion, a section on current challenges and opportunities in this growing field is forecasted at the end.

In Situ Assembly of Nanomaterials and Molecules for the Signal Enhancement of Electrochemical Biosensors

The physiochemical properties of nanomaterials have a close relationship with their status in solution. As a result of its better simplicity than that of pre-assembled aggregates, the in situ assembly of nanomaterials has been integrated into the design of electrochemical biosensors for the signal output and amplification. In this review, we highlight the significant progress in the in situ assembly of nanomaterials as the nanolabels for enhancing the performances of electrochemical biosensors. The works are discussed based on the difference in the interactions for the assembly of nanomaterials, including DNA hybridization, metal ion-ligand coordination, metal-thiol and boronate ester interactions, aptamer-target binding, electrostatic attraction, and streptavidin (SA)-biotin conjugate. We further expand the range of the assembly units from nanomaterials to small organic molecules and biomolecules, which endow the signal-amplified strategies with more potential applications.

Microfluidic devices based on textile threads for analytical applications: state of the art and prospects

Microfluidic devices based on textile threads have interesting advantages when compared to systems made with traditional materials, such as polymers and inorganic substrates (especially silicon and glass). One of these significant advantages is the device fabrication process, made more cheap and simple, with little or no microfabrication apparatus. This review describes the fundamentals, applications, challenges, and prospects of microfluidic devices fabricated with textile threads. A wide range of applications is discussed, integrated with several analysis methods, such as electrochemical, colorimetric, electrophoretic, chromatographic, and fluorescence. Additionally, the integration of these devices with different substrates (e.g., 3D printed components or fabrics), other devices (e.g., smartphones), and microelectronics is described. These combinations have allowed the construction of fully portable devices and consequently the development of point-of-care and wearable analytical systems.

Photoelectrochemical Assay Based on SnO2/BiOBr p-n Heterojunction for Ultrasensitive DNA Detection

Herein, a photoelectrochemical (PEC) assay was designed for a highly sensitive DNA determination relying upon the SnO₂/BiOBr p-n heterojunction as a photoactive material and SiO₂ as a signal quencher. Compared with most traditional heterojunctions, the SnO₂/BiOBr p-n heterostructure not only lessened the recombination of the photogenerated electron-hole pairs but also promoted the light-harvesting in the ultraviolet-visible (UV-vis) region, leading to further enhanced photoelectric conversion efficiency and photocurrent, which demonstrated 12.1-fold and 6.4-fold increments versus those of pure SnO₂ and BiOBr, respectively. Additionally, the limited quantity of target DNA (a fragment of p53 gene) could be transformed into abundant output DNA-SiO₂ by employing the Nt·BstNBI enzyme-assisted signal amplification procedure, leading to a highly improved detection sensitivity of the biosensor. Then, output DNA-SiO₂ hybridized with the capture DNA anchored on the modified electrode surface, remarkably diminishing the PEC signal and thus achieving sensitive DNA determination. The elaborated PEC biosensor demonstrated outstanding performance within the linear range between 0.5 fM and 5 nM and a low limit of detection down to 0.18 fM, paving a new way for fabricating heterojunction with exceptional photoactive performance and demonstrating the enormous potential for detecting multitudinous biomarkers in bioanalysis and clinical therapy.

Programming a "Crab Claw"-like DNA Nanomachine as a Super Signal Amplifier for Ultrasensitive Electrochemical Assay of Hg2

Herein, with skillfully engaging stable T-Hg²⁺-T bonding, a "Crab Claw"-like DNA nanomachine with concise and highly efficient assembly and enhanced recognition/conversion efficiency was engineered as a super signal amplifier, which was united with Pd@Cu@Pt multimetallic mesoporous nanomaterials (Pd@Cu@Pt MMNs) for ultrasensitive electrochemical assay of mercury ions (Hg²⁺). Specifically, the formed "Crab Claw"-like DNA nanomachine could simultaneously trigger four same cascade DNAzyme cleavage reactions with the help of Mg²⁺ DNAzyme for markedly converting target Hg²⁺ to enormous DNA segments labeled with ferrocene (Fc), improving the detection sensitivity. Subsequently, the prepared Pd@Cu@Pt MMNs could not only show commendable electrochemical catalysis to Fc but also act as an excellent immobilization matrix for capturing and accumulating abundant Fc around them to further strengthen the electrochemical signal. As a result, the well-designed electrochemical sensor could achieve a low limit of detection of 3.58 fM in the range from 10 fM to 100 nM for Hg²⁺detection. This strategy offers a simple and rapid avenue to detect heavy metal ions and shows promising application potential for environmental pollutant monitoring.

Co-catalytic Fc/HGQs/Fe3O4 nanocomposite mediated enzyme-free electrochemical biosensor for ultrasensitive detection of MicroRNA

Herein, a novel co-catalytic ferrocene/hemin/G-quadruplexes/Fe₃O₄ nanoparticles (Fc/HGQs/Fe₃O₄) nanocomposite was synthesized to significantly magnify the electrochemical signal of ferrocene (Fc) using the synergistic catalysis of hemin/G-quadruplexes (HGQs) and Fe₃O₄ nanoparticles as hydrogen peroxide enzyme mimics for the construction of ultrasensitive electrochemical biosensors. The fabricated electrochemical biosensor can achieve ultrasensitive detection of miRNA-155 ranging from 0.1 fM to 1 nM, as well as a limit of detection of 74.8 aM. This strategy provides a new route to exploring efficient signal labels for signal amplification and provides an impetus to find novel methods for the construction of biosensors for biological detection and the early clinic diagnosis of diseases.

Microfluidic cloth-based analytical devices: Emerging technologies and applications

Cloth (or fabric) is an omnipresent material that has various applications in everyday life, and has become one of the things people are most familiar with. It has some attractive properties such as low cost, ability to transport fluid by capillary force, high tensile strength and durability, good wet strength, and great biocompatibility and biodegradability. Hence, cloth is an ideal material for the development of economical and user-friendly diagnostic devices for many applications including food detection, environmental monitoring, disease diagnosis and public health. Microfluidic cloth-based analytical devices (μCADs) (or microfluidic fabric-based analytical devices (μFADs)) first emerged in 2011 as a low-cost alternative to conventional laboratory testing, with the goal of improving point of care testing and disease screening in the developing world. In this review, we examine the advances in the development of μCADs from 2011 to 2020, especially highlighting emerging technologies and applications related to the μCADs. First, different fabrication methods for μCADs are introduced and compared. Second, a series of cloth-based microfluidic functional components are discussed, including microvalves, fluid velocity control elements, micromixers, and microfilters. Then, electroanalytical μCADs are described, especially focusing on the use of cloth-based electrodes. Next, various detection methods for μCADs, together with their corresponding applications, are compared and categorized. In addition, the current development of wearable μCADs is also demonstrated. Finally, the future outlook and trends in this field are discussed.