DNA nanotechnology for nucleic acid analysis: sensing of nucleic acids with DNA junction-probes.

DNA nanotechnology deals with the design of non-naturally occurring DNA nanostructures that can be used in biotechnology, medicine, and diagnostics. In this study, we introduced a nucleic acid five-way junction (5WJ) structure for direct electrochemical analysis of full-length biological RNAs. To the best of our knowledge, this is the first report on the interrogation of such long nucleic acid sequences by hybridization probes attached to a solid support.

Cost-Effective Modular Biosensor for SARS-CoV-2 and Influenza A Detection.

A modular, multi-purpose, and cost-effective electrochemical biosensor based on a five-stranded four-way junction (5S-4WJ) system was developed for SARS-CoV-2 (genes S and N) and Influenza A virus (gene M) detection. The 5S-4WJ structure consists of an electrode-immobilized universal stem-loop (USL) strand, two auxiliary DNA strands, and a universal methylene blue redox strand (UMeB). This design allows for the detection of specific nucleic acid sequences using square wave voltammetry (SWV).

Single-Step Integration of Poly(3-Octylthiophene) and Single-Walled Carbon Nanotubes for Highly Reproducible Paper-Based Ion-Selective Electrodes.

Calibration of ion-selective electrodes (ISEs) is cumbersome, time-consuming, and constitutes a significant limitation for the development of single-use and wearable disposable sensors. To address this problem, we have studied the effect of ion-selective membrane solvent on ISE reproducibility by comparing tetrahydrofuran (THF) (a typical solvent for membrane preparation) and cyclohexanone. In addition, a single-step integration of semiconducting/transducer polymer poly(3-octylthiophene) (POT) with single-walled carbon nanotubes (SWCNTs) into the paper-based ISEs (PBISEs) substrate was introduced.

Selective Determination of Isothermally Amplified Zika Virus RNA Using a Universal DNA-Hairpin Probe in Less than 1 Hour.

The recent outbreak of the Zika virus (ZIKV) in the Americas and multiple studies that linked the virus to the cases of microcephaly and neurological complications have revealed the need for cost efficient and rapid ZIKV diagnostics tests. Here, a diagnostic platform relying on a four-way junction (4WJ)-based biosensor with electrochemical readout using a Universal DNA-Hairpin (UDH) probe for the selective recognition of an isothermally amplified ZIKV RNA fragment is developed. The 4WJ structure utilizes an electrode-immobilized stem-loop (DNA-hairpin) probe and two DNA adaptor strands complementary to both the stem-loop probe and the targeted fragment of a ZIKV amplicon.

A universal and label-free impedimetric biosensing platform for discrimination of single nucleotide substitutions in long nucleic acid strands.

We report a label-free universal biosensing platform for highly selective detection of long nucleic acid strands. The sensor consists of an electrode-immobilized universal stem-loop (USL) probe and two adaptor strands that form a 4J structure in the presence of a specific DNA/RNA analyte. The sensor was characterized by electrochemical impedance spectroscopy (EIS) using K[Fe(CN)]/K[Fe(CN)] redox couple in solution.

A Single Electrochemical Probe Used for Analysis of Multiple Nucleic Acid Sequences.

Electrochemical hybridization sensors have been explored extensively for analysis of specific nucleic acids. However, commercialization of the platform is hindered by the need for attachment of separate oligonucleotide probes complementary to a RNA or DNA target to an electrode's surface. Here we demonstrate that a single probe can be used to analyze several nucleic acid targets with high selectivity and low cost.

Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective Electrodes.

Preparation of ion-selective electrodes (ISEs) often requires long and complicated conditioning protocols limiting their application as tools for in-field measurements. Herein, we eliminated the need for electrode conditioning by loading the membrane cocktail directly with primary ion solution. This proof of concept experiment was performed with iodide, silver, and sodium selective electrodes.

Nanomolar detection limits of Cd²⁺, Ag⁺, and K⁺ using paper-strip ion-selective electrodes.

Paper-based ion-selective electrodes (ISEs) are simple, flexible, and cost-efficient in comparison to conventional solid-contact ISEs. Yet, paper-based ISEs have poor limits of detection (in the micromolar range) relative to conventional solid-contact ISEs. Here we describe the construction and optimization of ISEs based on commercially available filter paper modified with single-walled carbon nanotubes (SWCNTs), sputtered gold, and conductive polymer poly(3-octylthiophene) to support an ion-selective membrane.

Visible light activated ion sensing using a photoacid polymer for calcium detection.

Presented here is a sensing membrane consisting of a modified merocyanine photoacid polymer and a calcium ionophore in plasticized poly(vinyl chloride). This membrane is shown to actively exchange protons with calcium ions when switched ON after illumination at 470 nm, and the exchange can be followed by UV-vis spectroscopy. The sensing membrane shows no response in the ON state when calcium ions are absent.

Manipulating Mechanical Properties with Electricity: Electroplastic Elastomer Hydrogels.

The dawn of the 21st century has brought with it an increasing interest in emulating the adaptive finesse of natural systems by designing materials with on-demand, tunable properties. The creation of such responsive systems could be expected, based on historical precedent, to lead to completely new engineering design paradigms. Using a bioinspired approach of coupling multiple equilibria that operate on different length scales, a material whose bulk mechanical properties can be manipulated by electrical input has been developed.

A comparative study of enzyme immobilization strategies for multi-walled carbon nanotube glucose biosensors.

This work addresses the comparison of different strategies for improving biosensor performance using nanomaterials. Glucose biosensors based on commonly applied enzyme immobilization approaches, including sol-gel encapsulation approaches and glutaraldehyde cross-linking strategies, were studied in the presence and absence of multi-walled carbon nanotubes (MWNTs). Although direct comparison of design parameters such as linear range and sensitivity is intuitive, this comparison alone is not an accurate indicator of biosensor efficacy, due to the wide range of electrodes and nanomaterials available for use in current biosensor designs.

Non-invasive quantification of endogenous root auxin transport using an integrated flux microsensor technique.

Indole-3-acetic acid (IAA) is a primary phytohormone that regulates multiple aspects of plant development. Because polar transport of IAA is an essential determinant of organogenesis and dynamic tropic growth, methods to monitor IAA movement in vivo are in demand. A self-referencing electrochemical microsensor was optimized to non-invasively measure endogenous IAA flux near the surface of Zea mays roots without the addition of exogenous IAA.

Comparison Between Potentiometric and Stripping Voltammetric Detection of Trace Metals: Measurements of Cadmium and Lead in the Presence of Thalium, Indium, and Tin.

Recent advances in ion-selective electrodes have pushed the detection limits of direct potentiometry to the nanomolar concentration range. Here we present a direct comparison of the sensitivity and selectivity of potentiometric and stripping-voltammetric measurements of cadmium and lead. While both techniques offer a similar sensitivity, the potentiometric method offers higher selectivity in the presence of excess of metal ions (e.

Propulsion of nanowire diodes.

The propulsion of semiconductor diode nanowires under external AC electric field is described. Such fuel-free electric field-induced nanowire propulsion offers considerable promise for diverse technological applications.

High-temperature potentiometry: modulated response of ion-selective electrodes during heat pulses.

The concept of locally heated polymeric membrane potentiometric sensors is introduced here for the first time. This is accomplished in an all solid state sensor configuration, utilizing poly(3-octylthiophene) as the intermediate layer between the ion-selective membrane and underlying substrate that integrates the heating circuitry. Temperature pulse potentiometry (TPP) gives convenient peak-shaped analytical signals and affords an additional dimension with these sensors.

Chemical sensing based on catalytic nanomotors: motion-based detection of trace silver.

A motion-based chemical sensing involving fuel-driven nanomotors is demonstrated. The new protocol relies on the use of an optical microscope for tracking changes in the speed of nanowire motors in the presence of the target analyte. Selective and sensitive measurements of trace silver ions are illustrated based on the dramatic and specific acceleration of bimetal nanowire motors in the presence of silver.

Electrochemically-triggered motion of catalytic nanomotors.

An electrochemically-controlled movement of catalytic nanomotors, including a cyclic 'on/off' activation of the nanomotor motion and a fine speed control, is illustrated.

Thermal modulation of nanomotor movement.

Motion control is essential for various applications of man-made nanomachines. The ability to control and regulate the movement of catalytic nanowire motors is illustrated by applying short heat pulses that allow the motors to be accelerated or slowed down. The accelerated motion observed during the heat pulses is attributed primarily to the thermal activation of the redox reactions of the H(2)O(2) fuel at the Pt and Au segments and to the decreased viscosity of the aqueous medium at elevated temperatures.

Electrochemical sample matrix elimination for trace-level potentiometric detection with polymeric membrane ion-selective electrodes.

Potentiometric sensors are today sufficiently well understood and optimized to reach ultratrace level (subnanomolar) detection limits for numerous ions. In many cases of practical relevance, however, a high electrolyte background hampers the attainable detection limits. A particularly difficult sample matrix for potentiometric detection is seawater, where the high saline concentration forms a major interfering background and reduces the activity of most trace metals by complexation.

Determination of glutathione in hemolysed erythrocyte with amperometric sensor based on TTF-TCNQ.

Background: GSH has a relevant role in human metabolism as an indicator of disease risks. An amperometric sensor for glutathione (GSH) determination is described as an alternative method featuring simple construction procedure and short time analysis.

Method: The developed sensor was used to determine glutathione at low potential using a TTF-TCNQ complex.