Advances and challenges of fully integrated paper-based point-of-care nucleic acid testing

Molybdenum disulfide field-effect transistor biosensor for ultrasensitive detection of DNA by employing morpholino as probe

This work reports on a molybdenum disulfide (MoS₂) based field-effect transistor (FET) biosensor for ultrasensitive label-free detection of DNA via phosphorodiamidate morpholino oligos (PMO)-DNA hybridization. After the chip was fabricated and the sensing channel was modified with positive charges, the negatively charged MoS₂ nanosheet was drop-casted onto the channel, enabling MoS₂ to tightly bind to the sensing surface via electrostatic interactions. Meanwhile, DNA analogue, PMO, was immobilized on the MoS₂ surface, and detection of PMO-DNA hybridization was conducted by the fabricated MoS₂ FET biosensor. Due to the neutral character and high affinity of PMO, a limit of detection (LOD) down to 6 fM was obtained, which is lower than that of the previously reported MoS₂ FET DNA biosensor based on DNA-DNA hybridization. In addition, the MoS₂ FET biosensor also showed high sequence specificity capable of distinguishing the complementary DNA from one-base mismatched DNA, three-base mismatched DNA and noncomplementary DNA. Moreover, the unique FET biosensor was able to detect DNA in complex sample like serum, making the method potential in disease diagnostics.

Hand-powered centrifugal microfluidic platform inspired by the spinning top for sample-to-answer diagnostics of nucleic acids

Point-of-care (POC), sample-to-answer and electricity-free nucleic acid diagnostic tools are vital for health care and disease control in resource-limited settings where centralized medical facilities or even electric power may remain unreliable. Inspired by one of the oldest recognizable toys, the spinning top, here we report a fully hand-powered centrifugal microfluidic platform for the diagnostics of pathogenic bacteria. Assay procedures such as zeolite-based purification of nucleic acids, loop-mediated isothermal amplification (LAMP) and visual detection of fluorescence signals are integrated into a single microfluidic disc. A simple pull-out operation of the top rack of the customized centrifuge initiates high-speed rotation of the disc, resulting in efficient actuation and mixing of preloaded sample/reagent fluids. This microfluidic platform enables the simultaneous detection of six kinds of pathogenic bacteria within a small disc in an electricity-free manner, showing great promise in sample-to-answer nucleic acid detection in remote settings.

Handheld isothermal amplification and electrochemical detection of DNA in resource-limited settings

This paper demonstrates a new method for electrochemical detection of specific sequences of DNA present in trace amounts in serum or blood. This method is designed for use at the point-of-care (particularly in resource-limited settings). By combining recombinase polymerase amplification (RPA)- an isothermal alternative to the polymerase chain reaction - with an electroactive mediator, this electrochemical methodology enables accurate detection of DNA in the field using a low-cost, portable electrochemical analyzer (specifically designed for this type of analysis). This handheld device has four attributes: (1) It uses disposable, paper-based strips that incorporate screen-printed carbon electrodes; (2) It accomplishes thermoregulation with ±0.1 °C temperature accuracy; (3) It enables electrochemical detection using a variety of pulse sequences, including square-wave and cyclic voltammetry, and coulometry; (4) It is operationally simple to use. Detection of genomic DNA from Mycobacterium smegmatis (a surrogate for M. tuberculosis-the main cause of tuberculosis), and from M. tuberculosis itself down to ∼0.040 ng/μL provides a proof-of-concept for the applicability of this method of screening for disease using molecular diagnostics. With minor modifications to the reagents, this method will also enable field monitoring of food and water quality.

An Open Software Platform for the Automated Design of Paper-Based Microfluidic Devices

Paper-based microfluidic devices have many applications in biomedical and environmental analysis. However, the process of prototyping device designs can be tedious, error-prone, and time-consuming. Here, we present a cross-platform, open-source software tool—AutoPAD—developed to quickly create and modify device designs and provide a free alternative to commercial design software. The capabilities that we designed to be inherent to AutoPAD (e.g., automatic zone alignment and design refactoring) highlight its potential use in nearly any paper-based microfluidic device application and for creating nearly any desired design, which we demonstrate through the recreation of numerous device designs from the literature.