Two-Fluorophore Mobile Phone Imaging of Biplexed Real-Time NAATs Overcomes Optical Artifacts in Highly Scattering Porous Media

UbiNAAT: a multiplexed point-of-care nucleic acid diagnostic platform for rapid at-home pathogen detection

The COVID-19 pandemic increased demands for respiratory disease testing to facilitate treatment and limit transmission, demonstrating in the process that most existing test options were too complex and expensive to perform in point-of-care or home scenarios. Lab-based molecular techniques can detect viral RNA in respiratory illnesses but are expensive and require trained personnel, while affordable antigen-based home tests lack sensitivity for early detection in newly infected or asymptomatic individuals. The few home RNA detection tests deployed were prohibitively expensive. Here, we demonstrate a point-of-care, paper-based rapid analysis device that simultaneously detects multiple viral RNAs; it is demonstrated on two common respiratory viruses (COVID-19 and influenza A) spiked onto a commercial nasal swab. The automated device requires no sample preparation by the user after insertion of the swab, minimizing user operation steps. We incorporated lyophilized amplification reagents immobilized in a porous matrix, a novel thermally actuated valve for multiplexed fluidic control, a printed circuit board that performs on-device lysis and amplification within a cell-phone-sized disposable device. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) products are visualized via fluorescent dyes using a modified cell phone, resulting in detection of as few as 104 viral copies per swab across both pathogens within 30 minutes. This integrated platform could be commercialized in a form that would be inexpensive, portable, and sensitive; it can readily be multiplexed to detect as many as 8 different RNA or DNA sequences, and adapted to any desired RNA or DNA detection assays.

A portable smartphone-based hemoglobin point-of-care testing platform for accurate anemia diagnostics

Anemia affects over 2 billion people worldwide, with the heaviest burden borne by women and children. At present, anemia is diagnosed by measuring hemoglobin (Hb) levels, which must be done in hospitals or commercial laboratories by skilled operators. In this work, we report a portable, affordable ($3), easy-to-operate (1 min) and accurate smartphone-based Hb analyzer (SHbA) that uses a drop of finger-pricked blood for anemia point-of-care test (POCT) applications. POCT of Hb was achieved using a smartphone ambient light sensor (ALS) to accurately measure the absorbance of colorimetric Hb biochemical analysis reagents in a microcuvette, as well as an Android-based application for results analysis. SHbA validation results agreed well with those reported by a hematology analyzer, and the SHbA has an anemia diagnosis sensitivity of 95.4% and specificity of 96.3% for venous blood (n = 360) and a sensitivity of 96.39% and specificity of 95.58% for fingertip blood (n = 475). In addition, SHbA exhibits excellent performance in the diagnosis and treatment guidance of anemia high-risk populations, including tumor chemotherapy patients (n = 424), pregnant women (n = 214) and thalassemia patients (n = 208). Importantly, volunteer self-testing results (n = 20) indicate that SHbA can be used for home-based anemia diagnosis and monitoring. SHbA has the advantages of high sensitivity and specificity while being cheap and easy to operate, making it widely applicable for the diagnosis and treatment of anemia, especially for high-risk patients in areas with poor medical resources.

Near-digital amplification in paper improves sensitivity and speed in biplexed reactions

The simplest point-of-care assays are usually paper and plastic devices that detect proteins or nucleic acids at low cost and minimal user steps, albeit with poor limits of detection. Digital assays improve limits of detection and analyte quantification by splitting a sample across many wells (or droplets), preventing diffusion, and performing analyte amplification and detection in multiple small wells. However, truly digital nucleic acid amplification tests (NAATs) require costly consumable cartridges that are precisely manufactured, aligned, and operated to enable low detection limits. In this study, we demonstrate how to implement near-digital NAATs in low-cost porous media while approaching the low limits of detection of digital assays. The near-digital NAAT was enabled by a paper membrane containing lyophilized amplification reagents that automatically, passively meters and distributes a sample over a wide area. Performing a NAAT in the paper membrane while allowing diffusion captures many of the benefits of digital NAATs if the pad is imaged at a high spatial resolution during amplification. We show that the near-digital NAAT is compatible with a low-cost paper and plastic disposable cartridge coupled to a 2-layer rigid printed circuit board heater (the MD NAAT platform). We also demonstrate compatibility with biplexing and imaging with mobile phones with different camera sensors. We show that the near-digital NAAT increased signal-to-noise ratios by ~ 10×, improved limits of detection from above 10³ copies of methicillin-resistant Staphylococcus aureus genomic DNA to between 100 and 316 copies in a biplexed reaction containing 10⁵ copies of co-amplifying internal amplification control DNA, and reduced time-to-result from 45 min of amplification to 15-20 min for the positive samples.

Quantitative isothermal amplification on paper membranes using amplification nucleation site analysis

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to manage infectious diseases in outpatient clinics, low- and middle-income countries, and the home. Isothermal amplification methods are an emerging tool for POC NAATs as an alternative to traditional PCR-based workflows. Previous works have focused on relating isothermal amplification bulk fluorescence signals to input copies of target nucleic acids for sample quantification with limited success. In this work, we show that recombinase polymerase amplification (RPA) reactions on paper membranes exhibit discrete fluorescent amplification nucleation sites. We demonstrate that the number of nucleation sites can be used to quantify HIV-1 DNA and viral RNA in less than 20 minutes. An image-analysis algorithm quantifies nucleation sites and determines the input nucleic acid copies in the range of 67-3000 copies per reaction. We demonstrate a mobile phone-based system for image capture and onboard processing, illustrating that this method may be used at the point-of-care for qNAATs with minimal instrumentation.

Quantitative Isothermal Amplification on Paper Membranes using Amplification Nucleation Site Analysis

Quantitative nucleic acid amplification tests (qNAATs) are critical in treating infectious diseases, such as in HIV viral load monitoring or SARS-CoV-2 testing, in which viral load indicates viral suppression or infectivity. Quantitative PCR is the gold standard tool for qNAATs; however, there is a need to develop point-of-care (POC) qNAATs to manage infectious diseases in outpatient clinics, low- and middle-income countries, and the home. Isothermal amplification methods are an emerging tool for POC NAATs as an alternative to traditional PCR-based workflows. Previous works have focused on relating isothermal amplification bulk fluorescence signals to input copies of target nucleic acids for sample quantification with limited success. In this work, we show that recombinase polymerase amplification (RPA) reactions on paper membranes exhibit discrete fluorescent amplification nucleation sites. We demonstrate that the number of nucleation sites can be used to quantify HIV-1 DNA and RNA in less than 20 minutes. An image-analysis algorithm quantifies nucleation sites and determines the input nucleic acid copies in the range of 67-3,000 copies per reaction. We demonstrate a mobile phone-based system for image capture and onboard processing, illustrating that this method may be used at the point-of-care for qNAATs with minimal instrumentation.

Portable Molecular Diagnostics Device for Identification of Asini Corii Colla by Loop-Mediated Isothermal Amplification

Asini Corii Colla (ACC; donkey-hide glue) is one of the most valuable tonic traditional Chinese medicines. Because of the large demand for gelatinous Chinese medicines, bovine or swine skin was sometimes used to make adulterated gelatine in recent decades. Food chemicals can greatly harm people’s health, and detecting chemicals in foods is extremely important. A loop-mediated isothermal amplification (LAMP) device with smartphone detection is demonstrated in this study for detecting the DNA of Asini Corii Colla. The complete system is composed of a hand-held box equipped with a smartphone, a cartridge heater, an ultraviolet LED, a disposable reaction tube, and a homemade thermal module. All the processes are powered by a set of rechargeable batteries. Comprehensive experiments of measuring temperature profiles are presented, which showed the accuracy of temperature under thermal control is less than 0.5 °C. By implementing one heating module with an ATmega328p-au microcontroller in the device, the DNA mixture is heated directly up to the reaction temperature within 5 min. Next, a DNA segment of Asini Corii Colla is utilized to evaluate the sensitivity of the DNA amplification in the portable device. A limit of detection to a concentration of 10−4 ng/μL is achieved. Real-time detection of Asini Corii Colla by a smartphone camera can be achieved using this portable device. The unique architecture utilized in this device is ideal for a low-cost DNA analysis system.

Nucleic acid analysis on paper substrates (NAAPs): an innovative tool for Point of Care (POC) infectious disease diagnosis

The cost-effective rapid diagnosis of infectious diseases is an essential and important factor for curing such diseases in the global public health care picture. Owing to poor infrastructure and lack of sanitation, these diseases have an extreme impact on remote and rural areas, especially in developing countries, and there are unresolved challenges. Molecular diagnosis, such as nucleic acid analysis, plays a key role in the significant treatment of numerous infectious diseases. Current molecular diagnostic assays require a sophisticated laboratory setup with expensive components. Molecular diagnosis on a microfluidic point-of-care (POC) platform is attractive to researchers for disease detection with proper prevention. Compared to various microfluidic substrate materials, paper-based POC technologies offer significant cost-effective solutions over high-cost clinical instruments to fill the gap between the needs of users and affordability. Low-cost paper-based microfluidic POC technologies provide portable and disposable diagnostic systems for multiple disease detection that may be extremely useful in remote areas. This article presents a critical review of paper-based microfluidic device technology which has become an imminent platform to adjust the current health scenario for the detection of diseases using different stages of nucleic acid analysis, such as extraction, amplification and detection of nucleic acid, with future perspectives for paper substrates.