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Throughout the COVID-19 pandemic, we have witnessed the critical and expanding roles of testing.

In this review, we provide an overview of developments in point-of-care (POC) diagnostics during the COVID-19 pandemic. We review these advances within the framework of a holistic POC ecosystem, focusing on points of interest – both technological and non-technological – to POC researchers and test developers. Technologically, we review design choices in assay chemistry, microfluidics, and instrumentation towards nucleic acid and protein detection for severe acute respiratory coronavirus 2 (SARS-CoV-2), and away from the lab bench, developments that supported the unprecedented rapid development, scale up, and deployment of POC devices. We describe common features in the POC technologies that obtained Emergency Use Authorization (EUA) for nucleic acid, antigen, and antibody tests, and how these tests fit into four distinct POC use cases. We conclude with implications for future pandemics, infectious disease monitoring, and digital health.

It is traditionally difficult to incorporate two classes of diagnostic tests into a single platform. In this work, we demonstrate a microfluidic-based smartphone dongle that simultaneously measures concentration of hemoglobin and detects HIV antibodies. Specifically, we demonstrate how a previously published immunoassay device, which measured optical density of silver precipitation on gold colloids, can be expanded to quantitatively measure hemoglobin concentration via a colorimetric assay. By lysing whole blood components with CHAPS detergent, we achieved highly reproducible measurement of hemoglobin concentration with the device. We tested this dual test on 38 patient samples from Columbia University Medical Center. Compared with the Hemocue Hb 201+ analyzer, hemoglobin concentrations from our device were accurate within 1.2 g dL(-1), while the HIV immunoassay (in the presence of CHAPS detergent) showed 95% sensitivity and 95% specificity, comparable to our previous studies. This work demonstrates the feasibility of integrating two classes of diagnostic tests (a colorimetric-based quantitative measurement and an immunoassay based on silver precipitation on gold colloids) into a low-cost, fast, and low-power dongle that works with smartphones, and creates a novel dual panel with clinical utility for antenatal-care settings.

A multitude of cytotactic cues direct cell migration in development, cancer metastasis and wound healing. However, our understanding of cell motility remains fragmented partially because current migration devices only allow the study of independent factors. We developed a cell motility assay that allows competitive recruitment of a given cell population simultaneously by gradients of multiple cytotactic cues, observable under real-time imaging. Well-defined uniform gradients of cytotactic cues can be independently generated and sustained in each channel. As a case study, bone marrow mesenchymal stem/stromal cells (MSCs) were exposed to 15 cytokines that are commonly present in arthritis. Cytokines that induced robust recruitment of MSCs in multiple groups were selected to ‘compete’ in a final round to yield the most chemotactic factor(s) based on cell migration numbers, distances, migration indices and motility over time. The potency of a given cytokine in competition frequently differed from its individual action, substantiating the need to test multiple cytokines concurrently due to synergistic or antagonistic effects. This new device has the rare capacity to screen molecules that induce cell migration in cancer therapy, drug development and tissue regeneration.

Although advanced fluid handling using elastomeric valves is useful for a variety of lab-on-a-chip procedures, their operation has traditionally relied on external laboratory infrastructure (such as gas tanks, computers, and ground electricity). This dependence has held back the use of elastomeric microvalves for point-of-care settings. Here, we demonstrate that microfabricated microvalves, via liquid-filled control channels, can be actuated using only a handheld instrument powered by a 9 V battery. This setup can achieve on–off fluid control with fast response times, coordinated switching of multiple valves, and operation of a biological assay. In the future, this technique may enable the widely used elastomeric microvalves (made by multilayer soft lithography) to be increasingly adopted for portable sensors and lab-on-a-chip systems.

Despite the prevalence of microfluidic-based heterogeneous immunoassays (where analytes in solution are captured on a solid surface functionalized with a capture molecule), there is incomplete understanding of how assay parameters influence the amount of captured analytes. This study presents computational results and corresponding experimental binding assays in which the capture of analytes is studied under variations in both mass transfer and surface binding, constrained by real-world assay conditions of finite sample volume, assay time, and capture area. Our results identify: 1) a "reagent-limited" regime which exists only under the constraints of finite sample volume and assay time; 2) a critical flow rate (e.g. 0.5 microL min(-1) under our assay conditions) to gain the maximum signal with the fastest assay time; 3) an increase in signal by using a short concentrated plug (e.g. 5 microL, 100 nM) rather than a long dilute plug (e.g. 50 microL, 10 nM) of sample; 4) the possibility of spending a considerable fraction of the assay time out of the reaction-limited regime. Overall, an improved understanding of fundamental physical processes may be particularly beneficial for the design of point-of-care assays, where volumes of reagents and available samples are limited, and the desired time-to-result short.

This study demonstrates a versatile and fast method for patterning three-dimensional (3D) monolithic microstructures made of multiple (up to 24 demonstrated) types of materials, all spatially aligned, inside a microchannel. This technique uses confocal scanning or conventional fluorescence microscopy to polymerize selected regions of a photocurable material, and microfluidics to automate the delivery of a series of washes and photocurable reagents. Upon completion of lithographic cycles, the aligned 3D microstructures are suitable for microfluidic manipulation and analysis. We demonstrated the fabrication of composite 3D microstructures with various geometries, size scales (up to 1 mm2), spatial resolution (down to 3 microm), and materials. For a typical multi-cycle process, the total fabrication time was tens of minutes, compared to tens of hours for conventional methods. In the case of 3D hydrogels, a potential use is the direct patterning of inhomogeneous 3D microenvironments for studying cell behavior.

This paper demonstrates a methodology for micromixing that is sufficiently simple that it can be used in portable microfluidic devices. It illustrates the use of the micromixer by incorporating it into an elementary, portable microfluidic system that includes sample introduction, sample filtration, and valving. This system has the following characteristics: (i) it is powered with a single hand-operated source of vacuum, (ii) it allows samples to be loaded easily by depositing them into prefabricated wells, (iii) the samples are filtered in situ to prevent clogging of the microchannels, (iv) the structure of the channels ensure mixing of the laminar streams by interaction with bubbles of gas introduced into the channels, (v) the device is prepared in a single-step soft-lithographic process, and (vi) the device can be prepared to be resistant to the adsorption of proteins, and can be used with or without surface-active agents.

A large part of the excitement behind microfluidics is in its potential for producing practical devices, but surprisingly few lab-on-a-chip based technologies have been successfully introduced into the market. Here, we review current work in commercializing microfluidic technologies, with a focus on point-of-care diagnostics applications. We will also identify challenges to commercialization, including lessons drawn from our experience in Claros Diagnostics. Moving forward, we discuss the need to strike a balance between achieving real-world impact with integrated devices versus design of novel single microfluidic components.