We review the utility of centrifugal microfluidic technologies applied to point-of-care diagnosis in extremely under-resourced environments. The various challenges faced in these settings are showcased, using areas in India and Africa as examples. Measures for the ability of integrated devices to effectively address point-of-care challenges are highlighted, and centrifugal, often termed CD-based microfluidic technologies, technologies are presented as a promising platform to address these challenges. We describe the advantages of centrifugal liquid handling, as well as the ability of a standard CD player to perform a number of common laboratory tests, fulfilling the role of an integrated lab-on-a-CD. Innovative centrifugal approaches for point-of-care in extremely resource-poor settings are highlighted, including sensing and detection strategies, smart power sources and biomimetic inspiration for environmental control. The evolution of centrifugal microfluidics, along with examples of commercial and advanced prototype centrifugal microfluidic systems, is presented, illustrating the success of deployment at the point-of-care. A close fit of emerging centrifugal systems to address a critical panel of tests for under-resourced clinic settings, formulated by medical experts, is demonstrated. This emphasizes the potential of centrifugal microfluidic technologies to be applied effectively to extremely challenging point-of-care scenarios and in playing a role in improving primary care in resource-limited settings across the developing world.
In this paper we present a wirelessly powered array of 128 centrifugo-pneumatic valves that can be thermally actuated on demand during spinning. The valves can either be triggered by a predefined protocol, wireless signal transmission via Bluetooth, or in response to a sensor monitoring a parameter like the temperature, or homogeneity of the dispersion. Upon activation of a resistive heater, a low-melting membrane (Parafilm™) is removed to vent an entrapped gas pocket, thus letting the incoming liquid wet an intermediate dissolvable film and thereby open the valve. The proposed system allows up to 12 heaters to be activated in parallel, with a response time below 3 s, potentially resulting in 128 actuated valves in under 30 s. We demonstrate, with three examples of common and standard procedures, how the proposed technology could become a powerful tool for implementing diagnostic assays on Lab-on-a-Disc. First, we implement wireless actuation of 64 valves during rotation in a freely programmable sequence, or upon user input in real time. Then, we show a closed-loop centrifugal flow control sequence for which the state of mixing of reagents, evaluated from stroboscopically recorded images, triggers the opening of the valves. In our last experiment, valving and closed-loop control are used to facilitate centrifugal processing of whole blood.
Typical Lab-on-a-Disc (LoaD) platforms cannot make a continuous measurement while the disc is spinning; this drawback means that the disc usually must be stopped and aligned with a sensor. This can result in measurement errors in time-dependent assays along with inaccuracies due to liquid displacement and bubble formation in the absence of a stabilising centrifugal field. This paper presents a novel concept for a wirelessly electrified-Lab-on-a-Disc (eLoaD) platform that allows continuous measurement of experimental parameters while the disc is spinning. This platform incorporates all the components needed for measurement within the rotating frame of reference, and bidirectional transmission of data outside this reference frame, thus allowing for online measurement independent of the rotation of the disc. The eLoaD platform is conceived in a modular manner whereby an interchangeable and non-disposable 'Application Disc' can be fitted to the eLoaD platform and so the system can be adapted for a range of optical, electrochemical and other measurement types. As an application example, optical readout, using the Application Disc fitted with a silicon photomultiplier, is demonstrated using a tagged chemiluminescent antibody, which is commonly used, for instance, in ELISA assays. The precision of the eLoaD platform is >94%, while its accuracy, when compared to a commercial benchtop luminometer, is higher than 96%. The modular design of this platform will permit extension of this technology to many other LoaD applications.
We present a design for wireless power transfer, via inductively coupled coils, to a spinning disk. The rectified and stabilised power feeds an Arduino-compatible microcontroller (μC) on the disc, which in turn drives and monitors various sensors and actuators. The platform, which has been conceived to flexibly prototype such systems, demonstrates the feasibility of a wireless power supply and the use of a μC circuit, for example for Lab-on-a-disk applications, thereby eliminating the need for cumbersome slip rings or batteries, and adding a cogent and new degree of freedom to the setup. The large number of sensors and actuators included demonstrate that a wide range of physical parameters can be easily monitored and altered. All devices are connected to the μC via an I(2)C bus, therefore can be easily exchanged or augmented by other devices in order to perform a specific task on the disk. The wireless power supply takes up little additional physical space and should work in conjunction with most existing Lab-on-a-disk platforms as a straightforward add-on, since it does not require modification of the rotation axis and can be readily adapted to specific geometrical requirements.
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