In India, for example, approximately 30% of the population lacks access to primary care [1]. Kinematic quantities (blue) and forces (red) are shown for a fluid element moving with velocity (u) on a portion of the disk at a distance ¯r from the center of the disk. The Euler force appears opposite to the rotational acceleration in the plane of the disk.
In the so-called “shake mode”, mixing is achieved by using inertial effects to induce fluid mixing based on the change in the direction of rotation of the disk [47]. The permanent magnets are aligned in placement at radial positions that are in and out relative to the mean orbit (dashed circle) of the rotating mixing chamber. Disc flow control valves are particularly critical as a result of the unidirectional nature of centrifugal force.
Due to their dependence on contact angle, these valves are typically very sensitive to the disc's surface finish and manufacturing tolerances. Others have made efforts to develop valve mechanisms that are independent of spin rate. Rapid disc deceleration in combination with pneumatic bags has also been used for centripetal pumping [70,78].
Paramagnetic beads that specifically bind to target cells in whole blood are separated from background cells and unbound beads by the interplay of centrifugal force, lateral disk magnetic force, and hydrodynamic Stokes drag [92].
Centrifugal-Based Systems for Extreme Point-of-Care
The disk also makes a functional laboratory vortex or mixer using the pseudo forces introduced through rotation of the disk. Another exciting application of the microfluidic disk is as a hypergravity simulator, albeit on the microscale. Both optical and electrochemical recording and detection techniques have been applied to centrifugal microfluidic systems.
Absorbance measurements, based on changes in optical density, are among the most commonly used on the lab-on-a-disc platform. One of the most attractive qualities of electrochemical detection is the cost and size of the platform. Electrochemistry has been used in centrifugal microfluidic systems for glucose sensing [132], to detect proteins in body fluid [133], to perform rare cell detection [88], to pump through electrolysis [76].
This presents challenges, such as bridging the gap between the instruments and the disk, as well as managing the small duty cycles resulting from the disk spinning, which leads to expensive, highly sensitive, and power-hungry hardware requirements. Furthermore, the need for very precise speed control of the rotating motor would be reduced, since the actual centrifugal forces on the disc could be directly measured, and the fluid interface spreading could be used as a direct control signal. Control of the application can be achieved through an Arduino platform running on less than 190 mW.
Table 3 shows that, after taking into account the losses of the wireless power transmission and the other mentioned modules, there is still more than 3600 mW available for the specific application to be implemented on the centrifugal disk. To avoid thermal drift of the Peltier element due to heat accumulation on its hot side, the Peltier can be mounted on a copper plane (top) and connected by means to a heat spreader attached to a copper patch on the bottom of the disk is connected. . A disposable disc can connect to an integrated system to run the application on the disc, with the result being transmitted wirelessly to an external device (for example, a smartphone).
The advances and innovations of lab-on-a-disk technologies have evolved over time since the introduction of centrifugal microfluidic systems in the 1960s [ 145 ]. Comparison of different spinstand generations, highlighting the advantages and disadvantages of the slip ring setup, wireless power transfer with Qi and energy harvesting. On centrifugal microfluidic systems, there have been significant advances in the microfabrication technologies that can enable large-scale operations on a single unit.
Given the growing scope of large-scale integration application for POC devices, the development of such platforms will be one of the defining challenges in centrifugal microfluidics. The Abaxis company began development of its centrifugal-based blood chemistry analysis system more than 20 years ago [155] and is one of the few commercial centrifugal-based systems available today.
Ideal Panel of Tests for Extreme Point-of-Care
A comprehensive list of centrifugal microfluidic platforms that are currently commercially available, or close to commercialization, is provided by Strohmeier et al. The potential for centrifugal microfluidic systems to provide POC diagnostic solutions for extreme environments and specific life-threatening diseases has been demonstrated [99]. Tests for malaria and TB are also part of the critical panel, again showing the importance of developing effective POC tests for diagnosing these diseases and leading the focus of POC technology development, particularly on centrifugal microfluidic platforms, moving forward.
Critical panel of tests required for effective POC diagnostics in extreme settings and corresponding existing CD-based versions. Additional tests for the critical panel that still require CD-based implementations include malaria, thyroid function test (T3, T4, TSH) and typhoid fever test. Integrated ELISA for the detection of antigens and antibodies of hepatitis B virus, HBsAg and anti-HBs in parallel using whole blood [168].
Summary and Conclusions
Centrifugal microfluidic systems have evolved significantly in the past decade, resulting in a platform that has the potential to address many of the challenges faced in under-resourced clinical settings. By applying centrifugal microfluidic advances to critical test panels formulated by medical experts in the field, it is clear that centrifugal microfluidics significantly contributes to making such test panels a reality in extreme clinic environments, possible through integrated, self-contained systems that are affordable and accessible . Event-triggered logic flow control for comprehensive process integration of multi-step assays on centrifugal microfluidic platforms.
Paper Conclusion on the Timing of Multistep Fluid Handling Protocols in Event-Triggered Lab-on-a-Disc Microfluidic Centrifugal Platforms. Label-free resistance detection of cancer cells from whole blood on an integrated centrifugal microfluidic platform. All-in-One Centrifugal Microfluidic Device for Isolation of High Purity Size-Selective Circulating Tumor Cells.
CMAS: Fully integrated portable centrifugal microfluidic analysis system for on-site colorimetric analysis.RSC Adv. Rapid and fully automated detection of bacterial pathogens on a centrifugal-microfluidic laboratory disk using highly sensitive nested PCR with integrated sample preparation.
![Table 2. Comparison of optical vs. electrochemical detection techniques, compiled from information in a book series by Madou [108,127,128].](https://thumb-ap.123doks.com/thumbv2/pubpdfnet/10471205.0/14.892.117.772.689.918/table-comparison-optical-electrochemical-detection-techniques-compiled-information.webp)
