Low-cost optical sensors in electrified lab-on-a-disc platforms: liquid-phase boundary detection and automated diagnostics

Centrifugal microfluidic platforms are highly regarded for their potential in multiplexing and automation, as well as their wide range of applications, especially in separating blood plasma and manipulating two-phase flows. However, the need to use stroboscopes or high-speed cameras for monitoring these tasks hinders the extensive use of these platforms in research and commercial settings. In this study, we introduce an innovative and cost-effective strategy for using an array of light-dependent resistors (LDRs) as optical sensors in microfluidic devices, particularly centrifugal platforms. While LDRs are attractive for their potential use as photodetectors, their bulky size frequently restricts their ability to provide high-resolution detection in microfluidic systems. Here, we use specific waveguides to direct light beams from narrow apertures onto the surface of LDRs. We integrated these LDRs into electrified Lab-on-a-Disc (eLOD) devices, with wireless connectivity to smartphones and laptops. This enables many applications, such as droplet/particle counting and velocity measurement, concentration analysis, fluidic interface detection in multiphase flows, real-time monitoring of sample volume on centrifugal platforms, and detection of blood plasma separation as an alternative to costly stroboscope devices, microscopes, and high-speed imaging. We used numerical simulations to evaluate various fluids and scenarios, which include rotation speeds of up to 50 rad/s and a range of droplet sizes. For the testbed, we used the developed eLOD device to analyze red blood cell (RBC) deformability and improve the automated detection of sickle cell anemia by monitoring differences in RBC deformability during centrifugation using the sensors' signals. In addition to sickle cell anemia, this device has the potential to facilitate low-cost automated detection of other medical conditions characterized by altered RBC deformability, such as thalassemia, malaria, and diabetes.