Microfluidic platform for point-of-need diagnostics based on spatial modulation detection

Opto-fluidic systems based on fluorescence from fluorophore-tagged bio-particles offer high performance, e.g., single-molecule detection, but without a clear path to meeting the stringent requirements for SwaP-C. This presentation will describe an optical detection technique that delivers high signal-to-noise discrimination without complex optics or bulky, expensive light sources to enable an opto-fluidic system that can combine high performance, robustness, compactness, low cost, and ease of use. The technique termed “spatially modulated emission” is based on relative movement between an excited bio-particle and a patterned environment to produce a time-dependent signal that is analyzed with correlation techniques. The key advantage is high discrimination of the particle signal from background noise, with compact, robust optics. The technique has been used to detect native fluorescence from single cells and for medical diagnostics on complex biological fluids, specifically, with CD4 monitoring of CD4 T-lymphocytes in whole blood. The results obtained with a hand-held, battery-powered prototype in less than 10min from 5ml of whole blood were in excellent agreement with those from a state-of-the-art commercial instrument (BD FACSCount) for both absolute CD4 and percentage CD4.

The spatial modulation technique can be viewed as utilizing the principles of spread spectrum technology in the field of fluidic diagnostics platforms. The technique illustrates how the transfer of basic concepts from one discipline (communications) can overcome limitations in another (bio-medical instrumentation). Features of spread spectrum include resistance to interference and interception and increased transmission capacity, which relate to its inherent S/N discrimination capability.