Rapid optical interrogation of flowing cells or particles is a powerful tool in the field of biomedical diagnostics. Determination of size and composition of fast-flowing cells, with diameters in the range of 2-15 μm, often require complex open-space optics and expensive highspeed cameras. In this work, a method to overcome these challenges by using a hydrodynamic flow-based microfluidic platform coupled with on-chip integrated fiber optics is reported. The lab-scale portable device developed uses a combination of on-chip lensed and nonlensed optical fibers for precision illumination. The narrow light beam produced by the lensed fiber (f ¼ 150 μm) enables precise optical analysis with high sensitivity. A planar arrangement of optical fibers at various angles facilitates multi-parametric analysis from a single point of interrogation. As proof of concept, the laboratory-scale portable bench-top prototype is used to measure fluorescence signals from CD4 immunostained cells and human blood samples. The performance of microfluidic flow analyzer is also compared to the conventional Guava® easyCyte 8HT flow cytometer.

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The principle of operation of a successive approximation type direct displacement to digital converter for a floating-wiper resistive potentiometric sensor, presented earlier, is analyzed in detail to ascertain possible sources of error that can affect the performance of the transducer. Based on the analysis the method is suitably modified to improve its performance. To establish the efficacy of the altered scheme, a prototype signal conditioning circuit has been built and tested using both an emulated sensor and a prototype sensor. While the worst-case error in the former was found to be 0.5%, it was less than 0.8% in the latter. The test results indicate that the digital output is directly proportional to the per-unit displacement and is independent of the value of the coupling capacitance between the floating-wiper and the resistive element.