Figure 1. Depiction of the working principle of CD4⁺ T-lymphocyte counting microchip platform for the POC.

(a) Shadow images of captured cells were obtained using a large area CCD image sensor (24×34 mm, 10 mega pixel). A pinhole LED (Light Emitting Diode) was used as a light source. The POC platform has following two main processes. First, a microfluidic chip captured target CD4⁺ cells from unprocessed fingerprick volume of HIV-infected whole blood by anti-CD4 antibody which was immobilized on the microchip surface. Second, the captured cells were imaged using the wide field of view (FOV) lensless CCD platform within a second. White light generated from LED light source went through a 100 µm pinhole and illuminated captured cells. Cell shadows were automatically detected and rapidly counted by automated image recognition software on a portable laptop computer. (b) Schematic representation and drawing of the lensless imaging system for microfluidic CD4 count, (c) Photograph of entire POCT CD4 imaging system, (d) microfluidic CD4 chip on top of CCD sensor inside a black box, (e) lensless imaging and magnified image represents the diffracted shadow signal of the cell shape. Scale bar is 200 µm. Entire platform setup and operational details were shown in Text S1.