The presented work demonstrates novel functionalities of hybrid paper-polymer centrifugal devices for assay performance enhancement that leverage the advantages of both paper-based and centrifugal microfluidic platforms. The fluid flow is manipulated by balancing the capillary force of paper inserts with the centrifugal force generated by disc rotation to enhance the signal of a colorimetric lateral flow immunoassay for pathogenic . Low-cost centrifugation for pre-concentration of bacteria was demonstrated by sample sedimentation at high rotational speeds before supernatant removal by a paper insert via capillary force after deceleration. The live bacteria capture efficiency of the device was similar to a commercial centrifuge. This pre-concentrated sample when combined with gold nanoparticle immunoconjugate probes resulted in a detection limit that is 10× lower than a non-concentrated sample for a lateral flow immunoassay. Signal enhancement was also demonstrated through rotational speed variation to prevent the flow for on-device incubation and to reduce the flow rate, thus increasing the sample residence time for the improved capture of gold nanoparticle-bacteria complexes in an integrated paper microfluidic assay. Finally, multiple sequential steps including sample pre-concentration, filtration, incubation, target capture by an integrated paper microfluidic assay, silver enhancement and quenching, and index matching were completed within a single device. The detection limit was 10 colony forming units per ml, a 100× improvement over a similar paper-based lateral flow assay. The techniques utilize the advantages of paper-based microfluidic devices, while facilitating additional functionalities with a centrifugal microfluidic platform for detection performance enhancement in a low-cost, automated platform amenable to point-of-care environments.
Disposable, low-cost microfluidic cartridges for automated blood cell counting applications are presented in this article. The need for point-of-care medical diagnostic tools is evident, particularly in low-resource and rural settings, and a full blood count is often the first step in patient diagnosis. Total white and red blood cell counts have been implemented toward a full blood count, using microfluidic cartridges with automated sample introduction and processing steps for visual microscopy cell counting to be performed. The functional steps within the microfluidic cartridge as well as the surrounding instrumentation required to control and test the cartridges in an automated fashion are described. The results recorded from 10 white blood cell and 10 red blood cell counting cartridges are presented and compare well with the results obtained from the accepted gold-standard flow cytometry method performed at pathology laboratories. Comparisons were also made using manual methods of blood cell counting using a hemocytometer, as well as a commercially available point-of-care white blood cell counting system. The functionality of the blood cell counting microfluidic cartridges can be extended to platelet counting and potential hemoglobin analysis, toward the implementation of an automated, point-of-care full blood count.
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