Rapid, low cost screening of tuberculosis requires an effective enrichment method of Mycobacterium tuberculosis (MTB) cells. Currently, microfiltration and centrifugation steps are frequently used for sample preparation, which are cumbersome and time-consuming. In this study, the size-selective capturing mechanism of a microtip-sensor is presented to directly enrich MTB cells from a sample mixture. When a microtip is withdrawn from a spherical suspension in the radial direction, the cells that are concentrated by AC electroosmosis are selectively enriched to the tip due to capillary- and viscous forces. The size-selectivity is characterized by using polystyrene microspheres, which is then applied to size-selective capture of MTB from a sample mixture. Our approach yields a detection limit of 800 cells mL(-1), one of the highest-sensitivity immunosensors to date.

Megakaryocytes (MKs) are the precursor cells of platelets. Cryopreservation of MKs is critical for facilitating research investigations about the biology of this important cell and may help for scaling-up ex-vivo production of platelets from MKs for clinical transfusion. Determining membrane transport properties of MKs to water and cryoprotectant agents (CPAs) is essential for developing optimal conditions for cryopreserving MKs. To obtain these unknown parameters, membrane transport properties of the human UT-7/TPO megakaryocytic cell line were investigated using a microfluidic perfusion system. UT-7/TPO cells were immobilized in a microfluidic system on poly-D-lysine-coated glass substrate and perfused with various hyper-osmotic salt and CPA solutions at suprazero and subzero temperatures. The kinetics of cell volume changes under various extracellular conditions were monitored by a video camera and the information was processed and analyzed using the Kedem-Katchalsky model to determine the membrane transport properties. The osmotically inactive cell volume (V b = 0.15), the permeability coefficient to water (Lp) at 37°C, 22°C, 12°C, 0°C, -5°C, -10°C, and -20°C, and dimethyl sulfoxide (DMSO; Ps) at 22, 12, 0, -10, -20, as well as associated activation energies of water and DMSO at different temperature regions were obtained. We found that MKs have relatively higher membrane permeability to water (Lp = 2.62 mm/min/atm at 22°C) and DMSO (Ps = 1.8 · 10-3 cm/min at 22°C) than most other common mammalian cell types, such as lymphocytes (Lp = 0.46 mm/min/atm at 25°C). This information could suggest a higher optimal cooling rate for MKs cryopreservation. The discontinuity effect was also found on activation energy at 0°C-12°C in the Arrhenius plots of membrane permeability by evaluating the slope of linear regression at each temperature region. This phenomenon may imply the occurrence of cell membrane lipid phase transition.