Redesigned t-PFF-v device fabricated with one-step anisotropic chemical wet etching process: enhanced separation efficiency for colloidal particles in continuous-mode

A pinched flow fractionation device with trapezoid-shaped pinched segment and cross-flow side channels (t-PFF-v) was redesigned and fabricated with a one-stop anisotropic chemical wet etching process and its enhanced separation capability was demonstrated for spherical polystyrene (PS) particles with diameter ranges of 2–8 µ m. The tilted sidewalls and vertical focusing channels of the t-PFF-v device led to an improved separation resolution (R_m,n) via enhanced separation distance of PS particles at the pinched segment (Δ x_m,n) and reduced effluent particle distribution width (s_n). Using this t-PFF-v device with W_p (pinched segment width) of 25 µ m, PS particles with diameters of 4, 6, and 8 µ m were simultaneously separated with good separation resolution (R _4,6  =  3.2 and R_6,8  =  3.4). Moreover, by adapting even smaller pinched segment width (W_p  =  15 µ m), PS particles with diameters of 2 and 4 µ m, not well separated in the previous studies, were clearly separated with 9.5-fold improvement in R_2,4 compared with the normal PFF device (n-PFF). The effects of inlet flow rate ratio (Q ₂/Q ₁) on the separation efficiency were also carefully investigated and provided additional insight on the separation processes within the pinched segment of t-PFF-v device. The drain flow through the cross-flow v-channels helps better alignment of particles at the sidewall of pinched segment and resulted in significantly reduced distribution of effluent particles, even under the operating conditions with low Q₂/ Q₁ values. (paper)