Improving the capturing ability of swirl-based microfluidic chip by introducing baffle wall.

Microfluidics technology is promising in developing microparticle manipulation technology due to its nondestructive control and notable adaptability. The manipulation of microparticle based on swirling stagnation point is one of the feasible microfluidics biotechnologies. Aiming to improve the regulation and control of microparticle, baffle wall is introduced into the 2-microchannel flow field. The theory of wall attachment jet is employed to elucidate the effect of baffle wall. Subsequently, finite volume method simulation is conducted by modeling the swirling flow region (SFR), and the swirling strength is calculated to characterize the SFR's particle-capturing ability. Experimental validation of the modeling and simulation methods is performed using a printed microfluidic chip, which has demonstrated exceptional reliability. Simulation results show that the baffle wall makes considerable influence on the SFR. Strikingly, a global range adjustment of stagnation point is realized when the baffle wall is configured with a convex shape, which has remarkably outperformed our previous work, where the stagnation point could only move within half range of the field. This work significantly contributes to advanced flow field structure and provides insight into better regulation of stagnation point as well as microparticles. These findings have potential applications in the analysis of the effect of bio/chemical substances on single cell.

Particle sorting method based on swirl induction.

Fluid-based methods for particle sorting demonstrate increasing appeal in many areas of biosciences due to their biocompatibility and cost-effectiveness. Herein, we construct a microfluidic sorting system based on a swirl microchip. The impact of microchannel velocity on the swirl stagnation point as well as particle movement is analyzed through simulation and experiment. Moreover, the quantitative mapping relationship between flow velocity and particle position distribution is established. With this foundation established, a particle sorting method based on swirl induction is proposed. Initially, the particle is captured by a swirl. Then, the Sorting Region into which the particle aims to enter is determined according to the sorting condition and particle characteristic. Subsequently, the velocities of the microchannels are adjusted to control the swirl, which will induce the particle to enter its corresponding Induction Region. Thereafter, the velocities are adjusted again to change the fluid field and drive the particle into a predetermined Sorting Region, hence the sorting is accomplished. We have extensively conducted experiments taking particle size or color as a sorting condition. An outstanding sorting success rate of 98.75% is achieved when dealing with particles within the size range of tens to hundreds of micrometers in radius, which certifies the effectiveness of the proposed sorting method. Compared to the existing sorting techniques, the proposed method offers greater flexibility. The adjustment of sorting conditions or particle parameters no longer requires complex chip redesign, because such sorting tasks can be successfully realized through simple microchannel velocities control.

Microparticle Manipulation Performed on a Swirl-Based Microfluidic Chip Featured by Dual-Stagnation Points.

Stagnation-based microfluidics technology is promising for microparticle control due to its noncontact and low cost. However, the current research is still hindered by insufficient pose regulating ability and soft control. Based on our previous work on controlling single particles by generating a swirling flow region (SFR) with a stagnation point in the designed flow field, a new 3-microchannel structure is herein proposed for simultaneous control of two microparticles. It is addressed as the dual-stagnation model because there are two SFRs generated for particle capturing and manipulation. Simulation study is conducted to optimize the fluid field structure and explore the regulation of the two SFRs by adjusting velocities of microchannel inlets. Experiments are carried out on a 3D-printed microfluidic chip to validate the feasibility of the dual-stagnation model and the predicting capacity of the simulations. It is demonstrated that two SFRs with stagnation points are successfully formed in specific locations, indicating that two microparticles can be concurrently captured and controlled. Significantly, the results of simulation and experimental studies agree well with each other referring to flow streamlines and stagnation point regulation. During experiments, it is confirmed that microparticles with different shapes and varied sizes can be captured. Besides, the deviation between the positions of microparticles and the generated stagnation points is characterized to reveal the trapping stability of this microfluidic chip. This work contributes to an advanced flow field structure for swirl-based microfluidic chips and provides insights into soft contact and flexible manipulation of multiple microparticles for revealing the interaction between two bio-/chemical microparticles.

A structure-activity relationship of a thrombin-binding aptamer containing LNA in novel sites.

In this report, structural characterization, aptamer stability and thrombin of a new modified thrombin-ligand complex binding aptamer (TBA) containing anti-guanine bases and a loop position locked nucleic acid (LNA) are presented. NMR, circular dichroic spectroscopy and molecular modeling were used to characterize the three-dimensional structure of two G-quadruplexes. LNA-modification of the anti-guanosines yields G-quadruplexes that show affinity and inhibitory activity toward thrombin, whereas LNA-modification of a thymine nucleotide in the TGT loop increases the thermal stability of TBA. As assessed by denatured PAGE electrophoresis, all modified aptamers display an increase in environmental stability. The prothrombin time assay and fibrinogen assay showed that the aptamers still had good inhibitory activity, and 15 of them had the longest PT time. Therefore, the LNA modification is well suited to improve the physicochemical and biological properties of the native thrombin-binding aptamer.