Observations of phase changes in monoolein during high viscous injection.

Serial crystallography of membrane proteins often employs high-viscosity injectors (HVIs) to deliver micrometre-sized crystals to the X-ray beam. Typically, the carrier medium is a lipidic cubic phase (LCP) media, which can also be used to nucleate and grow the crystals. However, despite the fact that the LCP is widely used with HVIs, the potential impact of the injection process on the LCP structure has not been reported and hence is not yet well understood. The self-assembled structure of the LCP can be affected by pressure, dehydration and temperature changes, all of which occur during continuous flow injection. These changes to the LCP structure may in turn impact the results of X-ray diffraction measurements from membrane protein crystals. To investigate the influence of HVIs on the structure of the LCP we conducted a study of the phase changes in monoolein/water and monoolein/buffer mixtures during continuous flow injection, at both atmospheric pressure and under vacuum. The reservoir pressure in the HVI was tracked to determine if there is any correlation with the phase behaviour of the LCP. The results indicated that, even though the reservoir pressure underwent (at times) significant variation, this did not appear to correlate with observed phase changes in the sample stream or correspond to shifts in the LCP lattice parameter. During vacuum injection, there was a three-way coexistence of the gyroid cubic phase, diamond cubic phase and lamellar phase. During injection at atmospheric pressure, the coexistence of a cubic phase and lamellar phase in the monoolein/water mixtures was also observed. The degree to which the lamellar phase is formed was found to be strongly dependent on the co-flowing gas conditions used to stabilize the LCP stream. A combination of laboratory-based optical polarization microscopy and simulation studies was used to investigate these observations.

Recent Advances and Future Perspectives on Microfluidic Mix-and-Jet Sample Delivery Devices.

The integration of the Gas Dynamic Virtual Nozzle (GDVN) and microfluidic technologies has proven to be a promising sample delivery solution for biomolecular imaging studies and has the potential to be transformative for a range of applications in physics, biology, and chemistry. Here, we review the recent advances in the emerging field of microfluidic mix-and-jet sample delivery devices for the study of biomolecular reaction dynamics. First, we introduce the key parameters and dimensionless numbers involved in their design and characterisation. Then we critically review the techniques used to fabricate these integrated devices and discuss their advantages and disadvantages. We then summarise the most common experimental methods used for the characterisation of both the mixing and jetting components. Finally, we discuss future perspectives on the emerging field of microfluidic mix-and-jet sample delivery devices. In summary, this review aims to introduce this exciting new topic to the wider microfluidics community and to help guide future research in the field.

Mixing and jetting analysis using continuous flow microfluidic sample delivery devices.

Serial femtosecond crystallography (SFX) methods used at X-ray free electron lasers (XFELs) offer a range of new opportunities for structural biology. A crucial component of SFX experiments is sample delivery. Microfluidic devices can be employed in SFX experiments to precisely deliver microcrystals to the X-ray beam and to trigger molecular dynamics via rapid mix-and-inject measurements. Here, for the first time, we have developed a process based on high-resolution photolithography using SU8 on glass to fabricate microfluidic mix-and-inject devices. In order to characterise these devices a broad range of flow rates are used and the mixing and jetting response of the devices monitored. We observe that a stable jet is formed using these devices when injecting DI-water. Three different jetting regimes, liquid column, ribbon, and cylindrical jet, were observed. Furthermore, fluorescence experiments confirm that rapid and uniform mixing of the two injected solutions is possible using these devices indicating that they could be used to probe molecular dynamics on sub-microsecond timescales.

Magnetofluidic concentration and separation of non-magnetic particles using two magnet arrays.

The present paper reports the use of diluted ferrofluid and two arrays of permanent magnets for the size-selective concentration of non-magnetic particles. The micro magnetofluidic device consists of a straight channels sandwiched between two arrays of permanent magnets. The permanent magnets create multiple capture zones with minimum magnetic field strength along the channel. The complex interaction between magnetic forces and hydrodynamic force allows the device to operate in different regimes suitable for concentration of non-magnetic particles with small difference in size. Our experimental results show that non-magnetic particles with diameters of 3.1 µm and 4.8 µm can be discriminated and separated with this method. The results from this study could be used as a guide for the design of size-sensitive separation devices for particle and cell based on negative magnetophoresis.

Negative magnetophoresis in diluted ferrofluid flow.

We report magnetic manipulation of non-magnetic particles suspended in diluted ferrofluid. Diamagnetic particles were introduced into a circular chamber to study the extent of their deflection under the effect of a non-uniform magnetic field of a permanent magnet. Since ferrofluid is a paramagnetic medium, it also experiences a bulk magnetic force that in turn induces a secondary flow opposing the main hydrodynamic flow. Sheath flow rate, particle size, and magnetic field strength were varied to examine this complex behaviour. The combined effect of negative magnetophoresis and magnetically induced secondary flow leads to various operation regimes, which can potentially find applications in separation, trapping and mixing of diamagnetic particles such as cells in a microfluidic system.

Lab on a chip for continuous-flow magnetic cell separation.

Separation of cells is a key application area of lab-on-a-chip (LOC) devices. Among the various methods, magnetic separation of cells utilizing microfluidic devices offers the merits of biocompatibility, efficiency, and simplicity. This review discusses the fundamental physics involved in using magnetic force to separate particles, and identifies the optimisation parameters and corresponding methods for increasing the magnetic force. The paper then elaborates the design considerations of LOC devices for continuous-flow magnetic cell separation. Examples from the recently published literature illustrate these state-of-the-art techniques.