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Microfluidics-based liquid chromatography is based on the miniaturization of the different types of liquid chromatography (LC) systems (e.g., affinity, adsorption, size exclusion, ion exchange) on a microchip to perform on-chip separation of different types of analytes. On-chip chromatography finds applications in genomics, proteomics, biomarker discovery, and environmental analysis. Microfluidics-based chromatography has good reproducibility and small sample consumption. However, the on-chip chromatography fabrication techniques are often more challenging to perform than conventional LC column preparation. Different research groups have attempted to develop different techniques to fabricate microfluidics-based LC systems. In this review, we will summarize the recent advances in microfluidics-based chromatography.

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Whereas the separation by surface affinity represents an advanced technique for the separation of nanoparticles with distinct surface properties, how the interaction of particles with nanochannel impacts the separation performance is less understood. Herein, the dynamical density functional theory is employed to study the separation of two types of similar-sized particles with different surface affinities within nanochannels.We show that a proper design of the channel inner-surface, which attracts one type of particles while repelling the other, can promote the permeability and selectivity of particles. Meanwhile, the trade-off relations between permeability and selectivity are found and analyzed in nanochannels of different sizes. Based on dynamical density functional theory calculations, an extended model relating permeability to the equilibrium partition coefficient is proposed to analyze the permeability and selectivity, which displays good predictions of the transport of charged particles in comparison with experimental results. This work provides helpful insights for designing an efficient affinity-based separation of nanoparticles process through nanochannels.

It is promising yet challenging to develop efficient methods to separate nanoparticles (NPs) with nanochannel devices. Herein, in order to guide and develop the separation method, the thermodynamic mechanism of NP penetration into solvent-filled nanotubes is investigated by using classical density functional theory. The potential of mean force (PMF) is calculated to evaluate the thermodynamic energy barrier for NP penetration into nanotubes. The accuracy of the theory is validated by comparing it with parallel molecular dynamics simulation. By examining the effects of nanotube size, solvent density, and substrate wettability on the PMF, we find that a large tube, a low bulk solvent density, and a solvophilic substrate can boost the NP penetration into nanotubes. In addition, it is found that an hourglass-shaped entrance can effectively improve the NP penetration efficiency compared with a square-shaped entrance. Furthermore, the minimum separation density of NPs in solution is identified, below which the NP penetration into nanotubes requires an additional driving force. Our findings provide fundamental insights into the thermodynamic barrier for NP penetration into nanotubes, which may provide theoretical guidance for separating two components using microfluidics.