Microfluidic systems have advanced beyond natural and life science applications and lab‐on‐a‐chip uses. A growing trend of employing microfluidic technologies for environmental detection has emerged thanks to the precision, time‐effectiveness, and cost‐effectiveness of advanced microfluidic systems. This paper reviews state‐of‐the‐art microfluidic technologies for environmental applications, such as on‐site environmental monitoring and detection. Microdevices are extensively used in collecting environmental samples as a means to facilitate detection and quantification of targeted components with minimal quantities of samples. Likewise, microfluidic‐inspired approaches for separation and treatment of contaminated water and air, such as the removal of heavy metals and waterborne pathogens from wastewater and carbon capture are also investigated.

Breakup of droplets at bi-layer bifurcating junction in polydimethylsiloxane (PDMS) microchannel has been investigated by experiments and numerical simulation. The pressure drop in bi-layer bifurcating channel was investigated and compared with single-layer bifurcating channel. Daughter droplet size variation generated in bi-layer bifurcating microchannel was analyzed. The correlation was proposed to predict the transition between breakup and non-breakup conditions of droplets in bi-layer bifurcating channel using a phase diagram. In the non-breakup regime, droplets exiting port can be switched via tuning flow resistance by controlling radius of curvature, and or channel height ratio. Compared with single-layer bifurcating junction, 3-D cutting in diagonal direction from bi-layer bifurcating junction induces asymmetric fission to form daughter droplets with distinct sizes while each size has good monodispersity. Lower pressure drop is required in the new microsystem. The understanding of the droplet fission in the novel microstructure will enable more versatile control over the emulsion formation, fission and sorting. The model system can be developed to investigate the encapsulation and release kinetics of emulsion templated particles such as drug encapsulated microcapsules as they flow through complex porous media structures, such as blood capillaries or the porous tissue structures, which feature with bifurcating junctions.

For the past three decades since the dawn of the concept of scaling down fluidic processes and systems, various microfabrication techniques have been significantly explored and developed. Glass and elastomers, as first-generation microfluidic device materials, are still widely used, while other alternatives have emerged. We have seen a rise in novel and innovative device designs and fabrication in droplet microfluidics which enable easier and more cost-effective approach of generating droplets, such as the use of commercially available “off-the-shelf” components, plug-and-play modular devices, and 3D-printed droplet generators. This chapter aims to review some of these facile approaches for droplet generation and discuss the versatility and functionability of these designs for possible commercial formulations. Discussions of rationales for and challenges of the development of these conceptual devices are included.

Ionic liquids (ILs) are attractive reaction media in biocatalysis due to their excellent substrate solubilization properties and their promotion of mild and often environmentally friendly reaction conditions. However, enzyme activity is typically reduced at IL concentrations above 10%. In recent decades, continuous efforts in enzyme engineering have aimed to improve enzyme resistance to ILs, yet achieving robust enzymes remains challenging. In this review, we outline our endeavours over the past decades aimed at improving IL resistance of enzymes. Initially, we conducted systematic research on the interplay between enzymes and ILs, revealing that the primary effect of ILs is to strip water molecules from the enzyme surface. Subsequently, we generated a site saturation mutagenesis (SSM) library of Bacillus subtilis lipase A (BSLA), covering all 181 positions. Based on this library, screening in presence of four [BMIM]-based ILs ([BMIM]Cl, [BMIM]Br,[BMIM]I, and [BMIM][TfO]) revealed the general engineering principle: the hydration shell of enzymes determines their IL resistance. Finally, we designed strategies to identify functional positions for improved IL resistance and to effectively recombine beneficial substitutions. These engineering approaches minimize experimental effort while maximizing enzyme performance in ILs, providing a powerful and broadly applicable framework for the future design of IL-tolerant enzymes.

Biotransformation of naphthalene into phthalic acid via an in vitro multi-enzyme cascade reaction.