Pickering emulsion-based molecular imprinting

Abstract

Due to the specific recognition ability of the target molecules, molecularly imprinted polymers (MIPs) have been widely used in many fields. So far, the research in molecular imprinting mainly focused on two aspects: (1) synthesis of MIPs with more functions; (2) expanding applications of the traditional MIPs, especially for MIPs synthesized by precipitation polymerization. To address these points, our group recently introduced a new insight in molecular imprinting based on Pickering emulsion: (1) Pickering emulsion polymerization could be used to the synthesize water-compatible MIP spheres with well-controlled structures; (2) MIP nano/microparticles stabilized emulsions were introduced to molecular imprinting to endow the MIP particles with more functions, or to create new interfacial binding or catalytic systems for MIP nano/microparticles. It is noted that, although the first molecular imprinting in Pickering emulsion has been presented for only a few years, the publications in this field increased very fast. In this review, we summarized the synthesis of MIP spheres via Pickering emulsion polymerization, and discussed the advantages and limitations of this synthesis method. Due to the unique properties of the particle stabilized emulsion, the imprinted systems offered several advantages to the resulted MIP spheres, and which could be further utilized to solve the long-tern challenges in imprinting of small molecules: (1) well-designed hierarchical structures (surface nano-pores from the particle stabilizers and accessible molecular binding cavities from the templates); (2) group recognition of a series of chemicals with a similar moiety (epitope imprinting); and (3) specific recognition capability in aqueous conditions because of the hydrophilic surface of the MIPs. Moreover, for imprinting biomacromolecules and other large templates (virus particles, bacteria and animal cells), Pickering emulsion was also particularly interesting, because the templates themselves could be directly used as solid stabilizers to synthesis Pickering emulsion, and thus created accessible surface imprinted sites for the recognition. In this review, we also demonstrated that MIP nano/microparticles stabilized emulsions were promising interfacial systems in molecular imprinting. On one hand, this emulsion could be utilized for the fabrication of functional materials with pre-designed recognition ability towards the target molecules. As examples, the Janus MIP particles, which displayed attractive abilities as self-propelled transporters for controlled drug delivery, could be prepared via a wax-water Pickering emulsion. Multifunctional colloidosomes, which showed both specific molecular recognition of the MIP nanoparticles and dose-dependent fluorescence response to fructose, could be synthesized by using W/O Pickering emulsions stabilized by clickable nanoparticles: Alkyne-coated MIP nanoparticles and azide-modified nanoparticles, followed by an interfacial click reaction. On the other hand, the introduction of Pickering emulsion expanded tha application environment of the traditional MIP nano/microparticles to a oil-water interface. For example, MIP microgel stabilized Pickering emulsions with the capability to catalyze the formation of disulfide bonds in peptides at the O/W interface has been reported recently. These works system will greatly promote the application of molecular imprinting in various fields such as organic synthesis, disease diagnosis, proteomics and bio-imaging Moreover, we discussed the prospects of the applications of molecular imprinting in Pickering emulsion in a near future, (1) uniform MIP spheres should be fabricated by optimizing the emulsion systems and choosing suitable reactors; (2) stable Pickering emulsion systems should be developed for biomacromolecular imprinting, such as proteins, micro organisms and human cells; (3) MIP nano/microparticles prepared by Pickering emulsion should be designed for immunoassay, biomedicine, environmental governance and chemical catalysis. As a summary, we believed that molecular imprinting in Pickering emulsion provided a facile synthetic approach for producing new functional materials, as well as an interfacial binding or catalytic environment for appilication of the traditional MIP nano/microparticles. All these works show great potential in clinical pathogenic screening, noninvasive detection and drug delivery.