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Molecular recognition is a crucial process in biological systems. Natural biomolecules, such as enzymes, antigens, and hormones, exhibit specific interactions with substrates, antibodies, and receptors, which are essential for normal physiological functions. However, these biomolecules often face challenges such as complex preparation, poor stability, and difficulties in storage and handling. To overcome these limitations, molecular imprinting technology has emerged since the 1970s as a powerful method to create polymers with tailored recognition sites. These imprinted polymers offer advantages like high stability, ease of synthesis, and selective molecular recognition. Over time, various preparation methods have been developed, including bulk polymerization [1, 2], suspension polymerization [3, 4], precipitation polymerization [5, 6], and surface polymerization [7, 8]. As a result, molecularly imprinted polymers (MIPs) have found wide applications in chromatographic separation [9, 10], solid-phase extraction [11, 12], chemical sensing [13, 14], and simulated enzyme catalysis [15, 16].
Despite their potential, traditional cross-linking agents used in MIPs are limited, mainly consisting of olefinic compounds that participate in radical polymerization, such as methyl methacrylate, trimethoxypropane trimethacrylate, and divinylbenzene. These cross-linkers typically require organic solvents, which restricts their application. In contrast, the sol-gel technique offers a milder approach, allowing organosilane reagents to undergo hydrolysis in aqueous or organic phases to form high-polymer networks. Many organosilane compounds contain functional groups capable of interacting with imprinted molecules, making them suitable as monomers for MIP synthesis. This has led to rapid development in silicon-based MIPs.
To reduce the "embedding" phenomenon and improve adsorption kinetics, much research has focused on surface imprinting techniques, where MIPs are synthesized on the surface of matrix materials [17–19]. Among the available matrices, silicon-based materials are particularly favored due to their excellent compatibility, mechanical strength, stability, and ease of surface modification. This paper aims to summarize recent advances in the preparation and study of MIPs based on silicon materials.
2 Molecular Imprinting Technology
Molecular imprinting involves the formation of a complex between an imprinted molecule and a functional monomer through reversible interactions. The resulting complex is then polymerized in the presence of a cross-linker to form a highly cross-linked rigid network. After removal of the template molecule, the polymer retains binding sites that can selectively recognize the imprinted molecule among its analogs.
Two main approaches are commonly used in molecular imprinting: covalent and non-covalent methods. The covalent method, introduced by Wulff, involves the formation of a covalent bond between the template and the functional monomer, followed by cleavage of the bond after polymerization. This ensures precise positioning of the binding sites but may limit the speed of template elution. The non-covalent method, proposed by Mosbach, relies on weaker interactions such as hydrogen bonding, hydrophobic effects, and electrostatic forces. This method allows faster binding and recognition, making it more widely used. A hybrid approach combining both strategies is also employed, where the interaction during polymerization is covalent, but recognition occurs via non-covalent means.
3 Preparation of Molecularly Imprinted Polymers Based on Silicon Materials
Since the 1940s, researchers have explored the use of silicon-based materials for MIP preparation. Early work involved using silane as a matrix material, leading to the development of MIPs on surfaces with different morphologies. Today, various techniques are employed, including sol-gel processes, surface grafting, and microfabrication.
3.1 Using Silane as the Imprinted Polymer Matrix
Sol-gel techniques are commonly used to prepare MIPs under mild conditions. For example, Dai et al. [20] prepared a uranium(VI) imprinted silica gel using UO₂(NO₃)₂·6H₂O as the template and tetramethoxysilane as the precursor. The resulting material showed high selectivity for uranium ions compared to non-imprinted samples. Similarly, Collinson et al. [22, 23] used dopamine as the template and phenyltrimethoxysilane as the functional monomer to fabricate a dopamine-imprinted film on an electrode. The film exhibited specific adsorption capacity and could eliminate interferences from ascorbic acid.
3.2 Using Silica Gel as the Matrix
Silica gel is widely used due to its mechanical strength, stability, and ease of surface modification. Surface imprinting on silica gel enhances mechanical properties and reduces the "embedding" effect, improving adsorption kinetics. Various studies have demonstrated the effectiveness of this approach. For instance, Zhang et al. [32] prepared a 2,4,6-trinitrobenzene imprinted polymer on vinyl-functionalized silica nanoparticles, showing high adsorption capacity and fast kinetics. Other researchers have explored the use of silica fibers and monolithic columns as supports for MIPs, further expanding their applications in chromatography and sensing.
4 Applications of Imprinted Polymers Based on Silicon Materials
Silicon-based MIPs have shown great promise in various fields. In chromatographic separation, they serve as efficient stationary phases for selective analysis. In solid-phase extraction, they enable specific enrichment of target analytes, reducing non-specific adsorption. In simulated enzyme catalysis, they mimic enzymatic activity with high selectivity. In electrochemical sensing, they enhance sensitivity and specificity, making them valuable in biosensing and environmental monitoring.
5 Conclusion
Molecularly imprinted polymers based on silicon materials have evolved significantly, from spherical structures to more complex morphologies like nanotubes and porous layers. These advancements have improved mechanical strength, reduced embedding effects, and enhanced adsorption rates. Future research should focus on developing new functional monomers, understanding recognition mechanisms at the molecular level, exploring applications in biomolecule imprinting, and expanding commercial uses of MIPs. With continued innovation, silicon-based MIPs are expected to play an increasingly important role in analytical science and biotechnology.