Riboflavin (vitamin B2), a cis-diol-containing compound, is an essential vitamin for maintaining human health mainly in energy metabolism and is a critical component of enzyme cofactors and flavoproteins. Thus, the determination of riboflavin in food products is essential in riboflavin-fortified foods. However, analysis of riboflavin at natural levels in foods or biological samples is difficult because of its very low concentration level and the presence of undesirable matrix effects which could interfere with the measuring system. Thus, it is essential to develop efficient and selective enrichment approaches for riboflavin. Molecularly imprinted polymers can be well used for riboflavin extraction and pre-concentration from food samples. In this study, we present riboflavin-imprinted magnetic nanoparticles as an ideal sorbent for the selective enrichment of riboflavin followed by direct fluorometric determination. The riboflavin-imprinted magnetic nanoparticles were prepared according to a newly reported strategy, called boronate affinity-based surface initiated imprinting. Magnetic nanoparticles and vinylphenylboronic acid were used as supporting materials and a functional monomer, respectively. The prepared riboflavin-imprinted magnetic nanoparticles exhibited several significant advantages, such as excellent selectivity, high binding affinity and low binding pH toward riboflavin, which made the molecularly imprinted material become an ideal sorbent for the selective enrichment of riboflavin. The prepared riboflavin-imprinted magnetic nanoparticles were successfully applied to the analysis of riboflavin in milk.

Boronate affinity materials, as efficient sorbents for extraction, separation and enrichment of glycoproteins, have attracted more and more attention in recent years. However, conventional boronate affinity materials suffer from low binding affinity due to the use of single boronic acids, which makes the extraction of glycoproteins in trace concentration rather difficult or impossible. Here we present a type of high boronate avidity material, polyethyleneimine (PEI)-assisted boronic acid-functionalized magnetic nanoparticles (MNPs). Branched PEI was used as a scaffold to amplify the number of boronic acid moieties, while 2,4-difluoro-3-formyl-phenylboronic acid (DFFPBA), exhibiting high affinity and excellent water solubility toward cis-diol-containing compounds, was employed as an affinity ligand. Due to the PEI-assisted synergistic multivalent binding, the boronate avidity MNPs exhibited a high binding affinity toward glycoproteins with dissociation constants of 10⁻⁶–10⁻⁷ M, which was the highest among the reported boronic acid-functionalized materials that can be applied for a glycoproteomic analysis. Such an avidity enabled the selective extraction of trace glycoproteins as low as 2 × 10⁻¹⁵ M. This feature greatly favored the selective enrichment of trace glycoproteins from real samples. Meanwhile, the boronate avidity MNPs were tolerant to the interference of abundant sugars. In addition, the PEI-based boronate avidity MNPs exhibited high binding capacity and low binding pH. The feasibility for practical applications was demonstrated with the selective enrichment of trace glycoproteins in human saliva.

Many glycoproteins can be used as disease biomarkers for early clinical diagnostics and treatment of diseases. Selective enrichment is critical for the analysis of glycoproteins. Molecularly imprinted polymers (MIPs) have found important applications in the separation and enrichment of glycoproteins. However, template immobilization-based boronate affinity surface imprinting has not been used to prepare glycoprotein-imprinted silica nanoparticles using a new hydrophilic imprinting coating, poly(4-aminobenzyl alcohol). In this study, we use this imprinting strategy to prepare boronate affinity-based molecularly imprinted silica nanoparticles using poly(4-aminobenzyl alcohol) as an imprinting coating. After a glycoprotein template was covalently immobilized onto the surface of boronic acid functionalized silica nanoparticles, a thin imprinting coating of poly(4-aminobenzyl alcohol) was formed to cover the silica nanoparticle surface via in-water self-polymerization. After removing the template with an acidic solution, 3D cavities were formed in the imprinting layer. The imprinting coating was highly hydrophilic and presented limited residual boronic acid and therefore non-specific binding was avoided. The MIPs prepared under the optimal conditions exhibited several highly favorable features, including excellent specificity, a high binding strength of (0.71 ± 0.06) × 10⁻⁷ M and a low binding pH of 5.0. The MIPs prepared using this method were successfully applied in the determination of a TRF concentration of 2.75 ± 0.25 mg mL⁻¹ in human serum.

Novel boronate affinity-based surface-imprinted CdTe quantum dots (BA-CdTe@MIPs QDs) were fabricated to develop a selective and sensitive fluorescent nanosensor for the rapid and efficient detection of rutin. The boronate affinity-based MIP and CdTe quantum dots were used as recognition elements and signal-transduction materials, respectively. The MIPs ensure specificity, while the fluorescence detection provides sensitivity. Under the optimum conditions, the imprinting factor (IF) was evaluated to be 6.51, which implies that a lot of specific binding sites in BA-CdTe@MIPs QDs could be successfully established from the surface imprinting. The obtained BA-CdTe@MIPs QDs exhibited excellent selectivity and high sensitivity for rutin molecules. The relative fluorescence intensity of the BA-CdTe@MIPs QDs decreases linearly with an increasing concentration of rutin in the 0.1–30 μM concentration range, and the detection limit is 0.04 μM. The developed nanosensor was successfully applied to the detection of rutin in fruits, vegetables and medicinal plants. Good recoveries ranging from 94.0 to 101.1% with relative standard deviations (RSDs) below 1.63% were obtained. This study provides a facile and efficient fluorescence tool for rutin detection in real samples. In addition, this method also opens up new avenues for the rapid and efficient determination of cis-diol-containing flavonoids, such as rutin.