Preparation of reversed-phase/boronate affinity mixed-mode restricted access materials with zwitterionic polymer...

High-selectivity and high-exclusion restricted access materials (RAMs) benefit the demands of complex biological samples. In this study, mixed-mode-adsorption RAMs bearing zwitterionic polymer brushes as their outer layers were proposed. The reversed-phase/bronate affinity (RP/BA) mixed-mode adsorption layers on the surface of the silica gel were first formed by surface-initiated atom transfer radical polymerization (SI-ATRP) employing styrene (St) and 4-vinylphenylboronic acid (4-VPBA) as comonomers Afterward, zwitterionic poly(sulfobetaine methacrylate, SBMA) was grafted via another SI-ATRP reaction to establish the external hydrophilic layer. The selectivity of the developed Sil@poly(St-co-4-VPBA)@poly(SBMA) RAMs was examined employing different analytes (benzenes, tetracyclines, neurotransmitters, β-agonists, and their structural analogs), the results revealed the preferential adsorption of substances bearing phenyl and cis-diol groups owing to the multiple interactions (hydrophobic, π-π and BA forces) caused by the RAMs with RP/BA mixed-mode adsorption mechanism. On the other hand, the synergistic effect of the strong-hydrophilicity and high-density zwitterionic poly(SBMA) could efficiently promote the exclusion of RAMs. Moreover, the experimental data revealed that > 99% of bovine serum albumin (BSA, 1 g L^-1) could be excluded, although the tetracycline (50 µg L^-1) was completely adsorbed, indicating the maximized adsorption capacity of the RAMs toward small molecules after the efficient exclusion of protein interference. Solid-phase extraction (SPE) employing the developed Sil@poly(St-co-4-VPBA)@poly(SBMA) RAM coupled with high-performance liquid chromatography (HPLC) was successfully employed to determine the tetracycline content of a milk sample. The established method exhibited satisfactory linearity (10-700 µg L^-1), high recovery (93.1%-108.6%) and good precision (2.6%-8.4%). Finally, our proposed method for synthesizing RAMs could efficiently boost the adsorption selectivity and restricted access function of RAMs, thereby promoting their application in analyzing biological samples.