Antibodies and enzymes are currently considered the gold-standard molecular recognition elements as they facilitate the construction of biosensing systems and exhibit high specificity and affinity toward target molecules. However, the low stability of such systems and high associated production cost limit the practical applications of antibodies and enzymes, thereby necessitating the development of alternative molecular recognition elements. Molecularly imprinted polymers (MIPs) are synthetic polymer receptors that are capable of molecular recognition. These polymers contain binding cavities of various shapes and sizes that are complementary to the target molecule and aid in the capture of target molecules. However, although the original procedure for generating MIPs, developed before 2000, is simple, the resulting binding activity and selectivity are inferior to those of antibodies. Meanwhile, post-imprinting modification (PIM) involves site-directed chemical modification of functional monomer residues within the molecularly imprinted cavities to alter MIP functionality. In this review, we provide an overview of sophisticated PIM techniques for developing highly sensitive MIPs that can be used to recognize biomarker proteins. Toward this, we draw heavily on information from our own recent work. This article has the potential to provide important insights that would aid the development of synthetic polymer materials for biosensing.
In this study, solid-phase dispersive extraction (SPDE) was used for serum pretreatment and in the simultaneous analysis of analgesics and adjuvant analgesics (30 types in total) that are usually used as first-and second-choice treatments for pain patients, by liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS). Examination of the optimum conditions for SPDE using Oasis MCX as the solid-phase gel revealed that the recovery rates for serum samples deproteinized in advance were 49–87%, whereas the recovery rates were as high as 78–112% when deproteinization was not performed. The matrix effect was within ±10% regardless of the presence or absence of deproteinization, and its influence could be suppressed even if deproteinization was not performed. The results indicate that serum deproteinization was unnecessary when SPDE was used for pretreatment. In LC/TOF-MS measurement, gradient elution was carried out using core-shell type column Kinetex C18 (150 mm × 2.1 mm, 1.7 µm) as the LC column and 50 mM ammonium acetate buffer (pH 7.8)/acetonitrile/methanol mixture as the mobile phase. The 30 drugs were well separated, and the limit of quantification was 0.25–10 ng/mL, the correlation coefficients of the calibration curves were higher than 0.998, and the average recoveries ranged from 77.7 to 112.1%. The method would be useful to screen for analgesics and adjuvant analgesics (30 types in total) in serum in the fields of forensic science and emergency medicine.
Poly(4-vinylpyridine) (P4VP) was introduced as a stationary phase in liquid chromatography (LC) and the retention behavior of polycyclic aromatic compounds (PACs) on the P4VP phase has been investigated by comparing with that observed on commercially-available octadecylsilica (ODS) and phenylbutylsilica (PBS) phases. On the P4VP phase, a good linear relationship between the logarithmic retention factor and the molecular size of planar PACs was obtained, however, a unique selectivity for some planar PACs was also observed. The P4VP phase demonstrated a specific retention trend, where planar PACs having "square-like" molecular shape were strongly retained. The above trend clearly suggested a unique selectivity of the P4VP phase for PACs. In addition, compared to the typical ODS and PBS phases, the P4VP phase showed a good molecular shape recognition capability for planar/non-planar PACs with a similar two-dimensional molecular size. The P4VP phase showed a very small retention for various alkylbenzenes, suggesting somewhat limited contribution of the hydrophobicity of the analytes to the retention. In the investigation for the selectivity to structural isomers, the P4VP phase exhibited a unique selectivity for isomers of dichlorobenzene and dibromobenzene when compared to the typical ODS and PBS phases. The trend can be interpreted as a dipole-dipole interaction between pyridyl groups in the P4VP ligands and the analyte.
For the HPLC analysis of glycoprotein glycans, oligosaccharides released from glycoproteins are often derivatized with fluorescent tags to achieve quantitative separation. However, the influence of such fluorescent tags on the structure and retention of glycans is not completely understood. Here, to investigate the separation of labeled glycans, we prepared four types of derivatives (2-aminopyridine, 2-aminobenzoic acid, 2-aminobenzamide, and ethyl 4-aminobenzoate) of three model glycans (high-mannose oligosaccharides from ribonuclease B, complex oligosaccharides from bovine fetuin, and an isomaltooligosaccharide mixture). The glycan derivatives were separated on newly developed stationary phases, namely, an amino- and amide-bonded hydrophilic (AAH) phase and a capillary-packed monolithic ODS phase without end-capping treatment. The performance of these phases was compared with typical amide hydrophilic interaction chromatography (HILIC) and end-capped C18 packed columns. In the HILIC separation mode, the AAH column exhibited superior resolution for isomaltooligosaccharides, compared to those obtained on a conventional amide column. Nevertheless, the plate numbers were the same for glycoprotein glycans and the three linkage isomers of Man7GlcNAc2 could not be resolved, whereas they could be separated on the amide column. However, the cationic amino groups of the AAH column enhanced the resolution of sialylated complex glycans that could not be separated on the amide HILIC column. In the reversed-phase separation mode, the retention of glycan derivatives was mainly dependent on the hydrophobicity of the labeling groups. In contrast to the conventional packed ODS column, the monolithic capillary ODS column showed good resolution for neutral glycans.
To improve the detection sensitivity of cationic analytes with simple experimental procedures in microchip electrophoresis (MCE), large-volume sample stacking with an electroosmotic flow (EOF) pump (LVSEP) was performed in polymer-coated microchannels. At first, cationic polybrene (PB) was employed as the coating polymer to reverse the EOF. In the LVSEP analyses, however, the PB-coated microchannel gave insufficient enrichments and broader peaks for cationic standard dyes. By the application of neutral poly(vinyl alcohol) and cationic poly(allylamine) mixture-coating, on the other hand, good enrichments of histamine were achieved by LVSEP with a sensitive enhancement factor of 120.
Atmospheric gaseous alkanes adsorbed onto filter paper during sampling of particulate matter with a diameter less than 2.5 μm (PM2.5) were quantitatively evaluated. Air samples were collected using a high-volume air sampler equipped with a PM2.5 impactor. For the determination of gaseous alkanes adsorbed onto the filter paper, two filter papers were introduced into a air sampler. The PM and gaseous compounds were collected on the upstream filter. Part of the gaseous compounds passed through the upstream filter and were also adsorbed onto the downstream filter. The adsorbed alkanes were eluted using ultrasonication with dichloromethane, and subsequently determined using gas chromatography-mass spectrometry. In this study, the gaseous n-alkanes C13-C30 were determined from the downstream filter, and the adsorption profiles of these gaseous alkanes varied with air sampling volumes. The adsorption and evaporation profiles of the alkanes were also investigated using deuterium alkanes.