No abstract

Equipment-free detection devices are attractive for point-of-care analysis, especially in resource-limited regions. Distancebased detection is the measurement of color change along the detection path related to the concentration of analytes. Hydrogels are three-dimensional crosslinked polymer networks with tunable properties and may be suitable for distance-based sensors. However, only small ions have been used as the targets in the previous studies. In this work, we demonstrated the possibility of using hydrogel as the distance-based measurement of large biomolecules such as proteins. The hydrogel was prepared with poly(ethylene glycol) diacrylate and a fluorescein derivative as the fluorescent detection probe. The fluorescent alteration in the presence of a target protein, trypsin, can be observed in both intensity-based and distance-based detection. It was found that the effect of the concentration of a fluorescent reagent was not significantly impacted in distance-based detection, while it is essential in intensity-based detection. The relationship between the distance change and the trypsin concentration in the range of 0.5 -5 mM can be observed. This result showed the possibility of using hydrogel for distance-based detection of large biomolecules.

An on‐line sample preconcentration technique based on transient trapping (tr‐trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr‐trapping‐UV) and electrospray ionization mass spectrometry detection (tr‐trapping‐ESI‐MS). ESI‐MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI‐MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI‐MS system, so its interference in ESI‐MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr‐trapping‐ESI‐MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr‐trapping‐ESI‐MS protocol showed up to 540‐fold enhancements of the peak intensity and 50‐fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.

Molecularly imprinted polymer (MIP) is the superior material with molecular recognition ability that applies to various applications. In order to get high specificity recognition for target molecules, selecting polymerization conditions,...