High-Efficiency, Matrix Interference-Free, General Applicable Probes for Bile Acids Extraction and Detection

Abstract

Although bile acids (BAs) have been suggested as important biomarkers for endocrine diseases, the identification and quantification of different BAs are still challenges due to their enormous species and wide range concentrations. Herein, a copolymer probe based on β-cyclodextrin (β-CD) is fabricated through a simple in-mold photopolymerization for the selective extraction of BAs. Through the unique stereochemical affinity between BAs and the cavity of β-CD, the custom probe shows superior enriching capacities to series BAs. Moreover, the outstanding extraction ability is proved to be consistent in various interfering conditions, including pH changing and the addition of complex matrix. Further comparison shows that the stereostructure of the nucleus of BAs plays a vital role during the formation of the β-CD/BA complex, indicating the potential for efficient extraction of other BAs, including their structural analogues or some unknown ones. The developed probe is used for solid phase microextraction, and the limits of detection are lower than 0.075 ng mL^-1 by coupling to high performance liquid chromatography-tandem mass analysis. The results in this study highlight the potential for effective improvement of immediate detection and profiling of BAs in real samples, which will make a tremendous impact in the analytical field or clinical diagnosis.

Keywords: bile acid; host–guest interactions; matrix interference‐free; solid phase microextraction; β‐cyclodextrin.

Figure 1

The schematic diagram of fabrication procedure of copolymer probe.

Figure 2

Optimization results by changing the ratio of two monomers for polymerization. Statistics were calibrated by the highest extraction amounts.

Figure 3

a) FT‐IR spectra of ingredient β‐CD, the monomer β‐CD‐MA, and the β‐CD/PEG copolymer. b) TG graphs and c) DTG graphs of as‐prepared monomer (β‐CD‐MA), PEG, and synthesized copolymer (β‐CD/PEG). d,e) SEM images of the whole probe and its surface. f) Contact angel of water on the thin film copolymer.

Figure 4

Extraction capacity comparison between the copolymer probe to commercial SPME fibers (DVB and PA) and two custom fiber (PDDA dispersed PDMS fiber and the pure PEG fiber) (n = 6). Insets are the front view and top view of the β‐CD/UDCA complex obtained by molecular docking.

Figure 5

Extraction amount of the copolymer probe to UDCA under a) pH interfering (statistics were calibrated by the value obtained in solution with pH = 7.4, n = 6), and b) matrix effect (statistics were calibrated by the values obtained in matrix‐free solution, n = 6). c) The general molecular structure of bile acids. d) Extraction amounts of BAs with different nuclear structure on the probe (n = 6). e) Comparison of the affinity of free (UDCA, CA) and conjugated BAs (TUDCA, GCA) to the copolymer probe (statistics were calibrated by the value of the corresponding free BAs, n = 6).

Figure 6

Evaluation of the matrix effect on the total (upper bar charts) and individual extraction amounts of eight studied BAs on the probe (n = 6), statistics in the bottom histogram were calibrated by the values obtained in the matrix free solution respectively.