The paper reports a novel phenothiazine hyper-crosslinked polymer (PTZ-HCP) SPME fiber coating that enables sensitive, precise GC-FID quantification of nine short-chain fatty acids in rat feces and uses the method to show Coptis chinensis alters SCFA levels.

While not a therapeutic study, the work provides a robust analytical tool for measuring gut-derived SCFAs—key gut–brain axis biomarkers linked to Parkinson's disease—facilitating more reliable biomarker studies and evaluation of microbiome-targeted interventions.

Short-chain fatty acids (SCFAs) are key biomarkers of gut microbiota activity and are implicated in various metabolic, inflammatory, and neurological diseases. This study fabricated a phenothiazine-based hyper-crosslinked polymer (PTZ-HCP) and applied it as a solid-phase microextraction (SPME) fiber coating for the analysis of nine SCFAs in rat feces by gas chromatography with flame ionization detection (GC-FID). The prepared PTZ-HCP was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption-desorption measurements, and thermogravimetric analysis. These analyses confirmed its successful synthesis and revealed a porous structure, high specific surface area, and excellent thermal stability. Owing to these structural advantages and the capability for multiple functional groups, the PTZ-HCP coatings demonstrated outstanding extraction efficiency and high adsorption capacity for SCFAs. An SPME/GC-FID method using PTZ-HCP coated fibers were established and validated. The validation results demonstrated significant advantages, including a wide linear range (1.0 × 10-3-0.50 μg mL-1 for 2-methylvaleric acid; 1.0 × 10-3-2.0 μg mL-1 for 4-methylvaleric acid), low LODs (3.0 × 10-4 μg mL-1 for 2-methylvaleric acid and 4-methylvaleric acid), and good precision (≤ 9.5 %). This work presents a novel SPME coating material that effectively addresses key challenges in the extraction and analysis of SCFAs in rat fecal samples. Moreover, it verifies that Coptis chinensis modulates gut microbiota by altering SCFA levels, thereby offering important insights for research on the pathological mechanisms and treatment of Parkinson's disease.