| Short-chain fatty acids are defined as a class of saturated monocarboxylic acids with less than 6 carbon atoms,which are also the main metabolites of microbiota in human intestine.Recently,plenty of studies have shown that short-chain fatty acids are directly related to human physiology,such as immune response,energy metabolism,and blood pressure egulation.Because of the abundance of acetic acid,propionic acid,and butyric acid in human intestine,acetic acid,propionic acid and butyric acid have also become potential biomarkers of researches related to the effect of microorganisms on human physiological modulation and disease prevention.At present,gas chromatography and liquid chromatography have been hosen as detection methods in most of research.Both of them are time-consuming,costly,and non-portable,which has become an urgent problem in the short-chain fatty acid detection rocess.Therefore,it is of great significance to establish a fast,low-cost and portable short-chain fatty acid detection technology.Based on dynamic surface-enhanced Raman spectroscopy?D-SERS?technology,relevant detection conditions were optimized continuously and 1 mmol/L of acetic acid,propionic acid and butyric acid were detected successfully in the ionized water system.Then,combining D-SERS and liquid-liquid extraction,a rapid detection technology for short-chain fatty acids in a mixed solution system was established,and 1 mmol/L of acetic acid,propionic acid,and butyric acid was successfully detected in the culture medium system.The specific research content is as follows:Firstly,the butyric acid aqueous solution was chosen as the detection object,and its experimental conditions were optimized.1 mmol/L butyric acid was successfully detected,and its characteristic peak position was determined to be 870 cm-1,894 cm-1,930 cm-1,1038cm-1.Under the same conditions,1mmol/L of acetic acid and propionic acid were successfully detected.The characteristic peak of acetic acid was 930 cm-1,and the characteristic peak of propionic acid was 882 cm-1.Secondly,a simple mixed liquid system was formed by mixing a lipopolysaccharide?LPS?aqueous solution with a butyric acid solution.Based on this system,four sample pretreatment methods such as dialysis,ultrafiltration,nanofiltration,and liquid-liquid extraction were screened.A more complicated mixed liquid system was formed by adding the butyric acid aqueous solution to the mixed solution containing yeast extract and peptone,liquid-liquid extraction was determined as the most suitable pretreating method through this system.The process is the anhydrous ether containing butyric acid extracted from culture medium was detected by D-SERS.It only takes 10-15 minutes.Finally,the pH value of mixture was optimized to successfully detect acetic acid,propionic acid,and butyric acid in culture medium.In addition,three kinds of short-chain fatty acids coexisting in the culture medium system were also tested at different pH values.The results showed that the method is most suitable for detecting acetic acid at pH 4.02.When the pH value is 4.02,the main signal is derived from acetic acid in the spectrum,and its peak intensity is the strongest.In this study,a simple and fast D-SERS detection technology for short-chain fatty acids was established,which enabled the rapid detection of millimolar acetic acid,propionic acid,and butyric acid in the culture medium system.Compared with the existing detection technology,this detection technology has apparent advantages in terms of detection time and cost control.It has potential value in biological and clinical application. |
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