基于原子力显微镜研究黄原胶分子结构的云母片处理方法优化

Optimization of Mica Processing Method Based on Atomic Force Microscopy to Study the Molecular Structure of Xanthan Gum

原子力显微镜(Atomic Force Microscopy,AFM)成像常用于研究多糖分子结构,然而针对阴离子多糖,现有的制样方法较难在小范围观察区获得其清晰的单分子束结构图片。因此,本文以黄原胶为阴离子多糖代表,从不改变多糖本身结构、提升成像质量角度出发,对多糖样品浓度,云母片不同金属离子盐种类、浓度和处理时间等AFM制样方法进行了优化。结果表明,在空白云母片上,黄原胶浓度1~5μg/mL时可观测到多糖单分子束结构,但在15μm×15μm扫描范围内可观测的分子束较少。通过对云母片进行处理优化,最佳处理条件选定在0.5 mmol/L的CaCl_(2)溶液处理2 min或2 mmol/L CaCl_(2)溶液处理0.5 min。在此条件下,当黄原胶浓度为5μg/mL时,在3μm×3μm观测范围内,处理后云母片上的黄原胶分子束数量及成像质量相比空白云母片显著提升,且其单分子束高度与分子结构并未发生改变。此外,通过提高云母片干燥温度可以获取更均匀的黄原胶分子结构图片。本研究可为其他阴离子多糖AFM成像的样品制备提供可借鉴的方法参考。

Atomic Force Microscopy imaging is generally used for investigating the molecular structure of polysaccharides.However,for ionic polysaccharides,it is still difficult to obtain clear images with monolayer structure under the limited observation region based on the reported sample treatment methods.Taking xanthan gum as the typical ionic polysaccharide,in order to improve the image quality without changing the structure of polysaccharide,the sample preparation procedures were optimized,including sample concentration,variety and concentration of salt ions,and treatment time.The results showed that monolayer structure of xanthan was observed on clear mica when xanthan concentration was 1~5μg/mL.However,the observed monolayer structure became much less when the observation region was 15μm×15μm.Then,the mica was treated and the treatment conditions were optimized.The optimized treatment conditions were selected as 2 min treatment by using 0.5 mmol/L calcium chloride solution or 0.5 min treatment by using 2 mmol/L calcium chloride solution.Under this condition,the molecular structure of 5μg/mL xanthan gum was observed.The results illustrated that the number of monolayer xanthan gum molecular chains greatly increased within the observation region of 3μm×3μm,as compared with that on the untreated mica.Meanwhile,the treatment of mica could keep the height and morphology of monolayer structure of xanthan gum.In addition,the images of monolayer structure with more homogenous distribution could be obtained by increasing the drying temperature for mica.This study could provide an experimental reference for the sample preparation of other anionic polysaccharide in AFM imaging.