Directly determining the molecular weight of chitosan with atomic force microscopy

Abstract

Molecular weight will not only affect cytotoxicity, viscosity and other basic properties of molecules in physical and chemical fields, but also influence its efficiency of drug delivery in nanomaterial fields. It is of great importance to measure the molecular weight of a substance. In this study, we proposed a new method to directly determine the molecular weights of polymers with linear and repeated molecular structures. An empirical molecular weight formula of * / o n o M M L L = is the basic knowledge of this new method. The parameters of the repeated molecular unit weight (M o) and (L o) can be calculated according to the polymer's molecular formula. If the individual molecule length of L n can be measured with the instrument of Atomic Force Microscopy (AFM), the molecular weight of W can be obtained with the parameters of L n , M o and L o according to the formula of * / o n o M M L L = . Chitosan with different molecular weights were chosen to value our new proposed method. Our results imply that the molecular weight of chitosan obtained with the new method is reasonable. Moreover, the distributions of molecular weight and molecular lengths can also be acquired at the same time with this novel method.