Langmuir 2002, 18, 4071-4081
4071
Elasticity of Pseudomonas putida KT2442 Surface Polymers Probed with Single-Molecule Force Microscopy Nehal I. Abu-Lail and Terri A. Camesano* Worcester Polytechnic Institute, Department of Chemical Engineering, 100 Institute Road, Worcester, Massachusetts 01609 Received November 25, 2001. In Final Form: February 21, 2002
Single-molecule force microscopy was used to study the effect of solvent polarity and ionic strength on the elasticity of bacterial surface polymers. Adhesion forces were measured between Pseudomonas putida KT2442 bacterial cells and silicon nitride tips of an atomic force microscope (AFM). Force-extension profiles were analyzed to determine the elasticity of the polymer chains in several solvents (water, formamide, methanol, 0.1 M KCl, and 0.01 M KCl). Adhesion peaks were fit to entropic-based, statistical mechanical, random walk formulations (the freely jointed chain (FJC) and the wormlike chain (WLC) models). The experimental data showed better agreement with the FJC (average R2 ) 0.86 ( 0.20) than the WLC model (average R2 ) 0.76 ( 0.22). The segment length was 0.18-1.0 nm in all five solvents using the FJC model, with about 60% of the chains having a segment length of 0.154-0.20 nm. The persistence length was 0.18-0.83 nm using the WLC model, with about 78% of chains having a persistence length of 0.154-0.20 nm. The WLC model was not able to represent polymer properties for chains of
