Imaging of poly(NIPA-co-MAH)-HIgG conjugate with scanning tunneling microscopy

Random copolymers of N-isopropylacrylamide (NIPA) and 2-methacryloylamidohistidine (MAH) with different MAH contents in the range of 0.125-0.725 mmol/g copolymer and with different molecular weights in the range of 62.0-77.5 kg/mol were synthesized by free radical copolymerization. Copolymers were interacted with human immunoglobulin-G (HIgG) in the aqueous medium with different concentrations. FT-IR and NMR data revealed both copolymer and copolymer-HIgG conjugates. The decrease in the lower critical solution temperature (LCST) of the copolymer observed was related with the increase in the HIgG content within the medium. The main goal of this study was imaging poly(NIPA-co-MAH)-HIgG conjugates using Scanning Tunneling Microscopy (STM), which is one of the widely used methods with the capability of atomic level imaging for biological molecules. STM images of the copolymer, HIgG and copolymer-HIgG conjugates were taken at room temperature at atmospheric pressure, using a 1-1.5 V sample bias and a tunneling current of 10-20 pA, which clearly demonstrated the formation of conjugates.