Surface Modification of Graphene Oxide by Carboxyl-Group: Preparation, Characterization, and Application for Proteins Immobilization

Two-dimensional grapheme offers interesting electronic, thermal, and mechanical properties that are currently being explored for advanced electronics, membranes, and composites. Here we synthesize and explore the biological applications of grapheme oxide. The functionalization chemistry was developed to impart solubility and compatibility of grapheme oxide in biological environments. We found that the global myoglobin (Mb) - grapheme oxide hybrids (Mb-GO) could be successfully prepared by chemical deposition via carboxylic acid modified graphite oxide (GO-COOH) as the intermediate under mild conditions. The functioned grapheme oxide was characterized by many techniques including UV-Vis, FT-IR, Raman, SEM, and TEM. The results indicated that the hydroxyl groups and epoxide groups could be converted to carboxylic acid moieties under strongly basic conditions, and the carboxylic acid modified graphite oxide had increased water solubility and more carboxylic acid groups available for subsequent enzyme immobilization by covalent binding. The average amount of carboxylic acid groups in GO-COOH were determined to be 1.243 mmol in 100 mg GO-COOH by acid-base titration. And the average mole percentage of the carboxylic acid groups on GO-COOH was about 14.9%. The funcitionalization of GO with carboxylic acid groups provided basis for constructing various function materials, including biosensors, enzyme reactors, cellular imaging, and drug delivery.