Carboxyalkanethiols are utilized for the modification of a gold surface to introduce carboxylic groups on it. The carboxylic group is often converted to activated N-hydroxysuccinimide ester, which reacts with an amine group of biomaterials. Dojindo’s newly developed 15-Carboxy-1-pentadecanethiol has a 15-carbon chain, which is the longest alkanethiol available in the market among carboxyalkanethiols. Five different carboxyalkanethiols including Carboxy-EG6-undecanethiol are available for gold surface modification. Malone and others fabricated a highly sensitive SPR sensor using 15-Carboxy-1-pentadecanethiol.