Enhancement substrates of gold island films as studied in this work exhibit surface enhanced infrared absorption and are widely used for biosensing. The enhanced infrared absorption is optimized and quantified using thickness gradient substrates of gold island films covered with self-assembled monolayers of 4-mercaptobenzonitrile. Structural and optical properties of the bare and modified enhancement substrates are determined by various methods. A priori indication of the enhancement is obtained by the correlation of effective film thickness and surface enhanced infrared absorption activity. (C) 2016 Elsevier B.V. All rights reserved.