An oxidative stress (OS) state is characterized by the generation of Reactive Oxygen Species (ROS) in a biological system above its capacity to counterbalance them . Exposure to OS induces the accumulation of intracellular ROS, which in turn causes cell damage in the form of protein, lipid, and/or DNA oxidations. Such conditions are believed to be linked to numerous diseases or simply to the ageing of tissues. However, the controlled generation of ROS via photosensitizing drugs or photosensitizers (PS) is now widely used to treat various tumors and other infections [2,3]. Here we present a method to track the chemical changes in a cell after exposure to oxidative stress. OS is induced via fullerols, a custom made water soluble derivative of fullerene (C-60), under visible light illumination. Synchrotron-based Fourier Transform InfraRed Microspectroscopy (S-FTIRM) was used to assess the chemical makeup of single cells after OS exposure. Consequently, a chemical fingerprint of oxidative stress was probed in this study through an increase in the bands linked with lipid peroxidation (carbonyl ester group at 1740 cm(-1)) and protein phosphorylation (asymmetric phosphate stretching at 1240 cm(-1)). (C) 2010 Elsevier B.V. All rights reserved.