The cRGD-EtNBS-PEG construct is an effective PDT agent. No treatment cells (NT), cells given the cRGD-EtNBS-PEG construct only (PS only), and cells given cRGD only were not exposed to light. Cells treated with unPEGylated cRGD-EtNBS (−PEG) or the full construct EtNBS-cRGD-PEG (+PEG) were irradiated with 660 nm light at 100 mW/cm2 for a total dose of 100 J/cm2. The far-right bar corresponds to cells first pre-incubated with free cRGD before treatment with EtNBS-cRGD-PEG and subsequent irradiation (100 J (+PEG) + cRGD). Percentage cell viability as determined by the MTT assay is plotted for each group. All experiments were carried out in triplicate; the data presented is the mean of the measurements with the error bars are derived from the standard deviation. The 100 J +PEG treatment condition was found to be statistically significant against all other conditions by t-test (p < 0.05).