The samples were divided into two sets, one for the spectroscopic measurements and the other, for centrifugation. The samples in the latter set were subjected to centrifugation for 1 hour at 12500 rpm using an Eppendorf centrifuge 5430. The supernatant liquids were collected and were considered to be the dispersing media for the respective NP samples. This protocol was tested, using UV-visible spectroscopy, to be satisfactory for adequate removal of Au NPs from the dispersing medium (figure ). The supernatant liquid separated from each of the samples were further measured under the same spectroscopic conditions as used for the Au NP samples in the NP10, NP30 and NP50 series.