Metal oxide surfaces for enhanced colorimetric response in bioassays.

Physical stability of metal nanoparticle films on planar surfaces can be increased by employing surface modification techniques and/or type of metal nanoparticles. Subsequently, the enzymatic response of colorimetric bioassays can be increased for improved dynamic range for the detection of biomolecules. Using a model bioassay b-BSA, three planar platforms (1) poly (methyl methacrylate) (PMMA) with silver thin films (STFs), (2) silver nanowires (Ag NWs) on paper and (3) indium tin oxide (ITO) on polyethylene terephthalate (PET) were evaluated to investigate the extent of increase in the colorimetric signal. Bioassays for b-BSA and Ki-67 antigen (a real-life bioassay) in buffer were performed using microwave heating (total assay time is 25-30min) and at room temperature (a control experiment, total assay time is 3h). Model bioassays showed that STFs were removed from the surface during washing steps and the extent of ITO remained unchanged. The lowest level of detection (LLOD) for b-BSA bioassays were: 10-10M for 10nm STFs on PMMA and Ag NWs on paper and 10-11M for ITO. Bioassays for Ki-67 antigen yielded a LLOD of <10-9M on ITO platforms, while STFs platforms were deemed unusable due to significant loss of STFs from the surfaces.