The same phosphonic acid to In2O3 chemistry, along with the
N-(3-(dimethylamino)propyl)-N′-ethylcarbodiimide hydrochloride
(EDC)/N-hydroxysuccinimide (NHS) coupling to
biomolecules, has been demonstrated in previous studies on
In2O3 nanowire-based devices.3,5 Details of the surface
chemistry and fluorescence confirmation of the phosphonic
acid functionalization can be found in the Supporting
Information. Supporting Information Figure S6a and b show
schematic diagrams of how fluorescent experiments were
performed using biotin and fluorescent dye-tagged streptavidin
as the model probe-analyte system. The negative controls are
anchored with amine poly(ethylene glycol) (PEG) as the probe
instead of biotin. Supporting Information Figure S6c and d
show the substrate schematic diagram and its optical image,
respectively. Supporting Information Figure S6e−h show that
In2O3 ribbons with biotin probes are bright while the ribbons
with amine PEG probes are dark, confirming successful binding
of probe biomolecules using the phosphonic acid chemistry.
These four experiments also show that the phosphonic acid
chemistry will react with the SiO2 substrate, whereas the Si3N4
substrate can be used to suppress such competition binding if
necessary.