change (that is, the isoelectric point) occurring between
pH 6.5 and 7.0. The results and estimated isoelectric point are
consistent with our electrophoretic mobility measurements
made by using much higher concentrations and larger quantities
of virus. The fact that the p-type nanowire devices show a
reduced (increased) conductivity upon binding of single influenza
A viruses at pH 7 (7) also demonstrates clearly that
detection with the nanowire devices is caused by a field effect
and not a change in capacitance as reported for carbon nanotube
sensors (11). More generally, our results suggest that these
nanowire devices could be used to determine rapidly isoelectric
points for small quantities of viruses and other biomolecules. In
addition, the time scale of the discrete changes in conductance
associated with bindingunbinding depends on pH (Fig. 8),