Selective detection, the ability to specifically distinguish one
type of virus from another, is crucial for exploiting the high
sensitivity of these nanowire devices in most medical and
biothreat applications. Selectivity was first investigated by characterizing
how variations in the density of the influenza A
antibody receptors affect the bindingunbinding properties.
Simultaneous conductance and optical data recorded on devices
with average antibody coverage 10 times higher than above
(Fig. 4A and Movie 2, which is published as supporting information
on the PNAS web site) show sequential binding of virus
particles without unbinding on a 5- to 10-min time scale (vs.
unbinding on a 20-s time scale in Fig. 3). Sequential unbinding
of the viruses is observed after introducing pure buffer solution.
These data show that the unbinding kinetics can be substantially
slowed through increases in the density of specific antibodies and
provide strong evidence for selective binding of influenza A; that
is, the unbinding kinetics should be slowed as the number of
specific antibody–virus contact points increases.