An optical sensor is provided, comprising (a) a silicon nanowire of finite
length having an electrical contact pad at each end thereof; and (b) a
plurality of self-assembled molecules on a surface of the silicon
nanowire, the molecules serving to modulate electrical conductivity of
the silicon nanowire by either a reversible change in dipole moment of
the molecules or by a reversible molecule-assisted electron/energy
transfer from the molecules onto the silicon nanowire. Further, a method
of making the optical sensor is provided. The concept of molecular
self-assembly is applied in attaching functional molecules onto silicon
nanowire surfaces, and the requirement of molecule modification (hydroxy
group in molecules) is minimal from the point view of synthetic
difficulty and compatibility. Self-assembly will produce well-ordered
ultra-thin films with strong chemical bonding on a surface that cannot be
easily achieved by other conventional methods.