  Biosensors exploiting long-range surface plasmon polariton (LRSPP) waveguides
comprised of Au stripes embedded in Cytop with integrated and encapsulated
microfluidic channels are fabricated and demonstrated. A fabrication approach
was devised where the lower cladding and recessed Au stripes are fabricated on
a Si substrate, and the upper cladding and microfluidic channels are fabricated
on a glass substrate, followed by wafer bonding to assemble the wafers into
complete structures. The bond is centered over the full length of the optical
path, yet no evidence of optical scattering or excess loss due to the bond
could be observed, and no evidence of a bonding interface could be discerned
from high-magnification cross-sectional images. We also demonstrate wafer-scale
fabrication of in-plane microfluidic inlets and outlets, along with a fixture
for fluidic edge coupling that provides sealed interfaces to external fluidic
tubing and components. In-plane microfluidic interfaces are automatically
defined along chip facets upon wafer dicing, precluding the need to drill
through holes in lids. The performance of the chips was assessed by measuring
the attenuation of LRSPPs on fully cladded reference waveguides, on waveguides
passing through microfluidic channels, and by measuring the response of sensors
to changes in refractive index produced by injecting various sensing solutions.
Our fabrication approach based on wafer bonding and in-plane fluidic
interfacing is compelling for low-cost high-volume manufacturing.
