Squeezing light into
nanometer-sized metallic nanogaps can generate
extremely high near-field intensities, resulting in dramatically enhanced
absorption, emission, and Raman scattering of target molecules embedded
within the gaps. However, the scarcity of low-cost, high-throughput,
and reproducible nanogap fabrication methods offering precise control
over the gap size is a continuing obstacle to practical applications.
Using a combination of molecular self-assembly, colloidal nanosphere
lithography, and physical peeling, we report here a high-throughput
method for fabricating large-area arrays of triangular nanogaps that
allow the gap width to be tuned from ∼10 to ∼3 nm. The
nanogap arrays function as high-performance substrates for surface-enhanced
Raman spectroscopy (SERS), with measured enhancement factors as high
as 10
8
relative to a thin gold film. Using the nanogap
arrays, methylene blue dye molecules can be detected at concentrations
as low as 1 pM, while adenine biomolecules can be detected down to
100 pM. We further show that it is possible to achieve sensitive SERS
detection on binary-metal nanogap arrays containing gold and platinum,
potentially extending SERS detection to the investigation of reactive
species at platinum-based catalytic and electrochemical surfaces.