Posted: December 19, 2009

Imec demonstrates high-performance plasmonic nanoslit-cavity devices for molecular detection

(Nanowerk News) Metal-based nanophotonics (plasmonics) is a field concerned with manipulating and focusing light on nanoscale structures that are much smaller than conventional optic components. Plasmonic technology, today still in an experimental stage, has the potential to be used in future applications such as extremely sensitive (bio)molecular sensors, nanoscale optical interconnects for high performance computer chips, and highly efficient thin-film solar cells.
Plasmonic applications can be made from nanostructured (noble) metals. When such nanostructures are illuminated with visible to near-infrared light, the excitation of collective oscillations of conduction electrons – called surface plasmons – generates strong optical resonances, focusing electromagnetic energy in deep-subwavelength-scales. This local field enhancement can be used in spectroscopy technologies, such as SERS, surface-enhanced infrared spectroscopy, and surface-enhanced fluorescence emission.
SERS is a powerful approach for molecular detection, and one of the core analytical technologies in (bio)chemical sensors. It requires a high-performance plasmonic nanostructure with an extremely high field enhancement factor and spatial resolution. This results in extremely high sensitivity, detecting the chemical fingerprint of the analytes. In some case, it can even achieve single molecule level detection.
However, the high-performance plasmonic nanostructures currently used in SERS are mainly randomly formed colloidal aggregates or rough surfaces. They do not allow a good reproducibility of molecular detection experiments. Therefore, imec’s rationally designed plasmonic nanostructure with a high SERS performance is an important achievement.
Imec’s plasmonic nanostructure for SERS is based on a gold nanoslit exhibiting both a high SERS enhancement factor (>106) and a high spatial resolution (<10nm). This device has been fabricated starting from a SOI wafer, proceeding by standard micromachining processes. The strong SERS enhancement factor was studied by using a self-assembled monolayer of 4-amiothiophenol. The nanoslit-cavity itself can already generate a strong enhancement. With the presence of the periodic nanoantennas around it, the performance can be further improved. The second requirement, the high spatial resolution was studied by using a modified electron beam induced deposition (EBID) of carbonaceous nanoparticles. The small particles can be selectively placed inside and outside the field enhanced region of SERS. The significant distinction among the corresponding SERS spectra proves the localization of the enhanced region at ~10nm, meaning the high spatial resolution of the nanoslit-cavity device in a SERS application.
Imec’s results are published recently online on Small and Angew. Chem. Int. Ed.
Beyond the performance study of the device, this work was also commented as an important stepping stone in SERS dispute, citing a reviewer: ‘it is a welcome final punctuation to those who flog the localized SERS’.
Source: Imec