A nanoscale layer of chromium or titanium is commonly used in plasmonic nanoantennas to firmly adhere a gold film to a glass substrate, yet the influence of this layer on the antenna performance is often ignored. As a result, the need for the use of potentially better materials is not widely recognized.
Using a single nanoaperture milled in a gold film with 120 nm diameter as a nanobench for these investigations, we present the first experimental report of the strong dependence of the plasmonic enhancement of single-molecule fluorescence on the nature of the adhesion layer. By combining fluorescence correlation spectroscopy and fluorescence lifetime measurements, we show that this structure is very sensitive to the properties of the adhesion layer, and we detail the respective contributions of excitation and emission gains to the observed enhanced fluorescence.
Any increase in the absorption losses due to the adhesion layer permittivity or thickness is shown to lower the gains in both excitation and emission, which we relate to a damping of the energy coupling at the nanoaperture.
With this nanobench, we demonstrate the largest enhancement factor reported to date (25×) by using a TiO2 adhesion layer. The experimental data are supported by numerical simulations and argue for a careful consideration of the adhesion layer while designing nanoantennas for high-efficiency single-molecule analysis.
The editorial staff at ACS Nano choose to write a short niews & views on this paper, "Plasmonic Nanoantennas: Tuning in on the Adhesion Layer", see the link here.
Reprints can be ordered via my group's website Mosaic.
Porteur : Jérôme Wenger, Institut Fresnel / CNRS UMR6133
Partenaire : Christian Dominici, CP2M / Université Aix-Marseille III
See the link
My team is conducting a partnership with PicoQuant GmbH for fluorescence lifetime measurements with time-correlated single photon counting.
As a brief summary, we operate the following PicoQuant devices :
- LDH-P-635 picosecond laser diode working at 636 nm (special spectral selection has been set for free) + Laser diode driver SEPIA-II-SLM828
- Micro Photon Devices MPD-5CTC fast avalanche photodiode, with timing jitter about 50 ps and active area 50 μm
- PicoHarp 300 fast TCSPC module (resolution per channel 4 ps)
Overall, the best temporal resolution of our setup is 120 ps FWHM. We’re pretty pleased with that materials.
Once you get accustomed to TCSPC concepts (which may be a bit tricky at the beginning), the use of PicoQuant systems is very intuitive and efficient.
Our latest paper has been published in the July issue of the Journal of the Optical Society of America B. Free reprints for personal use only are available on our group website here.
In this manuscript, we investigate the interaction between a dipolar emitter and a dielectric microsphere under focused laser illumination. We present a detailed experimental analysis of the fluorescence emission characteristics, and relate our observations to numerical simulations.
Our findings demonstrate that the microsphere acts as a microlens placed in the emitter's near-field, allowing a more efficient focusing of the incident beam as well as increasing the collection of the fluorescence light up to 60% of the total emission. That last figure is more than all the emission normally emitted in the half-space towards the detectors.
This simple scheme outperforms the classical diffraction-limited detection of fluorescent particles, and opens new opportunities for low-cost and highly parallel single-molecule investigations.