Ultraviolet plasmonics has attracted recently a growing attention owing to the possibility to take advantage of increased light-matter interaction in the UV range. However, the core question of demonstrating the capacity of UV plasmonic structures to enhance the radiative emission rate of proteins has remained unproven yet.
In a recent article published in J . Phys D Appl. Phys, we report the first complete demonstration of the Purcell radiative rate enhancement for label-free proteins in plasmonic aluminum nanoapertures. Regardless of the complexity of protein structure and its low intrinsic emission quantum yield, we can clearly show that the aluminum plasmonic nanoapertures can significantly enhance the spontaneous UV emission rate of proteins. Our results show that concepts developed for single quantum sources in the visible can still be applied on complex proteins containing thousands of aminoacids.
Open access paper also freely available on arXiv 2107.06357
What happens when you shine a UV laser onto a single aluminum nanohole filled with water? See the video below of the experiment, accelerated 5x. Holes get brighter once exposed to the laser: this is laser-induced corrosion of the aluminum film by water molecules. It is not direct laser damage (we use a power of 60 µW, 3x below the direct photodamage threshold). This photocorrosion is very general once aluminum, water and UV laser are present, which correspond to 99% of the biosensing applications of UV plasmonics.
In a recent publication in ACS Applied Nano Materials, we use various metal oxides layers deposited by atomic layer deposition (ALD) or plasma-enhanced chemical vapor deposition (PECVD) on top of the aluminum to protect against UV photocorrosion. We discuss the best material choice, and report the influence of different experimental conditions. Choosing the optimum protection and conditions significantly extends the corrosion resistance by more than 20x.
This approach is the key to extend plasmonics into the UV range in water-based environments. We apply it to demonstrate the label-free UV detection of streptavidin proteins. Alternatively, the ALD/PECVD approach also improves the long-term corrosion resistance of Al structures in corrosive chloride solutions.
Preprint freely available on arXiv 2106.09392.
Our team-member Aleksandr Barulin recently got awarded the thesis prize of the Doctoral School "Physics and Sciences of the Matter" for his PhD work. Congratulations Aleksandr for this well-deserved prize!
Complete Electromagnetic Dyadic Green Function Characterization in a Complex Environment—Resonant Dipole-Dipole Interaction and Cooperative Effects
The Green function plays a central role in wave propagation, as it describes the response of a system to an arbitrary impulse. However, measuring it experimentally is very challenging since it needs to be measured in both amplitude and phase with deep subwavelength spatial resolution. These highly demanding requirements have significantly limited the experimental attempts towards measuring the Green function in optics.
In a recent Phys Rev X publication, we describe a method to measure both the real and imaginary parts of the Green function by recording the mutual impedance between two dipoles at microwave frequencies. The effectiveness of this approach is demonstrated by the full characterisation of the complex Green function inside a resonant planar cavity of parallel or non-parallel mirrors at a ultrahigh resolution 100x below the wavelength. With this data, we are able to investigate various aspects of resonant dipole-dipole interaction and cooperative effects inside a photonic cavity.
- We develop a new general methodology to fully measure the Green function in both amplitude and phase at ultrahigh spatial resolution.
- Our technique provides a powerful way to solve problems for which no analytic solution exists and where numerical simulations demand excessive computational resources.
- We characterize cooperative effects such as superradiance and cooperative Lamb shift inside a cavity which is relevant for various communities such as cavity QED, photovoltaics and nanophotonics.
Plasmonic nano-optical tweezers offers unprecedented abilities to manipulate nano-objects. However, measuring the trap stiffness at nanoscale dimensions remains a technical challenge, and as a consequence, very few reports have explored plasmonic designs to optimize their trapping performance.
In a recent publication released in Nanoscale, we detail a new approach to measure the trap stiffness taking advantage of the fluorescence emission of the trapped nanoparticle used for calibration. We relate our measurements to numerical simulations, and provide simple rules to optimize the design of the plasmonic structure to improve its trapping performance.
- We optimize the design of double nanohole apertures used for plasmonic trapping. Compared to the previous state-of-the-art, our double nanohole structure achieves a 10x higher trap stiffness.
- We detail a general optical method to measure the trap stiffness in virtually any nano-optical tweezers experiment.
- We show that numerical simulations of the peak local intensity inside the structure is a simple and reliable measure to optimize the plasmonic design and the trap performance.