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COMPLEXPLAS Report Summary

Project ID: 321331
Funded under: FP7-IDEAS-ERC
Country: Germany

Final Report Summary - COMPLEXPLAS (Complex Plasmonics at the Ultimate Limit: Single Particle and Single Molecule Level)

We have carried out a large number of different approaches towards nanophotonic and plasmonic sensing. Spectral ranges included the visible, near-IR as well as the mid-IR spectral range. We have pushed gas sensing further towards single antennas and extremely low numbers of molecules, however, the ultimate goal of single-molecule gas sensing could not yet be reached. Yet, the interplay between particle expansion, elastic energy, enthalpy, and hydride formation as well as the hysteresis behavior could be unraveled with our setup (Nature Materials).

The combination of plasmonics and magnetooptics was used to work towards nonreciprocal ultracompact Faraday isolators. The key mechanisms were unraveled and plasmon-induced absorption was used to achieve record Faraday rotation values of 14° within less than 200 nm thickness (Nature LSA, PRL, PRX).

We have utilized mid-IR nanoantennas and pushed the limits towards single-nanoantenna spectroscopy, being able to detect folding and unfolding of proteins between the alpha and beta state. We have utilized DNA based plasmonic nanoparticle assemblies which could be used to fabricate hybrid gold-DNA-palladium single particle gas sensors which were monitored optically to detect hydrogen-induced phase change in sub-5 nm Pd nanoparticles on the single particle level. Regarding chiral sensing, extensive experimental and theoretical work led to the conclusion that plasmonic enhancement of chiral signatures of molecular enantiomers would be only possible to about 1-2 orders of magnitude and possibly not lead to enantiomer discrimination on the single molecule level.

During the course of the grant work, we have constructed a dedicated laser and optical spectroscopy setup which allowed for tabletop mid-IR single particle spectroscopy that was possible previously only at synchrotrons. We even improved the measurement time of our setup compared to synchrotrons by a factor of 10. A startup company resulted from this work. We utilized this novel laser system in combination with a near-field scanning microscope to detect gas-inducedd phase changes in magnesium and palladium situ on a single particle level by simultaneously monitoring near- and far-field optical as well as structural information.

In order to grow bottom-up nanoplasmonic structures, we discovered a completely new route towards electrochemical growth of atomically flat, tens of µm large, single crystalline gold nanoparticles whose thickness could be extremely well controlled on the nanometer level. This led to the discovery of short-range plasmons and their propagation as well as “spin and orbital angular momentum” dynamics using orbital angular momentum excitation in combination with time-resolved 2-photon photoemission (Science, Science Advances).

During the work with chiral nanostructures, we utilized femtosecond direct laser writing on a submicrometer level. This led to the discovery that micro- and nanooptics could be fabricated in situ directly on fibers and CMOS detectors, which led to an entirely new research field, namely 3D printed complex microoptics. We were able to demonstrate diffraction limited 3D printed microscope objectives with aplanatic imaging properties (Nature Photonics, Nature Communications, Science Advances). This work has found widespread applications in medical and sensor technology, such as miniature endoscopes, optical sensors for self-driving cars, and for ubiquous virtual and augmented reality and another spin-off company is planned to being founded in December of 2018.

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