Nanophotonic manipulation of biological emitters

 

The field of nanophotonics is a very active field within physics that addresses the control of light and manipulation of emitters by metamaterials, photonic crystals, cavities or mirrors, to name a few. We are exploring the potential of nanophotonic manipulation and control of biological emitters – nanobiophotonics. Using the nanophotonics toolbox we not only passively observe, but actively manipulate the emission from biomolecules.

Our research on nanophotonic manipulation of biological emitters, carried out in close collaboration with the Complex Photonic Systems group of Prof. W. L. Vos, explores a range of different themes.

New effects:

We were able to infiltrate Fluorescent Proteins into artificial nanostructures, so called photonic crystals, and were able to show that that the protein emission color can be modulated by the photonic crystal.

Control of the apparent emission color of the same fluorescent protein by photonic crystals.

The color of the fluorescent protein was modified by changing the structure of the photonic crystal rather than by molecular changes of the protein itself. The photonic crystals used consist of air spheres and a supporting backbone of titania. By increasing the size of the air spheres the emitted color changes from orange – when photonically unmodified – to red and finally to green. The change in color results from the redistribution of light around the stop-band; some colors are strongly attenuated, while others are enhanced.

Accessing hidden properties

Since certain aspects of the photophysical properties of emitters cannot be analyzed with conventional methods, we research the potential of complex nanophotonic structures to answer these open questions.

We used nanophotonic manipulation to determine for the first time the fluorescence quantum efficiency of exclusively emitting states of visible fluorescent proteins (VFPs) without the influence from dark states.

We manipulated the local density of optical states (LDOS) of VFPs by positioning the VFPs at defined distances (with nanometer precision) to a metallic mirror. This results in characteristic changes in the fluorescence decay rate that we used to determine the radiative and nonradiative decay rates of the fluorophore. Since only the emitting species contribute to the change in total decay rate, only these emitting states are characterized. We determined the quantum efficiency of the emitting states to be 72%.

Nanophotonic manipulation of the VFP emission to access radiative and nonradiative decay rates and quantum efficiency of exclusively emitting states.

Additionally, we recently used fluorescent proteins to image for the first time the properties of photonic crystals well below their surface.

Although tremendous progress has been made in the fabrication of ordered nanophotonic materials, these structures are never perfect. The visualization of this inhomogeneity has so far been limited to the surface or the first few layers of 3D photonic crystals.

We showed that light that was emitted by natural fluorescent proteins embedded deep inside the photonic crystal strongly interacted with the surrounding photonic crystal. We used spectral imaging to quantitatively visualize the local interaction of light emitted by the fluorescent proteins and the photonic crystal.

Comparing subsurface photonic properties (a) to surface properties (b), of identical areas. Blue stands for high crystal quality, red for low crystal quality.

Selected publications

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Cesa, Y., C. Blum, J.M. van den Broek, A.P. Mosk, W.L. Vos, and V. Subramaniam, Manipulation of the local density of photonic states to elucidate fluorescent protein emission rates. Physical Chemistry Chemical Physics, 2009. 11(14): p. 2525-2531, doi:10.1039/b817902f.

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Blum, C., A.P. Mosk, W.L. Vos, and V. Subramaniam, Spectral emission imaging to map photonic properties below the crystal surface of 3D photonic crystals. Journal of the Optical Society of America B, 2009. 26(11): p. 2101–2108, doi:10.1364/JOSAB.26.002101.

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Blum, C., A.P. Mosk, I.S. Nikolaev, V. Subramaniam, and W.L. Vos, Color control of natural fluorescent proteins by photonic crystals. Small, 2008. 4(4): p. 492-496, doi:10.1002/smll.200701160.

PhD student: Niels Zijlstra, Martijn Stopel
Project leader: Christian Blum