Antti-Pekka Eskelinen

Plasmonic Surface Lattice Resonances at the Strong Coupling Regime

We show strong coupling involving three different types of resonances in plasmonic nanoarrays: surface lattice resonances (SLRs), localized surface plasmon resonances on single nanoparticles, and excitations of organic dye molecules. The measured transmission spectra show splittings that depend on the molecule concentration. The results are analyzed using finite-difference time-domain simulations, a coupled-dipole approximation, coupled-modes models, and Fano theory. The delocalized nature of the collective SLR modes suggests that in the strong coupling regime molecules near distant nanoparticles are coherently coupled.

Virus-Encapsulated DNA Origami Nanostructures for Cellular Delivery

DNA origami structures can be programmed into arbitrary shapes with nanometer scale precision, which opens up numerous attractive opportunities to engineer novel functional materials. One intriguing possibility is to use DNA origamis for fully tunable, targeted, and triggered drug delivery. In this work, we demonstrate the coating of DNA origami nanostructures with virus capsid proteins for enhancing cellular delivery. Our approach utilizes purified cowpea chlorotic mottle virus capsid proteins that can bind and self-assemble on the origami surface through electrostatic interactions and further pack the origami nanostructures inside the viral capsid. Confocal microscopy imaging and transfection studies with a human HEK293 cell line indicate that protein coating improves cellular attachment and delivery of origamis into the cells by 13-fold compared to bare DNA origamis. The presented method could readily find applications not only in sophisticated drug delivery applications but also in organizing intracellular reactions by origami-based templates.

Assembly of Single-Walled Carbon Nanotubes on DNA-Origami Templates through Streptavidin–Biotin Interaction

The exceptional self-assembly properties of DNA, which are based on simple base-paring rules, make it a very promising construction material in the nanoworld. [ 1 ] The development of the DNA-origami technique, [ 2 ] which is based on the folding of long single-stranded DNA with the help of hundreds of short oligonucleotides (so-called staple strands), opened new routes to relatively simple and fast fabrication of twoand three-dimensional nanostructures of exceptional complexity. [ 2–7 ] Since individual staple strands can be readily modifi ed with various functional groups, the DNA-origami structure can be used as a template for the organization of different materials, for example, proteins, [ 8–11 ] metal nanoparticles, [ 12–14 ] virus capsids, [ 15 ] and carbon nanotubes, [ 16 ]

Controlling the Formation of DNA Origami Structures with External Signals

Degradable Newkome-type and polylysine dendrons functionalized with spermine surface units are used to control the formation of DNA origami structures. The intact dendrons form polyelectrolyte complexes with the scaffold strands, therefore blocking the origami formation. Degradation of the dendron with an optical trigger or chemical reduction leads to the release of the DNA scaffold and efficient formation of the desired origami structure. These results provide new insights towards realizing responsive materials with DNA origami.

Surface plasmon polariton-controlled tunable quantum-dot emission

The unique properties of surface plasmon polaritons, such as strong field confinement and local field enhancement effects, make them ideal candidates to enhance and shape the emission of luminescent nanoparticles. Of these nanoparticles, quantum dots are highly versatile, suitable for vastly different applications due to their size and material tunability. In many cases however, the emission wavelength of the quantum dots is fixed after manufacturing, allowing no control over the in situ emission properties. Here, we show fully optical, in situ tunability of the emission wavelength of quantum dots, with shifts of over 30 nm, employing surface plasmon polaritons to control the emission wavelength.

Vacuum Rabi splitting for surface plasmon polaritons and Rhodamine 6G molecules

We report on strong coupling between surface-plasmon polaritons and Rhodamine 6G molecules at room temperature. As a reference to compare with, we first determine the dispersion curve of (uncoupled) surface plasmon polaritons on a 50 nm thick film of silver. Consequently, we determine the dispersion curve of surface plasmon polaritons strongly coupled to Rhodamine 6G molecules, which exhibits vacuum Rabi splitting. Depending on the Rhodamine 6G concentration, we find splitting energies between 0.05 eV and 0.13 eV.

From vacuum Rabi splitting towards stimulated emission with surface plasmon polaritons

We report on strong coupling between surface plasmon polaritons and Rhodamine 6G molecules at room temperature. As a reference to compare with, we first determine the dispersion curve of (uncoupled) surface plasmon polaritons on a 50 nm thick film of silver. Consequently, we determine the dispersion curve of surface plasmon polaritons strongly coupled to Rhodamine 6G molecules, which exhibits vacuum Rabi splitting. Furthermore, we present spontaneous emission spectra of Rhodamine 6G on silver, which are shown to change with detector angle due to surface plasmon polariton generation by Rhodamine 6G molecules.

Nanoantenna structures for strong coupling studies of surface plasmon polaritons and quantum dots

We present measurement and simulation results of local surface plasmon resonances on silver nanoantenna structures, fabricated with electron beam lithography. Such structures offer interesting possibilities to study strong coupling phenomena between surface plasmon polaritons (SPP) and, e.g., quantum dots, along the lines of our previous work on vacuum Rabi splitting for SPP and dye molecules.

DEP-Based Integration of G-quadruplex Structures

The unique properties of G4-based nucleic acids provide the base for a variety of applications.A whole set of biomedical as well as bioanalytical applications is based on the ability of G-quartets to stabilize defined three-dimensional nucleic acid structures that exhibit a high affinity to a target molecule. Such aptamers can therefore show similar binding properties as antibodies with comparable applications in diagnostics and therapy, but exhibit striking advantages like ex-vivo synthesis and increased physicochemical stability. Moreover, they can even show catalytic behavior that can be utilized for bioanalytical purposes. The chapter contains examples for applications in these fields.The structural properties described in previous chapters are the base for applications in molecular nanotechnology and –electronics. Nucleic acids represent the most promising materials in these fields, and here G4 structures show even outstanding mechanical stability and length control from the nano- into the micrometer range. An important step on the way to respective applications is the integration of G4-based nanostructures into technical environments such as microelectrodes. Here electrical field-based approaches – e.g. dielectrophoresis DEP – represent the most promising technique, which has been demonstrated for the integration and subsequent characterization of even single G4 structures. These techniques have also been used to enable the characterization of electrical properties of G4 assemblies as described in this chapter.In conclusion, by presenting various biomedical as well as nanobiotechnological demonstrations this chapter demonstrates the great application potential of G4-based nanostructures.