Jens Rafaelsen

Photonic Immobilization of BSA for Nanobiomedical Applications: Creation of High Density Microarrays and Superparamagnetic Bioconjugates

Light assisted molecular immobilization has been used for the first time to engineer covalent bioconjugates of superparamagnetic nanoparticles and proteins. The technology involves disulfide bridge disruption upon UV excitation of nearby aromatic residues. The close spatial proximity of aromatic residues and disulfide bridges is a conserved structural feature in proteins. The created thiol groups bind thiol reactive surfaces leading to oriented covalent protein immobilization. We have immobilized a model carrier protein, bovine serum albumin, onto Fe3O4@Au core–shell nanoparticles as well as arrayed it onto optically flat thiol reactive surfaces. This new immobilization technology allows for ultra high dense packing of different bio‐molecules on a surface, allowing the creation of multi‐potent functionalized active new biosensor materials, biomarkers identification and the development of nanoparticles based novel drug delivery system. Bioeng. 2011; 108:999–1010.

Towards Nanoscale Biomedical Devices in Medicine: Biofunctional and Spectroscopic Characterization of Superparamagnetic Nanoparticles

Medical interest in nanotechnology originates from a belief that nanoscale therapeutic devices can be constructed and directed towards its target inside the human body. Such nanodevices can be engineered by coupling superparamagnetic nanoparticle to biomedically active proteins. We hereby report the immobilization of a PhEst, a S-formylglutathione hydrolase from the psychrophilic P. haloplanktis TAC125 onto the gold coated surface of modified superparamagnetic core-shell nanoparticles (Fe3O4@Au). The synthesis of the nanoparticles is also reported. S-formylglutathione hydrolases constitute a family of ubiquitous enzymes which play a key role in formaldehyde detoxification both in prokaryotes and eukaryotes. PhEst was originally annotated as a putative feruloyl esterase, an enzyme that releases ferulic acid (an antioxidant reactive towards free radicals such as reactive oxygen species) from polysaccharides esters. Dynamic light scattering, scanning electron microscopy with energy dispersive X-ray spectroscopy, UV–visible absorption spectroscopy, fluorescence spectroscopy, magnetic separation technique and enzyme catalytic assay confirmed the chemical composition of the gold covered superparamagnetic nanoparticles, the binding and activity of the enzyme onto the nanoparticles. Activity data in U/ml confirmed that the immobilized enzyme is approximately 2 times more active than the free enzyme in solution. Such particles can be directed with external magnetic fields for bio-separation and focused towards a medical target for therapeutical as well as bio-sensor applications.

Size-effects in photoemission and optical second harmonic generation spectroscopy of Ge nano-dots on Si(111)

Ge nano-dots have been grown on Si(111) covered by a thin oxide layer using a wedge shaped deposition profile, resulting in varying nano-dot size along the sample profile. Samples were investigated by optical second harmonic generation (SHG) and photoemission spectroscopy (PES). The growth of the nano-dots was characterized by core level PES and scanning electron microscopy, and size effects were found in valence band PES. SHG spectra reveal two clearly resolvable resonances related to the E1 transitions in Si and Ge, respectively. Deposition of Ge leads to a field at the surface that modifies the SHG response from the Si substrate. The Ge SHG signal grows up during deposition and shifts towards lower energy with increasing particle size, demonstrating that size effects are also present in the optical transitions.

Optical resonances and nanofocusing in triangular metal nano-grooves

Optical resonances in a single triangular-shaped metal groove and a periodic array of grooves are studied theoretically with the Greens function surface integral equation method. In the case of a single groove we study the geometric resonances for different groove heights, and show that the groove resonances can be explained by standing waves in the gap being reflected at both the closed groove bottom and the open groove top. We also present the reflection that will be obtained for different cases of picking up the reflected light within a small or large angular range. Large resonant fields at the groove bottom are explained as being due to nanofocusing by the groove which can also be thought of as a closed tapered gap. In the case of a periodic array of grooves we find that resonances of individual grooves are still present in near-field enhancement spectra and reflection spectra but there are also e.g. very sharp resonances (Rayleigh anomalies) at wavelengths near the cutoff wavelength of higher grating-reflection orders. Typical resonant enhancements can easily be two times higher compared with the case of a single groove. The resonances can be realized in the wavelength range from the visible to the infrared by varying groove height, angle, and periodicity.