Nanoimprinted multifunctional nanoprobes for a homogeneous immunoassay in a top-down fabrication approach.

Multifunctional nanoparticles are discussed as versatile probes for homogeneous immunoassays for in-vitro diagnostics. Top-down fabrication allows to combine and tailor magnetic and plasmonic anisotropic properties. The combination of nanoimprint lithography, thin film deposition, and lift-off processing provides a top-down fabrication platform, which is both flexible and reliable. Here, we discuss the material compositions and geometrical designs of monodisperse multicomponent nanoparticles and their consequences on optical and magnetic properties. The rotational hydrodynamics of nanoparticles is measured and considered under the influence of magnetic shape anisotropy in the framework of the Stoner-Wohlfarth theory. The plasmon-optical properties are explained by discrete-dipole finite-element simulations. Rotational dynamical measurements of imprinted nanoprobes for two test proteins demonstrate the applicability as highly sensitive biomolecular nanoprobes.

Direct protein detection in the sample solution by monitoring rotational dynamics of nickel nanorods.

The feasibility of a recently introduced homogeneous immunodiagnostic approach to directly detect analyte binding by optical observation of the hydrodynamic properties of magnetically rotated nanorods ("PlasMag") is demonstrated experimentally. Specifically, it is shown that the phase lag of the long axis of nickel nanorods (magnetic core parameters: length 182 nm, diameter 26 nm) with respect to externally applied rotating magnetic fields significantly increases on the adhesion of bovine serum albumin (BSA) protein to their surfaces. To validate these results, the amount of bound protein molecules is independently determined by analysis of the electrophoretic mobility of the nanorods. Furthermore, the data also demonstrate the applicability of recently developed empirical models based on numerical solutions of the Fokker-Planck equation for describing the dynamics of magnetic nanoparticles in rotating magnetic fields.

Modeling and development of a biosensor based on optical relaxation measurements of hybrid nanoparticles.

We present a new approach for homogeneous real-time immunodiagnostics (denoted as "PlasMag") that can be directly carried out in sample solutions such as serum, thus promising to circumvent the need of sample preparation. It relies on highly sensitive plasmon-optical detection of the relaxation dynamics of magnetic nanoparticles immersed in the sample solution, which changes when target molecules bind to the surfaces of the nanoparticles due to the increase in their hydrodynamic radii. This method requires hybrid nanoparticles that combine both magnetic and optical anisotropic properties. Our model calculations show that core-shell nanorods with a cobalt core diameter of 6 nm, a cobalt core length of 80 nm, and a gold shell thickness of 5 nm are ideally suited as nanoprobes. On the one hand, the spectral position of the longitudinal plasmon resonance of such nanoprobes lies in the near-infrared, where the optical absorption in serum is minimal. On the other hand, the expected change in their relaxation properties on analyte binding is maximal for rotating magnetic fields as excitation in the lower kHz regime. In order to achieve high alignment ratios of the nanoprobes, the strength of the magnetic field should be around 5 mT. While realistic distributions of the nanoprobe properties result in a decrease of their mean optical extinction, the actual relaxation signal change on analyte binding is largely unaffected. These model calculations are supported by measurements on plain cobalt nanorod dispersions, which are the base component of the aspired core-shell nanoprobes currently under development.

Monitoring cellular stress responses to nanoparticles using a lab-on-a-chip.

As nanotechnology moves towards widespread commercialization, new technologies are needed to adequately address the potential health impact of nanoparticles (NPs). Assessing the safety of over 30,000 NPs through animal testing would not only be expensive, but it would also raise a number of ethical considerations. Furthermore, existing in vitro cell-based assays are not sufficient in scope to adequately address the complexity of cell-nanoparticle interactions including NP translocation, accumulation and co-transport of e.g. allergens. In particular, classical optical/fluorescent endpoint detection methods are known to provide irreproducible, inaccurate and unreliable results since these labels can directly react with the highly catalytic surfaces of NP. To bridge this technological gap we have developed a lab-on-a-chip capable of continuously and non-invasively monitoring the collagen production of primary human fibroblast cells (NHDF) using contactless dielectric microsensors. Human dermal fibroblast cells are responsible for the maintenance of soft tissue integrity, are found throughout the human body and their primary function is collagen expression. We show that cellular collagen production can be readily detected and used to assess cellular stress responses to a variety of external stimuli, including exposure to nanoparticles. Results of the study showed a 20% and 95% reduction of collagen production following 4 hour exposure to 10 µg mL(-1) gold and silver nanoparticles (dia.10 nm), respectively. Furthermore a prolonged perfusion of sub-toxic concentrations (0.1 µg mL(-1)) of silver NP reduced NHDF collagen production by 40% after 10 h indicating increased NP take up and accumulation. We demonstrate that the application of microfluidics for the tailored administration of different NP treatments constitutes a powerful new tool to study cell-nanoparticle interactions and nanoparticle accumulation effects in small cell populations.

Multispectral microbolometers for the midinfrared.

The spectral responsivity and the dynamic behavior of microbolometers with an integrated absorbing metamaterial are investigated. Wavelength tailoring and tuning in different microbolometers are achieved by varying the lateral extension of the absorber elements. Maximum sensitivity is tuned between 2.9 and 7.7 µm, with peak absorptions reaching up to 88%. The presence of a continuous metallic shielding layer affects heat conduction and leads to faster thermal response times.