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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.

The carbazole derivatives 94isocyanophenylcarbazole, 3,6dibromo94isocyanophenylcarbazole, and 9ethyl3isocyanocarbazole were prepared and used to synthesize [AuXCNcarbazole] X = Cl, C6F5, C6F4OEtp gold complexes. The Xray structures of [AuC6F4OEtp{94isocyanophenylcarbazole}] and [AuC6F59ethyl3isocyanocarbazole], and the luminescent properties of the ligands and the complexes in the solid state, in solution at room temperature, and in frozen solution of chloroform at 77 K were determined. All the gold complexes show a redshift in the emissions relative to that of the free ligand. The presence of electronwithdrawing substituents in 3,6dibromo94isocyanophenylcarbazole quenches the luminescence, but with the introduction of a gold atom some luminescence is recovered.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009