Magnetic Nano Sensor Particles with Up-conversion Capability

The joined research project aims to investigate multi-functional nano particles for optical chemical and biochemical sensing. The beneficial functionalities combined in one nano particle include: magnetism, luminescence up- conversion, sensing and light harvesting. These sensor particles are excited with near-infrared (NIR) light. The anti-Stokes phosphorescence generated is used to excite an indicator or label dye enabling the detection of chemical parameters and the performance of bioassays. The NIR excitation and the up-conversion effect do not induce background luminescence of the biological sample. These sensor particles can be easily separated from the sample and collected at distinct positions by magnetic fields. This "in-situ" sensor spot leads to a sensitivity enhancement due to the high concentration of luminescent label at this point. The sensors are read-out by luminescence lifetime measurements, which is advantageous, because they are virtually independent of the overall signal intensity. The necessary instrumentation is simple due to the long lifetime of the up-conversion nanocrystals (upcon NCs). The multi-functional nano-particles will be prepared by entrapping magnetic nanocrystals and upcon NCs in the polymeric host matrix. Depending on the application, plain and core-shell particles will be investigated. The surface shell of the multi-functional particles contains carboxyl groups to obtain stable suspensions in aqueous samples and to conjugate receptors, ligands, enzymes or fluorescent indicator dyes to introduce the sensing function. In addition, the highly innovative click-chemistry approach will be applied to conjugate these functional molecules to the surface. Alternatively, the polymeric core or shell will be doped with fluorescent indicator dyes to introduce sensitivity to chemical parameters. The nano sensor will be applied to monitor the key parameters oxygen and pH of bio-films and cell cultures and to perform model affinity binding assays using antibodies and DNA oligomers. The specialized and complementary expertises of the two groups will be fully exploited within this project.

In a joined research project the Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology and the Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg investigated multi-functional nano and micro particles for optical chemical and biochemical sensing. The beneficial functionalities combined in one particle include: magnetism, luminescence up-conversion and sensing. These sensor particles are excited with near-infrared (NIR) light at 980 nm and emit blue, green and red light with a shorter wavelength, which is used to excite an indicator dye. This enables the detection of chemical parameters and the performance of bioassays. The NIR excitation and the up-conversion effect do not induce background signal of the biological sample. These sensor particles can be separated from the sample and collected at distinct positions by magnetic fields. Customised Upconversion luminescence nano particles based on NaYF4 doped with the rare earth metals Yb and Er were provided by the partners from Regensburg. These nano particles, magnetic nanoparticles and analyte sensitive dyes were entrapped into a polymer. Micro particles were prepared from this polymer and characterised via luminescence spectroscopy. Oxygen could be detected in concentration range from 0 to 20%. The magnetically collected particles show a better signal and improved signal to noise ratio compared to non-magnetic particles. Furthermore, up-conversion nano particles for measuring pH were investigated. A pH indicator dye was immobilised at the surface of upconversion nano particles to minimize the emission by resonance energy transfer. The effects observed were small to be used for an analytical quantification. In addition, a dye sensitizing approach was investigated to increase the brightness of upconversion nanoparticles.