Noise properties of high-T-c superconducting flux transformers fabricated using chemical-mechanical polishing

Reproducible high-temperature superconducting multilayer flux transformers were fabricated using chemical mechanical polishing. The measured magnetic field noise of the flip-chip magnetometer based on one such flux transformer with a 9 x 9 mm(2) pickup loop coupled to a bicrystal dc SQUID was 15 fT/Hz(1/2) above 2 kHz. We present an investigation of excess 1/f noise observed at low frequencies and its relationship with the microstructure of the interlayer connections within the flux transformer. The developed high-T-c SQUID magnetometers may be advantageous in ultra-low field magnetic resonance imaging and, with improved low frequency noise, magnetoencephalography applications

The need for stable, mono-dispersed, and biofunctional magnetic nanoparticles for one-step magnetic immunoassays

We have developed a magnetic immunoassay system (MIA) using magnetic nanoparticle markers for biomolecule detection. We have magnetically characterized multi-core magnetic nanoparticles (MNPs) containing single-domain crystals of Fe3O4 and CoFe2O4 with our system using a high temperature superconducting quantum interference device as detector. We use a Helmholtz coil to excite the MNPs and study the AC-susceptibility. The data is fit to a model and information about the particle size distribution of the MNP system is extracted. We observe high stability of the unfunctionalized MNPs. However, our MIA measurements require stable functionalized MNPs. We have found a significant increase in hydrodynamic size of the functionalized MNP systems in the course of just a few days caused by agglomeration behaviour. Separate measurements performed at Imego AB with their AC-Susceptometer, DynoMAG, confirm these findings. Without stable, functionalized MNPs MIAs of this kind are impossible. © 2010 IOP Publishing Ltd

Noise properties of HTS flux transformers fabricated by chemical-mechanical polishing

We present on fabrication and noise properties of high-temperature superconducting (HTS) thin-film integrated multilayer flux transformers fabricated using planarization of YBCO films by chemical-mechanical polishing (CMP). The polishing allows fabrication of very shallow slope edges (less than 5°) in the YBa2Cu3O7, that makes it possible to avoid formation of grain boundary junctions in crossovers and obtain very high critical current densities in the top electrode of about 2•106 A/cm2. The same planarization process is used to create interconnections between top and bottom superconducting electrodes through the SrTiO3/PrBa2Cu3O7/SrTiO3 insulating layer. HTS multilayer flip-chip flux transformer with 8x8 mm2 pickup loop and 20-turn input coil was fabricated and coupled to a bicrystal dc SQUID in a flip-chip configuration. We measured magnetic field gain of 1.2 nT/Ф0 and magnetic flux noise of the magnetometer 10 µФ0/√Hz at 1 kHz, which corresponds to magnetic field noise of 12 ft/√Hz. FLUX NOISE AT LOW FREQUENCIES! The work is supported by European FP7 project "MEGMRI" under contract number 200859

A new approach for bioassays based on frequency- and time-domain measurements of magnetic nanoparticles

We demonstrate a one-step wash-free bioassay measurement system capable of tracking biochemical binding events. Our approach combines the high resolution of frequency- and high speed of time-domain measurements in a single device in combination with a fast one-step bioassay. The one-step nature of our magnetic nanoparticle (MNP) based assay reduces the time between sample extraction and quantitative results while mitigating the risks of contamination related to washing steps. Our method also enables tracking of binding events, providing the possibility of, for example, investigation of how chemical/biological environments affect the rate of a binding process or study of the action of certain drugs. We detect specific biological binding events occurring on the surfaces of fluid-suspended MNPs that modify their magnetic relaxation behavior. Herein. we extrapolate a modest sensitivity to analyte of 100 ng/ml with the present setup using our rapid one-step bioassay. More importantly, we determine the size-distributions of the MNP systems with theoretical fits to our data obtained from the two complementary measurement modalities and demonstrate quantitative agreement between them.

Towards an electrowetting-based digital microfluidic platform for magnetic immunoassays

We demonstrate ElectroWetting-On-Dielectric (EWOD) transport and SQUID gradiometer detection of magnetic nanoparticles (MNPs) suspended in a 2 mu l de-ionized water droplet. This proof-of-concept methodology constitutes the first development step towards a highly sensitive magnetic immunoassay platform with SQUID readout and droplet-based sample handling. Magnetic AC-susceptibility measurements were performed on MNPs with a hydrodynamic diameter of 100 nm using a high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer as detector. We observed that the signal amplitude per unit volume is 2.5 times higher for a 2 ml sample droplet compared to a 30 ml sample volume