Intrasurgical spectral-domain optical coherence tomography evaluation is feasible using the tested system and may positively influence surgical decisions and techniques resulting in an improved patient outcome.

The use of fine magnetic particles as labels for antibodies and the measurement of their remanent magnetization for the preparation of immunoassays is presented. Antibodies were coupled with magnetic nanoparticles and samples were prepared by reaction of the magnetically labeled antibodies with their solid phase adsorbed antigen. After exposing the samples to a field of some mT a dc-SQUID system measures the remanent sample magnetization in the absence of an external field. The combination of high moment labels and SQUIDS yields ultrasensitive immunoassays with a wide range of detectable analyte concentrations. In contrast to most standard techniques in our method the detected magnetic signal is specific only for bound reaction partners, thus eliminating the need for separation of unbound components.

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A fast SQUID (superconducting quantum interference device) magnetometer system using the latest multiloop magnetometer W7A with additional positive feedback has been built. A 3-dB bandwidth of 5 MHz has been achieved in a simple direct-coupled flux-locked loop. The feedback range is ±620 Φ0 or ±290 nT, the white-noise level 3.4×10−6 Φ0/√Hz or 1.6 fT/√Hz, and the 1/ f corner frequency ≂7 Hz. Above 1 MHz the noise level increases slightly, approximately with √SΦ ∝f1/6. At high signal frequencies a slew rate of about 8×105 Φ0/s has been measured. Below the pole frequency of the second integrator (480 kHz) the slew rate increases with decreasing frequency, having a maximum of 3×107 Φ0/s at 7.6 kHz. The total harmonic distortion (THD) decreases strongly with the signal amplitude below the slew rate limit. For a sinusoidal signal with half the maximum amplitude, the THD is ≂4% at 1 MHz, ≂0.04% at 100 kHz, and ≂2.7 ppm (1 ppm=10−6) at 10 kHz. Below about 2 kHz the THD becomes almost frequency independent and lies between 0.4 and 7 ppm for signal amplitudes between 2.5 and 620 Φ0.

Abstrmt-A novel technique for detecting immunochemical reactions based on a SQUID measurement system has recently been demonstrated. The reaction partners are labeled by magnetic nanoparticles which, after an immunochemical reaction, display changes of their magnetic relaxation behaviour due to a reduction of their mobility. We have developed a SQUID system dedicated to magnetic relaxation immunoassays (MARIAs) operating in unshielded environment. The system consists of 6 SQUID magnetometers electronically combined to a second-order gradiometer. The gradiometer is formed by electronic subtraction of FLL output signals or by the Three SQUID Gradiometer approach. By evaluating the amplitude of relaxation signals (average of 4 magnetization cycles) a minimnm amount of (selected) Fe20-j-particles corresponding to 600 pmol Fe was detected demonstrating the potential of the measurement system for biochemical laboratory diagnostics.

A low-Tc SQUID system was developed for measuring magnetic relaxation of polymer-coated magnetic nanoparticles (MNPs) in a liquid carrier (e.g. water). The system consists of two low-Tc SQUIDs which are electronically combined to form an axial gradiometer using high-bandwidth directly coupled FLL electronics. The system is operated in a magnetically shielded room. The magnetic relaxation of the investigated MNPs in a liquid carrier is dominated by Brownian motion. In a solid phase, when the MNPs are immobilized, the magnetization of the sample decays via the Néel mechanism. A similar situation occurs when the mobility of the MNPs is reduced by a biochemical binding reaction. This effect is used for identifying biological reactions for purposes of medical diagnostics, e.g. immunoassays. By investigating the magnetic relaxation of dried samples, quantities as small as 1 nmol Fe of -Fe2O3 were detected. In the first agglomeration assay the binding reaction of the biochemical model biotin-avidin complexes can be clearly identified down to concentrations of <1 µg avidin in a volume of 150 µl of human blood.

A completely noninvasive method is presented for the investigation of semiconductor wafers with high spatial resolution utilizing a superconducting quantum interference device (SQUID) magnetometer system. The method is based on the detection of the magnetic field caused by photocurrents generated in the semiconductor sample using a sensitive SQUID magnetometer. The photocurrents arise when laser light with a photon energy exceeding the band gap of the semiconductor is focused onto the sample surface in a region of a doping gradient. The spatial resolution of this detection method is mainly determined by the size of the excitation focus of about 20 μm. We report on measurements of silicon wafers with small growth-related doping fluctuations.

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