High-Tc SQUID gradiometer system for immunoassays

• A high-Tc dc SQUID (superconducting quantum interference device) gradiometer was developed for magnetic immunoassays where magnetic nanoparticles are used as markers todetect biological reactions. The gradiometer was fabricated on a 5 × 10 mm2 SrTiO3 bicrystal substrate and has a gradiometer resolution of 2.1 pT cm−1 Hz−1/2. A magnetic signal was detected from a sample of 1 μl of Fe3O4 nanoparticles in a 40 mg ml−1 solution kept in amicrocavity fabricated on Si wafers with Si3N4 membranes using MEMS (micro-electro-mechanical-systems) technology. It was found that volumes as small as 0.3 nl in principle would be detectable with our present device. This corresponds to a total number of particles of 2.2 × 107. The estimated average dipole moment per particle is 4.8 × 10−22 Am2.We are aiming at reading out immunoassays by detecting the Brownian relaxation of magnetic nanoparticles, and we also intend to integrate MEMS technology into our system.

Subject headings

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Annan teknik -- Övrig annan teknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies -- Other Engineering and Technologies not elsewhere specified (hsv//eng)

Keyword

Gradiometer

Magnetic nanoparticles

Immunoassays

SQUID

Publication and Content Type

art (subject category)

ref (subject category)