Magnetic Nanoparticles \textit{in-vivo} Detection of Transplant Rejection

Superparamagnetic nanoparticles are being used to develop methodology for the \textit{in-vivo} detection and imaging of immune system attacks on transplanted organs. The signature for impending rejection of a transplant is enhanced presence of T-cells. Magnetic nanoparticles coated with specific antibodies (CD-2 and CD-3) will target and attach to these T-cells. Approximately 3 $\cdot $10$^{5}$ nanoparticles can attach to each cell. When a pulsed external magnetic field is applied to the decorated cells for a fraction of a second, magnetic moments of the nanoparticles aligned with the field. After the pulse is switched off, the net magnetic moment decays over several seconds by the N\`{e}el mechanism. The resulting magnetic remanence field (typically 10$^{-11}$ T) is measured using a multi-channel SQUID array. We present the data from live T-cells placed in realistic kidney phantom. The detection sensitivity was $\sim $2$\cdot $10$^{3}$ T-cells - a small fraction of the number actually invading the rejected transplant. The 7-channel SQUID array allows us to image the cell clusters with a few millimeters resolution.