Abstract
We present a widefield microscopy system for imaging super-paramagnetic nanoparticles (SPNs), and propose to use it
as a bio-sensing system wherein SPNs are used as tags. Potential advantages of magnetic tags over conventional
fluorescent tags include the elimination of noise from auto-fluorescence, optical isolation of the biological system from
the measurement apparatus, and the potential for magnetic removal of non-specifically bound material. The microscope
magnetic sensing surface is composed of a thin layer of nitrogen-vacancy defect centers in the top 200 nm of a diamond
substrate. Nitrogen-vacancy centers in diamond have been shown to be suitable for use as highly sensitive
magnetometers due to their long spin-coherence time at room temperature. Furthermore, spin-dependent
photoluminescence allows for simple far-field optical readout of the spin state, which in turn allows for opticallydetected
magnetic resonance measurements. We will present our results detecting a single, lithographically defined 50
nm diameter by 100 nm thick iron nanodot. With the current sensitivity of 9 μT⋅Hz-1/2, we expect to be able to detect single 20 nm magnetite SPNs, our proposed tags, in less than one minute. By further optimizing the sensor surface, we predict DC magnetic sensitivities as low as 1 μT⋅Hz-1/2.
