Detection of a few metallo-protein molecules using color centers in nanodiamonds.

Nanometer-sized diamonds containing nitrogen-vacancy defect centers (NV) are promising nanosensors in biological environments due to their biocompatibility, bright fluorescence, and high magnetic sensitivity at ambient conditions. Here we report on the detection of ferritin molecules using magnetic noise induced by the inner paramagnetic iron as a contrast mechanism. We observe a significant reduction of both coherence and relaxation time due to the presence of ferritin on the surface of nanodiamonds. Our theoretical model is in excellent agreement with the experimental data and establishes this method as a novel sensing technology for proteins.