Negatively charged Nitrogen-Vacancy centers (NV -) can be used as probes for ultrasensitive detection of magnetic and electric fields , temperature , and nuclear spins at the nanoscale . NV -centers can be optically polarized with continuous irradiation of laser light at room temperature and at Earth's magnetic field , thus paving the way for applications in biomedical assays , as intracellular thermometers , optical magnetic imaging in living cells or optical magnetic detection of single-neuron action potentials . Moreover, optical pumping of NV -centers has been proposed as an alternative to dynamic nuclear polarization (DNP) for the hyperpolarization of nuclear spins .