UC Berkeley

Conventional chemical sensors face fundamental limits when measuring chemistry and biology in confined or living systems, where photobleaching, perturbation of the sample, and inability to report on multiple physical properties constrain what can be observed. Recent advances in quantum sensing have demonstrated that well-controlled spin systems can transduce chemical and physical observables at sensitivities and spatial scales unreachable by these classical probes. Among these quantum sensing materials, the nitrogen-vacancy (NV) center in diamond has emerged as a room-temperature solid-state sensor compatible with aqueous and biological environments. The NV centers can be optically initialized and read out and are sensitive to magnetic fields, temperature, and paramagnetic species. The surrounding lattice 13C nuclear spin ensemble provides a complementary sensing modality through optical hyperpolarization, enabling magnetometry protocols based on long-coherence nuclear spins. This thesis develops methods for improving the practical reach of diamond quantum sensors across experimental regimes: bulk single-crystal diamond, nanodiamonds suspended in aqueous droplets, and nanodiamonds deployed in living biological systems. In bulk diamond, we use a custom high-power optical apparatus and a three-rate kinetic framework to measure a 179-fold gain in 13C dynamic nuclear polarization rate over conventional low-power operation, identifying the optical pumping rate κe as the limiting parameter and opening downstream applications in spin-based gyroscopy, magnetometry, and hyperpolarized NMR signal generation. In nanodiamond suspensions, we combine monodisperse picoliter microdroplets with double lock-in detection to detect paramagnetic ions, reaching a limit of detection of 100 nM for paramagnetic gadolinium in two minutes and opening applications in portable chemical testing, amplification-free biological assays, and reactive oxygen species sensing. We demonstrate co-encapsulation of yeast cultures and bead-based immunoassays with nanodiamonds in microdroplets, toward single-cell assays. A transparent root-on-a-chip device enables NV-diamond sensors to access the rhizosphere of a living Brachypodium distachyon plant.