Nuclear magnetic resonance microscope based on diamond quantum sensors

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Project Summary Nuclear magnetic resonance (NMR) spectroscopy is among the most powerful analytical techniques ever invented. This has been recognized by, for example, the 6 Nobel Prizes awarded for NMR methods development alone. However, the sensitivity and detection volumes in conventional NMR systems are insufficient for metabolic analysis of picoliter sample volumes such as single mammalian cells. At the same time, there is an acute need for non-invasive, label-free, chemically-specific techniques that operate at the single-cell level and/or can be integrated into hyphenated microfluidic assays. The proposed research seeks to develop a new platform for NMR spectroscopy and imaging at the scale of single cells (picoliters). The platform is based on recently-developed sensors which use qubits (the logical bits in quantum computers) to detect environmental parameters, so-called “quantum sensors”. Specifically, fluorescent spin qubits in diamond are used to generate and detect nuclear magnetization. The hypothesis underlying this proposal is that the use of non-inductive diamond quantum sensors could lead to improvements in sensitivity, spectral resolution, spatial resolution, and microfluidic integration beyond what is currently available in small-volume NMR spectroscopy. The PI’s lab has recently demonstrated a proof of concept by embedding a diamond quantum sensor in a microfluidic chip and detecting two-dimensional NMR spectra of picoliter volumes of fluid analytes. However ​substantial improvements in sensor spectral resolution and sensitivity are required to quantify molecular composition at physiological concentrations with single-cell spatial resolution. That is the goal of this proposal. This is a high risk proposal and the outcomes of development efforts are unknown. However the proposed research plan seeks to cover the following four objectives: 1. The fractional spectral resolution of diamond NMR spectrometers will be improved to better than 10 parts per billion. This will involve constructing an apparatus that operates at 3 tesla and developing diamond quantum sensing protocols optimized for this higher field. 2. The sensitivity of diamond NMR spectrometers will be improved to better than 10 millimolar (signal-to-noise ratio of 3 after 1 second integration). This involves rigorous optimization of the diamond sensor and developing methods to enhance nuclear spin polarization via optical hyperpolarization. 3. The molecular composition of complex mixtures of metabolites in solution will be quantified using an optimized diamond NMR spectrometer. 4. A proof-of-principle experiment will be conducted to validate the imaging capabilities of diamond NMR. An NMR microscope will be constructed and used to characterize the conversion of pyruvate to lactic acid in breast cancer cells. If successful, the demonstration of ​picoliter NMR metabolomics may have a substantial impact on analytical biochemistry and single-cell biology.