Diamond-Based Nanoscale Quantum Relaxometry for Sensing Free Radical Production in Cells.

Diamond magnetometry makes use of fluorescent defects in diamonds to convert magnetic resonance signals into fluorescence. Because optical photons can be detected much more sensitively, this technique currently holds several sensitivity world records for room temperature magnetic measurements. It is orders of magnitude more sensitive than conventional magnetic resonance imaging (MRI) for detecting magnetic resonances. Here, the use of diamond magnetometry to detect free radical production in single living cells with nanometer resolution is experimentally demonstrated. This measuring system is first optimized and calibrated with chemicals at known concentrations. These measurements serve as benchmarks for future experiments. While conventional MRI typically has millimeter resolution, measurements are performed on individual cells to detect nitric oxide signaling at the nanoscale, within 10-20 nm from the internalized particles localized with a diffraction limited optical resolution. This level of detail is inaccessible to the state-of-the-art techniques. Nitric oxide is detected and the dynamics of its production and inhibition in the intra- and extracellular environment are followed.

Insight into a Fenton-like Reaction Using Nanodiamond Based Relaxometry.

Copper has several biological functions, but also some toxicity, as it can act as a catalyst for oxidative damage to tissues. This is especially relevant in the presence of H2O2, a by-product of oxygen metabolism. In this study, the reactions of copper with H2O2 have been investigated with spectroscopic techniques. These results were complemented by a new quantum sensing technique (relaxometry), which allows nanoscale magnetic resonance measurements at room temperature, and at nanomolar concentrations. For this purpose, we used fluorescent nanodiamonds (FNDs) containing ensembles of specific defects called nitrogen-vacancy (NV) centers. More specifically, we performed so-called T1 measurements. We use this method to provide real-time measurements of copper during a Fenton-like reaction. Unlike with other chemical fluorescent probes, we can determine both the increase and decrease in copper formed in real time.

Nanodiamond Relaxometry-Based Detection of Free-Radical Species When Produced in Chemical Reactions in Biologically Relevant Conditions.

Diamond magnetometry is a quantum sensing method involving detection of magnetic resonances with nanoscale resolution. For instance, T1 relaxation measurements, inspired by equivalent concepts in magnetic resonance imaging (MRI), provide a signal that is equivalent to T1 in conventional MRI but in a nanoscale environment. We use nanodiamonds (between 40 and 120 nm) containing ensembles of specific defects called nitrogen vacancy (NV) centers. To perform a T1 relaxation measurement, we pump the NV center in the ground state (using a laser at 532 nm) and observe how long the NV center can remain in this state. Here, we use this method to provide real-time measurements of free radicals when they are generated in a chemical reaction. Specifically, we focus on the photolysis of H2O2 as well as the so-called Haber-Weiss reaction. Both of these processes are important reactions in biological environments. Unlike other fluorescent probes, diamonds are able to determine spin noise from different species in real time. We also investigate different diamond probes and their ability to sense gadolinium spin labels. Although this study was performed in a clean environment, we take into account the effects of salts and proteins that are present in a biological environment. We conduct our experiments with nanodiamonds, which are compatible with intracellular measurements. We perform measurements between 0 and 108 nM, and we are able to reach detection limits down to the nanomolar range and typically find T1 times of a few 100 µs. This is an important step toward label-free nano-MRI signal quantification in biological environments.