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.

Following Polymer Degradation with Nanodiamond Magnetometry.

Degradable polymers are widely used in the biomedical fields due to non-toxicity and great biocompatibility and biodegradability, and it is crucial to understand how they degrade. These polymers are exposed to various biochemical media in medical practice. Hence, it is important to precisely follow the degradation of the polymer in real time. In this study, we made use of diamond magnetometry for the first time to track polymer degradation with nanoscale precision. The method is based on a fluorescent defect in nanodiamonds, which changes its optical properties based on its magnetic surrounding. Since optical signals can be read out more sensitively than magnetic signals, this method allows unprecedented sensitivity. We used a specific mode of diamond magnetometry called relaxometry or T1 measurements. These are sensitive to magnetic noise and thus can detect paramagnetic species (gadolinium in this case). Nanodiamonds were incorporated into polylactic acid (PLA) films and PLA nanoparticles in order to follow polymer degradation. However, in principle, they can be incorporated into other polymers too. We found that T1 constants decreased gradually with the erosion of the film exposed to an alkaline condition. In addition, the mobility of nanodiamonds increased, which allows us to estimate polymer viscosity. The degradation rates obtained using this approach were in good agreement with data obtained by quartz crystal microbalance, Fourier-transform infrared spectroscopy, and atomic force microscopy.

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.