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

Abstract

≈10 12 -10 18 nuclei (or a factor of 1000 fewer electron spins) to generate an observable signal. [6,7] To date, diamond magnetometry has been used to detect magnetic structures, [8][9][10][11] microwave signals, [12] and single proteins [13] and to record signals from magnetotactic bacteria, [14] cells labeled with magnetic particles, [15] or fixed and stained cell slices. [16] Relaxometry (or T 1 ), analogous to T 1 in conventional MRI, is a quantum sensing method that allows the efficient detection of surrounding magnetic noise. [17] First with gadolinium contrast, [18][19][20] it has been used in solution to detect free radicals [21] and monitor chemical reactions, [22,23] and in biological environments to sense the metabolic activity of mitochondria in macrophages [24] or detect nitric oxide production by endothelial cells. [25] Conventional methods for detecting radicals rely on chemical reactions with spin labels or dye molecules and on detection via electron spin resonance. The first generally requires large sample volumes, [26] and the second is poorly selective for free radicals, irreversibly consumes them, and is prone to bleaching, which complicates real-time monitoring. [27] Here, we detected nitric oxide signaling at the nanoscale with an optical resolution. In the human body, nitric oxide is particularly relevant for vascular and brain cell communication and therefore essential for understanding heart and brain diseases. [28,29] We were able to quantify and localize nitric oxide, formed either chemically or by live mammalian cells. Additionally, we determined the formation dynamics, which are inaccessible by state-of-the-art methods. Results and DiscussionAs evidenced previously, the relaxometry measurement sequence allows the detection of free radicals via the magnetic noise they generate. [18] In this work, we used this technique to localize the generation of biologically relevant nitric oxide and superoxide. Toward this goal, we conducted relaxometry measurements using nanodiamonds containing ensembles of nitrogen-vacancy (NV) centers. Such nanodiamonds can be internalized by different types of cells [30][31][32][33] and exhibit excellent biocompatibility. [34,35] In our experiments, the 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...

Fast, Broad-Band Magnetic Resonance Spectroscopy with Diamond Widefield Relaxometry

“…Yet, diamond-based EPR is not measuring the signal from a solution but rather from a thin layer of adsorbed ions on of the diamond surface. As developed in ref , the reason is that the sensitivity of NV centers to free radicals decreases very fast with their distance. Thus, in our spectrum, we assign the resonance peak (at g = 2.43 and 2.37) to the transition with g ∥ Cu in an adsorbed and partially free configuration.…”

“…14,15 This found various applications in chemistry, in monitoring reactions, 16,17 and biology, 18,19 in detecting free radicals in living cells. 20,21 Inherited from conventional magnetic resonance techniques, several measuring modes can be used when working with NVcenters. Different microwave and/or optical pulsing sequences to manipulate the NV-centers electronic state, can render the NV-center more sensitive or specific for spins with a certain Larmor frequency.…”

“…With this method, the detection of EPR spectra of different compounds − has been achieved with a sensitivity compatible with individual electron spins, external to the diamond . Further it is possible to image EPR signals , or to perform spectroscopy. , This found various applications in chemistry, in monitoring reactions, , and biology, , in detecting free radicals in living cells. , …”

Lipid peroxidation in diamond supported bilayers

“…1B), alongside its characteristic T 1 time that decreases in the presence of more free radicals. 15,16,17…”

Nanodiamond-Based Optical-Fiber Quantum Probe for Magnetic Field and Biological Sensing

“…As depicted in Figure 6a, a probe was sealed in a microfluidic tube (with an inner/outer diameter of 2/3 mm) and the copper wire antenna was wound around the tube. Because the effective detection range of an NV center to the magnetic noise source is limited to only several tens of nanometers, 46 MFCs were not used for paramagnetic sensing. Different concentrations of gadolinium nitrate [Gd(NO 3 ) 3 ] solutions were successively flowed through the tube, and the corresponding LI-ODMR spectra were recorded employing the same configuration shown in Figure 1k.…”