Biocompatible nanoscale probes for sensitive detection of paramagnetic species and molecules associated with their (bio)chemical transformations would provide a desirable tool for a better understanding of cellular redox processes. Here, we describe an analytical tool based on quantum sensing techniques. We magnetically coupled negatively charged nitrogen-vacancy (NV) centers in nanodiamonds (NDs) with nitroxide radicals present in a bioinert polymer coating of the NDs. We demonstrated that the T1 spin relaxation time of NV centers is very sensitive to the number of nitroxide radicals, with a resolution down to ~10 spins per ND (detection of approximately 10 -23 mol in a localized volume). The detection is based on T1 shortening upon the radical attachment and we propose a theoretical model describing this phenomenon. We further show this colloidally stable, water-soluble system can be used dynamically for spatiotemporal readout of a redox chemical process (oxidation of ascorbic acid) occurring near the ND surface in an aqueous environment under ambient conditions.
Fluorination of diamonds modulates their optical and electromagnetic properties and creates surfaces with increased hydrophobicity. In addition, fl uorination of diamonds and nanodiamonds has been recently shown to stabilize fl uorescent nitrogen-vacancy centers, which can serve as extremely sensitive single atomic defects in a vast range of sensing applications from quantum physics to high-resolution biological imaging. Traditionally, fl uorination of carbon nanomaterials has been achieved using harsh and complex experimental conditions, creating hydrophobic interfaces with diffi cult dispersibility in aqueous environments. Here, a mild benchtop approach to nanodiamond fl uorination is described using selective Ag + -catalyzed radical substitution of surface carboxyls for fl uorine. In contrast to other approaches, this highyielding procedure does not etch diamond carbons and produces a highly hydrophilic interface with mixed C−F and C−OH termination. This dual functionalization of nanodiamonds suppresses detrimental hydrophobic interactions that would lead to colloidal destabilization of nanodiamonds. It is also demonstrated that even a relatively low surface density of fl uorine contributes to stabilization of negatively charged nitrogen-vacancy centers and boosts their fl uorescence. The simultaneous control of the surface hydrophilicity and the fl uorescence of nitrogen-vacancy centers is an important issue enabling direct application of fl uorescent nanodiamonds as nanosensors for quantum optical and magnetometry measurements operated in biological environment.
The present study focuses on the development of a sensitive and specific approach for the visualization of sentinel lymph nodes draining the tumor using ultrabright 200‐nm fluorescent nanodiamonds (FNDs) equipped with a designed targeting surface architecture. The FNDs with a narrow size distribution are isolated by differential centrifugation, colloidally stabilized with alkyne‐functionalized poly(glycerol) and modified with a polyvalent array of mannose (FND‐p‐Man). In vitro experiments demonstrate an outstanding increase of the particle internalization by the mannose receptor CD206 (MR) and no significant toxicity. MR involvement is confirmed by blocking ligand binding with mannan and a 15.2 mAb (specific anti‐MR) in J774A.1 mouse macrophage cell line. In vivo mouse experiments confirm increased retention of FND‐p‐Man in sentinel lymph nodes of both healthy and B16 melanoma bearing animals. These results suggest that FND‐p‐Man has potential as a tracer for lymph node visualization in locoregional perioperative cancer diagnostics and as a tool for endoscopic/robotic fluorescence‐guided surgery.
Nanoparticle-cell interactions begin with the cellular uptake of the nanoparticles, a process that eventually determines their cellular fate. In the present work, we show that the morphological features of nanodiamonds (NDs) affect both the anchoring and internalization stages of their endocytosis. While a prickly ND (with sharp edges/corners) has no trouble of anchoring onto the plasma membrane, it suffers from difficult internalization afterwards. In comparison, the internalization of a round ND (obtained by selective etching of the prickly ND) is not limited by its lower anchoring amount and presents a much higher endocytosis amount. Molecular dynamics simulation and continuum modelling results suggest that the observed difference in the anchoring of round and prickly NDs likely results from the reduced contact surface area with the cell membrane of the former, while the energy penalty associated with membrane curvature generation, which is lower for a round ND, may explain its higher probability of the subsequent internalization.
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