from single photon producing nitrogenvacancy (NV) color centers consisting of a substitutional nitrogen atom next to a vacancy that is engineered artificially in the diamond lattice. The nanoscale effects related to artificially engineered NV color centers attracted important attention to diamond due to applications ranging from quantum computing to cell imaging. [2][3][4] The luminescence from NV centers is extremely stable without any photobleaching or photoblinking [5][6][7] and compared to better known quantum dots, ND brings additional advantages such as high biocompatibility [8,9] and simple C-surface chemistry. [10,11] This allows grafting of biomolecules that are interesting for cellular targeting [12,13] or biomolecular drug delivery. [14][15][16] However, for very small ND particles (5 nm) blinking of NV centers was observed, [17] showing that the surface effects are of importance for stabilization of NV luminescence properties.Here we describe how the surface chemistry effects can make the ND bulk luminescence sensitive to chemical processes ongoing at the ND surface, with the aim of using ND for monitoring a chemical environment such as surface charges or pH, cellular DNA/RNA hybridization, interaction with cell receptors, etc. The proposed method is based on the control of an electronic chemical potential at the

High pressure high temperature (HPHT) nanodiamonds (NDs) represent extremely promising materials for construction of fluorescent nanoprobes and nanosensors. However, some properties of bare NDs limit their direct use in these applications: they precipitate in biological solutions, only a limited set of bio-orthogonal conjugation techniques is available and the accessible material is greatly polydisperse in shape. In this work, we encapsulate bright 30-nm fluorescent nanodiamonds (FNDs) in 10–20-nm thick translucent (i.e., not altering FND fluorescence) silica shells, yielding monodisperse near-spherical particles of mean diameter 66 nm. High yield modification of the shells with PEG chains stabilizes the particles in ionic solutions, making them applicable in biological environments. We further modify the opposite ends of PEG chains with fluorescent dyes or vectoring peptide using click chemistry. High conversion of this bio-orthogonal coupling yielded circa 2000 dye or peptide molecules on a single FND. We demonstrate the superior properties of these particles by in vitro interaction with human prostate cancer cells: while bare nanodiamonds strongly aggregate in the buffer and adsorb onto the cell membrane, the shell encapsulated NDs do not adsorb nonspecifically and they penetrate inside the cells.

A novel approach for preparation of ultra-bright fluorescent nanodiamonds (fNDs) was developed and the thermal and kinetic optimum of NV center formation was identified. Combined with a new oxidation method, this approach enabled preparation of particles that were roughly one order of magnitude brighter than particles prepared with commonly used procedures.

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Efficient delivery of stabilized nucleic acids (NAs) into cells and release of the NA payload are crucial points in the transfection process. Here we report on the fabrication of a nanoscopic cellular delivery carrier that is additionally combined with a label-free intracellular sensor device, based on biocompatible fluorescent nanodiamond particles. The sensing function is engineered into nanodiamonds by using nitrogen-vacancy color centers, providing stable non-blinking luminescence. The device is used for monitoring NA transfection and the payload release in cells. The unpacking of NAs from a poly(ethyleneimine)-terminated nanodiamond surface is monitored using the color shift of nitrogen-vacancy centers in the diamond, which serve as a nanoscopic electric charge sensor. The proposed device innovates the strategies for NA imaging and delivery, by providing detection of the intracellular release of non-labeled NAs without affecting cellular processing of the NAs. Our system highlights the potential of nanodiamonds to act not merely as labels but also as non-toxic and non-photobleachable fluorescent biosensors reporting complex molecular events.

Fluorescent cellular biomarkers play an essential role in biology and medicine for in vitro and in vivo imaging in living cells. Recently, we have demonstrated that photoluminescence (PL) can be driven chemically by changing the occupation of NV− and NV0 states by H‐ or O‐termination. In the presented work we study, how the luminescence of NV centers at controlled depth from the surface changes upon different surface treatment. We compare NV luminescence of hydrogen (H) and oxygen (O) terminated surfaces in single crystal diamond (SCD) containing shallow‐implanted NV centers (3–10 nm) with similarly treated nanodiamond particles (ND) of various size distributions. The H‐termination leads to reduction of NV− related luminescence in both, ND and SCD. The effect is much stronger in ND in comparison with SCD. We mathematically model both situations and discuss parameters influencing the effect, including implantation energy and different contents of nitrogen in the diamond crystal lattice.

We show that fluorescent nanodiamonds (FNDs) are among the few types of nanosensors that enable direct optical reading of noncovalent molecular events. The unique sensing mechanism is based on switching between the negatively charged and neutral states of NV centers which is induced by the interaction of the FND surface with charged molecules.

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