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.

In this report, monodisperse upconversion NaYF:Yb/Er nanoparticles with superior optical properties were synthesized by the oleic acid-stabilized high-temperature co-precipitation of lanthanide chlorides in octadec-1-ene as a high-boiling organic solvent. To render the particles with biocompatibility and colloidal stability in bioanalytically relevant phosphate buffered saline (PBS), they were modified by using in-house synthesized poly(ethylene glycol)-neridronate (PEG-Ner), a bisphosponate. The NaYF:Yb/Er@PEG nanoparticles showed excellent long-term stability in PBS and/or albumin without any aggregation or morphology transformation. The in vitro cytotoxicity of the nanoparticles was evaluated using primary fibroblasts (HF) and a cell line derived from human cervical carcinoma (HeLa). The particles were subsequently modified by using Bolton-Hunter-hydroxybisphosphonate to enable radiolabeling with I for single-photon emission computed tomography/computed tomography (SPECT/CT) bimodal imaging to monitor the biodistribution of the nanoparticles in non-tumor mice. The bimodal upconversionI-radiolabeled NaYF:Yb/Er@PEG nanoparticles are prospective for near-infrared (NIR) photothermal/photodynamic and SPECT/CT cancer theranostics.