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

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