Due to its low toxicity and large chemical inertness, nanodiamond is an attractive material for biological applications. Biological moieties may be attached by either covalent or noncovalent bonding. Most publications available to date describe the noncovalent adsorption of proteins, antibodies, enzymes, viruses, etc. In some cases, the surface of the diamond particles is pretreated, for instance, by coating it with L - polylysine or cellobiose, before the adsorption of the biologically active unit itself is effected. The diamond hybrid particles thus obtained suit to the preparation of transporting vehicles for vaccines or pharmaceutical actives or to the controlled release of genes, etc., inside living cells. In this regard then, the small particle size is rather beneficial.
Moreover, an application on biochips for the determination of certain proteins in a serum has been presented. The attachment takes place, for instance, on an immobilized enzyme with the read-out of information normally being enabled by fluorescence labeling. Besides an external fluorescence label, it is also possible to employ the inherent luminescence of lattice defects in the diamond itself (Section 22.214.171.124). It is especially nitrogen defects that may be detected this way, that is, by fluorescence microscopy (Figure 5.46). Defective nanodiamond particles with surface functionalization may also be employed as fluorescence label in 3n vivo experiments, so a system complementary to the metal chalcogenide quantum dots usually applied is available here. The nanodiamond adducts in these processes are characterized by their small particle size, stable fluorescence, and (at least according to current knowledge) by their nontoxicity.
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