Abstract
Carboxylic acid is a commonly utilized functional group for covalent surface conjugation of carbon nanoparticles that is typically generated by acid oxidation. However, acid oxidation generates additional oxygen containing groups, including epoxides, ketones, aldehydes, lactones, and alcohols. We present a method to specifically enrich the carboxylic acid content on fluorescent nanodiamond (FND) surfaces. Lithium aluminum hydride is used to reduce oxygen containing surface groups to alcohols. The alcohols are then converted to carboxylic acids through a rhodium (II) acetate catalyzed carbene insertion reaction with tert–butyl diazoacetate and subsequent ester cleavage with trifluoroacetic acid. This carboxylic acid enrichment process significantly enhanced nanodiamond homogeneity and improved the efficiency of functionalizing the FND surface. Biotin functionalized fluorescent nanodiamonds were demonstrated to be robust and stable single-molecule fluorescence and optical trapping probes.
Highlights
Nanodiamonds (NDs) were first produced by graphite detonation in the USSR in the1960s [1]
Biotinylated fluorescent nanodiamond (FND) synthesized with this method were used to calibrate the evanescent field in a total internal reflection fluorescence (TIRF) microscope by attaching them to an individual DNA molecule that was supercoiled via magnetic manipulation, and we demonstrate high-efficiency optical trapping of single biotinylated FNDs attached to individual DNA molecules
The unenriched FND–biotin sample showed no change in average hydrodynamic diameter with increasing streptavidin concentration, indicating a negligible surface density of conjugated biotin. These results demonstrate that our carboxylic acid enrichment process significantly increased the functionalization of FNDs with biotin
Summary
Nanodiamonds (NDs) were first produced by graphite detonation in the USSR in the1960s [1]. Nanodiamonds (NDs) were first produced by graphite detonation in the USSR in the. Additional methods have been utilized to synthesize nanodiamonds, including chemical vapor deposition, laser ablation, and highpressure–high-temperature (HPHT) approaches [3,4,5]. With the discovery of fluorescent properties arising from Nitrogen-Vacancy (NV) centers in their lattice structure, fluorescent nanodiamonds (FNDs) show great promise in many cutting-edge applications [3], including quantum computing, [6] quantum sensing [7], and nanophotonics [8,9]. FNDs are typically prepared by bombarding nitrogen doped HPHT diamonds with a high-energy (1–10 MeV, typically 2 MeV) electron beam, followed by annealing at elevated temperatures (typically 800–900 ◦ C, 1–5 h, in vacuum or inert gas) to form NV centers by inducing vacancy diffusion. A final step consists of removing surface impurities and induced diamond graphitization by oxidation through treatment with nitric or sulfuric acid, or other oxidants [16,17]
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