2 research outputs found
Understanding the Surfaces of Nanodiamonds
Functional groups
and their associated charges are responsible
for the binding and release of molecules from the surfaces of particles
in nanodiamond colloids. In this work, we describe a combined set
of experimental and computational techniques that are used to characterize
these functional groups quantitatively. The surfaces of the particles
examined during this study are amphoteric, as one would expect for
surfaces made of carbon, with high concentrations of phenols, pyrones,
and sulfonic acid groups; the average 50-nm-diameter nanodiamond aggregate
has approximately 22000 phenols, 7000 pyrones, and 9000 sulfonic acids.
The aggregates also have at least 2000 fixed positive charges, stabilized
within pyrones and/or chromenes. No evidence for a significant concentration
of carboxylic acid groups was found, although some are probably present.
Hydroxyl and epoxide groups are present on some areas of the surfaces.
The surfaces are graphitized, so the presence of phenols and pyrones
is not surprising because such groups are common on graphitic surfaces.
The sulfonic acid is due to the sulfuric acid treatment used to remove
amorphous carbon and graphite during particle cleaning. The fixed
charges are also due to the cleaning procedure that includes the use
of KMnO<sub>4</sub> with the sulfuric acid. Based on titration and
zeta potential experiments, elemental and particle size analyses,
and modeling using semiempirical quantum mechanics, a model is proposed
for the types and concentrations of surface groups. The modeling shows
how functional groups form during the bead milling and cleaning used
in the preparation of the colloid. It also shows that the p<i>K</i><sub>a</sub> associated with the phenols and pyrones that
are formed (p<i>K</i><sub>a</sub> = 7.6–10.0) is
consistent with that predicted using titration experiments (p<i>K</i><sub>a</sub> ≥ 7.3). The positive surface potential
means that the latter p<i>K</i><sub>a</sub> value is significantly
larger than a Henderson–Hasselbalch-based estimate. The model
is shown to be useful in explaining a number of recent experiments
in which nanodiamonds were used to bind and release therapeutic drug
and polymer molecules
Nanodiamond Vectors Functionalized with Polyethylenimine for siRNA Delivery
The enormous therapeutic potential of RNA interference (RNAi) has long been recognized. While efficient small interfering RNA (siRNA) delivery vectors exist, many sacrifice biocompatibility, which can challenge their applicability as a therapeutic agent. Nanodiamonds (NDs) represent promising strategies for efficient siRNA delivery given the multitude of beneficial properties integrated into one platform that include uniform particle sizes, material scalability, the ability to carry nearly any type of therapeutic, and preserved biocompatibility, among others. Here we present a broadly applicable ND delivery platform that demonstrates biocompatible siRNA delivery with enhanced efficacy in media, signifying the translational potential of this approach