Methods of measuring effective density of nanoparticle agglomerates dispersed in a liquid using centrifugation
The invention includes a method of determining the effective density of nanomaterial agglomerates in liquids, such as but not limited to physiological fluids, using volumetric centrifugation. The method of the invention allows for the development of reliable and efficient in vitro dosimetry and methods for toxicological testing of engineered nanomaterials.
1. A method of determining the effective density of a nanomaterial agglomerate in a liquid, the method comprising:
providing a dispersion of a first mass of a nanomaterial in a liquid, wherein a nanomaterial agglomerate is present within the dispersion;
centrifuging the dispersion at a speed sufficient to yield a supernatant and a pellet, wherein the pellet comprises a fraction of the nanomaterial agglomerate;
measuring the volume of the pellet and the mass of the nanomaterial left in the supernatant; and,
calculating the effective density of the nanomaterial agglomerate (ρ E ) by applying the formula:
ρ
E
=
ρ
media
V
pellet
SF
+
[
(
1
-
ρ
media
ρ
ENM
)
×
(
M
ENM
-
M
ENMsn
)
]
V
pellet
SF
,
wherein:
ρ media is the density of the liquid;
V pellet is the measured volume of the pellet;
SF is the stacking factor for the nanomaterial;
ρ ENM is the density of the nanomaterial;
M ENM is the first mass of nanomaterial;
M ENMsn is the measured mass of nanomaterial left in the supernatant;
thus determining the effective density of the nanomaterial agglomerate.
2. The method of claim 1 , wherein the speed of centrifugation is equal to or less than about 6,000×g.
3. The method of claim 2 , wherein the speed of centrifugation is equal to or less than about 2,000×g.
4. The method of claim 1 , wherein the dispersion is centrifuged for about 3 hours or less.
5. The method of claim 4 , wherein the dispersion is centrifuged for about 1 hour or less.
6. The method of claim 1 , wherein the mass of nanomaterial agglomerate is greater in the pellet than in the supernatant.
7. The method of claim 6 , wherein the ratio of mass of nanomaterial agglomerate in the pellet and the supernatant is equal to or greater than about 96:4.
8. The method of claim 1 , wherein the nanoparticles stack as tight ordered spheres in the pellet.
9. The method of claim 8 , wherein the stacking factor for the nanoparticles is about 0.74048.
10. The method of claim 1 , wherein the liquid comprises a biological fluid.