Fluorescent silica nanoparticles through silica densification
Provided herein are core-shell silica nanoparticles with a dense silica shell. The nanoparticles have improved properties such as, for example, increased photo luminescence and stability. Also provided are methods for making the nanoparticles.
1. A method for producing core-shell silica nanoparticles comprising the steps of:
a) preparing a silica core by combining a silica precursor and a silica precursor covalently bound to a light-absorbing material and/or light-emitting fluorescent or phosphorescent material, under conditions such that the silica precursors are hydrolyzed resulting in formation of a silica core, wherein the light-emitting material and/or light-absorbing material is covalently bound to the silica network of the core; and
b) forming a silica shell encapsulating the silica core by adding a silica precursor at a temperature of at least 50° C., under conditions such that formation of new silica nanoparticles is not observed.
2. The method of claim 1 , wherein the core-shell silica nanoparticles exhibit a density of at least 1.4 g/cm 3 .
3. The method of claim 1 , wherein the silica precursor is TEOS and/or TMOS.
4. The method of claim 1 , wherein the ratio of mass of light-absorbing material and/or light-emitting material to mass of silica is from 1 to 50 to 1 to 2000.
5. The method of claim 1 , wherein in step b) the silica precursors are added in the form of at least 10 aliquots of silica precursor at a temperature of at least 50° C. over a period of at least 1 hour, wherein the time between addition of the aliquots is at least 6 minutes.
6. The method of claim 1 , wherein step b) is carried out at a temperature of from 50 to 100° C.
7. The method of claim 1 , wherein the silica core has a diameter of from 1 to 300 nanometers.
8. The method of claim 1 , wherein the silica shell has a thickness of from 1 to 300 nanometers.
9. The method of claim 1 , wherein the core-shell silica nanoparticle has a diameter of from 1 to 1000 nanometers.