2.1 AuNP suspension preparation
The commercially available AuNPs with diameter of 10 nm (NIST-8011) and
5 nm (nanoComposix) were combined with electrolyte, which was 50 mM
ammonium acetate (AmAc) in deionized water, at a volume ratio of 3:2 and
had the final AmAc concentration of 20 mM.
Centrifugal sedimentation was applied on AuNP solution to reduce the
amount of surfactant in original solution. 400 μl of the original AuNP
solution was centrifuged at 14,000 rpm for 15 minutes and AuNPs were
separated from the solvent by protein concentrator. 400 μl deionized
water were then added and pipetted for AuNP resuspension. To perform two
or more centrifugal cycles, AuNP suspensions were experienced another
centrifugal process and solvent replacement. The centrifugal treated
AuNP (in 400 μl deionized water) were mixed with 266 μl 50 mM AmAc
solution and the final AuNP suspensions with 20 mM AmAc were prepared
for ES-SMPS size scanning.
The thermal treatment was performed using a tube furnace installed
between aerosol generator and ES-SMPS for the burnout of the surfactant
in AuNP aerosols. 300 μl of the original AuNP solution was mixed with
200 μl 50 mM AmAc solution to form the AuNP suspensions with 20 mM AmAc.
Four temperatures 20 ˚C, 200 ˚C, 500 ˚C, 800 ˚C were performed in gas
condition.