4 Conclusion
The conventional NPs such as AuNPs have been known to show the measurement uncertainty in ES-SMPS system because of the addition of surfactant, and the surfactant-depended uncertainty is more serious especially for the NPs with sub-10 nm diameter. In this experiment, two treatments including centrifugation and heating were used to remove the surfactant while both were found to present little effect on the detected diameter. Instead of working on the size improvement of AuNPs, the self-disperse biological macromolecules were considered for the sub-10 nm RM. Bio-NPs of four proteins were examined and the BSA and ubiquitin were characterized to have the similar charging efficacy with the conventional NPs, where the monomer, dimer and trimer could be seen among their size distributions. The representative diameter of BSA was 6.9 nm and ubiquitin was 3.6 nm. The suspense stability of these bio-NPs was monitored and the consistence in the detected size was approved. In conclusion, the BSA and ubiquitin were suggested as the sub-10 nm RM for the ES-SMPS calibration.