Abstract
In this paper, the authors have investigated the effects of different cleaning methods (centrifugation and dialysis) on the surface chemistry and composition of 15 nm sodium citrate stabilized gold nanoparticles. The nuclear magnetic resonance (NMR) results indicate that three centrifugation cycles are sufficient to remove most of the citrate molecules, while centrifuged liquid sedimentation and dynamic light scattering data reveal some degree of nanoparticle aggregation when three centrifugation cycles are exceeded. Regarding the dialysis procedure, NMR analysis demonstrated that after nine cleaning cycles, the citrate concentration is comparable to that measured after the first centrifugation (about 6 × 10-4 M) but with an increase in the dispersion polydispersivity index as determined by dynamic light scattering. X-ray photoelectron spectroscopy results support the NMR findings and revealed a major hydrocarbon contamination after the nanoparticles cleaning process. The impact of cleaning on surface functionalization was tested using 1H,1H,2H,2H-perfluorodecanethiol hydrophobic thiols (PFT) to test thiol-citrate substitution. After 24 h exposure, the PFT coverage was less than 0.6 monolayer (ML) for both pristine nanoparticles and particles after three dialysis cycles, but about 0.8 ML after two centrifugation washes.
Highlights
Nanomaterials have great potential to be used in numerous applications ranging from energy to medicine and food
The nuclear magnetic resonance (NMR) results indicate that three centrifugation cycles are sufficient to remove most of the citrate molecules, while centrifuged liquid sedimentation and dynamic light scattering data reveal some degree of nanoparticle aggregation when three centrifugation cycles are exceeded
A comparison between dialysis and centrifugation steps as cleaning procedures to remove the excess of citrate from colloidal AuNPs has been made and the amount of residual citrate correlated to the stability of gold nanoparticles in solution
Summary
Nanomaterials have great potential to be used in numerous applications ranging from energy to medicine and food As a consequence, this revolutionary field of science and technology is being intensively studied as a possible means to help satisfy future societal needs.. Among the different metallic nanoparticles, gold nanoparticles (AuNPs) are probably the most studied because of their particular optical and electronic properties, the relative simplicity of their synthesis processes, and the wide range of possible surface modifications achievable via thiol based chemistry.. Among the different metallic nanoparticles, gold nanoparticles (AuNPs) are probably the most studied because of their particular optical and electronic properties, the relative simplicity of their synthesis processes, and the wide range of possible surface modifications achievable via thiol based chemistry.16–21 These properties make AuNPs very interesting for use in diverse industrial and technological sectors their successful application, in demanding areas such as biomedical and biosensing requires stable and sound surface functionalities based on robust, reliable, and reproducible functionalization protocols combined with systematic nanoparticle characterization.. (i.e., centrifugation and dialysis) on the physicochemical properties of AuNPs (15 nm in diameter) and on the degree of functionalization by an hydrophobic molecule
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