8.4 Characterization of bionanoparticles by electrospray-differential  (Page 4/4)

Applications of es-dma

• Determination of molecular weight of polymers and proteins in the range of 3.5 kDa to 2 MDa by correlating molecular weight and mobility diameter.
• Determination of absolute number concentration of nanoparticles in solution by obtaining the ES droplet size distributions and using statistical analysis to find the original monomer concentration. Dimers or trimers can be formed in the electrospray process due to droplet induced aggregation and are observed in the spectrum.
• Kinetics of aggregation of nanoparticles in solution by analysis of multimodal mobility distributions from which distinct types of aggregation states can be identified.
• Quantification of ligand adsorption to bionanoparticles by measuring the reduction in electrical mobility of a complex particle (particle-protein) that corresponds to an increase in mobility diameter.

Characterization of sam-functionalized gold nanoparticles by es-dma

Citrate ( [link] ) stabilized gold nanoparticles (AuNPs) with diameter in the range 10-60 nm and conjugated AuNPs are analyzed by ES-DMA. This investigation shows that the formation of salt particles on the surface of AuNPs can interfere with the mobility analysis because of the reduction in analyte signals. Since sodium citrate is a non volatile soluble salt, ES produces two types of droplets. One droplet consists of AuNPs and salt and the other droplet contains only salt. Thus, samples must be cleaned by centrifugation prior to determine the size of bare AuNPs. [link] presents the size distribution of AuNPs of distinct diameters and peaks corresponding to salt residues.

The mobility size of bare AuNPs (d _p0 ) can be obtained by using [link] , where d _p,m and d _s are mobility sizes of the AuNPs encrusted with salts and the salt NP, respectively. However, the presence of self-assembled monolayer (SAM) produces a difference in electrical mobility between conjugated and bare AuNPs. Hence, the determination of the diameter of AuNPs (salt-free) is critical to distinguish the increment in size after functionalization with SAM. The coating thickness of SAM that corresponds to the change in particle size (ΔL) is calculated by using [link] , where d _p and d _p0 are the coated and uncoated particle mobility diameters, respectively.

In addition, the change in particle size can be determined by considering a simple rigid core-shell model that gives theoretical values of ΔL ₁ higher than the experimental ones (ΔL). A modified core-shell model is proposed in which a size dependent effect on ΔL ₂ is observed for a range of particle sizes. AuNPs of 10 nm and 60 nm are coated with MUA ( [link] ), a charge alkanethiol, and the particle size distributions of bare and coated AuNPs are presented in [link] . The increment in average particle size is 1.2 ± 0.1 nm for 10 nm AuNPs and 2.0 ± 0.3 nm for 60 nm AuNPs so that ΔL depends on particle size.

Advantages of es-dma

• ES-DMA does not need prior information about particle type.
• It characterizes broad particle size range and operates under ambient pressure conditions.
• A few µL or less of sample volume is required and total time of analysis is 2-4 min.
• Data interpretation and mobility spectra simple to analyze compared to ES-MS where there are several charge states.

Limitations of es-dma

• Analysis requires the following solution conditions: concentrations of a few hundred µg/mL, low ionic strength (<100 mM) and volatile buffers.
• Uncertainty is usually ± 0.3 nm from a size range of a few nm to around 100 nm. This is not appropriate to distinguish proteins with slight differences in molecular weight.

Related techniques

A tandem technique is ES-DMA-APM that determines mass of ligands adsorbed to nanoparticles after size selection with DMA. APM is an aerosol particle mass analyzer that measures mass of particles by balancing electrical and centrifugal forces. DMA-APM has been used to analyze the density of carbon nanotubes, the porosity of nanoparticles and the mass and density differences of metal nanoparticles that undergo oxidation.

Bibliography

• http://www.iara.org/newsfolder/pioneers/8aerosolpioneereditedaugktwhitby.pdf
• E. O. Knutson and K. T. Whitby. Aerosol Sci. , 1975, 6 , 443.
• S. T. Kaufman, J. W. Skogen, F. D. Dorman, and F. Zarrin. Anal. Chem. , 1996, 68 , 1895.
• R. C. Flagan. KONA , 2008, 26 , 254.
• P. Intra and N. Tippayawong. Songklanakarin J. Sci. Technol ., 2008, 30 , 243.
• D. Tsai, R. A. Zangmeister, L. F. Pease III, M. J. Tarlov, and M. R. Zachariah. Langmuir , 2008, 24 , 8483.
• D. Tsai, L. F. Pease III, R. A. Zangmeister, M. J. Tarlov, and M. R. Zachariah. Langmuir , 2009, 25 , 140.
• G. Bacher, W. W. Szymanski, S. T. Kaufman, P. Zollner, D. Blaas, and G. Allmaier. J. Mass Spectrom. , 2001, 36 , 1038.
• M. Li, S. Guha, R. Zangmeister, M. J. Tarlov, and M. R. Zachariah. Langmuir , 2011, 27 , 14732.
• S. Guha, M. Li, M. J. Tarlov, and M. R. Zachariah. Trends Biotechnol ., 2012, 30 , 291.
• L. F. Pease III. Trends Biotechnol ., 2012, 30 , 216-224.
• S. Guha, X. Ma, M. J. Tarlov, and M. R. Zachariah. Anal. Chem. , 2012, 84 , 6308.
• Y. Tseng and L. F. Pease III. Nanomed-Nanotechnol ., 2014, 10 , 1591.