Measuring nanoparticle properties: experiences from NPL Caterina Minelli

Measuring nanoparticle properties: experiences from NPL Caterina Minelli

Measurement of Particles Types of materials: Metal Examples: Silver Gold Palladium Platinum Semiconductor Examples: Quantum Dots Metal oxides Examples: TiO2 Silica Zinc oxide Ceria Polymer Examples: PS PMMA PVA Co-polymers Low density Examples: Liposomes Emulsions Oil in water Bubbles Types of media: water buffer serum biological fluid organic dry powders Measurements of core properties: size distribution density chemistry crystal structure mechanical optical Measurements of surface properties: chemistry elemental and molecular composition coating thickness surface charge (zetapotential) Protein folding Measurement of behaviour: agglomeration stability and precipitation molecular binding electrochemical activity

NPL approach to nanoparticle analysis: XPS AFM EM Optical Spectroscopy TRPS SMPS DLS Complementary techniques provide different physical and chemical pieces of information DCS NTA SIMS LEIS SAXS Surface NMR

Example of method cross-validation Citrate Short peptide Bovine Serum Albumin (BSA) ImmunoglobulinG (IgG) 0.192 KDa 1.7 KDa 66.5 KDa 160 KDa GEPI sequence GGG spacing cysteine Au LSPR DLS DCS Belsey, et al, Biointerphases 10 (2015) 019012

Quantification in liquids λ = b(n s n w ) 1 exp T L n s = 1.42 ± 0.02 ~60% water (v/v) N(opt) = N AVol S (n s n w ) d M n IgG d c A few tens to several hundreds of protein molecules attached to each particle. Rapid increase in N at low values of ρ IgG and a slower rise after the surface of the particles has become saturated with proteins. Bell, et al, Analytical Methods 5 (2013) 4523

Coating thickness with XPS XPS can provide measurements of the chemistry and thickness of the shell. Shard, J. Phys. Chem. C 116 (2012) 16806

Measurement of NP coatings by XPS e - e - Shard method Chemical composition Thickness Number of IgG Belsey, et al. Biointerphases 10 (2015) 019012

In situ vs. in vacuum analysis DLS, DCS, LSPR (opt) Au peptides XPS Excellent agreement of in situ and in vacuum analysis. Similar results for other coatings. XPS is a more robust technique for analysis of nanoparticles coatings. Belsey, et al. Biointerphases 10 (2015) 019012

VAMAS inter-laboratory study Measurement of chemistry and thickness of nanoparticle coatings 24 participants: XPS, LEIS & MEIS Belsey, et al. J Phys Chem C 120 (2016) 24070 24079

When particles aggregate PEG-coated gold nanoparticles. Agglomerated particles: no DLS. Measure shell thickness and surface molecular density with combination of techniques. DCS XPS Minelli and Shard, Biointerphases 11 (2016)

Density of NPs by SAXS and DCS Continuous contrast variation SAXS to measure size and density of nanoparticles (BESSY II, PTB, Berlin). Bulk PMMA Cross-validation provided by analysis in liquids, by using analytical centrifugation (DCS) to measure density. Bulk PS R. Garcia-Diez, et al, European Polymer Journal 81 (2016) 641 649.

Size and density of particles with DCS At NPL, we developed a method to measure size and density of particles. Particle sedimentation and flotation via analytical centrifugation was used to simultaneously measure the size and density of polystyrene nanoparticles. Measured size: (98 ± 4) nm Measured density: (1.053 ± 0.004) g/cm 3 Sample volume: ~10 μl of initial solution

Structure of nanoparticles - - - -- -- - - --- - - - - - - - - - -- --- - -- -- -C-C- -C-C- C=O O + -C-C- Framework: size measurement of commercial carboxylated polystyrene (PS) nanoparticles by small angle X-ray scattering (SAXS). Outcome: inaccuracy, as SAXS data was not consistent with a homogeneous sphere model. Investigation: by analytical centrifugation we measured a particle density of 1.068 g/cm 3, well above that of polystyrene. Prompted, the manufacturer informed us of the addition of methacrylic acid (MAA) monomers during synthesis (confirmed by X- ray photoelectron spectroscopy). Materials may not be what you expect! Good interaction with manufacturer is beneficial. C. Minelli et al., SIA 46 (2014) 663

Nanoparticles in serum When nanoparticles enter serum, proteins adsorb to form a protein shell: Increased size; Changed density; Changed agglomeration; Changed surface charge. In case of agglomeration, dynamic light scattering (DLS) provides limited information on the sample. Here, combination of: Tunable resistive pulse sensing (TRPS); Differential centrifugal sedimentation (DCS); Aminated silica nanoparticles in serum We measure: Shell thickness; Effective density; Agglomeration; Surface charge. Sikora et al., Anal. Methods 7 (2016) 9835 Sikora et al., Langmuir 32 (2016) 2216 Gollwitzer et al., Anal. Methods, on line (2016)

Particle-by-particle ζ-potential TRPS = tunable resistive pulse sensing (Coulter counter technique) Sample volume: 40 μl, very diluted Size, surface charge, concentration TRPS For the first time we can observe variability in surface charge of as synthetized nanoparticles. This is large compared to, for example, protein coated NPs. Sikora et al., Anal. Methods 7 (2016) 9835 Sikora et al., Langmuir 32 (2016) 2216 Gollwitzer et al., Anal. Methods, on line (2016)

Summary There is no one technique that answers all the questions. The best approach is to use selected ones in concerto. The selection of the technique of use depends on the purpose: QA, accurate measurements, quantification, etc. Sample preparation is critical. Less traditional techniques for particle characterisation (e.g. XPS) are very valuable when correct methods are developed.

Acknowledgements NPL: Alex Shard Natalie Belsey David Cant Martin Seah All participants to VAMAS inter-laboratory study PTB (SAXS): Raul Garcia-Diez Christian Gollwitzer Michael Krumrey The National Physical Laboratory is operated by NPL Management Ltd, a whollyowned company of the Department for Business, Innovation and Skills (BIS).