The outline and latest status of fine bubble measurement techniques - - PowerPoint PPT Presentation

The outline and latest status of fine bubble measurement techniques

Dr Stephen Ward-Smith Malvern Instruments Ltd

Techniques used for characterising fine and ultrafine bubbles

› Particle tracking analysis (aka Nanoparticle tracking

analysis, NTA, PTA)

› Resonance Mass Measurement › Dynamic Light Scattering (aka Photon Correlation

Spectroscopy)

› Laser Diffraction › Zeta potential › Others (electrozone sensing, ultrasonics, static multiple

light scattering, image analysis)

› All are sizing techniques, bar Zeta Potential which is a

measure of particle charge

Brief Summary

Technique Size Range Laser Diffraction <100nm to >2mm Dynamic Light Scattering <1nm to >1 micron NTA <30nm to >1 micron Archimedes <35 nm to > 2micron Image Analysis <1um to >3 mm

› Particle size ranges will depend on the

sample and the sensor used.

Sensor Chip

Archimedes

Resonant Mass Measurement

Measuring Particle Mass in Fluid

• 150
• 100
• 50

50 100 150

• 400
• 300
• 200
• 100

Frequency Shift (mHz) Time (msec)

200

1. 3. 2. 1. 2. 3.

The buoyant mass of a particle is always measured relative to its surrounding

• fluid. A particle of dust will therefore have a negative buoyant mass in water,

and a bubble will have a positive buoyant mass in water

Buoyant Mass Measurement

Resonant Mass Measurement

› Populations of particles with negative and positive buoyant

can be detected using RMM.

› The limit of detection for RMM with ultrafine bubbles is around

about 100nm based on the sensitivity of the instrument and the mass differential of the fluid and 100nm bubbles.

› RMM is unique in its ability between dust particles and ultra

fine bubbles of the same size in the same sample.

› However as proven with NTA some ultrafine bubbles will be

generated beyond the limit of detection for RMM.

› Efforts are being made to push the limit of detection to smaller

sizes with RMM.

What are Microbubbles?

• Gas: Air, Perfluorocarbon, Sulfur

Hexafluoride, etc… – High Molecular Weight Gas

• Shell: Polymer, Lipid, Albumin, etc…
• Size: Typically < 8 μm for Contrast Agent

Applications

• Microbubble Contrast Agent

– Molecular Imaging – Blood Perfusion-Based Imaging – Gene Therapy

• DNA Fragmentation for Next

Generation Sequencing

• Semiconductor Cleaning
• Food Scenting

5 m

Generic example of ability of RMM to differentiate between bubbles and lipid droplets

Effect of Loading Pressure on Bubbles

5psi 10psi 20psi 30psi 35psi Bubbl es As PLoad increases, number of bubbles decreases

0.265 0.269 0.272 0.24 0.357 0.15 0.2 0.25 0.3 0.35 0.4 10 20 30 40

Mean Size (um) Loading Pressure (psi)

294 267 247 35 22 0.15 50.15 100.15 150.15 200.15 250.15 300.15 350.15 10 20 30 40

Number of Bubbles

Loading Pressure (psi)

As PLoad increases, mean bubble size increases

Update: Measuring bubbles with RMM ›

 Bubbles measured successfully during 2 customer demos in 2015

›

 During both demos used standard operating conditions Pload 35psi. Able to demonstrate measurement

• f lipids and bubbles.

›

 Concern that 35psi loading pressure may cause bubbles to collapse

›

 US customer provided us with samples to study loading pressures

5psi 10psi 20psi 30psi 35psi

Bubbles prepared by using agitation method Sample contains bubbles + excess lipid Samples used for each Archimedes measurement aliquoted from same vial Loading Pressures (psi): 35, 30, 20, 10, 5 Total number particles (lipid + bubble) counted per experiment: 500

Lipids As PLoad increases, number of lipid particles increases

206 233 253 465 478 100 200 300 400 500 600 10 20 30 40

Number of Lipid Particles Loading Pressure (psi)

› Shake Time

Bubb les Lipid s 20 seconds 45 seconds 90 seconds 20 seconds 45 seconds 90 seconds Mean size clearly increases with shake time –may be

due to coalescence Lots of lipid particles at 20sec shake time

161 10 1 20 40 60 80 100 120 140 160 180 20 40 60 80 100

Number of lipids

Shake Time (sec)

188 286 395 150 200 250 300 350 400 450 20 40 60 80 100

Size (nm) Shake Time (sec)

Effect of Gas Pressure

Bubb les 6 psi 11 psi 16 psi Lipid s 6 psi 11 psi 16 psi Change in mean bubble size does not seem significant Not much difference in 6 and 11 psi samples, but 16 psi has many more lipids. Suspect that higher pressure is preventing bubbles from forming, hence more lipids

Shelf Life – USA bubble samples shipped March 24th, 2016

5 days 25 days 70 days *These are the bubbles sent in March *Excellent shelf life

Zeta potential of bulk ultrafine bubbles: effects of salt, pH and surfactant

Zeta Potential

• Zeta potential measurement results in an absolute value reported in [mV] and serves

as a predictor of suspension stability.

High Zeta Potential

Low or Zero Zeta Potential

Unstable suspension Stable suspension

Electrophoretic Light Scattering (ELS)

Measured parameter is the frequency shift

• f the scattered light.

The frequency shift is proportional to the electrophoretic mobility, which is a function

• f the particle surface potential. Hence

ELS gives us information regarding the charge on the particle.

Measuring Zeta Potential

› Electrophoresis = movement of a charged particle

relative to the liquid it is suspended in under the influence of an applied electric field

Particles velocity dependent on:

 Zeta potential  Field strength  Dielectric constant of medium  Viscosity of the medium

Laser Doppler Electrophoresis

›

Scattered light is frequency (Doppler) shifted

›

Frequency shift

 = the particle velocity  = laser wavelength q = scattering angle

›

Frequency shifts determined by Fourier transformation and phase analysis light scattering

f = 2 sin(q/2)/

›

Measured electrophoretic mobility converted into zeta potential using Henry’s equation

Typical ultrafine bubble size distribution measured by NTA

Concentration (106 bubbles/mL)

Ultrafine bubbles generated in a salt solution are less stable than those generated in distilled water

Adding salt to a suspension of ultrafine bubbles reduces their stability

Generating ultrafine bubbles in a low pH medium reduces their stability

isoelectric line

Lowering the pH of a suspension of ultrafine bubbles reduces their stability

Adding surfactant to a suspension of ultrafine bubbles increases their stability

Further work

› Do DLS / Zeta in series with each other to see the effect

Zeta potential has on size. Would expect bubbles in systems with zeta potential in the -30 mV to + 30 mV area to grow larger over time compared to those outside this area.

› Need to do some daily monitoring experiments.

Acknowledgements

› Archimedes team at Malvern Instruments › US customer for supplying bubble / lipid samples › Mostafa Barigou and group at University of Birmingham

Thank you for your attention

• Any Questions?

Steve Ward–Smith - stephen.ward-smith@malvern.com 28