Stefan Ručman

Yes, DLS has been used in nano bubble research. A Google Scholar search will help you here. Also look at the work of the ISO TC281 Nanobubbles committee.

Is it possible to use it for in situ measurements? Introducing extra laser on top (opening) to make and measure bubbles in situ. @Alan F Rawle

Stefan Ručman

Yes, all of these things have been attempted. The issues are the apparent transient nature of the nanobubbles, the ease of removal on storage or transportation. the (usually) low concentration, and so on. This makes reproducibility more than difficult. However, all the preceding apply to all techniques that have found application in this area.

Alan is correct. DLS is used, and yes can do online (but normally specific online instruments for that) but as Alan says the concentration is on the low side. It's often 10^7 - 10^8 particles / ml, and DLS is better in the 10^9 or greater area.

The most prevalent technique is particle tracking analysis / nanoparticle tracking analysis as covers the size range and gives concentration as well as size (DLS can give concentration in some instrument configurations but not all.

ISO TC281 (as Alan mentioned) has a measurement matrix guide available which covers all the techniques used in the area and their strengths / weaknesses.

I have the great honor of being part of that group.

particle tracking analysis / nanoparticle tracking analysis PTA, how different from DLS is and where is this instrument available?

Similar in that both measure Brownian motion, but different in that one is based on tracking individual particles and the other is an ensemble technique. NTA measures size AND concentration, so these have BOTH become widely accepted measurands within the ultrafine bubble / nanobubble area. The Particle Tracking Analysis / Nanoparticle tracking analysis technique is widely available, Malvern Panalytical is a vendor (Nanosight) but there are other manufacturers too.

I see more NTA / PTA data than DLS for ultrafine / nanobubbles.

Since Air has a refractiv index of nearly 1 and water 1,33 the refreaction is not a problem, but nanobubbles usually have a rather small concentration, depending on the size the concentration can be to low. For inline measurements the DLS system from Colloid Metrix has the IPAS to dip in from the top. Assuring that the bubbles which are measured, are moving only by Brownian Motion.

Stephen Ward‐Smith thank you so much for the suggestion, in your opinion, if you would do it, what would you choose for nanobubble characterization? Can ultrasound be used for this? Since it is low concentration?

But I always thought that DLS doesn't have an issue with low concentration measurements? Philipp Schreier

Stefan Ručman Low Concentration is relativ like all things, DLS works quite nice for concentrations down to 0,001 %wt for partikels around 100nm even 0,0001%wt but that is still around 10^10 respectively 10^9 Partikels(Bubbles)/ml for lower concentrations i would recommend single partikel tracking.

It all depends on the concentration. As Philipp says 10^9 Particles / ml is fine for DLS, but many generator systems are 10^7 - 10^8.

Of course the other thing people forget is take your time. Bubble generation isn't always a fast process. Can take at least several hours to get a measurable stable concentration. Particle tracking IS the dominant technique in this area due to the concentration (plus the fact it measures the concentration so you can optimize the time conditions).

The final step is - Is it bubbles? There I recommend freezing the sample and defrosting. Cheap simple elimination, concentration before and after gives bubble concentration.

Hi Stefan Ručman

yes, DLS may work for nanobubbles - and it depends on the concentration. There probably have been more publications involving NTA for this application, due to the lower concentration requirements (NTA can handle samples with just a few nanobubbles per measurement volume, you just track for a longer time to get better statistics). Nevertheless, there are some interesting experimental results out there, we for example the references in https://www.materials-talks.com/blog/2019/02/07/nanobubbles-are-they-real/

thank you very much, very insightful and interesting. Ulf Nobbmann Stephen Ward‐Smith I found the NTA at my institution, it is g NanoSight NS300 (Malvern Instruments Ltd) equipped with a 488 nm laser. Samples were analyzed under constant flow conditions (flow rate = 30) at 25°C and were captured with a camera level of 13-14 using NTA software version 3.4 (Malvern). Two separate dilutions of samples were repeatedly analyzed for 5 times each at 60 seconds.

So I just worry now how can I use this instrument for in situ production? Because the samples in the department that has NTA are mostly blood and highly diluted serums (1:20000) so I wonder if it will work for characterization during production? or this Malvern model is not suitable for it?

There's online / in situ DLS but not in situ NTA (from any vendor). You'd really have to take grab samples every 15 minutes or so. The bubbles are long term stable, but it's just that initial period of set up that you may have to gather a lot of samples.

Though in situ DLS generally tends to work best at high concentrations.

However the NTA you have is perfect for off line grab samples. Right wavelength etc.

Is there anything similar to NTA that can be used for inline?

DLS or potentially diffraction (though it'll struggle at the bottom end) and whilst both are possible you will be fighting the concentration limit. At line grab samples with NTA whilst not ideally what you want to do may be the most effective solution.

You can to find more information in these article:

Chapter 3.2.1 - Dynamic light scattering (DLS)

Characterization of Nanoparticles

Measurement Processes for Nanoparticles Micro and Nano Technologies2020, Pages 137-172

Ulf Nobbmann Stephen Ward‐Smith Alan F Rawle I went to the facility that has NTA, they told me that time per sample is around one hour for machine to calculate size distribution. Is this common speed for this machine? this is unexpected drawback of using NTA. Also they told me it is difficult to control temperature if it is used long. Are these problems common for this type of machine?

No, should be taking them 10-15 mins sample including processing / cleaning. If measure very long time can heat, but not over the course of a measurement.

Hi Stefan Ručman

in the limited experience I have with NTA, actual measurements take at most a few minutes. It may be that your nanoparticle concentration is especially low, or especially small size, or especially small refractive index contrast between the material and the dispersant. I would recommend to reach out to the support team to get their guidance, they should be able to help you.

As far as measuring in flow, this can be done with a controlled, slow overall flow rate from an external pump, and can help improve counting statistics. However, I am not sure if this could be adapted to actually monitor a process 'in situ'.

Dynamic light scattering (DLS) technique overestimate the nanobubble size compared to the nanoparticle tracking analysis (NTA). Its better to use NTA. For more information follow the below paper:

Ma, X.; Li, M.; Pfeiffer, P.; Eisener, J.; Ohl, C.-D.; Sun, C. Ion adsorption stabilizes bulk nanobubbles. Journal of Colloid and Interface Science 2022, 606, 1380-1394.

Stefan Ručman Yes, this can be done. For a compact in-situ/in-line remote probe, you should give a try to Vasco Kin system from Cordouan Technologies. The software is able to perform a real-time distribution estimation (2 seconds resolution), and great post processing analysis too : https://www.cordouan-tech.com/products/vasco-kin/