Polydispersity Index and dynamic light scattering are essential to characterise nanoparticle size and stability. However is PDI necessary for the antimicrobial assay of nanoparticles with a plant extract, if yes how? Is it necessary to have a PDI value when I have performed FTIR, DLS and zeta potential analysis to check for the size, stability and composition of nanoparticles?
Sheshadri S Temkar
By determining the size of nanoparticles and taking spectra, you prove that you have obtained a certain size of nanoparticles in the extract, which is well combined with the body. Most nanoparticles are size-distributed because it is thermodynamically advantageous. Nanoparticles have antimicrobial properties due to their large specific surface area. The larger the specific surface, the better the microbial cell is adsorbed on the nanoparticle, the better the microbial properties of the nanoparticle. PDI does not affect the specific surface with the dimension m2/g.
Yuri Mirgorod It is advisable to have a PDI of less than 1 in the case of iron oxide nanoparticles. I have a PDI exceeding 1, will it have any effect on the antimicrobial assay of the nanoparticles especially when I'm coating the with a plant compound? (The size of the nanoparticles by DLS was confirmed to be less than 100nm)
Is FTIR, DLS and Zeta potential sufficient to characterise nanoparticles for a project aimed at estimating the antimicrobial activity? Yuri Mirgorod
By means of DLS you can simultaneously obtain the hydrodynamic diameter and PDI of your nanoparticles. The PDI is an important parameter to measure as it gives you information about the size distribution of your formulation. Especially if your nanoparticles are to be administered parenterally, you should maintain a monodisperse population of nanoparticles preferably with a PDI
Sheshadri S Temkar
FTIR, DLS and Zeta potential are essential for the characterization of nanoparticles. Antimicrobial properties must be studied according to a specific medical method approved in your country.
Eloy Pena Rodríguez Again, PDI is not a mandatory indicator for antimicrobial nanoparticles. May be 90 nm with PDI < 0.2. This is worse than 10 nm with PDI = 1, since the specific area of 10 nm nanoparticles will be larger and they will better adsorb bacteria.
The problem with not optimising a PDI as high as 1 is that even if the average population size is 10 nm, such a high polydispersity indicates many more populations, of different sizes, larger and smaller. In addition, DLS is designed for 1 or 2 different population sizes, so when you get very high PDIs, the information provided by DLS could be erroneous.
We are having a discussion of PDI being high or low, is there an acceptable range of PDI beyond which the samples are considered bad? Eg: I have nanoparticles with a size of 72.3nm but a PDI of 2.81, what can I infer from this result? Eloy Pena Rodríguez Yuri Mirgorod
When talking about nanoparticle population size characterization, the term "PDI" refers to the Polydispersity Index (PDI), which is a measure of particle size dispersion in a sample. The PDI is calculated by dividing the width of the particle size distribution by its mean value. The PDI value ranges from 0 to 1, where 0 indicates a sample with uniform particle sizes and 1 indicates a sample with a wide particle size distribution. In my opinion, PDI values higher than 0.3-0.5 is an indicator of a too polydisperse sample. But as I told you depending on the indication these polydisperse values could be acceptable. What I dont understand is why your PDI is higher than 1 as its range is from 0 to 1.
Sheshadri S Temkar
From my article. The values of the PdI index were optimal also(PdI) from 0.278 up to 0.591 . When PdI 7 thesystem contains particles with very broad size distribution. In this case the DLS method cannotbe applied to study the system. The baseline forall correlation functions was zero. Another its position means that there are very large fluctuations in the system (the presence of airbubbles). When the particles move free, the correlation function is always damped. The correlation function for large particles has a flatter slope than that for small particles. Analysis of the correlation function using the software provides the average particle size (Z) and the average distribution (PdI).
Correctly interpreting the usual *scatter intensity weighted* DLS results (the harmonic mean size and pdi) requires quite some caution: depending on the size range one is measuring, trends in the DLS pdi may not give a representative picture of what is happening to the relative width of the physical (i.e. volume weighted) PSD. For more info see the attched poster
In general the polydispersity is a significant parameter in the characterization of the nanoparticles. Specifically, if the value is small, it indicates a less broad distribution than a large polydispersity. So if you were to try to do any quality control on this nanoparticle assay with a PDI of 1 it would be very challenging to use PDI if the target is so polydisperse.
The PDI may not be "necessary" - however in the case of PDI 1 the DLS result may not give a repeatable representation of what is in your sample.
The assay activity is probably related to the overall surface area of your nanoparticles, and this value would change for example between a monodisperse and an aggregated nanoparticle dispersion. Here are a few links with further info that might be of interest:
https://www.materials-talks.com/faq-peak-size-or-z-average-size-which-one-to-pick-in-dls/
https://www.materials-talks.com/polydispersity-what-does-it-mean-for-dls-and-chromatography/
https://www.materials-talks.com/polydispersity-from-a-gold-standard/
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