Polydispersity Index is dimensionless and scaled such that values smaller than 0.05 are rarely seen other than with highly monodisperse standards. Values greater than 0.7 indicate that the sample has a very broad size distribution and is probably not suitable for the DLS technique. The various size distribution algorithms work with data that falls between these tow extremes. The calculations for these parameters are defined in the ISO standard document 13321:1996 E and ISO 22412:2008

Well that depend in what types of nanoparticles, the synthetic approach followed and the instrument used for DLS. For iron oxide obtained by coprecipitation you may have a PDI of 0.4 and be acceptable, however if you are using thermal decomposition the "acceptable" value is much lower (0.07-0.2).

regarding the DLS usually the manufacturer says that the PDI must be smaller than 0.6-0.7 to have a reliable measurement, at least for Zetasizer.

Practically it should be less than 0 .5 . Because it is an indicator of aggregation in the particles,as the value is more it shows a polydisperse system and if it is closer to zero it denotes the monodisperse system. Polydisperse have greater tendency to aggregation than monodisperse system

There is no general limit for acceptable polydispersity. It depends on the purpose you want to use the particles for. If you want to do investigations on monodisperse particles obviously it should be as small as possible. The acceptable should not be defined by the instrument reliability. It is the other way around (use of the instruments acceptable or not). Polydispersity can be due to aggregation/agglomeration but also simply by different primary size.

may i have the references about the acceptable limit of PDI? im doing research for polymeric nanoparticles. thank you

I am not familiar with nanoparticles but I need to understand one thing.

When I read about PI, it says value is equal or higher than 1. However, it seems in nano-scale it is almost always lower than 1.

Could anyone explain me about this please?

Thank you

A PDI value of 1 indicates that the sample has a very broad size distribution and may contain large particles or aggregates that could be slowly sedimenting.

PDI always is below 1 . for biologic polymers it may be 0.4-0.7. right value for these system is 0.4.

I am also looking for answers of the same question mentioned here. I have not much idea of PDI of nanoparticles. I have used inorganic carbonate apatite nanoprticles for treating breast ancer in mice through IV injection. I have measured the PDI for those particles. its around 0.4.

At which PDI value a particle can go inside the cells by endocytosis? Is there any correlation? 

Obviously polydispersity of nanoparticles can vary in a broad range. For bottom-up you may be able to obtain very narrowly distributed particles, for top-down naturally the opposite is usually the case.

If I understand well for passing the cell barrier beside surface properties only size of particles is important. Cannot imagine how polydispersity can play a role in this.

As I understand the aggregated particles may interfere in cellular uptake because of their bigger size than single particle. As endocytosis is size dependent, I am wondering whether pdi value could help to give sunsun

thank you all

What is the acceptable limit polydispersity index(pdi) of Proteins?

Polydispersity Index is dimensionless and scaled such that values smaller than 0.05 are rarely seen other than with highly monodisperse standards. Values greater than 0.7 indicate that the sample has a very broad size distribution and is probably not suitable for the DLS technique. The various size distribution algorithms work with data that falls between these tow extremes. The calculations for these parameters are defined in the ISO standard document 13321:1996 E and ISO 22412:2008

Raviteja,

You may want to look at these articles regarding PI:

https://www.researchgate.net/search.Search.html?type=publication&query=polydispersity+index

Good luck!

 would you please introduce a paper about acceptable PDI in nanoparticles as a refrence... 

Do you recognize a different PI cuttoff for nanoparticles than microparticles? in other words would the PI acceptable range would differ by size?

Dear Marjan,

If you are using DLS, you may find your answer in the following page.

http://www.materials-talks.com/blog/2014/10/23/polydispersity-what-does-it-mean-for-dls-and-chromatography/

the lower PdI value is much closer to achieving monodisperse system, values less than 0.7 indicate greater stability  for a nanodelivery/colloidal system.The values you achieved in this case show that the mean particle size for your nanoparticles is accurate. However z-average is also neccesary to draw concrete conclusion. In terms of pharmacodynamic and kinetic activity which nanoparticles were more effective particle size range will affect receptor affinity and effective binding to receptors.

Anyone can please suggest me that how can we reduce the PDI value of Nano-particles.

prepare nanoparticles with narrower size distribution, add narrow sized particles close to mean size, fractionate

In drug delivery the PDI ranging 0----0-05 monodispersive

More than 0.7. Polydispersive

See Wolfgang 2007 reference

Hi, Jabbar S Hadi,

Thanks for your reply, it is possible to give us the paper doi?

Merci!!Gracias!!

I recommend Titus's answer

Best Regards

Please, what is meant by PDI for microsphere? What is its limit?

Auda Braihi - PDI in the context of this discussion is Polydispersity Index, and is a parameter calculated from DLS using a method called Cumulants.

For a monomodal dispersion, we would theoretically expect a perfectly exponential decay of the autocorrelation function of the scattered light intensity.

PDI is derived from an extra term in the fit of an exponential, and describes how broad the range of sizes is.

Mathematically, PDI could be any positive number, but generally is only reported up to a value of 1.

As said, values around 0.1 may be considered good for a monomodal dispersion. Higher values mean that the distribution is broad, or that the particle size distribution is multimodal, in which case the average size value reported along side PdI becomes less relevant, and a distribution analysis is more representative.

I think you can find something here.

http://www.materials-talks.com/blog/2017/10/23/polydispersity-what-does-it-mean-for-dls-and-chromatography/

PDI measures the homogeneous of nanoparticles, the smaller the pdi the more homogeneous nanoparticles. Nanoparticles with pdi smaller than 0.4 is considered acceptable for drug delivery according to some references.

http://149.171.168.221/partcat/wp-content/uploads/Malvern-Zetasizer-LS.pdf

Hi,

The term “polydispersity” (or “dispersity” as recommended by IUPAC) is used to describe the degree of non-uniformity of a size distribution of particles [77,78]. Also known as the heterogeneity index, PDI is a number calculated from a two-parameter fit to the correlation data (the cumulants analysis). This index is dimensionless and scaled such that values smaller than 0.05 are mainly seen with highly monodisperse standards. PDI values bigger than 0.7 indicate that the sample has a very broad particle size distribution ....

From our recent publication:

Danaei, M.; Dehghankhold, M.; Ataei, S.; Hasanzadeh Davarani, F.; Javanmard, R.; Dokhani, A.; Khorasani, S.; Mozafari, M.R. Impact of Particle Size and Polydispersity Index on the Clinical Applications of Lipidic Nanocarrier Systems. Pharmaceutics 2018, 10, 57.

(attached)

I found the answer from Malvern DLS Zeta sizer Manual

"In summary, the cumulants analysis gives a good description ofthe size that is comparable with other methods of analysis for spherical, reasonably narrow monomodal samples, i.e. with polydispersity below a value of 0.1. For samples with a slightly increased width, the Z-average size and polydispersity will give values that can be used for comparative purposes. For broader distributions, where the polydispersity is over 0.5, it is unwise to rely on the Z-average mean, and a distribution analysis should be used to determine the peak positions."

Hope its still usefull.

This doesn't answer the original question. Titus Sobisch gave the most useful answer (5 years ago!)

This is what you have to do to determine the acceptable value:

1) Make enough separate batches of your product

2) Identify those which "pass" and those which "fail" whatever the performance specification. Ideally a specification that has a numerical value.

3) Measure the PDI for all of them and see if there is a correlation with passing/failing. If not, PDI isn't critical for that specification. If it is then you have a starting point to investigate further.

This is a very simple version of Quality by Design/Design for Manufacturing etc.