In 2008 the International Organization for Standardization (ISO) defined a nanoparticle as a discrete nano-object where all three Cartesian dimensions are less than 100 mm

@ Shivani, if any dimension of a particle is 100nm or less then you may call it as nano. But, if DLS studies shows your particle size is between 200-300 nm, then you cannot call it nano. You may look at the particle distribution; if some percentage of the particle, say 3%, is less than 100 nm size then you may designate 3% particle is under nano size.

But in 2011 the Commission of the European Union endorsed a more-technical but wider-ranging definition:

Under that definition a nano-object needs only one of its characteristic dimensions to be in the range 1–100 nm to be classed as a nanoparticle, even if its other dimensions are outside that range. (The lower limit of 1 nm is used because atomic bond lengths are reached at 0.1 nm.)

Thank you. But using TEM the obtained size of the spherical NPs are around 30 nm and using DLS the obtained average size is ~240 nm (the range of size distribution is 40-300 nm).

@ Shivani, DLS always gives you the average diameter and the distribution of the diameter size. Definitely you have some particle in nano range as you mentioned TEM shows the 30 nm size. Thats why I advises you to see the distribution table in DLS where you will conclusively say the percentage of particle present as nano form.

When the average size of particles is between 1 to 10 nm, the system is called quantum dots, and when the size range is less than 1 to 10 nm, it is called mesoparticles. Generally, when the size of particles is 10 to 100 nm, it is considered as nanoparticles. Sometimes upto 200 nm is also considered as nano-system, but in true sense, it is a submicron sized particles.

Is there any specific size range for mesoparticles????

You may see the attached links:

https://www.purestcolloids.com/mesoparticles.php

Best answer: colloidal

https://enlightenscientific.com/2018/12/07/you-say-nano-i-say/

This has already been alluded to but the internationally accepted definition of nano material (in Europe at least) is-

A natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm - 100 nm.

It is interesting that you note such a difference in size between TEM and DLS.

Are the particle dimensions you quote from TEM from free discrete particles?

Md. Abdur Rahman - size is not the only criteria by which something may be called a 'quantum dot' . Quantum dots are indeed within your quoted size range but also formed of semi-conductive material.

Shivani Bharti According to Wikipedia 200-300nm particles should be called microparticles https://en.wikipedia.org/wiki/Microparticle

In colloquial use you will see that size range still referred to as nanoparticles, especially (and correctly) if there is one dimension less than 100nm.

Thank You Ulf Nobbmann

Shivani Bharti , Up to my knowledge, Nano can be used for particle size up to 100nm, If size is 1000nm or more , can be said micro and if size varies from 100-1000nm then it is intermediate range or generally called Meso.

Janpreet Sidhu Yes that is true but the size obtained from TEM is below 100 nm and from DLS it's above 100 nm. So i think we can call it nanoparticle because the size obtained from DLS also includes the hydrated layer while TEM gives the size of particle only.

TEM and DLS use different weightings for their inherent measurement of size. Depending on the algorithm, TEM is length or area weighted. DLS is intensity weighted. If the particle size distribution is not monodisperse then DLS will give larger values than TEM.

One should note/mention the PDI value while reporting DLS, which indicate the monodispersity of the particle. The PDI value should be less than one to get correct value of nano-size by DLS.