I wanna know how I can measure or prove that a coating process was effective in nanoparticles. Some investigators have used the dynamic light scattering to prove it, but I think that if you change your media, you can change the aggregates formation. Since that, you'll change the NP's hydrodynamic size too. Is there another method or technique to detect / prove / measure if your coating process have worked? I've never synthetized NPs in my life and I will not, but I study them. This question came to my mind and I don't know if the standard methods (like DLS) is reliable.
Dear Andre Prospero, I think there are many specific and nonspecific methods to prove that your nanoparticles(NP) are covered.
1. A change of the size of NP compared to uncovered by DLS
2. A change of zeta-potential of NP using also nanosaizer.
3. Comparing a magnetization of NP before and after covering.
4. Comparing the IR-spectra before and after covering
5. Comparing the percent adsorption of analyte (or other properties that you are interested) before and after covering (this is an integral characteristic).
There a lot of other methods described in literature.
I wanted to say like change the properties of the liquid in which the particles are dispersed. I wanna know a coating efficiency test. The magnetic characterization, size distribution or crystal structure, aren't problems for me. I wanna know haow to know if a coating biomolecule have attached right in the particles.
If the surface of the particle is modified from my point of view HATR measurements of the samples (after Zentrifugation and washing) is convincing (if the coating contains organic). You might also use the procedure presented in the article (modify the HATR prism with the particles and rinsing with huge excess of solvent).
Article Synthesis and testing of ZnO nanoparticles for photo-initiat...
Dear Andre Prospero, I think there are many specific and nonspecific methods to prove that your nanoparticles(NP) are covered.
1. A change of the size of NP compared to uncovered by DLS
2. A change of zeta-potential of NP using also nanosaizer.
3. Comparing a magnetization of NP before and after covering.
4. Comparing the IR-spectra before and after covering
5. Comparing the percent adsorption of analyte (or other properties that you are interested) before and after covering (this is an integral characteristic).
There a lot of other methods described in literature.
There are many methods that directly and indirectly show if NPs are coated or not:
1: TEM: if coating is amorphous layer of for instance silica layer, you will see the coating. If there are just absorbed molecules (DBSA, recinoleic acid etc) you will not see.
2. DLS: compare uncoated and coated nanoparticles. But remember, uncoated can be unstaable so they can form agglomerates - larger size
3: Zeta potential measurment: if there is something on the surface - organic, it will most probably will change the surface potential. Compare coated and uncoated nanoparticles.
4: MASS loos and MAGNETIZATION will tell you that you have something in the product, but you will not know if this is on the particles or not
Think on your problem before the method: if you have agglomeration and precipitation of particles going on in your solution, you IN PRINCLE cannot measure particle sizes, because your particles are being formed (agglomeration) and precipitated, once they reach certain size. This all is happening during the time of measurement, so that your result will be time-dependent (Scientific Reports | 6:35450 | DOI: 10.1038/srep35450). Now, if your particles (coated or not) are stabilized by covalent bonds, or at least very-very strong van der Waals interactions, you have a chance to measure single-particle diameter with DLS by decreasing the concentration and, if needed, by increasing temperature. Just dilution works most of time. Remember to check that during a day or so your concentration is not changing (because of precipitation). Just repeat the measurements 3 times a day to make sure. If lucky, it should work :-)
Since you are dealing with magnetic NPs, after coating with a non-magnetic material, their magnetic saturation(Ms) will decrease. This can be examined by VSM technique.Also if you have an EDX analysis on the sample after coating you will find most the elements of the coated material. Sergei answer has more information for your question.
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