Nanoparticle size
Having accepted and validated methods to determine several characteristics and descriptors of NanoParticles (NP) is an open challenge, being size one of them.
Since the nanoparticle range, as the EC definition recommends (Recommendation 201/696/EU), stands between 1 and 100 nm, very different properties are found in this huge range of sizes, therefore different methods will be required for the extreme ranges.
It is accepted that NP size affects tremendously its properties, toxicity among them. There is an added difficulty since no on line standard method is accepted for the size determination of the smallest range in nanoparticles, despite Electron Microscopy (EM) methods are the most accepted ones.
Size measurement
Cylindrical DMAs are used for determining the size distribution of bigger NPs. However, for the smallest ranges, technical challenges are found due to the high mobility of the smallest charged NPs that drives to higher losses and low sensitivity. Additionally, the resolution (ability to distinguish NPS of similar sizes) of the cylindrical DMAs has limits with the smallest NP sizes.
To solve the technological challenges of the DMAs for the smallest NPs, RAMEM has developed a parallel plate DMA in which the NPs follows shorter and simpler trajectories, resulting in higher transmission, minimum losses and high sensitivity. The instrumental design has allowed a resolution 4 times higher than the classical cylindrical DMAs.
Challenges
The inversion between mobility and size is needed because with the smallest NPs, the charging stage is an open challenge. With the smallest NPs the charging efficiency is very low and some of the charged particles have multiple charges. Having a high yield of charged NP with only one charge avoiding radioactive charger and neutralizers is a challenge for this size range.
There are neutralizers in the market but their performance for the smallest NPs is still open. RAMEM is investigating different alternatives in order to achieve a well know equilibrium charge distribution in the smallest nanoparticles to univocally link the mobility with the size.
RAMEM will extend the actual working range of the High Resolution DMA to cover the range between 1 to 10nm. Therefore, it will overlap with many other techniques that are offering response for sizes bigger than 10nm. The resulting instrument will be able to distinguish NPs with differences of 2% for the smallest NPs.
