Deposition of nanoparticles.
Minimization of agglomeration and homogenous particle distribution
Electro Microscopy (EM) tecniques are the most accepted techniques for NanoParticle (NP) size analysis. However, the used sample preparation systems nowadays are not problem free. NP dispersions are deposited in the EM grids and solvents are evaporated.
The evaporation of the solvent to leave the NPs dry in the grids provokes agglomeration of the NPs, therefore the size analysis become challenging. Moreover the particles are not usually distributed homogenously on the grid. Automatic image treatment is impossible under these cicunstaces.
Electrospray fundamentals
Electrospray Source is an instrument to generate ions and charged nanoparticles from a liquid phase sample. This instrument is quite versatile and well suited for a broad range of applications, including, but not limited to: basic aerosol research, nanoparticle production, fundamental electrospray research, DMA calibration, and source of biomolecules (DNA, proteins…) for MS.
As opposed to the traditional atomization methods, the ES gives very narrow size distributions of nanoparticles. Ioner´s Electrospray sytems are based on a versatile approach and several capillaries are provided in order to allow the user to work with the dispersion unaltered, without using extra electrolytes. Samples of broad conductivities can be electrospayed directly.
In general, the sample is made up of a volatile organic solvent and analyte in dissolution or suspended colloidal particles. This sample which should have optimal properties (electrical conductivity, surface tension and viscosity) is injected through a capillary. Because of the electric field, a cone (“Taylor cone”) is formed on the end of the capillary. A jet of liquid is emitted from the tip. The fluid breaks into droplets because of surface tension instabilities. The droplets get reduced in size because of the evaporation of the solvent, which makes the surface charge of the droplets increase. When the surface charge is too high compared to surface tension and viscosity, the droplet breaks (Coulombian explosion) in order to generate more surface and accommodate the charge. The repetition of this process generates smaller and smaller droplets and end when all the solvent is evaporated and only the solid residue is left.
Electrospray deposition for EM systems
Having the NPs charged is a good way of avoiding the agglomeration due to coulombic repulsion between them. Ioner has designed and developed an ElectroSpray Deposition system especially for sample preparation of NP dispersions for EM techniques.
The ESI-Depo sytem is composed by a simplified electrospray chamber where the counter electrode is the collector supporting the grid.
By using conductive EM grids the charged NP are deposited on them minimizing the agglomeration due to the coulombic respulsion. Due to spraying, all grid surface is homogenously covered. Presure system or syringe pumps are the available impulsing systems.
