The Laser Zentrum Hannover (LZH) is using the NanoSight
nanoparticle characterisation LM10 system to study metal nanoparticles generated
by laser ablation.
The LZH research team of Dr Stephan Barcikowski in conjunction with the Medizinische
Hochschule in Hannover have been using nanoparticle tracking analysis (NTA)
to study silver nanoparticles generated in situ using laser ablation techniques.
Laser-generated nanoparticles show potential for medical applications since
they are free of impurities and toxicities. Furthermore, their electrical properties
allow a directionally controlled diffusion under externally applied electric
fields enabling deposition on conducting surfaces.
Dr Barcikowski chose to use the NanoSight system as it allows particle-by-particle
tracking in solution. By capturing the light scattered by the nanoparticles
at a frequency of 30 frames per second, the hydrodynamic diameter of the particles
may be calculated. The chamber of the system has been modified to take a silver
target which is ablated using a Ti:Sapphire laser. Initial ablation (over a
short pulse time, e.g. 30 seconds), a range of diameters of particle species
are observed in a range of 50-250nm. However, if the ablation process is increased,
e.g. to 400 seconds, the distribution shrinks to a single peak of approximately
50nm. This stabilisation process is due to interaction of the freshly generated
colloidal particles with the incident laser light. This is essentially a de-agglomeration
effect which is in accordance with observations of UV-VIS spectra.
The chamber of the system has been further modified to house a pair of electrodes.
This enables the mobility of the nanoparticles to be monitored as a function
of their charge. This has been applied to develop an electrodeposition technique
which is now being used for the deposition of gold on neuro implant electrodes.
This work was reported at the LPM2008 9th International Symposium on Laser
Precision Microfabrication. It clearly shows the relationship of the number
of pulses to the hydrodynamic diameter of the nanoparticles being produced,
a result that could not have been readily observed using conventional particle
characterisation techniques such as electron microscopy or dynamic light scattering.
The mobility studies are also not possible using a DLS system giving the NanoSight
technology another unique application.
A Menindez-Manjsn, J Jakobi, K Schwabe, J K Krauss, S Barcikowski: Mobility
of nanoparticles generated by femtosecond laser ablation in liquids and its
application to surface coatings. JLMN-Journal of Laser Micro/Nanoengineering.
In press (accepted 07.05.2009).