Department of Physics & Astronomy
Detroit, MI USA
LIBS Used To
Measure the Fe Concentration in gamma-Fe2O3
Magnetic Nanoparticles in a Bio-Compatible Alginate Matrix
Gamma-Fe2O3 nanoparticles are being study for a variety of medical and technological applications. One possible medical application is to take advantage of their magnetic properties and use them as a drug delivery system. Another medical application would again take advantage of their magnetic properties and use externally applied alternating current magnetic fields to generate heat from their movement as a way to attack cancerous tumors.
The gamma-Fe2O3 Nanoparticles in the Alginate Matrix (powdered form)
In the above picture you can see the pellet it is very thin and on the order of a few millimeters in diameter.
In the above picture the apparatus above the sample is the microscope objective which is focusing the laser. The white dot is the micro-plasma that is created from the ablation, the apparatus to the left is the translation stage which allows us to move the sample in the x and y dimensions, and the blue tube to the right is the fiber-optic cable which carries the light from the plasma back to the spectrometer for analysis.
This is the pellet after ablation. Each laser shot consists of five ablations, ten of these laser shots is one measurement, and each pellet was measured ten times overall this pellet has five hundred laser ablations.
The next step in the procedure was to start taking data. This was a slightly difficult process because it involved calibration of both the height between the microscope objective and the substrate as well as the fiber optic cable's distance from the micro-plasma. This was achieved by ablating the substrate until we got sufficient spectroscopic data. The following pictures are of the typical spectra we observed (from 200 to 840 nm).
LIBS Spectrum from Ag / alpha-Fe2O3
Boltzmann Plot to Calculate Plasma Temperature
PAPER
E. Brown, S.J. Rehse, “Laser-Induced Breakdown Spectroscopy of γ-Fe2O3 Nanoparticles in a Biocompatible Alginate Matrix”, Spectrochimica Acta Part B 62, 1475-1483, (2007).
This work was performed under an REU Grant from the National Science Foundation.
October 13, 2006
Back to the Rehse Group main page
Gamma-Fe2O3 nanoparticles are being study for a variety of medical and technological applications. One possible medical application is to take advantage of their magnetic properties and use them as a drug delivery system. Another medical application would again take advantage of their magnetic properties and use externally applied alternating current magnetic fields to generate heat from their movement as a way to attack cancerous tumors.
My
interest is in creating a method in which the iron concentration of
macroscopic
samples can be obtained. Laser-induced breakdown spectroscopy or LIBS
is a
perfect tool for this type of elemental analysis. The LIBS technique
has
several distinct advantages over other analytical methods. The
LIBS process requires minimal sample
preparation and can be carried out in situ,
rapidly, and in real time. Good detection limits and a wide dynamic
range have
been demonstrated in a variety of sample matrices. LIBS is inherently a
multi-element technique, i.e., it is capable of providing simultaneous
multi-element determinations. Difficulties with LIBS include the very
high
continuum background, which generally necessitates time resolution in
the
detection, and generally inferior precision due to the very strong
nonlinear
nature of the laser-material interaction. In many matrices,
calibration can be
difficult. Therefore, routine quantitative analysis has been elusive.
The gamma-Fe2O3 Nanoparticles in the Alginate Matrix (powdered form)
Armed
with this tool for elemental analysis I hoped to create a calibration
curve to
measure the iron concentration of a sample of gamma-Fe2O3
nanoparticles in an alginate matrix. The first step was to create
calibrated
samples. I was forced to use alpha-Fe2O3
because the amount of gamma-Fe2O3
needed for my
purposes
were not available. This will have no bearing on a concentration
measurement
because the difference in the two is just structural. The next step was
to
choose a matrix for the alpha-Fe2O3
from the
literature and
input from other faculty. I chose a silver matrix. This matrix
choice
was good
for several reasons; its spectrum did not contaminate the iron spectrum
I hoped
to see, it made the pellets physically stronger which made them easier
to
handle, and it gave us silver lines to ratio the iron lines with for
the
calibration curve.
The sample preparation consisted
of
thoroughly mixing the alpha-Fe2O3
and the silver,
placing it
in a cold press die, and compressing with a 20 ton press. Here are some
pictures of the pellet before laser ablation during, during ablation
and after
ablation.
In the above picture you can see the pellet it is very thin and on the order of a few millimeters in diameter.
In the above picture the apparatus above the sample is the microscope objective which is focusing the laser. The white dot is the micro-plasma that is created from the ablation, the apparatus to the left is the translation stage which allows us to move the sample in the x and y dimensions, and the blue tube to the right is the fiber-optic cable which carries the light from the plasma back to the spectrometer for analysis.
This is the pellet after ablation. Each laser shot consists of five ablations, ten of these laser shots is one measurement, and each pellet was measured ten times overall this pellet has five hundred laser ablations.
The next step in the procedure was to start taking data. This was a slightly difficult process because it involved calibration of both the height between the microscope objective and the substrate as well as the fiber optic cable's distance from the micro-plasma. This was achieved by ablating the substrate until we got sufficient spectroscopic data. The following pictures are of the typical spectra we observed (from 200 to 840 nm).
LIBS Spectrum from Ag / alpha-Fe2O3
Here we have identified numerous Ag
and Fe atomic emission lines for possible analysis, and selcted two
lines to study: an Fe line that will allow us to measure the Fe
concentration and an Ag line which we will normalize our data to.
We can calculate plasma parameters,
such as the excitation temeperature, by using a Boltzmann plot.
We plot the intensity of the emssion line (the area under the curves
seen above) against the energy of the upper electronic state that
comprises that atomic transition. The slope of a line fit to this
data tells us the temperature of the plasma (in this case, close to
7700K).
Boltzmann Plot to Calculate Plasma Temperature
Using
15 calibrated "standard" samples, a curve of Fe/Ag emission intensity
vs. Fe mass fraction was constructed. This is shown bleow.
Each pellet was measured 10 times, and each "X" is one
measurement. The average of those 10 measurements is shown as a
black dot with error bars given by the standeard deviation. An
exponential curve fits this data very well.
Lastly,
we used this calibration curve to calculate the actual concentration of
Fe in a nanoparticle/alginate/silver disc.
The
final calculated mass fraction of Fe in the alginate matrix was
0.51+/-0.03 which is very near previously reported values for such
systems!
POSTER
presented at LIBS2006
POSTER
presented at LIBS2006
PAPER
E. Brown, S.J. Rehse, “Laser-Induced Breakdown Spectroscopy of γ-Fe2O3 Nanoparticles in a Biocompatible Alginate Matrix”, Spectrochimica Acta Part B 62, 1475-1483, (2007).
This work was performed under an REU Grant from the National Science Foundation.
October 13, 2006
Back to the Rehse Group main page