The document discusses depositing tin oxide nanoparticles onto substrates using DC magnetron sputtering for electrochemical studies of amyloid peptides. Initial deposits on silicon substrates were too large and unevenly dispersed due to high temperature and exposure time. Adjusting these parameters resulted in more rounded, evenly dispersed nanoparticles on carbon glass, but further improvement was still needed. The goal is to produce nanoparticles with the highest possible surface area to ensure strong attachment to components in subsequent experiments.

1. Deposition of Tin Oxide Nanoparticles for
Electrochemical Studies of Amyloid Peptides
Alejandra M. De Jesús-Soto1
, Kenny J. Colón-Colón2
1
Department of Mathematics, University of Puerto Rico at Cayey, Puerto Rico
2
Department of Biology, University of Puerto Rico at Cayey, Puerto Rico
ABSTRACT
Nanoparticles are microscopic materials that have physical dimensions ranging between
1-100 nm. Film depositions of Tin oxide nanoparticles were performed using DC magnetron
sputtering, which is a physical process that vaporizes atoms from a solid target material in order
to form a layer on a substrate. This part of the experiment was conducted at the University of
Puerto Rico at Cayey. Then, sputtered Tin oxide nanoparticles will be tested with amyloid
peptides in a cyclic voltammetry at University of Puerto Rico at Rio Piedras. Compounds
obtained from the experiment showed decent deposition of the tin oxide nanoparticles. However,
the Nanoparticles did not have a round appearance as wanted on Silicium substrate.
Nanoparticles obtained after the deposition on Carbon glass substrate were closest to that
required for the second part of the experiment. Adjustments of temperature and time exposure
during film depositions will be performed in order to obtain an improved result.
1. Introduction
Nanoparticles are a group of
microscopic materials that share physical
dimensions ranging between 1 and 100
nanometers (nm). The use of nanoparticles
in the field of medicine has been increasing
due to the advantages they offer (Zhang et
al. 2008). Nanoparticles are more accurate
when they are needed to go directly to a
target cell, cellular tissue, gland or groups of
amino acids. Their size provides a greater
surface area, which facilitates links to
certain combinations of elements that would
react when they reached the desired bio-
compound. They could assure the
development of enhanced and cost-effective
tools for diagnosing a disease in a faster and
more accurate process.
Some studies regarding the use of
nanoparticles for treating diseases have
developed certain interest in the
neuroscience field, specifically in
Alzheimer’s disease (AD). This disease is
the most common chronic and progressive
form of neurodegeneration of brains of
patients that suffer from it (Brookmeyer et
al. 2007). The disease goes in response of
the deposition of β-amyloid (Aβ) peptides
that contain nearly between 36-42 amino
acids residues in the brain (Rauk. 2009;
Rolinski et al. 2010).
The research of Lin Liu et al. (2013)
suggest that the monomer form of the
amyloid peptides (Aβ (1-16)) can serve as a
biomarker for diagnosing AD using gold
nanoparticles and heme compound (iron)

2. modified to them forming Aβ(1-16)-heme-
AuNPs on a competitive assay. The product
obtained was supposed get attached to a
monoclonal antibody that was immobilized
to the electrode of a cyclic voltammetry
method which contained gold. These
antibodies will be the ones attracting the N-
terminus of the Aβ peptides and the Aβ (1-
16)-heme-AuNPs. When the Aβ (1-16)-
heme-AuNPs got attached to the monoclonal
antibody on the electrode containing gold,
readings from the cyclic voltammetry
showed electrocatalytic O2 reduction. On
another procedure of the same experiment,
the electrode that contained gold was pre-
incubated with Aβ, after adding the Aβ (1-
16)-heme-AuNPs, the readings from the
voltammetry responses showed a decrease
of the reduction current of O2 to H2O2. This
means that the competitive assay is sensitive
and selective to Aβ peptides. The
voltammetric responses varied with different
concentrations of Aβ (0.02-1.5 nM)
responding to a minimum limit of 10 pM
(Liu et al. 2013).
The positive result of the experiment
developed by Lin Liu et al. (2013) using
gold nanoparticles has been of interest to Dr.
Ana Guadalupe, a professor of the
University of UPR at Río Piedras. She
suggested the use of tin oxide nanoparticles
sputtered in a carbon glass substrate. Then,
Tin oxide nanoparticles will be tested with
amyloid peptides in a cyclic voltammetry.
She selected carbon glass as a substrate
because of its inert characteristic. Tin oxide
can be a reliable method for this research
due to the fact that they work as
semiconductor with iron thin films, meaning
that the heme compound would be added for
reading the electrocatalytic signals from the
voltammetry cycle when the monomer form
of the Aβ peptide would be modified to it.
The new intended experiment starts
with the sputtering protocol of the tin
nanoparticles onto the carbon glass
substrate. This part of the experiment would
be held at the University of Puerto Rico at
Cayey. First, the sputtering protocol would
be tested using silicium as the substrate for
assuring the correct standards of the vacuum
chamber. The problem as set refers as to
whether the sputtering method can work on
a silicium substrate and on a carbon glass
substrate using tin oxide nanoparticles. We
hypothesized that sputtered Tin oxide
nanoparticles on carbon glass substrate will
be viable to continue studies with amyloid
peptides. As the final product, it is required
to have the substrate sputtered with the most
rounded shaped and evenly dispersed
nanoparticles as possible to assure that a
larger surface area. This would help attach it
to a ferrocene connector during the
development of the other part of the
experiment.
2. Materials and Methods
Film deposition was performed by
DC (direct current) magnetron sputtering in
a vacuum chamber, using a pure tin target in
an Argon atmosphere. Basically, sputtering
is a physical process in which atoms are
ejected from a solid target material in order
to form a layer on a substrate. In a vacuum
environment, gas pressure is less than the
ambient atmospheric pressure. Therefore it
is also called low-pressure environment,
allowing a better flow of electrons and
atoms.

3. Before starting the deposition, it is
important to ensure that the chamber is
clean. If necessary, Nitrogen was used to
clean it. Then, the sample including the
substrate was placed into the vacuum
chamber in order to start the deposition
process by sputtering. Also, a target was
placed in the sputter source that has a
magnetron (Figure 1). After closing the
vacuum chamber, it was set to a base
pressure of approximately 1 x 10-5
torr. Then,
electrically neutral Argon atoms were
introduced into it. A DC voltage placed
between the target and substrate ionizes
atoms and creates plasma. Plasma is a
gaseous environment where there are
enough ions and electrons for there to be
appreciable electrical conductivity. Argon
ions accelerate to the target. Their collision
with the target ejects target atoms, which
travel to the substrate and eventually settle,
forming layers. Electrons released during
Argon ionization are accelerated to the
substrate, subsequently colliding with
additional Argon atoms and creating more
ions and free electrons in the process,
continuing the cycle until the deposition
time finishes. It is important to know that
during this process, both temperature and
time exposure can be adjusted. For better
understanding of this procedure, see Figure
2. Before opening the chamber, it is
important to remember to fill the chamber
with nitrogen to balance the pressure from
the outside. Sample was collected from the
chamber in order to see it in Scanning
Electron Microscope (SEM)
SEM is a type of electron
microscope that produces images of a
sample by scanning it with a focused beam
of electrons. Electrons interact with atoms in
the sample, producing various signals that
can be detected and that contain information
about the sample's surface topography and
composition.
Figure 1 Inside of a vacuum chamber and its parts.
Figure 2. What happens in a vacuum chamber during
sputtering process? An atomic view.

4. 3. Results
Figure 3. Results of the three depositions performed.
Compounds obtained from the experiment
showed decent deposition of the tin oxide
nanoparticles. On the other hand, the most
expected part of the sputtering process,
which was getting the nanoparticles in the
roundish and most evenly dispersed way as
possible, did not result as figured. However,
it was recognized that the issue was due to
maladjustments of temperature and time
exposure of the substrates in the vacuum
chamber. After using the silicium substrate,
nanoparticles sputtered were too large in
size and were not dispersed evenly because
of the high temperature (160ºC) and the time
exposure in the vacuum chamber (1 min).
On the other hand, because of the room
temperature into the vacuum chamber,
nanoparticles were more evenly organized
on the Silicium substrate. Nanoparticles did
not have a round appearance as wanted.
After reaching a certain balance of
temperature and time exposure, carbon glass
was used as a substrate. By exposing the
nanoparticles to 150ºC during 10 seconds
they reformed into a more spherical shape
and were almost no gaps between them. The
carbon glass worked as similarly measured.
However, it is still not the product wanted to
be send for further research.
Discussion
The sputtering system is a versatile
technique for depositing solid materials onto
other substrates. In addition, this procedure
assures the deposition of a film of tin
nanoparticles over the exposed area of the
silicium substrate and over the carbon glass
substrate. Although the tested carbon glass
substrate resulted nearly as figured, it is
clear that the substrate has to have an even
dispersion of the nanoparticles to assure the
correct attachment of them to the
monoclonal antibody and the ferrocine
connector in the next part of the experiment.
To make the nanoparticles more bound to
the ferrocene connector it will require as
much surface area to assure their attachment
to it. Therefore, it is a concern that the
product that would be developed for the
study of amyloid peptides has the proper

5. characteristics boundary for the most
accurate results. There are still some
adjustments that have to be done in order to
obtain an improved result. It is suggested
that an adjustment of more time exposure
would help cover those gaps that are still
visible on the carbon glass substrate. The
ferrocene will serve as a medium for
connecting the Amyloid peptide with the
electrode and the monoclonal antibody. It is
expected that when the Aβ peptide gets
attached to the monoclonal antibody, it
would show response on the voltammetry
reading, meaning that the compound
functioned correctly, in a different way a tin
oxide nanoparticle would respond when
reaching to any other monoclonal antibody.
Acknowledgments
The authors would like to thank Dr.
Wilfredo Otaño, Mr. Jose Cruz and the
RISE Program at University of Puerto Rico
at Cayey for their support during the entire
project.
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