This document describes research on using polymer-encapsulated silver nanoparticles to improve drug detection via surface-enhanced Raman spectroscopy (SERS). The researchers synthesized silver nanoparticles encapsulated within an amidated polyethyleneimine polymer to increase nanoparticle stability while maintaining SERS enhancement. Testing showed SERS enhancement for the drug benzotriazole at high concentrations but not lower concentrations or for acetaminophen. Future work will test SERS enhancement of these drugs using the polymer-encapsulated silver nanoparticles.

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Raman Shift (cm-1)
RelativeIntensity
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Raman Shift (cm-1)
0.5x10-2 M Acetaminophen
with Ag Nanoparticles
10-2 M Acetaminophen
0.5x10-5 M Acetaminophen
with Ag Nanoparticles
10-5 M Acetaminophen
Solid Acetaminophen
Raman Spectra of Acetaminophen
Improving Drug Detection via Polymer Encapsulated Silver Nanoparticles
Brandon Russell, Honey Madupalli, and Mary Tecklenburg
Department of Chemistry, Central Michigan University, Mount Pleasant, MI 48858
References
Aymonier, C.; Schlotterbeck, U.; Antonietti, L.; Zacharias, P.; Thomann, R.; Tiller, J.C.; Mecking, S. Hybrids of
silver nanoparticles with amphiphilic hyperbranched macromolecules exhibiting antimicrobial properties.
Chem. Commun. 2002, 3018-3019.
Gladitz, M.; Reinemann, S.; Radusch, H.J. Preparation of Silver Nanoparticle Dispersions via a Dendritic-Polymer
Template Approach and their Use for Antibacterial Surface Treatment. Macromol. Mater. Eng. 2009, 294, 178-
189.
Haynes, C.L.; McFarland, A.D.; Van Duyne, R.P. Surface-Enhanced Raman Spectroscopy. Analytical Chemistry.
2005, 338-346.
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Raman Shift (cm-1)
Solid BTAH
10-5 M BTAH
0.5x10-5 M BTAH with Ag Nanoparticles
10-1 M BTAH
0.5x10-1 M BTAH with Ag Nanoparticles
RelativeIntensity
Raman Spectra of BTAH
Benzotriazole
(BTAH)
Acetaminophen
The detection of drugs in the environment, like wastewater, is now more important than ever
and consequently methods that can detect trace amounts are extremely important. Raman
spectroscopy is a ubiquitous form of spectroscopy that can offer useful complementary
information to similar forms of spectroscopy such as IR. Raman can help to identify unknown
compounds and the effects the environment can have on the structural arrangement of a
compound. Raman is a great tool for field research as sample preparation is simple compared
to similar methods and can provide data quickly.
A relatively new form of Raman, Surface Enhanced Raman Spectroscopy (SERS), can
significantly enhance Raman signals of molecules that are adsorbed on metals surfaces such as
gold or silver. However, a problem with metal surfaces is that they degrade in air after a short
time period. The aim of this research is to investigate ways to increase the stability of silver
nanoparticles while maintaining the Raman signal enhancement provided by the
nanoparticles. This project investigated the use of an amidated polymer to encapsulate the
silver nanoparticles, improve their long term stability, and enhance the Raman signal via SERS.
Analysis was done on the drugs benzotriazole (BTAH) and acetaminophen.
Abstract
Metal surfaces such as gold or silver have strong electromagnetic fields generated by the
surface electrons of a metal called a surface plasmon. When the metal is a nano-sized
particle it generates a localized surface plasmon resonance (LSPR) which is exceptionally high
and is excited by visible light. The intensified electromagnetic field increases the magnitude
of the induced dipole in a molecule adsorbed on the metal nanoparticle surface and as a
result makes the molecule more polar and increasing the intensity of the Raman signal, the
basis of surface enhanced Raman spectroscopy (SERS).
However, a problem with these metal surfaces, particularly in nanoparticle form is that they
oxidize and degrade rather easily. This causes the source of the enhancement to become
useless relatively quickly, lasting only a few days or weeks. A possible solution to the
degradation of the metal surface is to protect the surface by encapsulating the metal
surface, such as silver nanoparticles in a polymer.
Surface Enhanced Raman Spectroscopy
The polymer used was Lupasol® WF, a hyperbranched polyethyleneimine (HPEI25K). The polymer
was amidated by reaction with palmitic acid and 1,1’-carbonyldiimidazole in chloroform. Excess
palmitic acid was removed by washing the polymer in a saturated brine solution. The polymer
solution was dried with anhydrous sodium sulfate and had the solvent removed via rotary
evaporator. The amidated polymer was analyzed with 1H NMR to check whether the palmitic acid
was a sufficiently removed.
In order to synthesize the polymer with silver nanoparticles, the polymer was dissolved in
chloroform and had silver nitrate (AgNO3) dissolved directly in the chloroform. An aqueous
sodium borohydride solution was mixed with the polymer/CHCl3 solution to reduce the silver ions
to metal and create the silver nanoparticles coordinated to secondary amine nitrogens in the
interior of the polymer. The silver encapsulated polymer was analyzed with UV-Vis to check for
the creation of the silver nanoparticles.
Preparation of Polymer Encapsulated Silver Nanoparticles
•SERS enhancement has been observed for BTAH at both 10-1 M and 10-5
M in in other labs and in other experiments in our lab. This shows the
sensitivity of the aqueous nanoparticles to solution conditions and the
instability of the silver nanoparticles.
•While SERS enhancement was not observed for acetaminophen at this
point we don’t know whether it is because of structural/electronic
features of the molecule or because of unstable silver nanoparticles.
Conclusion
•Continued research into the stability of silver nanoparticles for SERS
enhancement of BTAH and acetaminophen in solution.
•Testing for SERS enhancement for BTAH and acetaminophen with the
silver nanoparticles encapsulated in amidated polyethyleneimine.
Future Work
UV/Vis Spectra of Amidated Polymer
without Silver Nanoparticles
Amidated Polymer with Silver Nanoparticles
The UV-Vis for the amidated polymer does not show any absorbance peaks in the
wavelength range for silver absorption as expected. The spectra for the polymer with silver
nanoparticles has an absorbance peak at 427 nm, signifying the presence of silver
nanoparticles in the polymer.
The Raman spectra for 10-1 M BTAH shows peaks that correspond to the BTAH molecule
compared to the spectra for solid BTAH. However, when the BTAH was mixed with an
aqueous silver nanoparticle solution no enhancement of the present peaks was
observed. The spectra for 10-5 M BTAH shows no peaks with or without the aqueous
silver nanoparticle solution.
Raman testing was done using a Kaiser Optical Systems RNX microRaman spectrometer
with a 785 nm laser, a 10x objective, and quartz cuvettes. The target molecules were the
drugs benzotriazole (BTAH) and acetaminophen. The BTAH was dissolved in water with a
pH of 9 while the acetaminophen was dissolved in water with a pH of 10. The high pH was
used to place the target molecule in basic form that would be more sensitive to Raman
analysis.
Testing for SERS
1H NMR of Amidated Polymer
Amidated Polymer
Palmitic Acid
The Raman spectra for a 10-2 M acetaminophen solution without silver
nanoparticles had a few small observable peaks due to acetaminophen.
These peaks showed no enhancement in the acetaminophen solution
with silver nanoparticles. The spectra for a 10-5 M acetaminophen
solution with or without silver nanoparticles showed no observable
peaks due to the acetaminophen molecule.
Polymer Encapsulated Silver Nanoparticle
Model of a HBPEI with a
core/shell architecture