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Solid Acetaminophen

Raman Spectra of Acetaminophen

Improving Drug Detection via Polymer Encapsulated Silver NanoparticlesBrandon Russell, Honey Madupalli, and Mary Tecklenburg

Department of Chemistry, Central Michigan University, Mount Pleasant, MI 48858

ReferencesAymonier, 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 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 PolymerPalmitic 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