Utilizing Metallic Nanomaterial’s Unique Plasmonic Properties for Ultra-Sensitive
Chemical Detection
By Nathan L. Netzer
Currently, I am involved in the synthesis, characterization, and development of
metallic nanomaterials for molecular spectroscopy. Surface-enhanced Raman scattering
spectroscopy (SERS) is the ultra-sensitive analytical technique that we employ to actively
study the vibrational and rotational modes of analytes at extremely low concentration. In
1928, Sir C.V. Raman discovered that when light is scattered from molecules, not all the
photons are elastically scattered back (Rayleigh Scattering) with the same energy as the
incident light.1 He recognized that a very small fraction, roughly 1 out of every 10
million photons, exhibits an in-elastic scattering of light. By detecting this in-elastic
scattering of light, we are able to confidently identify the chemical composition or
“fingerprint” of an unknown sample. However, the small Raman scattering cross-section
causes weak signaling and is the major drawback of Raman scattering. In order to
overcome this drawback, we fabricate metallic nanowire substrates that utilize surface
plasmon resonance (SPR) to enhance the Raman signals via chemical and/or physical
mechanisms. The physical enhancement mechanism consists of bringing metallic
nanostructures within close proximity of each other and allows their SPR to generate an
enhanced electromagnetic field producing “hot spots.” The chemical enhancement
mechanism can also produce an increased Raman signal via charge transfer between the
probe molecule and substrate.2 Due to its ultra-sensitivity and accuracy, SERS has been
and continues to be readily studied by many researchers who have made contributions in
the areas such as planetary exploration,3, 4 homeland security,5, 6 conservation science,7
and biomedical sensing.8, 9
The project that I am currently working on, in Dr. Chaoyang Jiang’s lab group at the
University of South Dakota, is the synthesis, fabrication, and assembly of gold-silver
(Au-Ag) bimetallic porous nanowires to increase Raman activity. The synthesis of
bimetallic porous nanowires is a straightforward approach that consists of a room
temperature galvanic replacement reaction between previously synthesized Ag NWs and
chloroauric acid. Depicted in Fig. 1a is an optical image of several GRR Au-Ag
bimetallic porous nanowires and one pristine silver nanowire. The difference between
Figure 1 – Systematic study using a) 50x optical image, b) 5 x 5 µm AFM image and
c) Raman map of the same location. (All scale bars are 1 μm)
the two nanowire’s optical response can be attributed to a change in the wires
morphology, composition, crystallinity, etc.10 Fig. 1b shows an AFM image of the same
region as Fig. 1a, which illustrates an increase in overall size and roughness of the GRR
Au-Ag bimetallic porous nanowires compared to the pristine Ag NW. This increase in
size and roughness is a direct result of the replacement reaction. Fig. 1c shows a Raman
intensity map of the R6G Raman peak at 1632 cm-1. Fig. 1c clearly indicates that the
Raman signal is only present on the Au-Ag bimetallic porous nanowires and not the
pristine Ag NW. One should also note that the isolated Au-Ag bimetallic porous
nanowire in Fig. 1c exhibits SERS. A detailed explanation of this work is outlined in our
most recent Chemical Communication publication.11 To further this work I am currently
exploring the ability to align the Au-Ag bimetallic nanowires using Langmuir-Blodgett
assembly, which should be published shortly. In summary, SERS has many possible
applications and shows promising strides to become a very practical and important tool
for the sensing field.
References:
1.
2.
C V Raman, F. R. S., A new radiation*. Indian Journal of Physics 1928, 2, 12.
Kneipp, K.; Kneipp, H.; Itzkan, I.; Dasari, R. R.; Feld, M. S., Ultrasensitive Chemical Analysis by
Raman Spectroscopy. Chemical Reviews 1999, 99 (10), 2957-2976.
3. Martinez-Frias, F. R. P. a. J., Raman Spectroscopy goes to Mars. Spectroscopy Europe 2006, 18 (1),
18-21.
4. Tarcea, N.; Frosch, T.; Rösch, P.; Hilchenbach, M.; Stuffler, T.; Hofer, S.; Thiele, H.; Hochleitner, R.;
Popp, J., Raman Spectroscopy—A Powerful Tool for in situ Planetary Science
Strategies of Life Detection. Botta, O.; Bada, J. L.; Gomez-Elvira, J.; Javaux, E.; Selsis, F.; Summons, R.,
Eds. Springer US: 2008; Vol. 25, pp 281-292.
5. Qiu, C. M., Alfred; Jiang, Chaoyang, Trace detection of melamine by surface-enhanced Raman
scattering on silver nanostructured thin films. Nanoengineering and Nanomanufacturing 2011, 1 (1),
93-100.
6. Chamoun-Emanuelli Ana, M.; Primera-Pedrozo Oliva, M.; Barreto-Caban Marcos, A.; Jerez-Rozo
Jackeline, I.; Hernández-Rivera Samuel, P., Enhanced Raman Scattering of TNT on Nanoparticles
Substrates: Ag, Au and Bimetallic Au/Ag Colloidal Suspensions. In Nanoscience and Nanotechnology
for Chemical and Biological Defense, American Chemical Society: 2009; Vol. 1016, pp 217-232.
7. Casadio, F.; Leona, M.; Lombardi, J. R.; Van Duyne, R., Identification of Organic Colorants in Fibers,
Paints, and Glazes by Surface Enhanced Raman Spectroscopy. Accounts of Chemical Research 2010,
43 (6), 782-791.
8. Porter, M. D. L., R.J.; Siperko, L. M.; Wang, G.; Narayanana, R., SERS as a bioassay platform:
Fundamentals, design, and applications. Chemical Society Reviews 2008, 37 (1001-1011).
9. Kneipp, J. K., H.; Kneipp, K, a single-molecule and nanoscale tool for bioanalytics. Chemical Society
Reviews 2008, 37, 1052-1060.
10. Netzer, N. L.; Gunawidjaja, R.; Hiemstra, M.; Zhang, Q.; Tsukruk, V. V.; Jiang, C., Formation and
Optical Properties of Compression-Induced Nanoscale Buckles on Silver Nanowires. ACS Nano 2009,
3 (7), 1795-1802.
11. Netzer, N. L.; Qiu, C.; Zhang, Y.; Lin, C.; Zhang, L.; Fong, H.; Jiang, C., Gold-silver bimetallic
porous nanowires for surface-enhanced Raman scattering. Chemical Communications 2011, 47 (34),
9606-9608.
Publications:
Netzer, N. L.; Qiu, C.; Zhang, Y.; Lin, C.; Zhang, L.; Fong, H.; Jiang, C., Gold-silver
bimetallic porous nanowires for surface-enhanced Raman scattering. Chemical
Communications 2011, 47 (34), 9606-9608
Beer, T.; Tanaka, Z.; Netzer, N. L.; Rothschild, L. J.; Chen, B., Analysis of uncultured
extremophilic snow algae by non-invasive single cell Raman spectroscopy. 81520F81520F, 20011.
Netzer, N. L.; Gunawidjaja, R.; Hiemstra, M.; Zhang, Q.; Tsukruk, V. V.; Jiang, C.,
Formation and Optical Properties of Compression-Induced Nanoscale Buckles on
Silver Nanowires. ACS Nano 2009, 3 (7), 1795-1802
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