Bio-organism sensing via surface enhanced Raman spectroscopy on controlled metal/polymer nanostructured substrates
D. L. Allara
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N. Malvadkar and H. Wang Department of Engineering Science, The Pennsylvania State University, University Park
,
Pennsylvania 16802
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P. Kao Department of Chemistry, The Pennsylvania State University, University Park
,
Pennsylvania 16802
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Materials Research Institute and Department of Engineering Science, The Pennsylvania State University, University Park
,
Pennsylvania 16802
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Materials Research Institute and Department of Chemistry, The Pennsylvania State University, University Park
,
Pennsylvania 16802
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X. Gong and M. Poss Department of Biology and Center for Infectious Disease Dynamics, The Pennsylvania State University, University Park
,
Pennsylvania 16802
A new class of nonlithographically prepared surface enhanced Raman spectroscopy SERS substrates based on metalized, nanostructured poly p-xylylene films has been developed and optimized for surface plasmon response with a view to applications of SERS detection of microbial pathogens, specifically, bacteria and viruses. The main emphasis has been on achieving high spot to spot, sample to sample reproducibility of the SERS signals while maintaining useful enhancement factors. The use of these surfaces, metalized with either Ag or Au, provides a noninvasive and nondestructive method for spectral fingerprint analyses of both bacteria and viruses. Examples are given for the detection of bacteria E. coli and B. cereus and viruses respiratory syncytial virus and Coxsackievirus. Our method is able to distinguish Gram positive from Gram negative bacterial strains as well as enveloped and nonenveloped viruses. The results demonstrate the development of a new class of SERS substrates which can provide rapid, selective identification of infectious agents without amplification of cultures. 2009 American Vacuum Society. DOI: 10.1116/1.3147962
I. INTRODUCTION
Nanotechnology is being increasingly viewed as offering
new ways to generate technological advancements in a
variety of areas. One of the critical areas of potential benefit is
diagnostic microbiology where the central problem of
sensing and detecting microbial pathogens suffers from a general
lack of rapid, economical detection methods.1 For any
pathogen detection method to be successful three major barriers
must be overcome: 1 sensitivity, 2 reproducibility, and 3
selectivity. One technique that offers a potential solution is
surface enhanced Raman spectroscopy SERS. 2,3 Raman
spectroscopy, in general, offers advantages for analyzing
biological molecules due to its abilities to provide in situ
analyses directly in aqueous systems4 and the inherent fingerprint
characteristics of the spectra formed by the unique molecular
vibrations of each specific analyte molecule. This approach
can avoid the typical, more laborious methods involving
reagents and amplification of cultures. Raman spectroscopy,
however, suffers greatly from the problem of sensitivity.
Only bulk samples of the analyte of interest or reasonably
a Authors to whom correspondence should be addressed; electronic
addresses: and
concentrated solutions can give sufficient signal/noise to
generate useful spectra. For applications to rapid analyses of
microbial pathogens it is useful to be able to collect trace
amounts of the pathogens for example, from air samples on
surfaces and then analyze directly; a challenge that cannot be
met by standard Raman spectroscopy.
In contrast, in the SERS mode the Raman signal per
molecule can be amplified by factors of a million or more,5,6
even down to the single molecule level,7 leading to the
ability to generate useful detection signals for trace amounts of
pathogens. The major feature of a SERS active surface is the
presence of a metal, particularly Ag or Au, with nanoscale
size features capable of sustaining surface plasmon polariton
SPP resonances with the laser excitation used to generate
the Raman signal of the analyte molecules. Typically the
nanoscale features are produced by the use of nanoparticles,
roughened surfaces or lithographically fabricated
features,810 and can consist of combinations of sharply
pointed features and gaps. As these feature sizes decrease to
the limit of the atomic scale the SPP resonances are
dramatically enhanced, leading to extraordinarily large local
electromagnetic fields which, in turn, leads to huge magnifications
of the Raman scattering signals of molecules located at the
local feature hot spot. The combination of the high
sensitivity and the fingerprint spectral capability of SERS has led
to interest in a broad variety of biomedical types of
applications including rapid DNA sequencing,11 pathogen
detection,12 and food analysis.13 Of particular interest to us
has been the potential ability of SERS to obtain vibrational
spectra from surface collected pathogens that could be used
for detection and identification without reagents and further
provides the chemical composition of pathogen membranes,
which then could serve as a highly specific ide (...truncated)