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Surface-enhanced Raman scattering: a new optical probe in molecular biophysics and biomedicine
(2010)
Sensitive and detailed molecular structural
information plays an increasing role in molecular biophysics
and molecular medicine. Therefore, vibrational
spectroscopic techniques, such as Raman scattering, which
provide high structural information content are of growing
interest in biophysical and biomedical research. Raman
spectroscopy can be revolutionized when the inelastic
scattering process takes place in the very close vicinity of
metal nanostructures. Under these conditions, strongly
increased Raman signals can be obtained due to resonances
between optical fields and the collective oscillations of the
free electrons in the metal. This effect of surface-enhanced
Raman scattering (SERS) allows us to push vibrational
spectroscopy to new limits in detection sensitivity, lateral
resolution, and molecular structural selectivity. This opens
up exciting perspectives also in molecular biospectroscopy.
This article highlights three directions where SERS can offer interesting new capabilities. This includes SERS as a
technique for detecting and tracking a single molecule, a
SERS-based nanosensor for probing the chemical composition
and the pH value in a live cell, and the effect of socalled
surface-enhanced Raman optical activity, which
provides information on the chiral organization of molecules
on surfaces.
Two-photon vibrational spectroscopy for biosciences based on surface-enhanced hyper-Raman scattering
(2006)
In Vivo Molecular Probing of Cellular Compartments with Gold Nanoparticles and Nanoaggregates
(2006)
Surface-enhanced Raman (SERS) signatures were measured from single living cells at different times after the uptake of gold nanoparticles. The spectra are indicative of chemical changes in the environment of the nanostructures over time. The increase of the SERS signal strength and parallel TEM studies indicate the formation of nanoaggregates providing optimum SERS enhancement for ultrasensitive probing inside the endosomal compartment. The results have implications for medical and biotechnology applications of SERS nanosensors in cells.
During surface-enhanced Raman scattering (SERS), molecules exhibit a significant increase in their Raman signals when attached, or in very close vicinity, to gold or silver nanostructures. This effect is exploited as the basis of a new class of optical labels. Here we demonstrate robust and sensitive SERS labels as probes for imaging live cells. These hybrid labels consist of gold nanoparticles with Rose Bengal or Crystal Violet attached as reporter molecules. These new labels are stable and nontoxic, do not suffer from photobleaching, and can be excited at any excitation wavelength, even in the near infrared. SERS labels can be detected and imaged through the specific Raman signatures of the reporters. In addition, surface-enhanced Raman spectroscopy in the local optical fields of the gold nanoparticles also provides sensitive information on the immediate molecular environment of the label in the cell and allows imaging of the native constituents of the cell. This is demonstrated by images based on a characteristic Raman line of the reporter as well as by displaying lipids based on the SERS signal of the C—H deformation/bending modes at ~ 1470 cm-1.
We demonstrate spatially resolved probing and imaging of pH in live cells by mobile and biocompatible nanosensors using surface-enhanced Raman scattering (SERS) of 4-mercaptobenzoic acid (pMBA) on gold nanoaggregates. Moreover, we also show that this concept of pH nanosensors can be extended to two-photon excitation by using surface-enhanced hyper-Raman scattering (SEHRS). In addition to the advantages of two-photon excitation, the SEHRS sensor enables measurements over a wide pH range without the use of multiple probes.
Nanoaggregates formed by metal spheres of different radii and interparticle distances represent finite, deterministic, self-similar systems that efficiently concentrate optical fields and act as nanolenses. Here we verify experimentally the theoretical concept of nanolenses and explore their potential as enhancing nanostructures in surface enhanced Raman scattering (SERS). Self-similar structures formed by gold nanospheres of different sizes are generated by laser ablation from solid gold into water. These nanolenses exhibit SERS enhancement factors on the order of 109. The chemically clean preparation process provides several advantages over chemically prepared nanoaggregates and makes the stable and biocompatible gold nanolenses potent enhancing structures for various analytical and sensing applications.
This review introduces multifunctional optical nanosensors based on surface-enhanced Raman scattering (SERS) and demonstrates their application in live cells. The novel nanosensors have the potential to improve our understanding of cellular processes on the molecular level. The hybrid sensor consists of gold or silver nanoparticles with an attached reporter species. The sensor can be detected and imaged based on the SERS signature of the reporter. This results in several advantages, such as high spectral specificity, multiplex capabilities, improved contrast, and photostability. SERS sensors not only highlight cellular structures, based on enhanced Raman spectra of intrinsic cellular molecules measured in the local optical fields of the gold nanoparticles, they also provide molecular structural information on their cellular
environment. Moreover, the SERS signature of the reporter can deliver information on the local pH value inside a cell at subendosomal resolution. SERS sensors are suitable for one- and two-photon excitation.
The surface enhanced Raman scattering (SERS) spectrum of a reporter molecule attached to gold or silver nanostructures, which is pH-sensitive, can deliver information on the local pH in the environment of the nanostructure. Here, we demonstrate the use of a mobile SERS nanosensor made from gold nanaoaggregates and 4-mercaptobenzoic acid (pMBA) attached as a reporter for monitoring changes in local pH of the cellular compartments of living NIH/3T3 cells. We show that SERS nanosensors enable the dynamics of local pH in individual live cells to be followed at subendosomal resolution in a timeline of cellular processes. This information is of basic interest for a better understanding of a broad range of physiological and metabolic processes as well as for a number of biotechnological applications.
Raman signatures of the carotenoid component are studied in individual pollen grains from different species of trees. The information is obtained as differences in the strong pre-resonant Raman spectra measured before and after photodepletion of the carotenoid molecules. The results provide the first in situ evidence of interspecies differences in pollen carotenoid content, structure, and/or assembly between plant species without prior purification. The analysis of carotenoids in situ is confirmed by high-performance thin-layer chromatography (HPTLC)-supported resonance Raman data measured directly on the HPTLC plates after separation of carotenoids in pollen extracts. Utilization of the in situ, extraction-free procedure in carotenoid analysis will improve sensitivity and structural selectivity and provides insight into carotenoid structure and composition in single pollen grains.