Abstract.We have developed a Raman microspectroscopy system optimised for studying supported lipid bilayers (SLB). This system combines the benefits of Raman spectroscopy with the high spatial resolution of confocal microscopy. Furthermore, the additional incorporation of an atomic force microscope (AFM) makes it possible to directly correlate chemical information with spatial features of samples at the nanoscale. We focus on the limits of this system for detecting a single SLB and imaging its microdomains, and employ surface-enhanced Raman spectroscopy (SERS) to improve the sensitivity achieved with Raman microspectroscopy.

Large-scale two-dimensional (2D) arrays of metallic nanostructures formed by thin-film evaporation over hexagonally close-packed polystyrene spheres are established substrates for surface-enhanced Raman spectroscopy (SERS). By using these substrates with an integrated atomic force microscopy (AFM) and inverted Raman spectroscopy system, simultaneous topographical imaging and high-sensitivity chemical mapping can be performed. In this paper, we have used this technique to investigate supported bilayers of long-chain fatty acids and phospholipids deposited by the Langmuir-Blodgett (LB) and spin-coating techniques. Nanosphere lithography (NSL) substrates created from 384 and 1002 nm polystyrene spheres and silver (Ag) deposition on glass and sapphire substrates were characterized for SERS in terms of their structure, distribution, and level of enhancement. SERS mappings of rhodamine 6G (R6G) and p-aminothiophenol (p-ATP) monolayers on the 384 nm substrates demonstrate high and uniform enhancement at a micrometer scale. The enhancement was sufficiently high to enable measurement of SERS spectra for arachidic acid (AA) and dipalmitoylphosphatidylcholine (DPPC) layers on sapphire/Ag substrates. The roughness of these substrates (,2 nm) was lower than for glass/Ag (;5 nm); therefore, simultaneous to SERS it was possible to measure the topography of the samples by AFM and determine the number of layers of AA and DPPC. This study shows the potential of the combined AFM/SERS technique for spectral and topographical characterization of phospholipid bilayers. This may prove to be an interesting approach for further studies with more complex heterogeneous lipid mixtures aiming to measure spatially resolved features such as microdomains.

Downloaded From: http://nanophotonics.spiedigitallibrary.org/ on 08/27/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Abstract. Surface-enhanced Raman spectroscopy (SERS) substrates formed by nanosphere lithography were investigated for their spatial distribution and magnitude of electric field enhancement. An integrated atomic force microscopy and Raman micro-spectroscopy system was used to establish, with high accuracy, the correlation between the local SERS mappings and substrate topography. Using a monolayer of rhodamine 6G as a probe of the local electric field, the high resolution Raman mappings, showed that the highest electric field enhancement originates from the metallic nanostructures rather than the gaps between them. The enhancement factor of the substrates is calculated from Raman spectra of the substrates covered in a monolayer of p-aminothiophenol and spatial measurements, giving a value on the order of 10 5 . The experimental results were confirmed by theoretical calculations using the finite element method.C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Abstract. We report the use of dielectrophoresis to fabricate in-situ probes for tip-enhanced Raman spectroscopy (TERS) based on Au nanoparticles. A typical conductive atomic force microscope (AFM) was used to functionalize iridium-coated conductive silicon probes with Au nanoparticles of 10-nm diameter. Suitable TERS probes can be rapidly produced (30 to 120 s) by applying a voltage of 10 Vpp at a frequency of 1 MHz. The technique has the advantage that the Au-based probes are ready for immediate use for TERS measurements, minimizing the risks of tip contamination and damage during handling. Scanning electron microscopy and energy dispersive x-ray spectroscopy were used to confirm the quality of the probes, and used samples of p-ATP monolayers on silver substrates were used to demonstrate experimentally TERS measurements.

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