Single-molecule surface-enhanced Raman spectroscopy with nanowatt excitation.

We demonstrate the possibility of single molecule (SM) detection via surface-enhanced Raman spectroscopy (SERS) in two seemingly challenging and unexpected cases: first with ultra-low excitation powers of the order of nanowatts and second in as-synthesized and not deliberately-aggregated silver colloid solution. The experiments are carried out using the bi-analyte method on a methylated form of Rhodamine 6G and one of its isotopologues excited at 514 nm close to the electronic resonance. This study spectacularly highlights the fact that SM-SERS detection is much more common and easier to achieve than typically thought, in particular in the case of resonance Raman excitation.

Polypeptide multilayer self-assembly studied by ellipsometry.

A polypeptide nanofilm made by layer-by-layer (LbL) self-assembly was built on a surface that mimics nonwoven, a material commonly used in wound dressings. Poly-L-lysine (PLL) and poly-L-glutamic acid (PLGA) are the building blocks of the nanofilm, which is intended as an enzymatically degradable lid for release of bactericides to chronic wounds. Chronic wounds often carry infection originating from bacteria such as Staphylococcus aureus and a release system triggered by the degree of infection is of interest.

Tunable SERS using gold nanoaggregates on an elastomeric substrate.

We report on the self-assembly of colloidal gold nanoparticles on a stretchable, elastomeric membrane, and the use of this membrane as a base substrate for far-field confocal Raman measurements. Surface-enhanced Raman scattering (SERS) enhancement for such a substrate was estimated as 10(6) to 10(7). Atomic force microscopy has been used to study the changes in nanoparticle topography when the membrane is stretched.

Strong correlation between molecular configurations and charge-transfer processes probed at the single-molecule level by surface-enhanced Raman scattering.

Single-molecule (SM) electrochemistry studied by surface-enhanced Raman scattering (SERS) with high spectral resolution reveals a picture in which the frequency of Raman modes is correlated with the electrochemical process through the interaction with the surface. Previously unexplored phenomena can be revealed by the synergy of electrochemistry and SM-SERS, which explores in this case subtler spectroscopic aspects (like the frequency of a vibration within the inhomogeneous broadening of a many-molecules Raman peak) to gain the information. We demonstrate, among other things, that the interaction with the surface is correlated both with the molecule vibrational frequencies and with the ability of single molecules to be reduced/oxidized at different potentials along the electrochemical cycle.