title: SERS mapping in Langmuir-Blodgett films and single-molecule detection.
abstract: Plasmon-enhanced spectroscopic techniques have expanded single-molecule detection (SMD) and are revolutionizing areas such as bio-imaging and single-cell manipulation. Surface-enhanced (resonance) Raman scattering (SERS or SERRS) combines high sensitivity with molecular-fingerprint information at the single-molecule level. Spectra originating from single-molecule SERS experiments are rare events, which occur only if a single molecule is located in a hot-spot zone. In this spot, the molecule is selectively exposed to a significant enhancement associated with a high, local electromagnetic field in the plasmonic substrate. Here, we report an SMD study with an electrostatic approach in which a Langmuir film of a phospholipid with anionic polar head groups (PO4(-)) was doped with cationic methylene blue (MB), creating a homogeneous, two-dimensional distribution of dyes in the monolayer. The number of dyes in the probed area of the Langmuir-Blodgett (LB) film coating the Ag nanostructures established a regime in which single-molecule events were observed, with the identification based on direct matching of the observed spectrum at each point of the mapping with a reference spectrum for the MB molecule. In addition, advanced fitting techniques were tested with the data obtained from micro-Raman mapping, thus achieving real-time processing to extract the MB single-molecule spectra.
authors: Faculdade de Ciências e Tecnologia, UNESP Universidade Estadual Paulista, Presidente Prudente/SP, 19060-900, Brazil.
authors: Pedro H B
authors: PH
authors: Aoki
authors: Eduardo G E
authors: EG
authors: Carreon
authors: Diogo
authors: D
authors: Volpati
authors: Milton H
authors: MH
authors: Shimabukuro
authors: Carlos J L
authors: CJ
authors: Constantino
authors: Ricardo F
authors: RF
authors: Aroca
authors: Osvaldo N
authors: ON
authors: Oliveira
authors: Fernando V
authors: FV
authors: Paulovich