Nicholas P. W. Pieczonka

Single molecule analysis by surfaced-enhanced Raman scattering

Our main objective in this tutorial review is to provide insight into some of the questions surrounding single molecule detection (SMD) using surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). Discovered thirty years ago, SERS is now a powerful analytical tool, strongly tied to plasmonics, a field that encompasses and profits from the optical enhancement found in nanostructures that support localized plasmon excitations. The spectrum of the single molecule carries the quantum fingerprints of the system modulated by the molecule-nanostructure interactions and the electronic resonances that may result under laser excitation. This information is embedded in vibrational band parameters. The dynamics and the molecular environment will affect the bandwidth of the observed Raman bands. In addition, the localized surface plasmon resonances (LSPR) empower the nanostructure with a number of optical properties that will also leave their mark on the observed inelastic scattering process. Therefore, controlling size, shape and the formation of the aggregation state (or fractality) of certain metallic nanostructures becomes a main task for experimental SERS/SERRS. This molecule-nanostructure coupling may, inevitably, lead to spectral fluctuations, increase photobleaching or photochemistry. An attempt is made here to guide the interpretation of this wealth of information when approaching the single molecule regime.

Challenges and Approaches for High-Voltage Spinel Lithium-Ion Batteries

Lithium-ion (Li-ion) batteries have been developed for electric vehicle (EV) applications, owing to their high energy density. Recent research and development efforts have been devoted to finding the next generation of cathode materials for Li-ion batteries to extend the driving distance of EVs and lower their cost. LiNi(0.5)Mn(1.5)O(4) (LNMO) high-voltage spinel is a promising candidate for a next-generation cathode material based on its high operating voltage (4.75 V vs. Li), potentially low material cost, and excellent rate capability. Over the last decade, much research effort has focused on achieving a fundamental understanding of the structure-property relationship in LNMO materials. Recent studies, however, demonstrated that the most critical barrier for the commercialization of high-voltage spinel Li-ion batteries is electrolyte decomposition and concurrent degradative reactions at electrode/electrolyte interfaces, which results in poor cycle life for LNMO/graphite full cells. Despite scattered reports addressing these processes in high-voltage spinel full cells, they have not been consolidated into a systematic review article. With this perspective, emphasis is placed herein on describing the challenges and the various approaches to mitigate electrolyte decomposition and other degradative reactions in high-voltage spinel cathodes in full cells.

SERRS for Single-Molecule Detection of Dye-Labeled Phospholipids in Langmuir−Blodgett Monolayers

The coupling of molecular excitations to localized surface plasmon resonances (LSPR) in silver or gold nanostructures is at the center of single-molecule detection (SMD) using surface-enhanced Raman scattering (SERS). The effect is attributed to the enhanced scattering power caused by coupling with the surface plasmons of the metal. The most efficient coupling is attained when the excitation is in resonance with the molecule and the nanostructure, the case of surface-enhanced resonance Raman scattering (SERRS). This incredible effect has the potential to be a powerful optical tool when used in conjunction with vibrationally differentiable chromophores. Here we present a unique study where the targeted system is a phospholipid that is tagged with a xanthene dye (the SERRS probe), a chromophore that dominates the Raman signal when the laser is in resonance with its absorption. The labeled phospholipid was incorporated into a single fatty acid Langmuir monolayer at varying concentrations and transferred onto a silver nanoparticle film to form Langmuir-Blodgett (LB) monolayers. Because the xanthene dye is tagged to a much larger molecule, the chances of dye aggregation (formation of dimers or higher aggregates) is negligible. Single-molecule detection of the dye tag (SERRS probe monomer) is readily achieved and demonstrated through the use of doped LB monolayers, Raman microscopy, spectral mapping, and efficient coupling of the laser line into the dye absorption band and plasmon resonances.

Surface-enhanced Raman scattering and SERRS imaging of phthalocyanine mixed films

The objective of the present work is the study of the surface-enhanced spectroscopy of mixed thin solid films of metallophthalocyanine (MPc; M ≡ Cu, Co) and bis(n-propylimido)perylene (Bis-PTCDPr) materials fabricated by vacuum co-evaporation onto silver island films. The surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) of neat Bis-PTCDPr, CuPc and CoPc were also recorded using visible 514.5 and 633 nm laser lines and near-infrared excitation at 780 nm. During the investigation it was found that the Raman scattering (RS) and resonance Raman scattering (RRS) spectra of CuPc and CoPc films were sensitive to the irradiance at the sample. To further explore the effect of local heating on the vibrational spectrum, a temperature dependence (between −180 and 200 °C) study was carried out using the 514.5 nm laser line with constant laser power. The overtones and combinations of the CuPc and CoPc molecules were also clearly observed in the RRS and SERRS spectra. The study of the SER(R)S spectra allowed us to conclude that the dyes of the mixed films were physically adsorbed onto the silver islands. It is also shown that, in mixed films, differences in the absorption properties can be used to tune into the spectrum of any one of the components of the mixture with the appropriate laser line. For the first time, SERRS mapping and global imaging of mixed films obtained with the 514.5 nm laser line are reported. Complementary information about the quality of the films, homogeneity and phase separation may be obtained using SERRS imaging.

Applications of the Enhancement of Resonance Raman Scattering and Fluorescence by Strongly Coupled Metallic Nanostructures

In this Chapter, we have described several applications of the enhancement of resonance Raman scattering and molecular fluorescence toward the characterization of single molecules, monolayers, and thin solid films on metal-island films, colloidal metal nanoparticles, and nanocomposite films. While this review is by no means extensive, we believe it does serve to shed light on some of the more critical considerations of this work, and also to highlight some of the very powerful potential uses of resonant surface-enhanced spectroscopies.