Luis M. Liz-Marzán

Directed Self-Assembly of Nanoparticles

Within the field of nanotechnology, nanoparticles are one of the most prominent and promising candidates for technological applications. Self-assembly of nanoparticles has been identified as an important process where the building blocks spontaneously organize into ordered structures by thermodynamic and other constraints. However, in order to successfully exploit nanoparticle self-assembly in technological applications and to ensure efficient scale-up, a high level of direction and control is required. The present review critically investigates to what extent self-assembly can be directed, enhanced, or controlled by either changing the energy or entropy landscapes, using templates or applying external fields.

Modelling the optical response of gold nanoparticles

This tutorial review presents an overview of theoretical methods for predicting and understanding the optical response of gold nanoparticles. A critical comparison is provided, assisting the reader in making a rational choice for each particular problem, while analytical models provide insights into the effects of retardation in large particles and non-locality in small particles. Far- and near-field spectra are discussed, and the relevance of the latter in surface-enhanced Raman spectroscopy and electron energy-loss spectroscopy is emphasized.

Recent Progress on Silica Coating of Nanoparticles and Related Nanomaterials

In recent years, new strategies for silica coating of inorganic nanoparticles and organic nanomaterials, which differ from the classical methodologies, have emerged at the forefront of materials science. Silica as a coating material promises an unparalleled opportunity for enhancement of colloidal properties and functions by using core-shell rational designs and profiting from its synthetic versatility. This contribution provides a brief overview of recent progress in the synthesis of silica-coated nanomaterials and their significant impact in different areas such as spectroscopy, magnetism, catalysis, and biology.

High-yield synthesis and optical response of gold nanostars

Multipod Au nanoparticles (nanostars) with single crystalline tips were synthesized in extremely high yield through the reduction of HAuCl(4) in a concentrated solution of poly(vinylpyrrolidone) (PVP) in N,N-dimethylformamide (DMF), in the presence of preformed Au nanoparticle seeds, but with no need for external energy sources. Nanostar dispersions display a well-defined optical response, which was found (through theoretical modeling) to comprise a main mode confined within the tips and a secondary mode confined in the central body. Calculations of the surface enhanced Raman scattering (SERS) response additionally show that this morphology will be relevant for sensing applications.

Zeptomol Detection Through Controlled Ultrasensitive Surface-Enhanced Raman Scattering

SERS permits identifying the nature of molecules in extremely low concentrations, but it is hindered by poor enhancement or low reproducibility. We demonstrate controllable approximately 10(10) signal amplification reaching the zeptomol detection limit for a nonresonant molecule by sandwiching the analyte between the tips of star-shaped gold nanoparticles and a planar gold surface using a simple synthetic procedure. This unprecedented control over light-intensity amplification opens a new avenue toward high-yield, fully reproducible, SERS-based, zeptomol detection and holds promise for nonlinear optics applications at the single-particle level.

Gold nanorods 3D-supercrystals as surface enhanced Raman scattering spectroscopy substrates for the rapid detection of scrambled prions

Highly organized supercrystals of Au nanorods with plasmonic antennae enhancement of electrical field have made possible fast direct detection of prions in complex biological media such as serum and blood. The nearly perfect three-dimensional organization of nanorods render these systems excellent surface enhanced Raman scattering spectroscopy substrates with uniform electric field enhancement, leading to reproducibly high enhancement factor in the desirable spectral range.

Silica encapsulation of quantum dots and metal clusters

The use of nanometre thick silica shells as a means to stabilize metal clusters and semiconductor particles is discussed, and its potential advantages over conventional organic capping agents are presented. Shell deposition depends on control of the double layer potential, and requires priming of the core particle surface. Chemical reactions are possible within the core, via diffusion of reactants through the shell layer. Quantum dots can be stabilized against photochemical degradation through silica deposition, whilst retaining strong fluorescence quantum yields and their size dependent optical properties. Ordered 3D and 2D arrays of a macroscopic size with uniform particle spacing can be created. Thin colloid films can also be created with well-defined interparticle spacing, allowing controlled coupling of exciton and surface plasmon modes to be investigated. A number of future core–shell nanocomposite structures are postulated, including quantum bubbles and single electron capacitors based on Au@SiO2.

Plasmonic nanosensors with inverse sensitivity by means of enzyme-guided crystal growth

Lowering the limit of detection is key to the design of sensors needed for food safety regulations, environmental policies and the diagnosis of severe diseases. However, because conventional transducers generate a signal that is directly proportional to the concentration of the target molecule, ultralow concentrations of the molecule result in variations in the physical properties of the sensor that are tiny, and therefore difficult to detect with confidence. Here we present a signal-generation mechanism that redefines the limit of detection of nanoparticle sensors by inducing a signal that is larger when the target molecule is less concentrated. The key step to achieve this inverse sensitivity is to use an enzyme that controls the rate of nucleation of silver nanocrystals on plasmonic transducers. We demonstrate the outstanding sensitivity and robustness of this approach by detecting the cancer biomarker prostate-specific antigen down to 10(-18) g ml(-1) (4 × 10(-20) M) in whole serum.

Stabilization of CdS semiconductor nanoparticles against photodegradation by a silica coating procedure

Abstract Nanometre-sized CdS semiconductor particles were synthesized in the presence of sodium citrate, and subsequently surrounded by a homogeneous silica shell. The coating procedure makes use of 3-(mercaptopropyl) trimethoxy silane (MPS) as a surface primer to deposit a thin silica shell in water. The dispersion is then transferred into ethanol, where thicker shells can be grown. The citrate-stabilized particles are slowly degraded through photochemical oxidation in the presence of dissolved oxygen. This destabilizing process is suppressed when a homogeneous, microporous silica shell is built up around the particles, through a limited access of O 2 molecules to the CdS surface.

SERS-based diagnosis and biodetection.

Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most powerful analytical techniques for identification of molecular species, with the potential to reach single-molecule detection under ambient conditions. This Concept article presents a brief introduction and discussion of both recent advances and limitations of SERS in the context of diagnosis and biodetection, ranging from direct sensing to the use of encoded nanoparticles, in particular focusing on ultradetection of relevant bioanalytes, rapid diagnosis of diseases, marking of organelles within individual cells, and non-invasive tagging of anomalous tissues in living animals.