Does Lorenz-Mie scattering theory for active particles lead to a paradox?

Electromagnetic Nanoparticles for Sensing and Medical Diagnostic Applications

A modeling and design approach is proposed for nanoparticle-based electromagnetic devices. First, the structure properties were analytically studied using Maxwell's equations. The method provides us a robust link between nanoparticles electromagnetic response (amplitude and phase) and their geometrical characteristics (shape, geometry, and dimensions). Secondly, new designs based on "metamaterial" concept are proposed, demonstrating great performances in terms of wide-angle range functionality and multi/wide behavior, compared to conventional devices working at the same frequencies. The approach offers potential applications to build-up new advanced platforms for sensing and medical diagnostics. Therefore, in the final part of the article, some practical examples are reported such as cancer detection, water content measurements, chemical analysis, glucose concentration measurements and blood diseases monitoring.

Extinction by a homogeneous spherical particle in an absorbing medium

We use a recent computer implementation of the first-principles theory of electromagnetic scattering to compute far-field extinction by a spherical particle embedded in an absorbing unbounded host. Our results show that the suppressing effect of increasing absorption inside the host medium on the ripple structure of the extinction efficiency factor as a function of the size parameter is similar to the well-known effect of increasing absorption inside a particle embedded in a nonabsorbing host. However, the accompanying effects on the interference structure of the extinction efficiency curves are diametrically opposite. As a result, sufficiently large absorption inside the host medium can cause negative particulate extinction. We offer a simple physical explanation of the phenomenon of negative extinction consistent with the interpretation of the interference structure as being the result of interference of the field transmitted by the particle and the diffracted field due to an incomplete wavefront resulting from the blockage of the incident plane wave by the particle's geometrical projection.

Sensing using plasmonic nanostructures and nanoparticles

Nanoparticles are widely used in various fields of science and technology as well as in everyday life. In particular, gold and silver nanoparticles display unique optical properties that render them extremely attractive for various applications. In this review, we focus on the use of noble metal nanoparticles as plasmonic nanosensors with extremely high sensitivity, even reaching single molecule detection. Sensors based on plasmon resonance shifts, as well as the use of surface-enhanced Raman scattering and surface-enhanced fluorescence, will be considered in this work.