We describe the operating principle and performance of a recently developed surface plasmon-enhanced optical sensor that utilizes two-photon excited luminescence of a planar gold film as the reporter signal. The sensor enables direct visualization of nanoscopic binding events near a sensing surface. Light is coupled to the Au/sample interface in an objective-based Kretschmann configuration to excite surface plasmon polariton (SPP) modes at a metal−dielectric interface. The gold luminescence induced by the confined optical field between the particle and the film is detected in the epi-direction by a far-field camera where individual binding events show up as diffraction limited bright spots against a dark background. We study the sensor's emission spectrum and the distance dependence between the target and substrate, which both suggest that the optical signal of the sensor originates from electron−hole pair excitations in the planar Au film. In addition, we show that the well-behaved pointspread function of the sensor enables a straightforward implementation of superresolution techniques. Finally, we demonstrate the utility of the sensor for detecting DNA binding events, underlining the sensor's usefulness for label-free imaging of nanoscopic particles and biomolecular interactions.

We discuss an experimental configuration consisting of {Au film}− molecule−{Au particle} or {Au film}−molecule−{Si particle} nanojunctions for performing wide-field surface-enhanced CARS (SE-CARS) measurements in a reproducible and controllable manner. While the allowable illumination dosage in the {Au film}−molecule−{Au particle} case is limited by the strong two-photon background from the gold, we successfully generate a detectable coherent Raman response from a molecular monolayer using the lowest reported average power densities to date. With a vision to minimize the two-photon background and the intrinsic losses observed in allmetal plasmonic systems, we examine the possibility of using high-index dielectric particles on top of a thin metal film to generate strong nanoscopic hot spots. We demonstrate repeatable SE-CARS measurements at the {Au film}−molecule−{Si particle} heterojunction, underlining the utility of this experimental geometry. This work paves the way for the development of next-generation chemical and biomolecular sensing assays that can minimize some of the major drawbacks encountered in fragile and lossy all-metal plasmonic systems.

This study addresses the recovery of recovery of zinc (Zn) and manganese (Mn) from spent dry cell (Zn-C battery) batteries using a hydrometallurgical approach. Every year, a significant number of Zn-C dry cell batteries are consumed and disposed worldwide. Zn-C dry cell batteries constitute more than 60% of Zn and Mn together. Higher amount of Zn and Mn present in Zn-C dry cells shows an industrial interest in recycling and recovering Zn and Mn. In this study the recovery of Zn and Mn from spent dry cells was investigated through an energy efficient hydrometallurgical route. Zn-C batteries were manually dismantled to collect the battery paste. Neutral leaching was carried out to remove potassium and non-metal contents. The battery powder was leached in sulfuric acid medium with glucose as reducing agent. The experiments were conducted according to ‘24 full factorial design’. The purpose of the design was to identify the most effective and optimum condition for Zn and Mn recovery from spent Zn-C batteries. Using the optimum operating condition, up to 86.54 % of Mn and 82.19% of Zn were recovered from the original battery powder.

Surface-enhanced coherent anti-Stokes Raman scattering (SE-CARS) takes advantage of surface plasmon resonances supported on metallic nanostructures to amplify the coherent Raman response of target molecules. While these metallic antennas have found significant success in SE-CARS studies, photoinduced morphological changes to the nanoantenna under ultrafast excitation introduce significant hurdles in terms of stability and reproducilibty. These hurdles need to be overcome in order to establish SE-CARS as a reliable tool for rapid biomolecular sensing. Here, we address this challenge by performing molecular CARS measurements enhanced by nanoantennas made from high-index dielectric particles with more favorable thermal properties. We present the first experimental demonstration of enhanced molecular CARS signals observed at Si nanoantennas, which offer much improved thermal stability compared to their metallic counterparts.

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