Single-Molecule Detection in Nanogap-Embedded Plasmonic Gratings

Surface Plasmon Enhanced Fluorescence Temperature Mapping of Aluminum Nanoparticle Heated by Laser

Partially aggregated Rhodamine 6G (R6G) dye is used as a lights-on temperature sensor to analyze the spatiotemporal heating of aluminum nanoparticles (Al NPs) embedded within a tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV) fluoropolymer matrix. The embedded Al NPs were photothermally heated using an IR laser, and the fluorescent intensity of the embedded dye was monitored in real time using an optical microscope. A plasmonic grating substrate enhanced the florescence intensity of the dye while increasing the optical resolution and heating rate of Al NPs. The fluorescence intensity was converted to temperature maps via controlled calibration. The experimental temperature profiles were used to determine the Al NP heat generation rate. Partially aggregated R6G dyes, combined with the optical benefits of a plasmonic grating, offered robust temperature sensing with sub-micron spatial resolution and temperature resolution on the order of 0.2 °C.

Surface plasmon-coupled emission imaging for biological applications

Fluorescence imaging technology has been extensively applied in chemical and biological research profiting from its high sensitivity and specificity. Much attention has been devoted to breaking the light diffraction-limited spatial resolution. However, it remains a great challenge to improve the axial resolution in a way that is accessible in general laboratories. Surface plasmon-coupled emission (SPCE), generated by the interactions between surface plasmons and excited fluorophores in close vicinity of the thin metal film, offers an opportunity for optical imaging with potential application in analysis of molecular and biological systems. Benefiting from the highly directional and distance-dependent properties, SPCE imaging (SPCEi) has displayed excellent performance in bioimaging with improved sensitivity and axial confinement. Herein, we give a brief overview of the development of SPCEi. We describe the unique optical characteristics and constructions of SPCEi systems and highlight recent advances in the use of SPCEi for biological applications. We hope this review provides readers with both the insights and future prospects of SPCEi as a new promising imaging platform for potentially widespread applications in biological research and medical diagnostics. Graphical abstract.

Enhanced fluorescence for in situ temperature mapping of photothermally heated aluminum nanoparticles enabled by a plasmonic grating substrate

In situ dynamic temperature mapping of photothermally heated aluminum nanoparticles (Al NPs) embedded in a fluoropolymer (THV) is achieved using fluorescent dye (rhodamine 6G). A plasmonic grating substrate enhances the dye fluorescence intensity by a factor of seven over a glass substrate, to enable image capture rates of 500 frames per second. Further, the fluorescence intensity is linearly related to temperature and reversible. Photothermal heating of embedded Al NPs using a 2380 W cm^-2 incident flux produced an Al NP heating rate of 1.2 × 10⁴ °C s^-1. Localized Al NP motion was also observed and attributed to thermal expansion and melting of the polymer. Multiphysics simulation provided agreement with experimental observations, bolstering confidence in the technique. The plasmonic grating platforms were shown to significantly improve both fluorescence intensity and the photothermal heating of Al compared to glass substrates, opening a new path for fast and high-resolution in situ temperature mapping.

In Situ Characterization of Photothermal Nanoenergetic Combustion on a Plasmonic Microchip

Plasmonic gratings facilitate a robust in situ diagnostic platform for photothermal combustion of nanoenergetic composite thin films using an optical microscope and a high-speed camera. Aluminum nanoparticles (Al NPs) embedded in a fluoropolymer oxidizer are cast onto a plasmonic grating microchip and ignited using a low-power laser. The plasmonic grating enhances both spatial resolution and sufficient photothermal coupling to combust small Al NP clusters, initiating localized flames as small as 600 nm in size. Two-color pyrometry obtained from a high-speed color camera indicates an average flame temperature of 3900 K. Scattering measurements using polarized light microscopy enabled precise identification of individual Al NPs over a large field of view, leading to 3D reconstruction of combustion events.