Metallic nanohole arrays (NHAs) with a high hole density have emerged with potential applications for surface-enhanced Raman spectroscopy (SERS) including the detection of analytes at ultra-low concentrations. However, these NHA structures generally yield weak localized surface plasmon resonance (LSPR) which is a prerequisite for SERS measurements. In this work, a compact three-dimensional (3D) tunable plasmonic cavity with extraordinary optical transmission properties serves as a molecular sensor with sub-femtomolar detection. The 3D nanosensor consists of a gold film containing a NHA with an underlying cavity and a gold nanocone array at the bottom of the cavity. These nanosensors provide remarkable surface plasmon polariton (SPP) and LSPR coupling resulting in a significantly improved detection performance. The plasmonic tunability is evaluated both experimentally and theoretically. A SERS limit of detection of 10-16 M for 4-Nitrothiophenol (4-NTP) is obtained along with 28 distribution mapping of the molecule on the 3D plasmonic nanosensor. This results in an 29 improved SERS enhancement factor (EF) of 10 6 obtained from a femtolitre plasmonic cavity 30 volume. The tunability of these sensors can give rise to a potential opportunity for use in optical 31 trapping while providing SERS sensing of a molecule of interest. 32
This study investigates the feasibility of changing the shield radius of an RF coil to shift the resonant frequency from 1H to 19F for multinuclear imaging. The method proposed in this investigation was verified by changing the resonant frequency of a 129Xe RF Coil a total of 1.18 MHz by changing the shield radius, allowing it to be used in a 2.9T Siemens MRI and a 3.0T GE MRI. It was found that altering the shield radius had similar effects on the resonant frequency as using a variable tuning capacitor, allowing for one coil to be compatible with multiple scanners.
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