A conical cross-section gold nanoholes array is fabricated on a multi-mode optical fiber tip with an electron-beam lithography process. Underneath the conical gold nanoholes, nanocavities are etched into the substrate fiber glass to increase the light–matter interaction volume. Localized surface plasmon resonance of the fabricated fiber optical device is characterized by measuring the optical transmittance through the fiber tip in the visible and near infrared spectral range. The fiber optical device is used as an index of refraction sensor to detect isopropyl alcohol, ethanol, and methanol. A largely enhanced sensitivity of 652 nm per refractive index unit due to the conical cross-section gold nanoholes and the nanocavities in the fiber glass substrate is observed. Additionally, the response and recovery times of the fiber-tip plasmon sensor are measured for the first time.
In this work, a 2D metallic nano-trench array was fabricated on gold metal surface by using an e-beam lithography patterning and etching process. Optical reflectance from the device was measured at oblique angles of incidence for TE and TM polarization. Near perfect light trapping was observed at different wavelengths for TE and TM polarization at oblique angle of incidence. As angle of incidence increases, light trapping wavelength has a red-shift for TM polarization and blue shift for TE polarization. The fabricated nano-trench device was also investigated for chemical sensor application. It was found that by varying the angle of incidence, the sensitivity changes with opposite trends for TE and TM polarization. Sensor sensitivity increases for TM polarization and decreases for TE polarization with increase of the oblique incident angle.
Localized surface plasmon resonance has been extensively investigated for biochemical sensor applications. In traditional localized surface plasmon resonance biosensors, resonance spectra were measured in the reflection or transmission from the nanostructure devices. In this work, we demonstrate a new surface plasmon resonance sensor platform with which the localized surface plasmon resonance and shift were measured by using a CCD imager instead of using an optical spectrometer. In additional to the metal nanostructures which support localized plasmon resonance, we pattern the nanostructures into diffraction gratings with super-wavelength grating periods. The nanostructure diffraction gratings support localized plasmon resonance and also diffract localized plasmon resonance radiations into non-zeroth order diffractions. Plasmon resonance spectrum and shift are measured with a CCD imager in one of the diffraction orders. The new plasmon resonance spectrometer sensor combines the functions of sensing and spectral analysis into one apparatus and is capable of real-time visualization of the biochemical bonding process with an imager.
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