Chemical and Biomedical Sensing Applications Based on Performance Enhanced Palladium-Gold Localized Surface Plasmon Resonance

Abstract

Localized surface plasmon resonance (LSPR) is an optical phenomenon due to the incident electromagnetic wave exciting the plasma oscillation on the nanostructure and causing a resonance at certain frequency. The excited plasma is confined at the very surface of the nanostructure which is susceptible to environment variation. As a result, plasmonic nanomaterial array with enhanced LSPR effect is developed to perform biomedical and chemical sensing applications based on the high sensitivity to the local refractive index change.

Gold (Au) and silver nanostructures exhibit powerful optical performance and biocompatibility is intensively developed for variety of sensors by many research groups. However, Palladium (Pd) has recently emerged as a third plasmonic material which also attracts interest in research owing to its good catalytic performance and comparable refractive index susceptibility to existing materials. Moreover, bimetallic nanostructures or hybrid with composite material have been found to have more charge transfer among the material and provide great potential in enhancing the LSPR performance than that of the single element based LSPR sensors. Therefore, this thesis presents investigations on the novel nanomaterial synthesized from Pd-Au film deposition and thermal annealing method. The surface of the finally annealed film was found to in the form of nanoislands.

In order to analyze the fabricated Pd-Au nanomaterial in detail, ultraviolet-visible spectroscopy (UV-Vis), atomic force microscopy (AFM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements were conducted to provide comprehensive understanding of the synthesized nanomaterial. With the above-mentioned materials characterization techniques, the novel material is confirmed to be a hybrid of PdO and Au nanoislands structure. The optical absorption, LSPR performance and refractive index susceptibility provided interesting and competitive results to those from previously investigation with Au nanoislands. In order to perform high specificity biosensing and detection of chemical substances, functionalization on the PdO/Au hybrid nanoislands based on existing protocols were tested and optimized for further LSPR sensor development. Further, density functional theory numerical analysis was carried out to help explain the mechanism of absorption between the nanoisland material and the functionalized material.

To demonstrate the feasibility of the PdO/Au hybrid nanoislands for biosensing, detection of acrylamide and immuno-biosensing of alpha-synuclein were carried out. Based on the established functionalization, outstanding performance was found for their detection. In acrylamide detection, glutathione functionalized PdO/Au hybrid nanoislands show good affinity to acrylamide and the limit of detection reached 1.69 ppb with the dynamic range covering 4 orders of magnitude up to 50 ppm. On the other hand, by dielectric functionalized PdO/Au hybrid nanoislands, the detection of alpha-synuclein, which is a dementia related substance, attained the limit of detection to 37.9 pM, and with a wide dynamic range up to at least 5 orders of magnitude. Therefore, the investigated PdO/Au hybrid nanoisland sensing chips can become a powerful and potential material to provide a new platform for LSPR related field.

Date of Award	6 Jul 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Lawrence WU (Supervisor)