The Optical Nanoparticle Spectroscopy For Photonic Application (ONSPA) Laboratory seeks to understand and control how energy decays optically in nanoparticles and materials for photonic applications. We study this through various linear and nonlinear microscopy/spectroscopy techniques and explore the use of engineered nanoparticles in cancer therapy, biolabeling, deep tissue imaging, optical circuitry, data storage and solar cells.
We’re exploring the understanding of optical energy decay pathways for nanoparticles of various material (semiconductor, metal, dielectric), size (10–500 nm) and shapes (ellipsoidal, spherical and spheroidal). We focus on the following types of particles and materials:
- Au nanoparticle superstructures for plasmonic and photothermal applications such as cancer therapy and biolabeling
- Si nanoparticles for deep-tissue imaging biolabeling development
- Graphene and Au nanosheet hybrid structures for SERS enhancement.
We’re equipped with a multiphoton microscopy and spectroscopy facility, a unique capability with multiple modes of microscopy operation. It incorporates confocal microscopies with femtosecond pulsed and continuous-wave lasers in the entire UV-VIS-NIR wavelength range (250 nm–2 μm). This allows interchangeable modes of operation between confocal (fluorescence, scattering or reflection modes), multiphoton (two-, three- or four-photon excitation modes) and nonlinear (second- and third-harmonic generation) microscopies.
The nanoparticle fabrication facility produces semiconductor (Si, Ge), metal (Au) and dielectric nanoparticles (SiO2) of controlled sizes (10 – 500 nm range) for deep-tissue imaging biolabel development. Together with Z-scan spectroscopy, it utilises regeneratively amplified laser with pulse energy reaching up to 4 mJ. Other suites of characterisation capabilities in this facility include super-resolution, dark-field, Raman and atomic force microscopies.
Our research projects
Multiphoton luminescence of Au superstructures
In this project, we study multiphoton luminescence of plasmon coupled superstructures (~ 1 micron diameter) of tiny Au nanoparticles (~ 10 nm) by means of linear and non-linear luminescence spectroscopy. We aim to understand the field enhancement mechanism inside the superstructure where plasmon coupling is expected to play a key role. We hope this will lead to control of their luminescence quantum efficiency of the structure.
This project will help develop novel, non-toxic, highly efficient, linear and nonlinear luminescent markers that are stable and free of blinking or bleaching. Such markers will be great assets for targeted cell imaging, photodynamic cancer therapy and high-density optical storage.
Silicon nanoparticle fabrication for multiphoton luminescence deep tissue imaging
Silicon nanoparticles (SiNP) have recently received much attention due to their extraordinary light scattering ability in visible and infrared colour range. The so-called “magnetic nanoantenna” are special because they can pick up both magnetic and electric field of light, and the frequency tuning of these nanoantennae can be dialled by changing the size of the particle. They are also stable and non-toxic, making them an ideal candidate as labels in live animal imaging.
At our laboratory, various sizes of SiNPs can be synthesised using femtosecond (fs) laser ablation technique. It directs high-energy (up to 1 mJ per pulse), extremely short pulses (100 fs) to silicon wafer, causing damage to the wafer and creating a plume of SiNPs. In this setup, a wide variety of nanoparticle size can be produced, ranging from a few nanometers to micrometers in diameter, all of which have unique colour channels in visible and infrared. In this project, we hope to demonstrate the idea of using SiNPs as nonlinear biolabels for deep tissue imaging. Multiphoton excited luminescence from SiNPs was demonstrated to be nonlinearly excited at 1500 nm pulsed laser, ideal wavelength for 3PM.
Aggregation and uptake kinetics of gold nanoparticles in cancer cells
Gold nanoparticles (AuNPs) are being developed as biomarking and cancer therapy agents. For the full realisation of their potential in this area AuNP uptake, aggregation and its cytotoxicity inside cells have to be studied in more detail. The aim of this project is to test a new technique called high order ICS (HICS) to quantify the uptake and aggregation of AuNPs inside live cells. We propose to use HICS together with plasmon coupling. The combination of these techniques overcome the limitations of ICS and provides microscopic and macroscopic information on nanoparticle interactions within a cellular environment. This technique could be used in many biological applications including cancer therapy, drug delivery, disease diagnosis and also for probing membrane protein stoichiometry and dynamics.
Graphene hybridization with plasmonic nanostructures
We study single-layer graphene hybridised with plasmonic nanosheets using Raman spectroscopy and dark-field scattering. Our aim is to understand the interaction between the two materials and introduce new functionalities integrating the properties of graphene and plasmonic nanosheet. This new hybrid material will be applicable to single-molecule sensing, sub-nanometre distance and charge sensing.