The doctoral dissertation in the field of Photonics will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus and online.
What is the topic of your doctoral research? Why is it important to study the topic?
My doctoral research focuses on controlling the plasmonic field distribution in optical biosensors to overcome the limitations of current optical biosensors in terms of novelty, miniaturization, and sensitivity. This work opens different ways to advance optical biosensors towards diagnostics applications, holding great promise for the early detection of infectious diseases and cancers.
What are the key findings or observations of your doctoral research?
In this thesis, we developed three distinct optical biosensing techniques. First, we introduced a novel technique called distance-controlled surface-enhanced Raman spectroscopy (SERS) for extracting spatial information of Raman signals. Second, we designed a high-performance miniaturized grating-based surface plasmon resonance (SPR) system. Third, we demonstrated grating-coupled SPP-enhanced upconversion luminescence (UCL) for highly sensitive biosensing.
How can the results of your doctoral research be utilised in practice?
First, distance-controlled SERS is applicable in analyzing layered biological particles, for example, extracellular vesicles (EVs) in medical diagnostics. This method helps identify whether the compositional information of EVs comes from their surface or interior, which can be linked to specific diseases like cancer. Second, our SPR system shows great potential for point-of-care applications thanks to its compact design and cost-effectiveness. However, our study lacked surface functionalization, which is essential for SPR sensors to capture specific analytes. Third, our plasmon-enhanced UCL method shows an enhancement factor of up to sixty-five at low excitation power densities. This improvement at lower power levels is beneficial for UCL imaging systems, enabling faster measurements compared to conventional scanning techniques. Furthermore, the increased UCL intensities enhance the signal-to-noise ratio, thereby improving the sensitivity of UCNP-based biosensors.
What are the key research methods and materials used in your doctoral research?
In three optical biosensing techniques, plasmonic nanostructures were first modeled and optimized in COMSOL Multiphysics. The nanostructures were then fabricated and characterized. Measurements were conducted and compared with simulation results. In distance-controlled SERS, gold nanospheres, purchased from Nanocs Inc., were conjugated with polystyrene beads using biotin-streptavidin binding, and the samples were measured using a time-gated Raman spectrometer. Both SPR and plasmon-enhanced UCL sensors were designed and optimized in COMSOL Multiphysics. They were then fabricated using the nanoimprinting technique. The fabricated SPR sensors were characterized with glucose solutions with our custom-developed SPR system, while the plasmon-enhanced UCL sensors were functionalized with UCNPs and then measured with our custom-developed UCL reading setup.
The doctoral dissertation of Duc Le, MSc, entitled Plasmon field effects on the operation of optical biosensors be examined at the Faculty of Science, Forestry and Technology, Joensuu Campus and online. The opponent will be Associate Professor Nicklas Anttu, Faculty of Science Åbo Akademi University, and the custos will be Professor Matthieu Roussey, University of Eastern Finland. Language of the public defence is English.
For more information, please contact:
Duc Le, Duc.Le@vtt.fi
