Title: Seeing the motion: hexagonal boron nitride for nanomotion spectroscopy integrated with fluorescence imaging
Research proposal No: 1.1.1.9/LZP/1/24/138
Duration: 01.02.2025.-31.01.2028.
Project Leader: Ph.D. Līga Jasulaņeca
Total budget: 184 140 EUR
European Regional Development Fund (ERDF) funding: 156 519 EUR
ISSP UL budget: 9 207 EUR
Project description:
Nanomechanical vibrations have recently emerged as a powerful tool for single-cell rapid antibiotic susceptibility testing, enabled by motion transducing graphene nanodrums. While graphene has demonstrated strong potential for detecting the movement and viability of single bacteria, its high quenching of fluorescence signal impedes determination of the source of intracellular nanomotion. To overcome this limitation, this project will investigate alternative two-dimensional materials for developing sensitive, miniaturized, flexible, and biocompatible nanodrum sensors that are based on optical interferometric detection to enable simultaneous nanomotion and fluorescence signal read-out.
Specifically, we propose using hexagonal boron nitride (hBN) to enable simultaneous fluorescence imaging of labeled bacteria and measurement of their intrinsic vibrations. By analyzing the variance in vibrational signals, we aim to correlate optical and mechanical data. This approach will provide insights into intracellular sources of bacterial motion and ultimately facilitate rapid, in vivo single-cell antibiotic testing.
PROJECT PROGRESS
Time period: 01.02.2025. – 30.04.2025.
The project was initiated with a mobility visit to Delft University of Technology in the Netherlands, where, together with collaboration partners from the Micro and Nanosystems Dynamics group led by Dr. Farbod Alijani, we discussed the planned development and measurement of boron nitride nanomotion sensors. I participated in several meetings, getting to know group members and potential collaborators from other groups researching both the applications of hexagonal boron nitride (hBN) in biotechnology and use of alternative two-dimensional materials (such as graphene) in nanomotion sensors.
I learned the dry transfer technique, which allows crystalline two-dimensional materials to be transferred to desired locations on a substrate to create “nanodrums.” One nanodrum sensor was fabricated by transferring an approximately 60 nm thin hBN flake onto a cavity in a silicon substrate. For successful project implementation and nanomotion measurements of bacteria, many such nanodrums must be created; therefore, further project efforts will focus on developing methods to transfer larger-area hBN flakes at once.
I also learned to use the interferometry setup that will be used for nanomotion sensor measurements. Interferometric detection is based on changes in interfering laser beams – one reflecting off the hBN surface, the other from the silicon mirror substrate. To optimize the sensor’s sensitivity, I calculated the cavity depth that corresponds to the strongest interference signal depending on the thickness of the hBN.
In the next mobility visit in April, I traveled to Delft to participate in the "Measuring by Light" conference with a poster presentation titled “Hexagonal Boron Nitride Nanodrums for Combined Nanomotion Spectroscopy and Fluorescence Microscopy of Single Cells.” The conference brought together representatives from academia and industry to share ideas and techniques for measuring vibrations using light. The project idea of correlating vibration measurements with fluorescence data to determine the sources of nanomotion in bacteria was met with great interest.
At the Institute of Solid State Physics, a method was developed for creating cavities in silicon/silicon dioxide substrates, which serve two essential functions in the nanodrum sensors – they allow the hBN flake to oscillate and provide a reflective surface for interferometric detection. The substrates were fabricated using electron beam lithography and reactive ion etching.