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: 01.04.2026. – 30.06.2026.
In the following phase, the main focus shifted toward analysis of the experimental data obtained during the previous mobility and measurement activities, as well as preparation of the first scientific publication resulting from the project.
A significant part of the work was devoted to processing and interpreting dynamic measurement data from two-dimensional membrane devices. The analysis focused on extracting and comparing the mechanical response of monolayer amorphous carbon membranes and assessing their suitability as a material platform for nanomotion sensing. Particular attention was paid to understanding the relationship between the interferometric signal, membrane dynamics, and experimental measurement conditions.
The data analysis also supported the broader project goal of benchmarking different two-dimensional materials for nanomotion sensor development. While the project is centered on hexagonal boron nitride-based sensors, the investigation of monolayer amorphous carbon provides an important complementary route. It helps identify material properties that are favorable for sensitive vibration detection and supports the development of alternative membrane platforms for biological sensing.
During this period, work continued on finalizing the first scientific manuscript related to the project, prepared in collaboration with international partners from the University of Southampton, Delft University of Technology, and the National University of Singapore. The manuscript focuses on the dynamics of suspended monolayer amorphous carbon membranes in the two-dimensional amorphous limit. Using optothermal actuation and interferometric readout, the study analyzes both linear and nonlinear resonant motion of MAC nanodrums, including thermomechanical motion, driven resonances, multimode spectra, Duffing-type nonlinearities, nonlinear damping, and signatures of mode coupling. These results establish monolayer amorphous carbon as a mechanically robust membrane platform and provide important knowledge for the broader project goal of developing sensitive two-dimensional material-based nanomotion sensors.
The results obtained so far also informed the planning of the next experimental steps. These include further optimization of membrane-based devices, refinement of bacterial immobilization procedures, and preparation for systematic experiments where nanomotion signals can be compared with fluorescence microscopy information about bacterial position and activity.
Overall, this period consolidated the experimental progress made during the first part of the year. The focus on data analysis and manuscript preparation helped transform the obtained measurements into publishable scientific results and supported the transition toward the next stage of the project: combined nanomotion and fluorescence-based studies of bacteria on two-dimensional sensors.
Time period: 01.01.2026. – 31.03.2026.
During this phase of the project, the work focused on strengthening the experimental basis for nanomotion sensing with two-dimensional membrane-based nanodrums and on communicating the project idea to a wider audience.
A major activity during this period was participation in the European Commission’s science communication event “Science is Wonderful!” in Brussels, organized in the framework of Marie Skłodowska-Curie Actions. Over three days, the project was presented to schoolchildren, teachers, researchers, and other visitors through an interactive demonstration devoted to bacterial vibrations. The activity introduced the public to the idea that living cells and bacteria produce tiny mechanical movements, which can be detected using highly sensitive nanoscale sensors. This provided an engaging way to explain the broader aim of the project: developing sensor platforms that can help “listen” to bacteria and better understand their activity.
The project activity at the event was also highlighted in a Horizon Magazine article about the Brussels science fair, where bacterial vibrations were presented as one of the examples of how frontier research can be made accessible to children and the wider public. This contributed to the communication objectives of the project and helped present nanomotion spectroscopy in a simple and memorable way.
Shortly afterwards, a mobility visit to Delft University of Technology was carried out in collaboration with the Micro and Nanosystems Dynamics group. During the visit, additional dynamic measurements were performed on two-dimensional membranes, including monolayer amorphous carbon and hexagonal boron nitride-based structures. The measurements focused on the interferometric characterization of membrane motion and on understanding how the detected signal depends on experimental parameters, such as the power of the detection laser. These experiments are important for interpreting future nanomotion measurements and for evaluating how optical read-out conditions may influence the mechanical response of the membranes.
The mobility period also supported the biological part of the project. Training was completed in handling biological samples, including bacterial culture preparation, plating, and induction procedures. Surface functionalization approaches for bacterial immobilization were studied, which is an important step toward ensuring that future nanomotion signals originate from bacterial activity rather than uncontrolled movement of cells across the surface. Additional nanomotion experiments with bacteria were also performed, strengthening practical experience with the measurement workflow and data interpretation.
During the visit, the project results obtained so far were presented in a seminar at the Faculty of Applied Sciences of TU Delft. The presentation focused on the dynamic properties of two-dimensional amorphous carbon membranes and their relevance for nanomotion sensing. Discussions with researchers working on nanomechanics, two-dimensional materials, and biosensing helped clarify the next steps for sensor optimization and biological measurements.
Overall, this period combined experimental progress, international collaboration, biological training, and public communication. The work strengthened the connection between two-dimensional membrane mechanics and future applications in bacterial nanomotion sensing.
Time period: 30.04.2025. – 01.01.2026.
In the subsequent phase of the project, the development of experimental sensors and material studies continued, expanding the range of two-dimensional materials used and strengthening international collaboration.
During a mobility visit in July 2025, I investigated the mechanical and structural properties of amorphous carbon as a material for sensor fabrication, assessing its suitability for nanomotion sensor development. The mechanical properties and stability of the membranes were analyzed in order to identify potential advantages for nanomotion signal detection.
In parallel with the characterization of the mechanical properties of the sensors, I investigated bacterial behavior on the sensor surfaces. For this purpose, fluorescent E. coli bacteria were used, which exhibited strong fluorescence signals even when located on the sensor surface.
These promising results were presented at conferences dedicated to two-dimensional materials and to microscopy and life sciences, held in Braga, Portugal. The discussions highlighted the broad potential of two-dimensional membranes for applications in biosensing.
In the subsequent period, advanced fabrication and transfer techniques for two-dimensional amorphous carbon membranes onto previously fabricated cavity structures were developed. The membrane transfer procedures were refined to improve reproducibility and mechanical stability, which are critical for long-term nanomotion measurements in liquid environments. The acquired expertise broadens the range of materials employed in the project and provides an alternative approach to the realization of nanomotion sensors.
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.