Author: Martin Selin

Minitweezers 2.0, Paving the way for fully autonomous optical tweezers experiments.
Martin Selin
Single-Molecule Sensors and NanoSystems International Conference – S3IC 2023
23 November 2023, 11:51 (CET)

Since their invention by Ashkin et al. in the 1980s, optical tweezers have evolved into an indispensable tool in physics, especially in biophysics, with applications spanning from cell sorting to stretching single DNA strands. By the 2000s, commercial systems became available. Nevertheless, owing to their unique requirements, many labs prefer to construct their own, often drawing inspiration from existing designs.

A prominent optical tweezers design is the “miniTweezers” system, pioneered by Bustamante’s group in the late 1990s. This system has been widely adopted globally for force spectroscopy experiments on single molecules, including DNA, proteins, and RNA.

In this presentation, we unveil an advanced iteration of the miniTweezers. By enhancing its control and acquisition capabilities, we’ve augmented its versatility, enabling new experiment types. A significant breakthrough is the integration of real-time image feedback, which paves the way for automated procedures via deep learning-based image analysis, the first of which we demonstrate in this presentation.

We showcase this system’s capabilities through three distinct experiments:

1. A pulling experiment on a λ-DNA strand. By tethering DNA between two polystyrene beads – one anchored in a micropipette and the other manipulated by the tweezer – we illustrate near-complete automation, with the system autonomously handling bead trapping, attachment of the DNA and the pulling procedure.
2. An exploration of Coulomb interactions between charged particles. Here, one particle remains in a micropipette, while the other orbits the stationary bead, providing a 3D map of the interaction.
3. A non-contact stretching experiment on red blood cells is conducted under low osmotic pressure conditions. Modulating the laser power induces cell elongation along the laser’s propagation direction. By correlating this elongation with the optical force exerted by the lasers, we present a simple and non-invasive method to measure membrane rigidity.

In summary, these advancements mark a significant leap in the capabilities and applications of optical tweezers in biophysics. As we push the boundaries of automation and precision, we envision a future where such instruments can unravel even more intricate molecular interactions and cellular mechanics, setting the stage for groundbreaking discoveries.

Automating optical tweezers experiments using deep learning and custom electronics
Martin Selin
30 June 2023, 13:00 CEST

Optical tweezers are powerful tools for manipulating and studying the mechanical properties of single biomolecules, such as DNA. However, conducting such experiments manually is both time-consuming and labor-intensive limiting the amount of data collectable. In this work, we present a method to automate optical tweezers with the use of deep learning applying it to DNA pulling experiments.

A typical DNA pulling experiment can be divided into three main steps, each of which we have automated. The first is positioning of a bead in a micropipette(or secondary optical trap), second is connecting DNA of a another optically trapped bead with the bead in the micropipette and lastly the stretching of the DNA by moving the trapped bead while monitoring the force.

We have used deep learning, in particular a unet, to track beads and identify important features in the sample such as the micropipette. Combining this with realtime feedback allows the system to both trap beads and carefully position trap beads.

We demonstrate the viability of our method by stretching lambda DNA, showing human like reliability in performing the experiments. We expect our method to find use in the study of small biomolecules enabling more and faster data collection as well as longer running experiments.

Martin Selin completed the first half of his doctoral studies and defended his half-time on the 2nd of September 2022.

The presentation was held in hybrid format, with part of the audience in the Von Bahr room and the rest connected through zoom. The half-time consisted of a presentation of Martins two main projects followed by a discussion and questions proposed by Martins opponent Dag Hanstorp.

The presentation started providing a background on optical tweezers and continued with the ongoing project of positioning quantum dots using optical tweezers. Thereafter the presentation continued with the Minitweezers project. Data on DNA stretching was presented and shown to be in good agreement with results found in literature. Lastly the future of the two projects were outlined. Specifically, how to address the challenging task of detecting moving quantum dots and how to improve on the Minitweezers system through automation.