Tag: Martin Selin

Mapping the adsorption dynamics of core-shell particles at liquid-liquid interfaces with optical tweezers
Martin Selin, Maret Ickler, Gerardo Campos-Villalobos, Fabrizio Camerin, Nicolas Vogel, Antonio Ciarlo, Giovanni Volpe, and Marcel Rey
Date: 6 August 2025
Time: 4:30 PM – 4:45 PM PDT
Place: Conv. Ctr. Room 3

Colloidal systems are integral to industries such as food and cosmetics, where liquid-liquid interfaces—like oils dispersed in water—are common. Whether colloidal particles adsorb to these interfaces depends on multiple factors such as particle surface chemistry, pH and salinity.

Here, we investigate how core–shell particles breach a liquid-liquid interface by using optical tweezers to gently push the particles into dodecane-water interfaces formed by microbubbles. Our core–shell particles feature a silica core and a PDMAEMA shell and by varying the amount of monomer added during synthesis the size of the shell can be tuned. Using the tweezers we measure the extent of the polymer shell. Importantly, we find that uncoated silica particles do not adsorb in pure water, whereas polymer coated particles absorb rapidly once the polymer layer contacts the interface, also when the core itself remains microns away. The longer the polymer the greater the distance from which the particle absorbs.

We also observe similar adsorption other polymer shells like PNIPAM and PVP, indicating that the presence of a polymer coating, rather than its specific chemical composition, is the key factor governing adsorption. At low and high pH the polymer shell contracts, also the binding energy becomes weaker making the absorption slower. In very acidic conditions the binding is so weak that the optical tweezers can pull particles out from the interface, allowing us to directly observe individual polymers detaching. These findings provide new insight into how polymer coatings dictate particle-interface interactions, paving the way for improved control of colloidal behavior.

Advanced autonomous optical tweezers experiments
Martin Selin, A. Ciarlo, G. Pesce, L. Bengtsson, J. Camuñas-Soler, V. Sundar Rajan, F. Westerlund, L. M. Wilhelmsson, I. Pastor, F. Ritort, S. B. Smith, C. Bustamante, G. Volpe
Date: 5 August 2025
Time: 4:30 PM – 4:45 PM PDT
Place: Conv. Ctr. Room 4

Single-molecule studies are vital for elucidating fundamental biological processes, including protein folding, DNA transcription, and replication. However, performing these experiments manually on individual molecules is notoriously time-consuming and costly. To address this challenge, we have developed a fully autonomous single-molecule force spectroscopy platform by integrating a custom-built optical tweezers instrument with real-time deep-learning-based image analysis and adaptive control protocols. Our system achieves human-level throughput in terms of experiments per hour while remaining robust enough to operate continuously for hours without intervention. We demonstrate the versatility of our platform by having it perform DNA pulling experiments on both lambda DNA and DNA hairpins fully autonomously. These results push the boundaries of high-throughput data collection in single-molecule biophysics, paving the way for merging single-molecule studies with large-scale, data-driven approaches—ultimately enabling new insights into the dynamic, transient states of complex biological systems.

Optical Tweezers applications: From particle adsorption to single molecules.

Martin Selin
Date: 11 April 2025
Time: 10:30
Place: University of Münster, Germany

Optical tweezers are powerful tools for probing microscale forces in systems ranging from colloidal particles to single molecules. Here, we demonstrate their use in two different fields. First, by trapping individual colloidal particles, we study their adsorption dynamics at liquid–liquid interfaces, highlighting the critical role of surface chemistry and the presence of polymer shells. We also observe reversible polymer attachments and stretching. Second, we apply tweezers to study single-molecule mechanics. By automating these complex biophysical experiments, we enable high-throughput measurements of molecular dynamics. Our results suggest that, like DNA, synthetic polymers can be effectively described by the worm-like chain model.

Optical tweezers reveal how polymer coated particles jump into liquid-liquid interfaces

Martin Selin
Date: 8 April 2025
Time: 17:40
Place: Center for Interdisciplinary Research, Bielefeld University, Germany

Colloidal particles typically require salt to overcome electrostatic barriers and adsorb to liquid-liquid interfaces. Here, we show that coating particles with polymers enables spontaneous adsorption without salt. Our model system consists of silica cores coated with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA). Using optical tweezers, we track individual particles showing that the polymer shell makes particles jump into a dodecane–water interface. This behavior extends to other polymers. By tuning pH, we control polymer swelling and adsorption distance. At very low pH, the attachment to the interface is weak enough that the optical tweezers can pull particles out from the interface. During this desorption process we observe single polymers detaching. These findings offer new approaches for designing responsive emulsions.

Integrating real-time deep learning for automation of optical tweezers experiments
Martin Selin
SPIE-ETAI, San Diego, CA, USA, 18 – 22 August 2024
Date: 19 August 2024
Time: 4:10 PM – 4:25 PM
Place: Conv. Ctr. Room 6D

The perhaps most widely used tool for measuring forces and manipulating particles at the micro and nano-scale are optical tweezers which have given them widespread adoption in physics, chemistry and biology. Despite advancements in computer interaction driven by large-scale generative AI models, experimental sciences—and optical tweezers in particular—remain predominantly manual and knowledge-intensive, owing to the specificity of methods and instruments. Here, we demonstrate how integrating the components of optical tweezers—laser, motor, microfluidics, and camera—into a single software simplifies otherwise challenging experiments by enabling automation through the integration of real-time analysis with deep learning. We highlight this through a DNA pulling experiment, showcasing automated single molecule force spectroscopy and intelligent bond detection, and an investigation into core-shell particle behavior under varying pH and salinity, where deep learning compensates for experimental drift. We conclude that automating experimental procedures increases reliability and throughput, while also opening up the possibility for new types of experiments.

From stretching DNA to probing polymer stiffness: expanding experimental reach with automated optical tweezers
Martin Selin
SPIE-OTOM, San Diego, CA, USA, 18 – 22 August 2024
Date: 18 August 2024
Time: 12:15 PM – 12:45 PM
Place: Conv. Ctr. Room 6D

Optical tweezers have become ubiquitous tools in science with use in disciplines ranging from biology to physics, chemistry, and material sciences with thousands of users around the world and a continuously growing number of applications. Here we show how a specially designed instrument, called miniTweezers2.0, can be made both highly versatile and user friendly. We demonstrate the system on three different experiments, which thanks to the close integration of the various parts of the tweezers into a single software are performed fully autonomously. The first experiment involves DNA stretching, a fundamental single molecule force spectroscopy experiment. The second experiment involved the stretching of red blood cells, which can be used to gauge the membrane stiffness of the cells. Lastly, we investigate the interaction between core-shell particles in various environments. Showing how the soft polymer layer extends, or contracts depending on pH and salinity. Our work show potential of automated and versatile optical tweezers systems in advancing our understanding of nano and micro-scale systems.