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Delayed Active Swimmer in a Velocity Landscape on ArXiv

Experimental setup. (Top) Thermophoretic microswimmer undergoes active Brownian motion in a spatially-varying laser intensity profile that controls the self-thermophoretic propulsion of the swimmer using a feedback loop. (Bottom) Sample trajectory of the microswimmer over 15 minutes in a chamber. Colors indicate instantaneous velocity. (Image from the manuscript.)
Delayed Active Swimmer in a Velocity Landscape
Viktor Holubec, Alexander Fischer, Giovanni Volpe, Frank Cichos
arXiv: 2505.11042

Self-propelled active particles exhibit delayed responses to environmental changes, modulating their propulsion speed through intrinsic sensing and feedback mechanisms. This adaptive behavior fundamentally determines their dynamics and self-organization in active matter systems, with implications for biological microswimmers and engineered microrobots. Here, we investigate active Brownian particles whose propulsion speed is governed by spatially varying activity landscapes, incorporating a temporal delay between environmental sensing and speed adaptation. Through analytical solutions derived for both short-time and long-time delay regimes, we demonstrate that steady-state density and polarization profiles exhibit maxima at characteristic delays. Significantly, we observe that the polarization profile undergoes sign reversal when the swimming distance during the delay time exceeds the characteristic diffusion length, providing a novel mechanism for controlling particle transport without external fields. Our theoretical predictions, validated through experimental observations and numerical simulations, establish time delay as a crucial control parameter for particle transport and organization in active matter systems. These findings provide insights into how biological microorganisms might use response delays to gain navigation advantages and suggest design principles for synthetic microswimmers with programmable responses to heterogeneous environments.

Aitor González Marfil joins the Soft Matter Lab

(Photo by A. Ciarlo.)
Aitor González Marfil starts his visiting period at the Physics Department of the University of Gothenburg on 19 May 2025.

Aitor is a PhD student at the University of the Basque Country.

During his visit, that will last until the 19 of August, he will focus on machine learning for image analysis.

Robert Sosa Principe joins the Soft Matter Lab

(Photo by A. Ciarlo.)
Robert Sosa Principe started his visit at the Physics Department at the University of Gothenburg on 17 May 2025.

Robert is a PostDoc in the group of Prof. Carlos Bustamante at the University of California, Berkeley.

During his visit, he will focus on experiments of single-molecule biophysics.

Invited talk by Sreekanth K. Manikandan at the online Workshop on Stochastic Thermodynamics (WOST), 14th May 2025

Recent advances in nonequilibrium physics allow extracting thermodynamic quantities, such as entropy production, directly from dynamical information in microscopic movies. (Image by S. Manikandan.)
Localizing entropy production in cellular processes
Sreekanth Manikandan
Date: 14 Mar 2025
Time: 17:30 CEST
Place: Online
Part of the Workshop on Stochastic Thermodynamics

Quantifying the spatiotemporal forces, affinities, and dissipative costs of cellular-scale non-equilibrium processes from experimental data and localizing it in space and time remain a significant open challenge. Here, I explore how principles from stochastic thermodynamics, combined with machine learning techniques, offer a promising approach to addressing this issue. I will present preliminary results from experiments on fluctuating cell membranes and simulations of non-equilibrium systems in stationary and time-dependently driven states. These studies reveal potential strategies for localizing entropy production in experimental biophysical contexts while also highlighting key challenges and limitations that must be addressed.

SmartTrap: Automated Precision Experiments with Optical Tweezers on ArXiv

Illustration of three different experiments autonomously performed by the SmartTrap system: DNA pulling experiments (top), red blood cell stretching (bottom left), and particle-particle interaction measurements (bottom right). (Image by M. Selin.)
SmartTrap: Automated Precision Experiments with Optical Tweezers
Martin Selin, Antonio Ciarlo, Giuseppe Pesce, Lars Bengtsson, Joan Camunas-Soler, Vinoth Sundar Rajan, Fredrik Westerlund, L. Marcus Wilhelmsson, Isabel Pastor, Felix Ritort, Steven B. Smith, Carlos Bustamante, Giovanni Volpe
arXiv: 2505.05290

There is a trend in research towards more automation using smart systems powered by artificial intelligence. While experiments are often challenging to automate, they can greatly benefit from automation by reducing labor and  increasing reproducibility. For example, optical tweezers are widely employed in single-molecule biophysics, cell biomechanics, and soft matter physics, but they still require a human operator, resulting in low throughput and limited repeatability. Here, we present a smart optical tweezers platform, which we name SmartTrap, capable of performing complex experiments completely autonomously. SmartTrap integrates real-time 3D particle tracking using
deep learning, custom electronics for precise feedback control, and a microfluidic setup for particle handling. We demonstrate the ability of SmartTrap to operate continuously, acquiring high-precision data over extended periods of time, through a series of experiments. By bridging the gap between manual  experimentation and autonomous operation, SmartTrap establishes a robust and open source framework for the next generation of optical tweezers research, capable of performing large-scale studies in single-molecule biophysics, cell mechanics, and colloidal science with reduced experimental
overhead and operator bias.

Series of lectures by C. Bustamante, Waernska Professorship lectures, 29 April – 7 May 2025

Carlos Bustamante. (Photo by H. P. Thanabalan.)
Fundamentals and Applications of Single Molecule Force Spectroscopy – Waernska Professorship lectures
Professor Carlos Bustamante, who is visiting the Soft Matter Lab between 28 April and 27 May and is a winner of the Waernska Professorship, will be giving a series of lectures on Fundamentals and Applications of Single Molecule Force Spectroscopy.

Professor Carlos Bustamante from UC Berkeley is a pioneer in the use of optical tweezers for the biomechanical study of single molecules. He will explain the basics of how and why you can perform single-molecule experiments with them.

Here is the schedule and location of the lectures:
– 29 April 2025 from 13:00 to 17:00 in Gustaf Dalén-salen;
– 05 May 2025 from 13:00 to 17:00 in FL71;
– 06 May 2025 from 13:00 to 17:00 in Lecture Hall FL71;
– 07 May 2025 from 13:00 to 17:00 in Lecture Hall KB.

Professor Carlos Bustamante, winner of the Waernska Professorship, visits the Soft Matter Lab

Carlos Bustamante. (Photo by H. P. Thanabalan.)
We are delighted to welcome Professor Carlos Bustamante to the Soft Matter Lab as the winner of the prestigious Waernska Professorship.

Professor Bustamante is a world-renowned expert in single-molecule biophysics and a Full Professor of Molecular and Cell Biology, Chemistry and Physics at the University of California, Berkeley, USA.

His pioneering work has significantly advanced our understanding of the physical behaviour of biological molecules. Using techniques such as optical tweezers, atomic force microscopy and fluorescence microscopy, Professor Bustamante has provided key insights into molecular motors, protein and RNA folding, and the mechanisms of gene expression and regulation.

We are honoured to host Professor Bustamante at the Soft Matter Lab and look forward to exciting scientific exchanges and collaborations during his visit.

His visit is currently planned between 28 April and 27 May 2025.
An additional visit, yet to be confirmed, might take place during the fall of 2025.

Invited talk by L. Viaene at the first PhD Conference at the University of Gothenburg, 25 April 2025

Linde Viaene presenting at the PhD conference. (Image by S. Kilde Westberg.)
Studying heat adaptation in yeast one-molecule at a time: The use of single-molecule microscopy for aggregate identification and tracking.

Linde Viaene
Date: 25th of April
Time: 13:00
Place: Veras Gräsmatta, Gothenburg

The importance of protein folding and misfolding is indicated by the broad range of clinical manifestations that have protein aggregation at the base, such as neurodegenerative diseases, cancer and type II diabetes. A key factor in (energy) homeostasis is the DNA configuration of chromatin which allows for essential gene expression and adaptation to environmental factors. The Rpd3 deacetylase histone complex (DHAC) plays a crucial role in gene regulation and its disruption impairs stress-induced gene activation, highlighting its importance in cellular adaptation.
Using Saccharomyces cerevisiae as a model system, we aim to investigate the role of chromatin remodelling components in protein aggregation and cellular rejuvenation, which may influence aggregate retention and recovery speed. We will expose yeast cells to stressors such as heat shock, metabolic shifts, and oxidative stress to assess their effects on protein homeostasis and chromatin regulation. Growth assays will evaluate survival rates, while Western blotting will measure Hsp104 expression, a key heat shock protein involved in aggregate clearance. By employing our bespoke single-molecule fluorescence microscope, we will track aggregate formation, clearance, and spatial localization in live cells at molecular precision.
Our preliminary results indicate that some components of the Rpd3L complex, respectively alter the recovery rate after heat stress exposure. Hence, the goal is to explore further candidate genes and to determine their role in the stress-induced response. By elucidating the role of chromatin remodelers in stress adaptation, our findings may inform novel therapeutic strategies for age-related diseases.

Invited Talk by G. Volpe at OPIC/OMC 2025, Yokohama, Japan, 21 April 2025 (Online, Pre-recorded)

DeepTrack 2 Logo. (Image from DeepTrack 2 Project)
How can deep learning enhance microscopy?
Giovanni Volpe
Optics & Photonics International Congress 2025 (OPIC 2025), The 11th Optical Manipulation and Structured Materials Conference (OMC2025)
Date: 21 April 2025
Time: 13:45 JST
Place: Yokohama, Japan (Online, Pre-recorded)