Jerome Wenger NanoBioPhotonics

Detecting polymer nanoparticles remains a significant challenge due to their weak optical contrast. In this work, we demonstrate a counterintuitive phenomenon: UV illumination enhances rather than bleaches the intrinsic autofluorescence of polystyrene (PS) nanoparticles. This enhancement enables the autofluorescence detection of individual PS nanoparticles down to 100 nm in diameter using a simple, cost-effective UV microscope setup.

Key Discoveries:
- Unexpected Behavior: Contrary to conventional photobleaching, the autofluorescence intensity of PS nanoparticles increases during UV exposure.
- Mechanism: The enhancement arises from reactive oxygen species (ROS)-mediated surface photodecomposition, which exposes fresh emissive domains of the nanoparticle.
- Performance: A 15× signal improvement pushes the limit of detection to 100 nm, enabling reliable single-particle imaging.
- Versatility: The phenomenon is preserved across various sizes and polymer materials (e.g., PMMA, melamine resin) and allows direct discrimination between polymer and metal nanoparticles.

By leveraging a simple UV microscope, this method offers a cost-effective and accessible alternative to more complex techniques like Raman spectroscopy or interferometric scattering microscopy. This approach unlocks new possibilities for high-sensitivity detection of polymer-based nanoparticles in fields such as analytical chemistry, biosensing and/or environmental monitoring.

Read the full paper on free repository: HAL-05686837

We are thrilled to announce that our latest research, "Single Nanoparticle Dynamics in Opto-Thermal Tweezers: Resolving the Temporal Resolution of Depletion Force Trapping", has been accepted for publication in ACS Nano!

In this work, we achieve a milestone by resolving the temporal dynamics of single 40 nm polystyrene nanoparticles in optothermal traps with sub-millisecond resolution. Using time-resolved fluorescence microscopy, we distinguish for the first time between transient localization and stable trapping, a critical ambiguity in previous studies that relied on ensemble averaging.

Our results reveal that residency times exceeding 1 second require PEG concentrations above 7% and IR intensities exceeding 6 mW/µm². Numerical simulations confirm our experimental observations, elucidating the interplay between thermophoresis and diffusiophoresis that governs nanoparticle motion.

This advance deepens our understanding of optothermal trapping mechanisms and paves the way for applications in single nanoparticle studies, nanoscale assembly, and drug delivery systems. We look forward to engaging with the community on these exciting findings!

We are thrilled to announce our latest publication in Advanced Functional Materials: "DNA-Origami-Assembled Rhodium Nanoantennas for Deep-UV Label-Free Single-Protein Detection" (DOI: 10.1002/adfm.202532006).

In this work, we pioneer a robust strategy for functionalizing rhodium nanocubes with DNA, enabling their assembly into programmable UV-plasmonic nanoantennas on DNA origami scaffolds. This breakthrough allows for the precise positioning of a single streptavidin protein within the plasmonic hotspot, achieving up to 22× brightness enhancement in deep-UV autofluorescence detection. Our approach overcomes the limitations of traditional UV-plasmonic materials by combining the chemical stability of rhodium with the addressability of DNA origami, opening new avenues for label-free, single-molecule spectroscopy in the deep-UV range.

This research marks a significant step toward deterministic, high-precision sensing of individual proteins without the need for fluorescent labels, with potential applications in structural biology and bioanalytical chemistry. It establishes label-free UV autofluorescence detection at the single protein level.

Read the full paper here.

Metal oxide nanoparticles play a pivotal role across many fields of nanoscience and nanotechnology, yet their detection remains challenging, requiring expensive SEM or TEM microscopies. Moreover, metal oxide nanoparticles generally form complex nanoaggregates of different sizes and morphologies, requiring experiments to be performed at the level of a single nanoaggregate to yield meaningful information.

In our recent article published in Particle & Particle Systems Characterization, we detail a novel application of ultraviolet (UV) microscopy for detecting metal oxide nanoparticles with high sensitivity and versatility. By leveraging the strong absorption of metal oxides in the UV spectral range, we demonstrate robust detection capabilities, validated through correlative electron microscopy and numerical simulations. Our results provide critical information characterizing the material and morphology parameters determining the UV response of metal oxide nanoaggregates

This work offers significant advancements for nanoparticle analysis, with potential applications spanning across material science, biotechnology, and environmental monitoring.

We are delighted to congratulate Malavika Kayyil Veedu on the successful defense of her PhD thesis, “Exploring and improving fluorescence correlation spectroscopy (FCS) sensitivity from nanoprobe to label-free proteins for biosensing and nanopore applications,” defended on January 29, 2026, at the Institut Fresnel in Marseille.

Malavika’s work explored innovative strategies to push the limits of fluorescence correlation spectroscopy (FCS) and its time-resolved variant (FLCS). By tackling key challenges such as background noise, spectral overlap, and photobleaching, she developed approaches that improve sensitivity and enable the study of weakly fluorescent nanoparticles or label-free proteins. Her research opens exciting perspectives for biosensing and nanopore-based optical detection.

The thesis jury included:

• Dr. Thomas Pons (LPEM, INSERM Paris) – Reviewer
• Dr. Karen Perronet (LuMIn, CNRS Gif-sur-Yvette) – Reviewer
• Dr. Serge Monneret (Institut Fresnel, CNRS Marseille) – Examiner
• Prof. Antoine Delon (LIPhy, Université Grenoble Alpes) – Jury President
• Dr. Jérôme Wenger (Institut Fresnel, CNRS Marseille) – Thesis Supervisor

We warmly congratulate Dr. Kayyil Veedu for her excellent work, dedication and team spirit throughout her PhD journey. We wish her all the best for her future endeavors!