Theobald Lohmüller

We report that photolipid‐supported bilayer (SpLB) membranes assembled from the photolipid azo‐PC can be photopatterned in defined regions of varying diffusivity through photoisomerization by using structured light illumination. We investigate the temporal stability of such diffusivity landscapes and find that homogeneously illuminated bilayer membranes exhibit diffusion coefficients consistent with their respective photostationary states (PSS), while photopatterned SpLBs show spatially varying diffusivity and lipid mixing at boundaries between trans/cis illuminated regions. Furthermore, single‐particle tracking reveals that superdiffusive particle motion preferentially oriented with respect to the photopattern boundaries is observed more frequently in photopatterned SpLBs than Brownian, non‐directed particle motion, which dominates in homogeneous membranes. Overall, this approach provides a practical route to generate laterally compartmentalized lipid bilayer platforms with programmable diffusivity and establishes photopatterned SpLBs as an adaptable system for studying lipid intermixing and transport properties in supported bilayer membranes.

Optical printing with laser light is a powerful method for patterning plasmonic nanoparticles on a solid support. However, using particles that display sharp features, such as gold nanostars or bipyramids, can be challenging because plasmonic heating involved in the printing process can lead to tip blunting and melting. This adversely affects the performance of these particles for spectroscopic or catalytic applications. Therefore, strategies need to be implemented to avoid thermal reshaping of complex‐shaped nanoparticles either by minimizing plasmonic heating or by dissipating heat away from the particles. Here, an alternative view is proposed. Rather than avoiding plasmonic heating, it is demonstrated that optothermal printing can be leveraged to transform gold nanorods into ellipsoidal or lemon‐shaped particles with sharper tips and enhanced local electromagnetic field intensities compared to the initial rods. The potential of these “nano‐lemons” for spectroscopic applications is exemplified through surface enhanced Raman scattering measurements of azobenzene photoisomerization within supported photolipid bilayer membranes.

Photoswitchable lipids based on azobenzene offer efficient optical control over membrane properties, making them advanced molecular nanoagents for biomedical applications. However, many details regarding their photoswitching dynamics in complex lipid environments or under physiological temperatures are still poorly understood. Here, we investigate how temperature and membrane charge affect the mixing and photoswitching efficiency of the photolipid azo-PC in membrane assemblies. In giant unilamellar vesicles (GUVs), the presence of charge lowers the mixing temperature, while small liposomes reveal a striking temperature dependence in photoswitching dynamics and efficiency. These findings show that temperature plays a critical role in enabling more complete switching in lipid mixtures, underscoring the need to account for thermal effects and charge in lipid systems for biomedical applications.

The lipid composition of cellular membranes is highly dynamic and undergoes continuous remodeling, affecting the biophysical properties critical to biological function. Here, we introduce an optical approach to manipulate membrane viscosity based on an exogenous synthetic fatty acid with an azobenzene photoswitch, termed FAAzo4. Cells rapidly incorporate FAAzo4 into phosphatidylcholine and phosphatidylethanolamine in a concentration- and cell type-dependent manner. This generates photoswitchable PC and PE analogs, which are predominantly located in the endoplasmic reticulum. Irradiation causes a rapid photoisomerization that decreases membrane viscosity with high spatiotemporal precision. We use the resulting "PhotoCells" to study the impact of membrane viscosity on ER-to-Golgi transport and demonstrate that this two-step process has distinct membrane viscosity requirements. Our approach provides an unprecedented way of manipulating membrane biophysical properties directly in living cells and opens novel avenues to probe the effects of viscosity in a wide variety of biological processes.

Understanding the biophysical and biochemical properties of molecular nanocarriers under physiological conditions with minimal interference is critical for advancing photopharmacology, drug delivery, nanotheranostics and synthetic biology. However, analytical methods often struggle to combine precise chemical imaging and dynamic measurements without perturbative labeling. This challenge is exemplified by azobenzene-based photoswitchable lipids, which are intriguing reagents for controlling nanocarrier properties on fast timescales, enabling precise light-induced drug release. Here, we leverage the chemical recognition and high spatio-temporal resolution of scattering-type scanning near-field optical microscopy (s-SNOM) to demonstrate a non-destructive, label-free technique for mid-infrared imaging and spectroscopy of individual photoswitchable liposomes. Our transient nanoscopy approach enables imaging below the diffraction limit and tracks dynamics with sampling times as fast as 30 ms. We resolve photoinduced changes in shape and MIR spectral signature of individual vesicles and discover abrupt and delayed photoisomerization dynamics. Our findings highlight the method’s potential for studying complex dynamics of unlabeled nanoscale soft matter.

This comprehensive review summarizes the past, present, and future of plasmonic NP-based sensors in terms of different sensing platforms, different chemical and biological analytes, and the expected future technologies.

Azobenzene molecular switches are widely used to photocontrol material properties, and biological activity in cell culture, via photoisomerisation between E and Z isomers. However, because population photoswitching is incomplete, their dynamic range of property control is often small; and because they cannot be operated with red/NIR light, they are usually not applicable in deep tissue. Here, we demonstrate a general method for efficient single-photon photocontrol of azobenzenes, and of glutamate receptor activity, at >700 nm in live tissue. We use red/NIR chromophore auxiliaries to perform intramolecular energy transfer to bioactive azobenzenes, which drives fast bulk Z→E isomerisation up to even >97% completeness. The auxiliary/azobenzene dyads allow >700 nm photoswitching with photon-efficiency that can be even higher than for direct azobenzene E→Z isomerisation in the UV region; and they are biocompatible and photostable. Crucially, their performance properties are intrinsic, i.e. auxiliary-based intramolecular switching will perform identically at any dilution and will not be affected by biodistribution. We show that these dyads can be created straightforwardly from most azobenzene systems, with most auxiliary chromophores, without tricky molecular redesign or re-optimisation. After outlining some rules of auxiliary-based photoswitching, which can guide its broader adoption, we conclude by using dyads to make the first demonstration of single-photon NIR chemical photoswitching control over biological activity, in cell culture and intact brain tissue.

Nanophotonic devices excel at confining light into intense hot spots of electromagnetic near fields, creating exceptional opportunities for light-matter coupling and surface-enhanced sensing. Recently, all-dielectric metasurfaces with ultrasharp resonances enabled by photonic bound states in the continuum (BICs) have unlocked additional functionalities for surface-enhanced biospectroscopy by precisely targeting and reading out the molecular absorption signatures of diverse molecular systems. However, BIC-driven molecular spectroscopy has so far focused on end point measurements in dry conditions, neglecting the crucial interaction dynamics of biological systems. Here, we combine the advantages of pixelated all-dielectric metasurfaces with deep learning-enabled feature extraction and prediction to realize an integrated optofluidic platform for time-resolved in situ biospectroscopy. Our approach harnesses high-Q metasurfaces specifically designed for operation in a lossy aqueous environment together with advanced spectral sampling techniques to temporally resolve the dynamic behavior of photoswitchable lipid membranes. Enabled by a software convolutional neural network, we further demonstrate the real-time classification of the characteristic cis and trans membrane conformations with 98% accuracy. Our synergistic sensing platform incorporating metasurfaces, optofluidics, and deep learning reveals exciting possibilities for studying multimolecular biological systems, ranging from the behavior of transmembrane proteins to the dynamic processes associated with cellular communication.

The photo‐isomerization of the photolipid azo‐PC, a derivative of phosphatidylcholine containing an azobenzene group in its sn2 acyl chain, enables optical control over key properties of supported lipid bilayers (SLBs), such as membrane fluidity and bilayer thickness. However, azobenzenes are well‐known for their interaction with various dyes through photo‐modulation and ‐sensitization pathways, presenting a challenge in bilayer characterization by fluorescence microscopy. Label‐free tools capable of monitoring the switching process of photolipid SLBs at the nanoscale are therefore highly desired. In this study, the use of dark field scattering spectroscopy on gold nanorods as a highly sensitive approach is demonstrated for analyzing the reversible photo‐isomerization dynamics of photolipid SLBs in real time at the single particle level.