Soft matter nanoscopy

\u3cp\u3eSuper-resolution microscopy (SRM), also known as nanoscopy, has gained ground in the past decade as a valuable imaging and characterization tool to investigate sub-μm architectures. Widespread is its usage in cell biology and biophysics, while visualization of the inner life of man-made materials is still in its infancy. In this contribution, we review pioneering studies in this emerging application area focusing on the SRM imaging of mesoscale structures within soft nanomaterials, and its impact on the rational design of their functional properties. These studies on (supramolecular) polymers, colloidal particles, emulsions, foams and association colloids showcase the broad application perspective of nanoscopy owing to its high spatial resolution, low invasiveness, high penetration depth, high sensitivity, chemical specificity, and straightforward sample preparation.\u3c/p\u3

IPAINT:A general approach tailored to image the topology of interfaces with nanometer resolution

\u3cp\u3eUnderstanding interfacial phenomena in soft materials such as wetting, colloidal stability, coalescence, and friction warrants non-invasive imaging with nanometer resolution. Super-resolution microscopy has emerged as an attractive method to visualize nanostructures labeled covalently with fluorescent tags, but this is not amenable to all interfaces. Inspired by PAINT we developed a simple and general strategy to overcome this limitation, which we coin 'iPAINT: interface Point Accumulation for Imaging in Nanoscale Topography'. It enables three-dimensional, sub-diffraction imaging of interfaces irrespective of their nature via reversible adsorption of polymer chains end-functionalized with photo-activatable moieties. We visualized model dispersions, emulsions, and foams with ∼20 nm and ∼3° accuracy demonstrating the general applicability of iPAINT to study solid/liquid, liquid/liquid and liquid/air interfaces. iPAINT thus broadens the scope of super-resolution microscopy paving the way for non-invasive, high-resolution imaging of complex soft materials.\u3c/p\u3

Interaction of ice binding proteins with ice, water and ions

\u3cp\u3eIce binding proteins (IBPs) are produced by various cold-adapted organisms to protect their body tissues against freeze damage. First discovered in Antarctic fish living in shallow waters, IBPs were later found in insects, microorganisms, and plants. Despite great structural diversity, all IBPs adhere to growing ice crystals, which is essential for their extensive repertoire of biological functions. Some IBPs maintain liquid inclusions within ice or inhibit recrystallization of ice, while other types suppress freezing by blocking further ice growth. In contrast, ice nucleating proteins stimulate ice nucleation just below 0 °C. Despite huge commercial interest and major scientific breakthroughs, the precise working mechanism of IBPs has not yet been unraveled. In this review, the authors outline the state-of-the-art in experimental and theoretical IBP research and discuss future scientific challenges. The interaction of IBPs with ice, water and ions is examined, focusing in particular on ice growth inhibition mechanisms.\u3c/p\u3

Super-resolution microscopy on single particles at fluid interfaces reveals their wetting properties and interfacial deformations

\u3cp\u3eSolid particles adsorbed at fluid interfaces are crucial for the mechanical stability of Pickering emulsions. The key parameter which determines the kinetic and thermodynamic properties of these colloids is the particle contact angle, θ. Several methods have recently been developed to measure the contact angle of individual particles adsorbed at liquid-liquid interfaces, as morphological and chemical heterogeneities at the particle surface can significantly affect θ. However, none of these techniques enables the simultaneous visualization of the nanoparticles and the reconstruction of the fluid interface to which they are adsorbed, in situ. To tackle this challenge, we utilize a newly developed super-resolution microscopy method, called iPAINT, which exploits non-covalent and continuous labelling of interfaces with photo-activatable fluorescent probes. Herewith, we resolve with nanometer accuracy both the position of individual nanoparticles at a water-octanol interface and the location of the interface itself. First, we determine single particle contact angles for both hydrophobic and hydrophilic spherical colloids. These experiments reveal a non-negligible dependence of θ on particle size, from which we infer an effective line tension, τ. Next, we image elliptical particles at a water-decane interface, showing that the corresponding interfacial deformations can be clearly captured by iPAINT microscopy.\u3c/p\u3