Ultrafast carrier dynamics in gold/iron-oxide nanocrystal heterodimers

Colloidal nanocrystal heterodimers composed of a gold domain and an iron oxide domain have been investigated by femtosecond transient absorption spectroscopy. The measured decay times were compared with the ones obtained from samples of "only" gold nanocrystals and iron oxide nanocrystals. Our results indicate that there is no significant charge transfer at the interface between gold and iron oxide in heterodimers

Clathrin mediates both internalization and vesicular release of triggered T cell receptor at the immunological synapse

Ligation of T cell receptor (TCR) to peptide-MHC (pMHC) complexes initiates signaling leading to T cell activation and TCR ubiquitination. Ubiquitinated TCR is then either internalized by the T cell or released toward the antigen-presenting cell (APC) in extracellular vesicles. How these distinct fates are orchestrated is unknown. Here, we show that clathrin is first recruited to TCR microclusters by HRS and STAM2 to initiate release of TCR in extracellular vesicles through clathrin- and ESCRT-mediated ectocytosis directly from the plasma membrane. Subsequently, EPN1 recruits clathrin to remaining TCR microclusters to enable trans-endocytosis of pMHC-TCR conjugates from the APC. With these results, we demonstrate how clathrin governs bidirectional membrane exchange at the immunological synapse through two topologically opposite processes coordinated by the sequential recruitment of ecto- and endocytic adaptors. This provides a scaffold for direct two-way communication between T cells and APCs

Spatiotemporally Super-Resolved Volumetric Traction Force Microscopy

Quantification of mechanical forces is a major challenge across biomedical sciences. Yet such measurements are essential to understanding the role of biomechanics in cell regulation and function. Traction force microscopy remains the most broadly applied force probing technology but typically restricts itself to single-plane two-dimensional quantifications with limited spatiotemporal resolution. Here, we introduce an enhanced force measurement technique combining 3D super-resolution fluorescence structural illumination microscopy and traction force microscopy (3D-SIM-TFM) offering increased spatiotemporal resolution, opening-up unprecedented insights into physiological three-dimensional force production in living cells

Effect of Morphology on Ultrafast Carrier Dynamics in Asymmetric Gold–Iron Oxide Plasmonic Heterodimers

Understanding how nanoscale interfaces affect electrical and optical properties of multifunctional nanocrystal heterostructures is of paramount importance for their technological application. In this context, we investigated the ultrafast carrier dynamics of rodlike gold–iron oxide nanocrystal heterodimers, in a spectral region close to the surface plasmon resonance frequency, by means of broad-band transient absorption spectroscopy. We found that the electron–phonon relaxation time is independent of the morphology of the iron oxide domain. Moreover, we revealed a transient shift in the surface plasmon resonance frequency, which can be related to charge transfer at the interface between gold and iron oxide

Plasmon Bleaching Dynamics in Colloidal Gold–Iron Oxide Nanocrystal Heterodimers

Colloidal nanocrystal heterodimers composed of a plasmonic and a magnetic domain have been widely studied as potential materials for various applications in nanomedicine, biology, and photocatalysis. One of the most popular nanocrystal heterodimers is represented by a structure made of a Au domain and a iron oxide domain joined together. Understanding the nature of the interface between the two domains in such type of dimer and how this influences the energy relaxation processes is a key issue. Here, we present the first broad-band transient absorption study on gold/iron oxide nanocrystal heterodimers that explains how the energy relaxation is affected by the presence of such interface. We found faster electron–electron and electron–phonon relaxation times for the gold “nested” in the iron oxide domain in the heterodimers with respect to gold “only” nanocrystals, that is, free-standing gold nanocrystals in solution. We relate this effect to the decreased electron screening caused by spill-out of the gold electron distribution at gold/iron oxide interface

Plasmon Dynamics in Colloidal Au₂Cd Alloy–CdSe Core/Shell Nanocrystals

Metal–semiconductor nanocrystal heterostructures are model systems for understanding the interplay between the localized surface plasmon resonances in the metal domain and the relaxation of the excited carriers in the semiconductor domain. Here we report the synthesis of colloidal Au₂Cd (core)/CdSe (shell) nanocrystal heterostructures, which were characterized extensively with several structural and optical techniques, including time-resolved fluorescence and broad-band transient absorption spectroscopy (both below and above the CdSe band gap). The dynamics of the transient plasmon peak was dominated by the relaxation of hot carriers in the metal core, its spectral shape was independent of the pump wavelength, and the bleaching lifetime was about half a picosecond, comparable with the value found in the AuCd seeds used for the synthesis

Astigmatic traction force microscopy (aTFM)

Quantifying small, rapidly progressing three-dimensional forces generated by cells remains a major challenge towards a more complete understanding of mechanobiology. Traction force microscopy is one of the most broadly applied force probing technologies but ascertaining three-dimensional information typically necessitates slow, multi-frame z-stack acquisition with limited sensitivity. Here, by performing traction force microscopy using fast single-frame astigmatic imaging coupled with total internal reflection fluorescence microscopy we improve the temporal resolution of three-dimensional mechanical force quantification up to 10-fold compared to its related super-resolution modalities. 2.5D astigmatic traction force microscopy (aTFM) thus enables live-cell force measurements approaching physiological sensitivity

Improving the Spatial Resolution in Direct Laser Writing Lithography by Using a Reversible Cationic Photoinitiator

none7siDirect laser writing (DLW) lithography has emerged as a competitive additive tool for the fabrication of detailed three-dimensional (3D) structures with a minimum feature size close to the nanometer scale. However, the minimal distance between adjacently written features with no overlapping, that is the writing resolution, is not in the same scale as the feature size. This is a consequence of the so-called "memory effect", namely, the accumulation of radicals between polymerized structures, which prevents the development of DLW for commercial applications. To overcome these limitations, we propose an original approach based on the reversible formation of the active species triggering the polymerization to decrease the impact of the "memory effect" on the writing resolution. We have selected the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) molecule as the cationic photoinitiator in combination with an oxidizing agent, AgPF6, to trigger the polymerization of the photoresist. The two-photon absorption (2PA) ability of the PCBM material was explored by using the open aperture z-scan technique, obtaining a 2PA cross-section of â¼400 GM. We have also utilized pump-probe spectroscopy to demonstrate the formation of the radical cation of the PCBM via a photoinduced electron transfer reaction with the Ag+cation (ÎG < 0). Moreover, the regeneration of the primary photoinitiating system PCBM/AgPF6was investigated with the flash photolysis technique, proving the absence of excited species in the μs time scale. This is the key point of our approach: the reversible character of the electron transfer process allows the partial regeneration of the primary photoinitiator in the interstice between polymerized structures avoiding the "memory effect". The implementation of this approach with commonly used resists, SU-8 or Araldite, has resulted in a notable improvement of the spatial resolution, from 600 to 400 nm when using a conventional photoinitiator compared to our PCBM/AgPF6system.Duocastella, Martí; Vicidomini, Giuseppe; Korobchevskaya, Kseniya; Pydzińska, Katarzyna; Ziółek, Marcin; Diaspro, Alberto; De Miguel, GustavoDuocastella, Martí; Vicidomini, Giuseppe; Korobchevskaya, Kseniya; Pydzińska, Katarzyna; Ziółek, Marcin; Diaspro, Alberto; De Miguel, Gustav