The surface coatings of nanoparticles determine their interaction with biomembranes, but studies have been limited almost exclusively to nanoparticles with a uniform surface chemistry. Although nanoparticles are increasingly made with complex surface chemistries to achieve multifunctionalities, our understanding of how a heterogeneous surface coating affects particle-biomembrane interaction has been lagging far behind. Here we report an investigation of this question in an experimental system consisting of amphiphilic "two-faced" Janus nanoparticles and supported lipid membranes. We show that amphiphilic Janus nanoparticles at picomolar concentrations induce defects in zwitterionic lipid bilayers. In addition to revealing the various effects of hydrophobicity and charge in particle-bilayer interactions, we demonstrate that the Janus geometry-the spatial segregation of hydrophobicity and charges on particle surface-causes nanoparticles to bind more strongly to bilayers and induce defects more effectively than particles with uniformly mixed surface functionalities. We combine experiments with computational simulation to further elucidate how amphiphilic Janus nanoparticles extract lipids to rupture intact lipid bilayers. This study provides direct evidence that the spatial arrangement of surface functionalities on a nanoparticle, rather than just its overall surface chemistry, plays a crucial role in determining how it interacts with biological membranes.

Glutaraldehyde causes especially high autofluorescence. It reacted with proteins and peptides to generate visible to near-IR emitters. A model indicated that ethylenediamine and a secondary amine in the molecule were key components for the formation of emissive species. The mechanism enables us to control the generation and elimination of autofluorescence.

We report a strategy for using magnetic Janus microparticles to control the stimulation of T cell signaling with single-cell precision. To achieve this, we design Janus particles that are magnetically responsive on one hemisphere and stimulatory to T cells on the other side. By manipulating the rotation and locomotion of Janus particles under an external magnetic field, w e control the orientation of the particle-cell recognition and thereby initiation of T cell activation. This study demonstrates a step towards employing anisotropic material properties of Janus particles to control single cell activities without the need of complex magnetic manipulation devices.

This Letter describes how the endosomal organization of immunostimulatory nanoconstructs can tune the in vitro activation of macrophages. Nanoconstructs composed of gold nanoparticles conjugated with unmethylated cytosine-phosphateguanine (CpG) oligonucleotides have distinct endosomal distributions depending on the surface curvature. Mixed-curvature constructs produce a relatively high percentage of hollow endosomes, where constructs accumulated primarily along the interior edges. These constructs achieved a higher level of toll-like receptor (TLR) 9 activation along with the enhanced secretion of proinflammatory cytokines and chemokines compared to constantcurvature constructs that aggregated mostly in the center of the endosomes. Our results underscore the importance of intraendosomal interactions in regulating immune responses and targeted delivery.

The in vitro activation of T cells by synthetic particles is a promising technique for adoptive cancer immunotherapy. While it is known that cell-surface receptors form clusters during T cell activation, the use of clustered ligands on synthetic particles to modulate T cell response is a largely unexplored concept. Building upon our previous finding that T cells respond differently to various micro-sized patterns of ligands, we here investigate the effect of nano-sized ligand clusters on T cell activation. Two-faced Janus nanoparticles were fabricated to display ligands of different functions in spatially segregated clusters on single nanoparticles. Going beyond our earlier qualitative study, here we precisely quantified and controlled the surface density and the total amount of ligands on single nanoparticles. We show that nanoparticles with clustered ligands activate T cells to a greater level than ones uniformly coated with the same number of ligands. The enhanced effect is due to increased local surface density of ligands. The results demonstrate that the spatial arrangement of ligands on particles influences activation response of T cells and may be used as a new strategy to increase T cell stimulation in the presence of insufficient amount of stimuli. This fundamental study also represents an initial step in using nanoscale Janus particles for manipulating immune cell responses.