Nanoscale objects are typically internalized by cells into membrane-bounded endosomes and fail to access the cytosolic cell machinery. Whereas some biomacromolecules may penetrate or fuse with cell membranes without overt membrane disruption, no synthetic material of comparable size has shown this property yet. Cationic nano-objects pass through cell membranes by generating transient holes, a process associated with cytotoxicity. Studies aimed at generating cell-penetrating nanomaterials have focused on the effect of size, shape and composition. Here, we compare membrane penetration by two nanoparticle 'isomers' with similar composition (same hydrophobic content), one coated with subnanometre striations of alternating anionic and hydrophobic groups, and the other coated with the same moieties but in a random distribution. We show that the former particles penetrate the plasma membrane without bilayer disruption, whereas the latter are mostly trapped in endosomes. Our results offer a paradigm for analysing the fundamental problem of cell-membrane-penetrating bio-and macro-molecules. Nanomaterials are of great interest for use in biomedicine as imaging tools 1-3 , phototherapy agents 4,5 and gene delivery carriers 6,7 . Their interactions with cell membranes are of central importance for all such applications. For example, many drugdelivery systems are based on the transport of therapeutic agents to the cytosol or nucleus of cells by nanoparticles; efficient delivery must be achieved while avoiding cytotoxicity during passage through cell membranes to reach intracellular target compartments 8,9 . Indeed, membrane penetration by synthetic 10 as well as by biologically derived 11 molecules/particles is currently under intense investigation. Some biomacromolecules, such as cell-penetrating peptides (CPPs), may be capable of penetrating membranes without overt lipid bilayer disruption/poration 12-15 . Likewise, synthetic nanomaterials with very small dimensions (molecules, metal nanoclusters 16 , small dendrimers 10 and carbon nanotubes 17 ) can also pass through cell membranes. However, to the best of our knowledge, no synthetic material larger than a few nanometres in size can pass through membranes without disrupting the integrity of these biological barriers. For example, charged particles (such as cationic quantum dots or dendrimers, mostly assisted by some degree of hydrophobicity) induce transient poration of cell membranes to enter cells, a process associated with cytotoxicity 18 . Alternatively, nanoparticles have been designed to explicitly disrupt endolysosomal membranes to enter the cell by force 19 or enter the cell aided by exogenous agents such as CPP chaperones 20 . In contrast, most nanoparticles are trapped in endosomes 21 and hence do not reach the cytosol.The surface properties of nanomaterials play a critical role in determining the outcome of their interactions with cells 22 . Recently, we found that when gold nanoparticles are coated with binary mixtures of hydrophobic and hydrophilic organic mo...

High particle uniformity, high photoluminescence quantum yields, narrow and symmetric emission spectral lineshapes and minimal single dot emission intermittency (known as blinking) have been recognized as universal requirements for the successful use of colloidal quantum dots (QDs) in nearly all optical applications. However, synthesizing samples that simultaneously meet all these four criteria has proven challenging. Here, we report the synthesis of such high-quality CdSe/CdS core/shell QDs in an optimized process which maintains a slow growth rate of the shell through the use of octanethiol and cadmium oleate as precursors. In contrast with previous observations, single-QD blinking is significantly suppressed with only a relatively thin shell. In addition, we demonstrate the elimination of the ensemble luminescence photodarkening that is an intrinsic consequence of QD blinking statistical aging. Furthermore, the small size and high photoluminescence quantum yields of these novel QDs render them superior in vivo imaging agents compared to conventional QDs. We anticipate that this new generation of QDs will also result in significant improvement in the performance of QDs in other applications such as solid-state lighting and illumination.

The potential of superparamagnetic iron oxide nanoparticles (SPIONs) in various biomedical applications, including magnetic resonance imaging (MRI), sensing, and drug delivery, requires that their surface be derivatized to be hydrophilic and biocompatible. We report here the design and synthesis of a compact and water-soluble zwitterionic dopamine sulfonate (ZDS) ligand with strong binding affinity to SPIONs. After ligand exchange, the ZDS coated SPIONs exhibit small hydrodynamic diameters (HD), and stability with respect to time, pH, and salinity. Furthermore, small ZDS coated SPIONs were found to have a reduced non-specific affinity (compared to negatively charged SPIONs) towards serum proteins; streptavidin/dye functionalized SPIONs were bioactive and thus specifically targeted biotin receptors.

We present a bioorthogonal and modular conjugation method for efficient coupling of organic dyes and biomolecules to quantum dots (QDs) using a norbornene−tetrazine cycloaddition. The use of noncoordinating functional groups combined with the rapid rate of the cycloaddition leads to highly efficient conjugation. We have applied this method to the in situ targeting of norbornene-coated QDs to live cancer cells labeled with tetrazine-modified proteins.

We present the synthesis of Cd(3)As(2) colloidal quantum dots luminescent from 530 to 2000 nm. Previous reports on quantum dots emitting in the infrared are primarily limited to the lead chalcogenides and indium arsenide. This work expands the availability of high quality infrared emitters.

Detailed Charge arrangements: A new set of zwitterionic quantum dots were synthesized and used to study the influence of microscopic charge arrangements on the in vivo behavior of nanoparticles. Experiments using cultured cells and live mice demonstrate that the microscopic arrangement of surface charges strongly influence nonspecific binding, clearance behavior, and in vivo transport of nanoparticles.

We have isolated a cold-inducible gene (designated OsCK1) from Oryza sativa by a differential cDNA screening technique. Sequence analysis indicated that the open reading frame of the OsCK1 gene consists of 1350 bp encoding 449 amino acid residues, which is very similar to a family of calcineurin B-like protein (CBL)-interacting protein kinases (CIPKs) or salt overly sensitive 2 (SOS2)-like protein kinases (PKS) in Arabidopsis. CIPKs/PKS are a group of Ser/Thr protein kinases associated with the AtCBL/SOS3-like calcium-binding proteins (SCaBP). OsCK1 actually interacts with AtCBL3 through the C-terminal region in a yeast two-hybrid system, suggesting that OsCK1 is probably a rice orthologue of one of the CIPK/PKS members. Expression of the OsCK1 gene was detected mainly in the shoots and highly inducible by diverse signals such as cold, light, salt, sugar and cytokinins. In addition, calcium increased the OsCK1 transcript level, whereas a calcium ionophore, A23187, partially abolished stimulus-induced expressions. OsCK1 phosphorylated itself and a generic substrate, myelin basic protein, in the preference of Mn2+. Deletion of the C-terminal region from OsCK1 significantly decreased autophosphorylation activity without affecting the ability for substrate phosphorylation. These findings suggest that the CBL/CIPK or SCaBP/PKS signaling pathways recently found in Arabidopsis may also exist in rice and function in cold response in which calcium signal serves as a second messenger.

Metagenomic studies suggest that only a small fraction of viruses existing in nature have been identified and studied. Characterization of unknown viral genomes is hindered by many nonspecific genomes populating any virus sample. Here, we report a new platform integrating dropbased microfluidics and computational analysis that enables purification of any single viral species from a complex, mixed virus sample and the retrieval of complete genome sequences. Using this platform, we retrieve the genome sequence of a 5243 bp dsDNA virus that was spiked into wastewater with > 96% sequence coverage and > 99.8% identity. This platform holds great potential for virus discovery as it allows enrichment and sequencing of previously undescribed viruses as well as known viruses. KeywordsMicrofluidics; Microemulsions; Viruses; Genome sequencing; High throughput screening * Corresponding author: Department of Physics, School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA, weitz@seas.harvard.edu. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptViruses are the most abundant biological entities on Earth and significantly impact living organisms by causing diseases and shaping their immune systems. Despite their ubiquity and influence, less than 0.01% of viruses are sequenced [1] . Establishment of an extensive virus database is crucial to identify potential emerging infectious diseases [2] and to improve our understanding of virus diversity, ecology, adaption and evolution. The major roadblock to characterizing unknown viral genomes is the lack of technologies enabling efficient enrichment of various types of viruses. Enrichment of a target viral species is required for the most common virus samples such as environmental samples, which generally harbor diverse viral populations [3] , or clinical samples where the amount of viral genomes is often lower than the amount of host genomes and the virions are localized to a small subset of cells in the tissue. An enrichment step is particularly crucial for viral genome sequencing because other abundant DNA in the sample such as genomic fragments of host DNA is often much larger than viral genomes and dominate the sequence space even with a small number of copies. Traditional enrichment methods for viruses include cell culture [4] , immunoscreening [5] followed by sequence-independent PCR [6] and differential hybridization [7] . All of these methods are labor-intensive, inefficient and more importantly, only applicable to a limited subset of viruses. Recently, a flow cytometric method was developed to disperse single virions into microwells and obtain their individual genome sequences [8] . However, this method does not employ a selection strategy. A selection strategy allows efficient usage of sequencing power and enables rare virus sequencing with a reasonable sequencing cost and time.In this paper, we report the development of a platform to isolate and sequence any single viral species from a large ge...