Dendrimers in Nanoscale Confinement: The Interplay between Conformational Change and Nanopore Entrance

Hyperbranched dendrimers are nanocarriers for drugs, imaging agents, and catalysts. Their nanoscale confinement is of fundamental interest and occurs when dendrimers with bioactive payload block or pass biological nanochannels or when catalysts are entrapped in inorganic nanoporous support scaffolds. The molecular process of confinement and its effect on dendrimer conformations are, however, poorly understood. Here, we use single-molecule nanopore measurements and molecular dynamics simulations to establish an atomically detailed model of pore dendrimer interactions. We discover and explain that electrophoretic migration of polycationic PAMAM dendrimers into confined space is not dictated by the diameter of the branched molecules but by their size and generation-dependent compressibility. Differences in structural flexibility also rationalize the apparent anomaly that the experimental nanopore current read-out depends in nonlinear fashion on dendrimer size. Nanoscale confinement is inferred to reduce the protonation of the polycationic structures. Our model can likely be expanded to other dendrimers and be applied to improve the analysis of biophysical experiments, rationally design functional materials such as nanoporous filtration devices or nanoscale drug carriers that effectively pass biological pores

The Nanopore-Tweezing-Based, Targeted Detection of Nucleobases on Short Functionalized Peptide Nucleic Acid Sequences

The implication of nanopores as versatile components in dedicated biosensors, nanoreactors, or miniaturized sequencers has considerably advanced single-molecule investigative science in a wide range of disciplines, ranging from molecular medicine and nanoscale chemistry to biophysics and ecology. Here, we employed the nanopore tweezing technique to capture amino acid-functionalized peptide nucleic acids (PNAs) with α-hemolysin-based nanopores and correlated the ensuing stochastic fluctuations of the ionic current through the nanopore with the composition and order of bases in the PNAs primary structure. We demonstrated that while the system enables the detection of distinct bases on homopolymeric PNA or triplet bases on heteropolymeric strands, it also reveals rich insights into the conformational dynamics of the entrapped PNA within the nanopore, relevant for perfecting the recognition capability of single-molecule sequencing

MOCVD InP/AlGaInAs distributed Bragg reflector for 1.55 [micro sign]m VCSELs

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Optical injection locking of transverse modes in 1.3-mu m wavelength coupled-VCSEL arrays

Optical injection locking of 1.3-mu m phase-locked VCSEL arrays defined by patterned tunnel junctions and wafer fusion is investigated experimentally and theoretically. The impact of the overlap between the master laser injection beam and the injected modes is demonstrated and explained with a rate equation model that incorporates the spatial variations. (C) 2014 Optical Society of Americ

Optical injection locking of polarization modes and spatial modes in single-aperture VCSELs and VCSEL arrays emitting at 1.3 mu m

We report the injection locking of specific spatial modes and polarization modes of 1.3 mu m wavelength vertical surface emitting lasers (VCSELs) in single-aperture devices and phase-coupled arrays. The optical injection is realized using a master laser (ML) VCSEL, the beam of which is directed onto the output facet of the slave laser (SL) VCSEL or VCSEL array. We measured the emission spectra of the SL as the ML operating conditions (frequency, power) were varied systematically, and present the results on two-dimensional stability maps of power versus detuning of the ML from the injected modes

Polarization mode control of long-wavelength VCSELs by intracavity patterning

Polarization mode control is enhanced in wafer-fused verticalcavity surface-emitting lasers emitting at 1310 nm wavelength by etching two symmetrically arranged arcs above the gain structure within the laser cavity. The intracavity patterning introduces birefringence and dichroism, which discriminates between the two polarization states of the fundamental transverse modes. We find that the cavity modifications define the polarization angle at threshold with respect to the crystal axes, and increase the gain anisotropy and birefringence on average, leading to an increase in the polarization switching current. Experimental measurements are explained using the spin-flip model of VCSEL polarization dynamics. (C) 2016 Optical Society of Americ