Multigigahertz bandwidth FM response of frequency tunabletwo-electrode DFB lasers

The FM response of frequency-tunable two-electrode distributed-feedback (DFB) lasers operating at 1.35 μm is discussed. Under certain bias conditions, an FM response of ~1 GHz/mA is flat over a range of modulating frequencies from 10 kHz to several hundred megahertz. This region is followed by a shallow dip and a high-frequency relaxation resonance peak, allowing an overall 3-dB FM bandwidth of ~5 GHz. This is believed to be the widest FM bandwidth reported to date for such lasers; however, variations of the phase of the FM response could limit the useful bandwidth in a frequency-shift keying (FSK) system. The experimental response is a function of static tuning conditions, with significant differences between regions of red and blue frequency shift with increasing current. The observed behavior is well represented by theoretical curves derived from a small-signal analysis     

Nonlinear Distortion in a Silicon Microring-Based Electro-Optic Modulator for Analog Optical Links

We analyze silicon microring modulators for analog signal generation, in terms of harmonic and intermodulation distortions. Free carrier plasma dispersion effect in silicon, Lorentzian-shaped resonance profile, and cavity photon lifetime are identified as the sources of modulation nonlinearity. Simulations show that the silicon microring modulators exhibit good modulation index and carrier-to-distortion ratio (CDR). For the generation of 10-GHz suboctave analog signals, a high optical-modulation-index of up to 46%, a CDR of 57 dB, and a spurious free dynamic range of 96 dB can be obtained. In fiber transmission, the microring-generated signal CDR can be improved by 10 dB due to the interaction between frequency chirp and chromatic dispersion.      

Iodinated Biaryls Synthesized by the Direct Dehydrodimerization of Iodoarenes Using Phenyliodine(III) Bis(trifluoroacetate) (PIFA)

Multiply iodinated biaryls can be prepared in yields up to 75% by direct oxidative coupling reaction of the iodinated arenes. The PIFA‐mediated dehydrodimerization is superior to all other known methods. The developed protocol is reliable and easy to perform.     

Dip‐Pen‐Nanolithographic Patterning of Metallic,Semiconductor, and Metal Oxide Nanostructures on Surfaces

Dip‐pen nanolithography (DPN) is a powerful method to pattern nanostructures on surfaces by the controlled delivery of an “ink” coating the tip of an atomic force microscope upon scanning and contacting with surfaces. The growing interest in the use of nanoparticles as structural and functional elements for the fabrication of nanodevices suggests that the DPN‐stimulated patterning of nanoparticles on surfaces might be a useful technique to assemble hierarchical architectures of nanoparticles that could pave methodologies for functional nanocircuits or nanodevices. This Review presents different methodologies for the nanolithographic patterning of metallic, semiconductor, and metal oxide nanostructures on surfaces. The mechanisms involved in the formation of the nanostructures are discussed and the effects that control the dimensions of the resulting patterns are reviewed. The possible applications of the nanostructures are also addressed.

     

Nanostructured Gold Colloid Electrodes

Recent advances in the assembly of nanoparticle superstructures on electrodes are addressed here. Methods for the assembly and characterization of these arrays are summarized and their electronic, photoelectrochemical, and sensor applications are discussed. The Figure shows a one‐layer architecture of Au nanoparticles and tetracationic cyclophanes on an amine‐functionalized ITO support.     

Optical aptasensors for the analysis of the vascular endothelial growth factor (VEGF)

The vascular endothelial growth factor, VEGF, is an important biomarker for different diseases and clinical disorders. We present a series of optical aptasensor-based sensing platforms for VEGF that include the following: (i) A FRET-based sensor that involves the VEGF-induced separation of aptamer-functionalized quantum dots blocked by a quencher nucleic acid (detection limit 1 nM). (ii) A FRET-based sensor based on the VEGF-induced assembly of the aptamer subunits functionalized with QDs and a dye acceptor (Cy5), respectively (detection limit 12 nM). (iii) A chemiluminescence aptasensor based on VEGF-induced assembly of a hemin/G-quadruplex catalyst (detection limit 18 nM). (iv) A chemiluminescence aptasensor based on the VEGF-stimulated assembly of two aptamer subunits into the hemin/G-quadruplex catalyst (detection limit 2.6 nM). (v) A chemiluminescence resonance energy transfer (CRET) aptasensor based on the VEGF-induced assembly of a semiconductor QDs-hemin/G-quadruplex supramolecular structure (detection limit 875 pM). Furthermore, an amplified optical aptasensor system based on the Exonuclease III (Exo III) recycling of the VEGF analyte was developed. In this system, one aptamer subunit is modified at its 5' and 3' ends with QDs and a black hole quencher, respectively. The VEGF-induced self-assembly of the aptamer subunits result in the digestion of the quencher units and the autonomous recycling of the analyte, while triggering-on the luminescence of the QDs (detection limit 5 pM). The system was implemented to analyze VEGF in human sera samples.     

Growing Metal Nanoparticles by Enzymes

Enzymes act as catalysts for the growth of metallic nanoparticles (NPs). The enzyme‐mediated growth of metallic NPs provides a general means to follow biocatalyzed transformations, and to develop optical sensors for different substrates such as glucose, L‐DOPA, alcohols, lactate or nerve gas analogs. Enzymes modified with Au NPs act as biocatalysts for the fabrication of metallic nanowires. The dip‐pen nanolithography of NP‐functionalized enzymes on Si surfaces yields biocatalytic templates that enable the orthogonal evolution of nanowires consisting of different metals.