Optical Heating and Temperature Determination of Core–Shell Gold Nanoparticles and Single‐Walled Carbon Nanotube Microparticles

The real‐time temperature measurement of nanostructured materials is particularly attractive in view of increasing needs of local temperature probing with high sensitivity and resolution in nanoelectronics, integrated photonics, and biomedicine. Light‐induced heating and Raman scattering of single‐walled carbon nanotubes with adsorbed gold nanoparticles decorating silica microparticles are reported, by both green and near IR lasers. The plasmonic shell is used as nanoheater, while the single‐walled carbon nanotubes are Raman active and serve as a thermometer. Stokes and Anti‐Stokes Raman spectra of single‐walled carbon nanotubes serve to estimate the effective light‐induced temperature rise on the metal nanoparticles. The temperature rise is constant with time, indicating stability of the adsorption density. The effective temperatures derived from Stokes and Anti‐Stokes intensities are correlated with those measured in a heating stage. The resolution of the thermal experiments in our study was found to be 5–40 K.     

Selectivity of Threefold Symmetry in Epitaxial Alignment of Liquid Crystal Molecules on Macroscale Single‐Crystal Graphene

Epitaxial alignment of organic liquid crystal (LC) molecules on single‐crystal graphene (SCG), an effective epitaxial molecular assembly template, can be used in alignment‐layer‐free liquid crystal displays. However, selectivity among the threefold symmetric easy axes of LCs on graphene is not well understood, which limits its application. Here, sixfold symmetric radial LC domains are demonstrated by dropping an LC droplet on clean SCG, which reveals that the graphene surface does not have an intrinsic preferential direction. Instead, the first contact geometry of the LC molecules determines the direction. Despite its strong anchoring energy on graphene, the LC alignment direction is readily erasable and rewritable, contrary to previous understanding. In addition, the quality of the threefold symmetric alignment is sensitive to alien residue and graphene imperfections, which can be used to detect infinitesimal impurities or structural defects on the graphene. Based on this unique epitaxial behavior of LCs on SCG, an alignment‐layer‐free electro‐optical LC device and LC alignment duplication, which can result in practical graphene‐based flexible LC devices, are realized.     

Chirality‐Selective Photoluminescence Enhancement of ssDNA‐Wrapped Single‐Walled Carbon Nanotubes Modified with Gold Nanoparticles

In this work, a convenient method to enhance the photoluminescence (PL) of single‐walled carbon nanotubes (SWNTs) in aqueous solutions is provided. Dispersing by single‐stranded DNA (ssDNA) and modifying with gold nanoparticles (AuNPs), about tenfold PL enhancement of the SWNTs is observed. More importantly, the selective PL enhancement is achieved for some particular chiralities of interest over all other chiralities, by using certain specific ssDNA sequences that are reported to recognize these particular chiralities. By forming AuNP–DNA–SWNT nanohybrids, ssDNA serves as superior molecular spacers that on one hand protect SWNT from direct contacting with AuNP and causing PL quench, and on the other hand attract the AuNP in close proximity to the SWNT to enhance its PL. This PL enhancement method can be utilized for the PL analysis of SWNTs in aqueous solutions, for biomedical imaging, and may serve as a prescreening method for the recognition and separation of single chirality SWNTs by ssDNA.     

Plasmonic‐Nanopore Biosensors for Superior Single‐Molecule Detection

Plasmonic and nanopore sensors have separately received much attention for achieving single‐molecule precision. A plasmonic “hotspot” confines and enhances optical excitation at the nanometer length scale sufficient to optically detect surface–analyte interactions. A nanopore biosensor actively funnels and threads analytes through a molecular‐scale aperture, wherein they are interrogated by electrical or optical means. Recently, solid‐state plasmonic and nanopore structures have been integrated within monolithic devices that address fundamental challenges in each of the individual sensing methods and offer complimentary improvements in overall single‐molecule sensitivity, detection rates, dwell time and scalability. Here, the physical phenomena and sensing principles of plasmonic and nanopore sensing are summarized to highlight the novel complementarity in dovetailing these techniques for vastly improved single‐molecule sensing. A literature review of recent plasmonic nanopore devices is then presented to delineate methods for solid‐state fabrication of a range of hybrid device formats, evaluate the progress and challenges in the detection of unlabeled and labeled analyte, and assess the impact and utility of localized plasmonic heating. Finally, future directions and applications inspired by the present state of the art are discussed.     

Single‐Carbon‐Nanotube Manipulations and Devices Based on Macroscale Anthracene Flakes

Because of the outstanding mechanical and electrical properties of carbon nanotubes (CNTs), a CNT‐based torsion pendulum is demonstrated to show great potential in nano‐electromechanical systems. It is also expected to achieve various manipulations for further characterization and increase device sensitivity using ultrlong CNTs and macroscale moving parts. However, the reported top‐down method limits the CNT performance and device size by introducing inevitable contamination and destruction, which greatly hinders the development of single‐molecule devices. Here, a bottom‐up method is introduced to fabricate heterostructures of anthracene flakes (AFs) and suspended CNTs, providing a nondamaging CNT mechanical measurement before further applications, especially for the twisting behavior, and providing a controllable and clean transfer method to fabricate CNT‐based electrical devices under ambient conditions. Based on the unique geometry of CNT/AF heterostructures, various complex manipulations of single‐CNT devices are conducted to investigate CNT mechanical properties and prompt novel applications of similar structures in nanotechnology. The AF‐decorated CNTs show high Young's modulus (≈1 TPa) and tensile strength (≈100 GPa), and can be considered as the finest and strongest torsional springs. CNT‐based torsion balance enables to measure fN‐level forces and the torsional spring constant is two orders of magnitude lower than previously reported values.