High-quality quantum-dot/polystyrene nanofibers (QD/PS NFs) are synthesized by drawing solvated PS doped with CdSe/ZnS QDs. As-drawn QD/PS NFs offer ultra-long-term photostability, flexibility, and excellent optical properties for sensing applications. Based on these active NFs, optical humidity sensors with extremely low power consumption, fast response, and long-term stability are successfully demonstrated, which may lead to a new category of nanometer-scale optical sensors.

This paper reports the fabrication and characterization of polymer nanofibers embedded with gold nanorods in uniaxial alignment for applications in optical waveguiding and sensing. Using a waveguiding approach, we demonstrated highly efficient excitation of localized surface plasmon resonance in the embedded gold nanorods with a photon-to-plasmon-conversion efficiency as high as 70% for a single nanorod at its longitudinal resonance wavelength. On the basis of waveguiding polymer nanofibers embedded with gold nanorods, we further demonstrated compact optical humidity sensors with a response time of 110 ms and an operation optical power as low as 500 pW.

We report a general approach to light-emitting polymer nanofibers (PNFs) based on waveguiding excitation. By waveguiding excitation light along the PNFs, we demonstrated that the interaction of light with PNFs is enhanced over 3 orders of magnitude compared with the currently used irradiating excitation. Intriguing advantages such as enhanced excitation efficiency, low excitation power operation down to nW levels, tightly confined excitation with low cross talk, and high photostability of the light-emitting PNFs are obtained. The waveguiding excitation allows incorporation of various fluorescent dyes into PNFs to generate multicolor emitting sources covering the entire visible spectrum. The light-emitting single PNFs via waveguiding excitation may find widespread nanophotonic applications in chemical and biological sensors, multicolor emitting sources, and lasers.

Bandgap engineering of semiconductor nanowires is important in designing nanoscale multifunctional optoelectronic devices. Here, we report a facile thermal evaporation method, and realize the spatial bandgap engineering in single CdS(1-x)Se(x) alloy nanowires. Along the length of these achieved nanowires, the composition can be continuously tuned from x = 0 (CdS) at one end to x = 1 (CdSe) at the other end, resulting in the corresponding bandgap (light emission wavelength) being modulated gradually from 2.44 eV (507 nm, green light) to 1.74 eV (710 nm, red light). In spite of the existing composition (crystal lattice) transition along the length, these multicolor nanowires still possess high-quality crystallization. These bandgap engineered nanowires will have promising applications in such as multicolor display and lighting, high-efficiency solar cells, ultrabroadly spectral detectors, and biotechnology.

Hot, nonequilibrium carriers formed near the interfaces of semiconductors or metals play a crucial role in chemical catalysis and optoelectronic processes. In addition to optical illumination, an efficient way to generate hot carriers is by excitation with tunnelling electrons. Here we show that the generation of hot electrons makes the nanoscale tunnel junctions highly reactive and facilitates strongly confined chemical reactions which can in turn modulate the tunnelling processes. We designed a device containing an array of electrically-driven plasmonic nanorods with up to 1011 tunnelling junctions per square centimeter, which demonstrates hot-electron activation of oxidation and reduction reactions in the junctions, induced by the presence of O2 and H2 molecules, respectively. The kinetics of the reactions can be monitored in-situ following the radiative decay of tunnelling-induced surface plasmons. This electrically-driven plasmonic nanorod metamaterial platform can be useful for the development of nanoscale chemical and optoelectronic devices based on electron tunnelling.

We demonstrated a substrate-moving vapor-liquid-solid (VLS) route for growing composition gradient ZnCdSSe alloy nanowires. Relying on temperature-selected composition deposition along their lengths, single tricolor ZnCdSSe alloy nanowires with engineerable band gap covering the entire visible range were obtained. The photometric property of these tricolor nanowires, which was determined by blue-, green-, and red-color emission intensities, can be in turn controlled by their corresponding emission lengths. More particularly, under carefully selected growth conditions, on-nanowire white light emission has been achieved. Band-gap-engineered semiconductor alloy nanowires demonstrated here may find applications in broad band light absorption and emission devices.

Single-nanoparticle detection and sizing is demonstrated using a nanofiber pair in an aqueous environment. The sizing of nanoparticles with a single radius (100 nm) and of mixed nanoparticles with different radii (100 nm and 170 nm) are both realized, and the experimental results agree well with predictions of Rayleigh-Gans scattering, by taking the inhomogeneous field distribution of the nanofibers into account.

We report a microfibre absorption sensor by using a 900 nm diameter silica microfibre embedded in a 125 μm wide microchannel with a detection length of 2.5 cm. Investigated by measuring the absorbance of methylene blue (MB), the sensor shows a detection limit down to 50 pM with excellent reversibility in a concentration range of 0-5 nM. The sensor has also been applied to bovine serum albumin (BSA) measurement, with a detection limit of 10 fg mL(-1). In addition, the sample volume requirement is merely 500 nL with a probing light power of about 150 nW, which is very promising for safe detection of single or a few molecules of biological specimens.