Sensitivity gains in chemosensing by optical and structural modulation of ordered assembly arrays of ZnO nanorods

Optomechanical effects caused by non-zero field quantities in multiple evanescent waves

Evanescent waves, with their high energy density, intricate local momentum, and spatial distribution of spins, have been the subject of extensive recent study. These waves offer promising applications in near-field particle manipulation. Consequently, it becomes imperative to gain a deeper understanding of the impacts of scattering and gradient forces on particles in evanescent waves to enhance and refine the manipulation capabilities. In this study, we employ the multipole expansion theory to present analytical expressions for the scattering and gradient forces exerted on an isotropic sphere of any size and composition in multiple evanescent waves. The investigation of these forces reveals several unusual optomechanical phenomena. It is well known that the scattering force does not exist in counter-propagating homogeneous plane waves. Surprisingly, in multiple pairs of counter-propagating evanescent waves, the scattering force can arise due to the nonzero orbital momentum (OM) density and/or the curl part of the imaginary Poynting momentum (IPM) density. More importantly, it is found that the optical scattering force can be switched on and off by simply tuning the polarization. Furthermore, optical forces typically vary with spatial position in an interference field. However, in the interference field generated by evanescent waves, the gradient force becomes a spatial constant in the propagating plane as the particle's radius increases. This is attributed to the decisive role of the non-interference term of the electromagnetic energy density gradient. Our study establishes a comprehensive and rigorous theoretical foundation, propelling the advancement and optimization of optical manipulation techniques harnessed through multiple evanescent waves. Specifically, these insights hold promise in elevating trapping efficiency through precise control and manipulation of optical scattering and gradient forces, stimulating further explorations.

Aerosol Dry Printing for SERS and Photoluminescence-Active Gold Nanostructures Preparation for Detection of Traces in Dye Mixtures

We proposed a novel method of nanostructure preparation for observation of surface-enhanced Raman spectroscopy (SERS) and metal-enhanced fluorescence (MEF) based on the deposition of gold nanoparticles (GNPs) above the thin dye film by dry aerosol printing. We detected various enhanced SERS and MEF signals of films of malachite green (MG) and rhodamine B (RhB) mixtures, depending on the surface packing density of Au NPs on the strip, and found the optimum one to achieve the 3.5 × 10⁵ SERS enhancement. It was shown that statistical methods of chemometrics such as projection on latent structures provided the opportunity to distinguish SERS of MG from 100 ppm RhB in a mixture, whereas separation of MEF signals are feasible even for a mixture of MG and 1 ppm RhB due to two-photon excitation.

Perylene Bisimide Derivative-Based Fluorescent Film Sensors: From Sensory Materials to Device Fabrication

Film-based fluorescent sensors have become an important field of sensor research due to abundant acquirable signals, real-time monitoring, and ease of miniaturization and integration, where chemically sensitive films are the most vital component of the sensor devices. In this feature article, we introduce hardware structures of film-based fluorescent sensors following the examination/investigation of the recent progress of such sensors with perylene bisimide (PBI) derivatives as sensing fluorophores in the films. PBI derivatives were specially chosen because of their outstanding chemical, photochemical, and thermal stabilities as well as their unusual high-fluorescence quantum yields. And finally, we provide a prediction for the future developments and challenges of this emerging field.

Qualitative Detection Toward Military and Improvised Explosive Vapors by a Facile TiO2 Nanosheet-Based Chemiresistive Sensor Array

A facile TiO₂ nanosheets-based chemiresistive gas sensor array was prepared to identify 11 kinds of military and improvised explosive vapors at room temperature. The morphology of TiO₂ nanosheets was well-controlled by adjusting the concentration of HF applied during the preparation. Owing to the morphology difference, the TiO₂ nanosheet-based sensors show different response values toward 11 kinds of explosives, which is the basis of the successful discriminative identification. This method owes lots of advantages over other detection techniques, such as the facile preparation procedure, high response value (115.6% for TNT and 830% for PNT) at room temperature, rapid identifying properties (within 30 s for 9 explosives), simple operation, high anti-interference property, and low probability of misinforming, and consequently has a huge potential application in the qualitative detection of explosives.

Artificial Olfactory System for Trace Identification of Explosive Vapors Realized by Optoelectronic Schottky Sensing

A rapid, ultrasensitive artificial olfactory system based on an individual optoelectronic Schottky junction is demonstrated for the discriminative detection of explosive vapors, including military explosives and improvised explosives.

Lasing mode regulation and single-mode realization in ZnO whispering gallery microcavities by the Vernier effect

The wide direct bandgap and strong exciton binding energy of ZnO have inspired examinations of ultraviolet lasing over the previous decades. However, regulation of the lasing mode, especially the realization of single mode lasing, is still a challenge. In this study, a ZnO comb-like structure with an array of microrods was selected to design coupled whispering-gallery-mode cavities, wherein the naturally varied air-gap between the adjacent microrods created a flexible condition for optical field coupling without any complicated micromanipulation. Spectral behaviour of lasing and coupling interaction between coupled ZnO microrods were systematically investigated. By regulating the nano-scale inter-space of dual coupled microrods, stable single-mode lasing with a higher Q factor and lower threshold was obtained successfully based on the Vernier effect. The formation conditions and the mechanism of single-mode lasing derived from the coupled ZnO microrods were discussed in detail. It also demonstrated an approach to construct high quality single-mode lasing by tuning the diameters of the coupled ZnO microrods.

Ultrasensitive, Real-time and Discriminative Detection of Improvised Explosives by Chemiresistive Thin-film Sensory Array of Mn(2+) Tailored Hierarchical ZnS

A simple method combing Mn²⁺ doping with a hierarchical structure was developed for the improvement of thin-film sensors and efficient detection of the explosives relevant to improvised explosive devices (IEDs). ZnS hierarchical nanospheres (HNs) were prepared via a solution-based route and their sensing performances were manipulated by Mn²⁺ doping. The responses of the sensors based on ZnS HNs towards 8 explosives generally increase firstly and then decrease with the increase of the doped Mn²⁺ concentration, reaching the climate at 5% Mn²⁺. Furthermore, the sensory array based on ZnS HNs with different doping levels achieved the sensitive and discriminative detection of 6 analytes relevant to IEDs and 2 military explosives in less than 5 s at room temperature. Importantly, the superior sensing performances make ZnS HNs material interesting in the field of chemiresistive sensors, and this simple method could be a very promising strategy to put the sensors based on thin-films of one-dimensional (1D) nanostructures into practical IEDs detection.

Schiff Base Substituent-Triggered Efficient Deboration Reaction and Its Application in Highly Sensitive Hydrogen Peroxide Vapor Detection

The organic thin-film fluorescence probe, with the advantages of not polluting the analyte and fast response, has attracted much attention in explosive detection. Different with nitro explosives, the peroxide-based explosives are hardly to be detected because of their poor ultraviolet absorption and lack of an aromatic ring. As the signature compound of peroxide-based explosives, H2O2 vapor detection became more and more important. Boron ester or acid is considered to be a suitable functional group for the detection of hydrogen peroxide due to its reliable reactive activity. Its only drawback lies on its slow degradation velocity. In this work, we try to introduce some functional group to make the boron ester to be easily oxidized by H2O2. Herein, 4-(phenyl(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amino)benzaldehyde (OTB) was synthesized and its imine derivatives, OTBXAs, were easily obtained just by putting OTB films in different primary amines vapors. OTBXAs show fast deboronation velocity in H2O2 vapor compared with OTB. The complete reaction time of (E)-N-phenyl-4-((propylimino)methyl)-N-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)aniline (OTBPA) was even shortened 40 times with a response time of seconds. The detection limit for H2O2 vapor was as low as 4.1 parts per trillion (ppt). Further study showed that it is a general approach to enhance the sensing performance of borate to hydrogen peroxide (H2O2) vapor by introducing an imine into an aromatic borate molecule via a solid/vapor reaction.

Synthesis of Ni-doped ZnO nanostructures by low-temperature wet chemical method and their enhanced field emission properties

In this study, we report an enhancement in the field emission (FE) properties of ZnO nanostructures obtained by doping with Ni at a base pressure of ∼1 × 10⁻⁸ mbar, which were grown by a simple wet chemical process.

Borate ester endcapped fluorescent hyperbranched conjugated polymer for trace peroxide explosive vapor detection

The hyperbranched polymer S1/ZnO nanorod array composite is very promising for a highly sensitive fluorescence device for detecting peroxide explosives.

Optical modulation of waveguiding in spiropyran-functionalized polydiacetylene microtube

Optical modulation of waveguiding and logic operations play significant roles in highly integrated optical communication components, optical computing, and photonic circuits. Herein, we designed and synthesized spiropyran-functionalized polydiacetylene (SFPDA) microtubes, and realized reversible optical modulation of waveguiding in SFPDA microtubes through fluorescence resonance energy transfer (FRET) between the PDA matrix and spiropyran in open merocyanine (MC) form within the surface of the microtubes. Because of the reversible isomerization characteristics of spiropyran units, we have realized resettable, multireadout logic system that includes OR and INHIBIT logic operations in SFPDA microtube.

Well-aligned ZnO nanowires with excellent field emission and photocatalytic properties

Well-aligned ZnO nanowires (NWs) were successfully synthesized on Si(100) by the process of carbothermal reduction and vapor-liquid-solid method. Scanning electron microscopy and transmission electron microscopy results confirmed that ZnO NWs were single crystalline wurtzite structures and grew along the [0001] direction. The influences of substrate temperature and total pressure on the growth were discussed. The well-aligned ZnO NWs show good field emission properties, and the emitter constructed of pencil-like ZnO NWs exhibited a low turn-on field (3.82 V μm(-1)) and a high field enhancement factor (β = 2303). Finally, we demonstrated that the as-prepared ZnO NWs with small diameter on the substrate have good photocatalytic activity toward degradation of methylene blue. Using ZnO NWs with Au nanoparticles (NPs) would decrease the recombination rate of hole-electron pairs due to the great shift of the Fermi level to the conduction band. Hence, adding Au NPs was a promising method to enhance the photocatalytic performance of ZnO NWs. It is significant that photocatalyst fabricated by ZnO NWs can apply to the degradation of organic pollution, and solve the environmental issues.