Single Upconversion Nanoparticle–Bacterium Cotrapping for Single‐Bacterium Labeling and Analysis

Detecting and analyzing pathogenic bacteria in an effective and reliable manner is crucial for the diagnosis of acute bacterial infection and initial antibiotic therapy. However, the precise labeling and analysis of bacteria at the single‐bacterium level are a technical challenge but very important to reveal important details about the heterogeneity of cells and responds to environment. This study demonstrates an optical strategy for single‐bacterium labeling and analysis by the cotrapping of single upconversion nanoparticles (UCNPs) and bacteria together. A single UCNP with an average size of ≈120 nm is first optically trapped. Both ends of a single bacterium are then trapped and labeled with single UCNPs emitting green light. The labeled bacterium can be flexibly moved to designated locations for further analysis. Signals from bacteria of different sizes are detected in real time for single‐bacterium analysis. This cotrapping method provides a new approach for single‐pathogenic‐bacterium labeling, detection, and real‐time analysis at the single‐particle and single‐bacterium level.     

A Solution‐Processed Ultrafast Optical Switch Based on a Nanostructured Epsilon‐Near‐Zero Medium

All the optical properties of materials are derived from dielectric function. In spectral region where the dielectric permittivity approaches zero, known as epsilon‐near‐zero (ENZ) region, the propagating light within the material attains a very high phase velocity, and meanwhile the material exhibits strong optical nonlinearity. The interplay between the linear and nonlinear optical response in these materials thus offers unprecedented pathways for all‐optical control and device design. Here the authors demonstrate ultrafast all‐optical modulation based on a typical ENZ material of indium tin oxide (ITO) nanocrystals (NCs), accessed by a wet‐chemistry route. In the ENZ region, the authors find that the optical response in these ITO NCs is associated with a strong nonlinear character, exhibiting sub‐picosecond response time (corresponding to frequencies over 2 THz) and modulation depth up to ≈160%. This large optical nonlinearity benefits from the highly confined geometry in addition to the ENZ enhancement effect of the ITO NCs. Based on these ENZ NCs, the authors successfully demonstrate a fiber optical switch that allows switching of continuous laser wave into femtosecond laser pulses. Combined with facile processibility and tunable optical properties, these solution‐processed ENZ NCs may offer a scalable and printable material solution for dynamic photonic and optoelectronic devices.     

Phonon‐Assisted Electro‐Optical Switches and Logic Gates Based on Semiconductor Nanostructures

High‐performance nanostructured electro‐optical switches and logic gates are highly desirable as essential building blocks in integrated photonics. In contrast to silicon‐based optoelectronic devices, with their inherent indirect optical bandgap, weak light‐modulation mechanism, and sophisticated device configuration, direct‐bandgap‐semiconductor nanostructures with attractive electro‐optical properties are promising candidates for the construction of nanoscale optical switches for on‐chip photonic integrations. However, previously reported semiconductor‐nanostructure optical switches suffer from serious drawbacks such as high drive voltage, limited operation spectral range, and low modulation depth. High‐efficiency electro‐optical switches based on single CdS nanobelts with low drive voltage, ultra‐high on/off ratio, and broad operation wavelength range, properties resulting from unique electric‐field‐dependent phonon‐assisted optical transitions, are demonstrated. Furthermore, functional NOT, NOR, and NAND optical logic gates are demonstrated based on these switches. These switches and optical logic gates represent an important step toward integrated photonic circuits.     

Single‐Stimulus‐Induced Modulation of Multiple Optical Properties

Stimuli‐responsive smart optical materials hold great promise for applications in active optics, display, sensing, energy conversion, military camouflage, and artificial intelligence. However, their applications are greatly restricted by the difficulty of tuning different optical properties within the same material, especially by a single stimulus. Here, magnetic modulations of multiple optical properties are demonstrated in a crystalline colloidal array (CCA) of magnetic nanorods. Small‐angle X‐ray scattering studies reveal that these nanorods form an unusual monoclinic crystal in concentrated suspensions. The CCA exhibits optical anisotropy in the form of a photonic bandgap and birefringence, thus enabling magnetic tuning of the structural color and transmittance at a rate of 50 Hz. As a proof‐of‐concept, it is further demonstrated that the fabrication of a multifunctional device for display, anticounterfeiting, and smart‐window applications based on this multiple magneto‐optical effect. The study not only provides a new model system for understanding colloidal assembly, but also opens up opportunities for new applications of smart optical materials for various purposes.     

Biotinylated Photopolymers for 3D‐Printed Unibody Lab‐on‐a‐Chip Optical Platforms

The present work reports the first demonstration of straightforward fabrication of monolithic unibody lab‐on‐a‐chip (ULOCs) integrating bioactive micrometric 3D scaffolds by means of multimaterial stereolithography (SL). To this end, a novel biotin‐conjugated photopolymer is successfully synthesized and optimally formulated to achieve high‐performance SL‐printing resolution, as demonstrated by the SL‐fabrication of biotinylated structures smaller than 100 µm. By optimizing a multimaterial single‐run SL‐based 3D‐printing process, such biotinylated microstructures are incorporated within perfusion microchambers whose excellent optical transparency enables real‐time optical microscopy analyses. Standard biotin‐binding assays confirm the existence of biotin‐heads on the surfaces of the embedded 3D microstructures and allow to demonstrate that the biofunctionality of biotin is not altered during the SL‐printing, thus making it exploitable for further conjugation with other biomolecules. As a step forward, an in‐line optical detection system is designed, prototyped via SL‐printing and serially connected to the perfusion microchambers through customized world‐to‐chip connectors. Such detection system is successfully employed to optically analyze the solution flowing out of the microchambers, thus enabling indirect quantification of the concentration of target interacting biomolecules. The successful application of this novel biofunctional photopolymer as SL‐material enables to greatly extend the versatility of SL to directly fabricate ULOCs with intrinsic biofunctionality.