A Colloidal‐Quantum‐Dot‐Based Self‐Charging System via the Near‐Infrared Band

A novel self‐charging platform is proposed using colloidal‐quantum‐dot (CQD) photovoltaics (PVs) via the near‐infrared (NIR) band for low‐power electronics. Low‐bandgap CQDs can convert invisible NIR light sources to electrical energy more efficiently than wider spectra because of reduced thermalization loss. This energy‐conversion strategy via NIR photons ensures an enhanced photostability of the CQD devices. Furthermore, the NIR wireless charging system can be concealed using various colored and NIR‐transparent fabric or films, providing aesthetic freedom. Finally, an NIR‐driven wireless charging system is demonstrated for a wearable healthcare bracelet by integrating a CQD PVs receiver with a flexible lithium‐ion battery and entirely embedding them into a flexible strap, enabling permanent self‐charging without detachment.     

In situ Visualization of Gene Expression Using Polymer‐Coated Quantum–Dot–DNA Conjugates

Imaging of specific mRNA targets in cells is of great importance in understanding gene expression and cell signaling processes. Subcellular localization of mRNA is known as a universal mechanism for cells to sequester specific mRNA for high production of required proteins. Various gene expressions in Drosophila cells are studied using quantum dots (QDs) and the fluorescence in situ hybridization (FISH) method. The excellent photostability and highly luminescent properties of QDs compared to conventional fluorophores allows reproducible obtainment of quantifiable mRNA gene expression imaging. Amine‐modified oligonucleotide probes are designed and covalently attached to the carboxyl‐terminated polymer‐coated QDs via EDC chemistry. The resulting QD–DNA conjugates show sequence‐specific hybridization with target mRNAs. Quantitative analysis of FISH on the Diptericin gene after lipopolysaccharide (LPS) treatment shows that the intensity and number of FISH signals per cell depends on the concentration of LPS and correlates well with quantitative real‐time PCR results. In addition, our QD–DNA probes exhibit excellent sensitivity to detect the low‐expressing Dorsal‐related immunity factor gene. Importantly, multiplex FISH of Ribosomal protein 49 and Actin 5C using green and red QD–DNA conjugates allows the observation of cellular distribution of the two independent genes simultaneously. These results demonstrate that highly fluorescent and stable QD–DNA probes can be a powerful tool for direct localization and quantification of gene expression in situ.     

On‐Chip Magnetic Platform for Single‐Particle Manipulation with Integrated Electrical Feedback

Methods for the manipulation of single magnetic particles have become very interesting, in particular for in vitro biological studies. Most of these studies require an external microscope to provide the operator with feedback for controlling the particle motion, thus preventing the use of magnetic particles in high‐throughput experiments. In this paper, a simple and compact system with integrated electrical feedback is presented, implementing in the very same device both the manipulation and detection of the transit of single particles. The proposed platform is based on zig‐zag shaped magnetic nanostructures, where transverse magnetic domain walls are pinned at the corners and attract magnetic particles in suspension. By applying suitable external magnetic fields, the domain walls move to the nearest corner, thus causing the step by step displacement of the particles along the nanostructure. The very same structure is also employed for detecting the bead transit. Indeed, the presence of the magnetic particle in suspension over the domain wall affects the depinning field required for its displacement. This characteristic field can be monitored through anisotropic magnetoresistance measurements, thus implementing an integrated electrical feedback of the bead transit. In particular, the individual manipulation and detection of single 1‐μm sized beads is demonstrated.     

Configurable Integration of On‐Chip Quantum Dot Lasers and Subwavelength Plasmonic Waveguides

The integration of on‐chip dielectric lasers and subwavelength plasmonic waveguides has attracted enormous attention because of the combination of both the advantages of the high performances of the small dielectric lasers and the subwavelength plasmonic waveguides. However, the configurable integration is still a challenge owing to the complexity of the hybrid structures and the damageability of the gain media in the multistep micro/nanofabrications. By employing the dark‐field optical imaging technique with a position uncertainty of about 21 nm and combining the high‐resolution electron beam lithography, the small colloidal quantum dot (CQD) lasers without any damages are accurately aligned with the silver nanowires. As a result, the integration of the CQD lasers and the silver nanowires can be flexibly configured on chips. In the experiment, the tangential coupling, radial coupling, and complex coupling between the high‐performance CQD lasers and the subwavelength silver nanowires are demonstrated. Because of the subwavelength field confinements of the silver nanowires, the deep‐subwavelength coherent sources (multimode, one‐color single‐mode, or two‐color single‐mode) with a mode area of only 0.008λ² are output from these hybrid structures. This configurable on‐chip integration with high flexibility and controllability will greatly facilitate the developments of the complex functional hybrid photonic–plasmonic circuits.     

Oxidized Quasi‐Carbon Nitride Quantum Dots Inhibit Ice Growth

Antifreeze proteins (AFPs), a type of high‐efficiency but expensive and often unstable biological antifreeze, have stimulated substantial interest in the search for synthetic mimics. However, only a few reported AFP mimics display thermal hysteresis, and general criteria for the design of AFP mimics remain unknown. Herein, oxidized quasi‐carbon nitride quantum dots (OQCNs) are synthesized through an up‐scalable bottom‐up approach. They exhibit thermal‐hysteresis activity, an ice‐crystal shaping effect, and activity on ice‐recrystallization inhibition. In the cryopreservation of sheep red blood cells, OQCNs improve cell recovery to more than twice that obtained by using a commercial cryoprotectant (hydroxyethyl starch) without the addition of any organic solvents. It is shown experimentally that OQCNs preferably bind onto the ice‐crystal surface, which leads to the inhibition of ice‐crystal growth due to the Kelvin effect. Further analysis reveals that the match of the distance between two neighboring tertiary N atoms on OQCNs with the repeated spacing of O atoms along the c‐axis on the primary prism plane of ice lattice is critical for OQCNs to bind preferentially on ice crystals. Here, the application of graphitic carbon nitride derivatives for cryopreservation is reported for the first time.     

Hybrid PbS Quantum‐Dot‐in‐Perovskite for High‐Efficiency Perovskite Solar Cell

In this study, a facile and effective approach to synthesize high‐quality perovskite‐quantum dots (QDs) hybrid film is demonstrated, which dramatically improves the photovoltaic performance of a perovskite solar cell (PSC). Adding PbS QDs into CH₃NH₃PbI₃ (MAPbI₃) precursor to form a QD‐in‐perovskite structure is found to be beneficial for the crystallization of perovskite, revealed by enlarged grain size, reduced fragmentized grains, enhanced characteristic peak intensity, and large percentage of (220) plane in X‐ray diffraction patterns. The hybrid film also shows higher carrier mobility, as evidenced by Hall Effect measurement. By taking all these advantages, the PSC based on MAPbI₃‐PbS hybrid film leads to an improvement in power conversion efficiency by 14% compared to that based on pure perovskite, primarily ascribed to higher current density and fill factor (FF). Ultimately, an efficiency reaching up to 18.6% and a FF of over ≈0.77 are achieved based on the PSC with hybrid film. Such a simple hybridizing technique opens up a promising method to improve the performance of PSCs, and has strong potential to be applied to prepare other hybrid composite materials.     

Electron Mobility of 24 cm2 V−1 s−1 in PbSe Colloidal‐Quantum‐Dot Superlattices

Colloidal quantum dots (CQDs) are nanoscale building blocks for bottom‐up fabrication of semiconducting solids with tailorable properties beyond the possibilities of bulk materials. Achieving ordered, macroscopic crystal‐like assemblies has been in the focus of researchers for years, since it would allow exploitation of the quantum‐confinement‐based electronic properties with tunable dimensionality. Lead‐chalcogenide CQDs show especially strong tendencies to self‐organize into 2D superlattices with micrometer‐scale order, making the array fabrication fairly simple. However, most studies concentrate on the fundamentals of the assembly process, and none have investigated the electronic properties and their dependence on the nanoscale structure induced by different ligands. Here, it is discussed how different chemical treatments on the initial superlattices affect the nanostructure, the optical, and the electronic‐transport properties. Transistors with average two‐terminal electron mobilities of 13 cm² V^?1 s^?1 and contactless mobility of 24 cm² V^?1 s^?1 are obtained for small‐area superlattice field‐effect transistors. Such mobility values are the highest reported for CQD devices wherein the quantum confinement is substantially present and are comparable to those reported for heavy sintering. The considerable mobility with the simultaneous preservation of the optical bandgap displays the vast potential of colloidal QD superlattices for optoelectronic applications.