Microcellular sensing media with ternary transparency states for fast and intuitive identification of unknown liquids.

Rapid, accurate, and intuitive detection of unknown liquids is greatly important for various fields such as food and drink safety, management of chemical hazards, manufacturing process monitoring, and so on. Here, we demonstrate a highly responsive and selective transparency-switching medium for on-site, visual identification of various liquids. The light scattering­based sensing medium, which is designed to be composed of polymeric interphase voids and hollow nanoparticles, provides an extremely large transmittance window (>95%) with outstanding selectivity and versatility. This sensing medium features ternary transparency states (transparent, semitransparent, and opaque) when immersed in liquids depending on liquid-polymer interactions and diffusion kinetics. Several different types of these transparency-changing media can be configured into an arrayed platform to discriminate a wide variety of liquids and also quantify their mixing ratios. The outstanding versatility and user friendliness of the sensing platform allow the development of a practical tool for discrimination of diverse organic liquids.

Metallic Woodpile Nanostructures for Femtomolar Sensing of Alzheimer's Neurofilament Lights.

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, accompanies a massive degradation of neurons including axonal injury. Being an axonal neuron-specific protein, neurofilament light (NfL) is a blood biomarker that reflects the neurodegeneration in AD, but no attempt has been made yet to develop sensing platforms that target NfLs in blood serum or plasma. Here, we report three-dimensional cross-stacked Pt nanowire arrays for the ultrasensitive photoelectrochemical (PEC) detection of NfLs. We constructed a woodpile-like Pt nanowire array (PtWP)-based biocathode by printing multilayer Pt nanowire arrays in an orthogonal configuration and conjugating them with NfL-specific DA2 antibodies. According to our collective electrochemical analyses, the five-layered PtWP electrode modified with DA2 antibodies exhibited high oxygen reduction activities due to the large electrochemical active surface area and the effective electron transfer properties. We have combined the DA2-PtWP biocathode with a water-oxidizing, iron oxyhydroxide-deposited bismuth vanadate (FeOOH/BiVO4) photoanode to assemble a bias-free PEC detection system. Powered by a white-light-emitting diode, the unbiased PEC platform accurately recognizes NfLs in blood plasma with the limit-of-detection of 38.2 fg/mL and limit-of-quantification of 853 fg/mL, which is 40 times lower than the NfL levels in AD patients' blood.

Thermodynamic-driven polychromatic quantum dot patterning for light-emitting diodes beyond eye-limiting resolution.

The next-generation wearable near-eye displays inevitably require extremely high pixel density due to significant decrease in the viewing distance. For such denser and smaller pixel arrays, the emissive material must exhibit wider colour gamut so that each of the vast pixels maintains the colour accuracy. Electroluminescent quantum dot light-emitting diodes are promising candidates for such application owing to their highly saturated colour gamuts and other excellent optoelectronic properties. However, previously reported quantum dot patterning technologies have limitations in demonstrating full-colour pixel arrays with sub-micron feature size, high fidelity, and high post-patterning device performance. Here, we show thermodynamic-driven immersion transfer-printing, which enables patterning and printing of quantum dot arrays in omni-resolution scale; quantum dot arrays from single-particle resolution to the entire film can be fabricated on diverse surfaces. Red-green-blue quantum dot arrays with unprecedented resolutions up to 368 pixels per degree is demonstrated.

Desolvation-Triggered Versatile Transfer-Printing of Pure BN Films with Thermal-Optical Dual Functionality.

Although hexagonal boron nitride (BN) nanostructures have recently received significant attention due to their unique physical and chemical properties, their applications have been limited by a lack of processability and poor film quality. In this study, a versatile method to transfer-print high-quality BN films composed of densely stacked BN nanosheets based on a desolvation-induced adhesion switching (DIAS) mechanism is developed. It is shown that edge functionalization of BN sheets and rational selection of membrane surface energy combined with systematic control of solvation and desolvation status enable extensive tunability of interfacial interactions at BN-BN, BN-membrane, and BN-substrate boundaries. Therefore, without incorporating any additives in the BN film and applying any surface treatment on target substrates, DIAS achieves a near 100% transfer yield of pure BN films on diverse substrates, including substrates containing significant surface irregularities. The printed BNs demonstrate high optical transparency (>90%) and excellent thermal conductivity (>167 W m-1 K-1) for few-micrometer-thick films due to their dense and well-ordered microstructures. In addition to outstanding heat dissipation capability, substantial optical enhancement effects are confirmed for light-emitting, photoluminescent, and photovoltaic devices, demonstrating their remarkable promise for next-generation optoelectronic device platforms.

Order-of-Magnitude, Broadband-Enhanced Light Emission from Quantum Dots Assembled in Multiscale Phase-Separated Block Copolymers.

Achieving high emission efficiency in solid-state quantum dots (QDs) is an essential requirement for high-performance QD optoelectronics. However, most QD films suffer from insufficient excitation and light extraction efficiencies, along with nonradiative energy transfer between closely adjacent QDs. Herein, we suggest a highly effective strategy to enhance the photoluminescence (PL) of QD composite films through an assembly of QDs and poly(styrene-b-4-vinylpyridine)) (PS-b-P4VP) block copolymer (BCP). A BCP matrix casted under controlled humidity provides multiscale phase-separation features based on (1) submicrometer-scale spinodal decomposition between polymer-rich and water-rich phases and (2) sub-10 nm-scale microphase separation between polymer blocks. The BCP-QD composite containing bicontinuous random pores achieves significant enhancement of both light absorption and extraction efficiencies via effective random light scattering. Moreover, the microphase-separated morphology substantially reduces the Förster resonance energy transfer efficiency from 53% (pure QD film) to 22% (BCP-QD composite), collectively achieving an unprecedented 21-fold enhanced PL over a broad spectral range.

Tuning Solute-Redistribution Dynamics for Scalable Fabrication of Colloidal Quantum-Dot Optoelectronics.

Solution-processed colloidal quantum dots (CQDs) are attractive materials for the realization of low-cost and efficient optoelectronic devices. Although impressive CQD-solar-cell performance has been achieved, the fabrication of CQD films is still limited to laboratory-scale small areas because of the complicated deposition of CQD inks. Large-area, uniform deposition of lead sulfide (PbS) CQD inks is successfully realized for photovoltaic device applications by engineering the solute redistribution of CQD droplets. It is shown experimentally and theoretically that the solute-redistribution dynamics of CQD droplets are highly dependent on the movement of the contact line and on the evaporation kinetics of the solvent. By lowering the friction constant of the contact line and increasing the evaporation rate of the droplets, a uniform deposition of CQD ink in length and width over large areas is realized. By utilizing a spray-coating process, large-area (up to 100 cm2 ) CQD films are fabricated with 3-7% thickness variation on various substrates including glass, indium tin oxide glass, and polyethylene terephthalate. Furthermore, scalable fabrication of CQD solar cells is demonstrated with 100 cm2 CQD films which exhibits a notably high efficiency of 8.10%.

Area-Selective Lift-Off Mechanism Based on Dual-Triggered Interfacial Adhesion Switching: Highly Facile Fabrication of Flexible Nanomesh Electrode.

With the recent emergence of flexible and wearable optoelectronic devices, the achievement of sufficient bendability and stretchability of transparent and conducting electrodes (TCEs) has become an important requirement. Although metal-mesh-based structures have been investigated for TCEs because of their excellent performances, the fabrication of mesh or grid structures with a submicron line width is still complex due to the requirements of laborious lithography and pattern transfer steps. Here, we introduce an extremely facile fabrication technique for metal patterns embedded in a flexible substrate based on submicron replication and an area-selective delamination (ASD) pattern. The high-yield, area-specific lift-off process is based on the principle of solvent-assisted delamination of deposited metal thin films and a mechanical triggering effect by soft wiping or ultrasonication. Our fabrication process is very simple, convenient, and cost-effective in that it does not require any lithography/etching steps or sophisticated facilities. Moreover, their outstanding optical and electrical properties (e.g., sheet resistances of 0.43 Ω sq-1 at 94% transmittance), which are markedly superior to those of other flexible TCEs, are demonstrated. Furthermore, there is no significant change of resistance over 1000 repeated bending cycles, with a bending radius of 5 mm, and immersion in various solvents such as salt water and organic solvents. Finally, we demonstrate high-performance transparent heaters and flexible touch panels fabricated using the nanomesh electrode, confirming the long-range electrical conduction and reliability of the electrode.

Highly Asymmetric n(+)-p Heterojunction Quantum-Dot Solar Cells with Significantly Improved Charge-Collection Efficiencies.

The depletion region width of metal-oxide/quantum-dot (QD) heterojunction solar cells is increased by a new method in which heavily boron-doped n(+)-ZnO is employed. It is effectively increased in the QD layer by 30% compared to the counterpart with conventional n-ZnO, and provides 41% and 37% improvement of J(sc) (16.7 mA cm(-2) to 23.5 mA cm(-2) ) and power conversion efficiency (5.52% to 7.55%), respectively.