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Quantitative detection of various molecules at very low concentrations in complex mixtures has been the main objective in many fields of science and engineering, from the detection of cancer-causing mutagens and early disease markers to environmental pollutants and bioterror agents 1 – 5 . Moreover, technologies that can detect these analytes without external labels or modifications are extremely valuable and often preferred 6 . In this regard, surface-enhanced Raman spectroscopy can detect molecular species in complex mixtures on the basis only of their intrinsic and unique vibrational signatures 7 . However, the development of surface-enhanced Raman spectroscopy for this purpose has been challenging so far because of uncontrollable signal heterogeneity and poor reproducibility at low analyte concentrations 8 . Here, as a proof of concept, we show that, using digital (nano)colloid-enhanced Raman spectroscopy, reproducible quantification of a broad range of target molecules at very low concentrations can be routinely achieved with single-molecule counting, limited only by the Poisson noise of the measurement process. As metallic colloidal nanoparticles that enhance these vibrational signatures, including hydroxylamine–reduced-silver colloids, can be fabricated at large scale under routine conditions, we anticipate that digital (nano)colloid-enhanced Raman spectroscopy will become the technology of choice for the reliable and ultrasensitive detection of various analytes, including those of great importance for human health. Research published in Nature shows that surface-enhanced Raman spectroscopy carried out with colloids can quantify a range of molecules down to concentrations at the femtomolar level.

Lipid nanoparticles (LNPs) are effective vehicles to deliver mRNA vaccines and therapeutics. It has been challenging to assess mRNA packaging characteristics in LNPs, including payload distribution and capacity, which are critical to understanding structure-property-function relationships for further carrier development. Here, we report a method based on the multi-laser cylindrical illumination confocal spectroscopy (CICS) technique to examine mRNA and lipid contents in LNP formulations at the single-nanoparticle level. By differentiating unencapsulated mRNAs, empty LNPs and mRNA-loaded LNPs via coincidence analysis of fluorescent tags on different LNP components, and quantitatively resolving single-mRNA fluorescence, we reveal that a commonly referenced benchmark formulation using DLin-MC3 as the ionizable lipid contains mostly 2 mRNAs per loaded LNP with a presence of 40%–80% empty LNPs depending on the assembly conditions. Systematic analysis of different formulations with control variables reveals a kinetically controlled assembly mechanism that governs the payload distribution and capacity in LNPs. These results form the foundation for a holistic understanding of the molecular assembly of mRNA LNPs. Lipid nanoparticles (LNPs) are effective vehicles to deliver mRNA vaccines and therapeutics but assessing the mRNA packaging characteristics in LNPs is challenging. Here, the authors report that mRNA and lipid contents in LNP formulations can be quantitatively examined by multi-laser cylindrical illumination confocal spectroscopy at the single-nanoparticle level.

Defect engineering is an effective strategy to improve the activity of two-dimensional molybdenum disulfide base planes toward electrocatalytic hydrogen evolution reaction. Here, we report a Frenkel-defected monolayer MoS 2 catalyst, in which a fraction of Mo atoms in MoS 2 spontaneously leave their places in the lattice, creating vacancies and becoming interstitials by lodging in nearby locations. Unique charge distributions are introduced in the MoS 2 surface planes, and those interstitial Mo atoms are more conducive to H adsorption, thus greatly promoting the HER activity of monolayer MoS 2 base planes. At the current density of 10 mA cm −2 , the optimal Frenkel-defected monolayer MoS 2 exhibits a lower overpotential (164 mV) than either pristine monolayer MoS 2 surface plane (358 mV) or Pt-single-atom doped MoS 2 (211 mV). This work provides insights into the structure-property relationship of point-defected MoS 2 and highlights the advantages of Frenkel defects in tuning the catalytic performance of MoS 2 materials. While material defect sites are active for chemical reactions, it is important to understand how different defect types impact reactivity. Here, authors prepare Frenkel-defected MoS 2 monolayers and demonstrate improved performances for H 2 evolution electrocatalysis than pristine or doped MoS 2 .

Room-temperature bismuth telluride (Bi 2 Te 3 ) thermoelectrics are promising candidates for low-grade heat harvesting. However, the brittleness and inflexibility of Bi 2 Te 3 are far reaching and bring about lifelong drawbacks. Here we demonstrate good pliability over 1,000 bending cycles and high power factors of 4.2 (p type) and 4.6 (n type) mW m −1  K −2 in Bi 2 Te 3 -based films that were exfoliated from corresponding single crystals. This unprecedented bendability was ascribed to the in situ observed staggered-layer structure that was spontaneously formed during the fabrication to promote stress propagation whilst maintaining good electrical conductivity. Unexpectedly, the donor-like staggered layer rarely affected the carrier transport of the films, thus maintaining its superior thermoelectric performance. Our flexible generator showed a high normalized power density of 321 W m −2 with a temperature difference of 60 K. These high performances in supple thermoelectric films not only offer useful paradigms for wearable electronics, but also provide key insights into structure–property manipulation in inorganic semiconductors. The development of flexible thermoelectrics is limited by the low power factor and brittleness of materials. Here the authors present strategy to turn Bi 2 Te 3 -based single crystals into flexible films with staggered-layer structure while maintaining superior thermoelectric performance.

Lithium metal anodes offer high theoretical capacities (3,860 milliampere-hours per gram) 1 , but rechargeable batteries built with such anodes suffer from dendrite growth and low Coulombic efficiency (the ratio of charge output to charge input), preventing their commercial adoption 2 , 3 . The formation of inactive (‘dead’) lithium— which consists of both (electro)chemically formed Li + compounds in the solid electrolyte interphase and electrically isolated unreacted metallic Li 0 (refs 4 , 5 )—causes capacity loss and safety hazards. Quantitatively distinguishing between Li + in components of the solid electrolyte interphase and unreacted metallic Li 0 has not been possible, owing to the lack of effective diagnostic tools. Optical microscopy 6 , in situ environmental transmission electron microscopy 7 , 8 , X-ray microtomography 9 and magnetic resonance imaging 10 provide a morphological perspective with little chemical information. Nuclear magnetic resonance 11 , X-ray photoelectron spectroscopy 12 and cryogenic transmission electron microscopy 13 , 14 can distinguish between Li + in the solid electrolyte interphase and metallic Li 0 , but their detection ranges are limited to surfaces or local regions. Here we establish the analytical method of titration gas chromatography to quantify the contribution of unreacted metallic Li 0 to the total amount of inactive lithium. We identify the unreacted metallic Li 0 , not the (electro)chemically formed Li + in the solid electrolyte interphase, as the dominant source of inactive lithium and capacity loss. By coupling the unreacted metallic Li 0 content to observations of its local microstructure and nanostructure by cryogenic electron microscopy (both scanning and transmission), we also establish the formation mechanism of inactive lithium in different types of electrolytes and determine the underlying cause of low Coulombic efficiency in plating and stripping (the charge and discharge processes, respectively, in a full cell) of lithium metal anodes. We propose strategies for making lithium plating and stripping more efficient so that lithium metal anodes can be used for next-generation high-energy batteries. Titration gas chromatography is developed as an analytical method of distinguishing between lithium metal and lithium compounds within a cycled battery and assessing the amount of unreacted metallic lithium available.

Anticounterfeiting labels based on physical unclonable functions (PUFs), as one of the powerful tools against counterfeiting, are easy to generate but difficult to duplicate due to inherent randomness. Gap-enhanced Raman tags (GERTs) with embedded Raman reporters show strong intensity enhancement and ultra-high photostability suitable for fast and repeated readout of PUF labels. Herein, we demonstrate a PUF label fabricated by drop-casting aqueous GERTs, high-speed read using a confocal Raman system, digitized through coarse-grained coding methods, and authenticated via pixel-by-pixel comparison. A three-dimensional encoding capacity of over 3 × 10 15051 can be achieved for the labels composed of ten types of GERTs with a mapping resolution of 2500 pixels and quaternary encoding of Raman intensity levels at each pixel. Authentication experiments have ensured the robustness and security of the PUF system, and the practical viability is demonstrated. Such PUF labels could provide a potential platform to realize unbreakable anticounterfeiting. Physical unclonable functions with inherent randomness are promising candidates for secure labeling systems. Here the authors demonstrate such a function using gap-enhanced Raman tags to create high-capacity and high-security labels for anticounterfeiting.

Light detection and ranging (LiDAR) technology, a laser-based imaging technique for accurate distance measurement, is considered one of the most crucial sensor technologies for autonomous vehicles, artificially intelligent robots and unmanned aerial vehicle reconnaissance. Until recently, LiDAR has relied on light sources and detectors mounted on multiple mechanically rotating optical transmitters and receivers to cover an entire scene. Such an architecture gives rise to limitations in terms of the imaging frame rate and resolution. In this Review, we examine how novel nanophotonic platforms could overcome the hardware restrictions of existing LiDAR technologies. After briefly introducing the basic principles of LiDAR, we present the device specifications required by the industrial sector. We then review a variety of LiDAR-relevant nanophotonic approaches such as integrated photonic circuits, optical phased antenna arrays and flat optical devices based on metasurfaces. The latter have already demonstrated exceptional functional beam manipulation properties, such as active beam deflection, point-cloud generation and device integration using scalable manufacturing methods, and are expected to disrupt modern optical technologies. In the outlook, we address the upcoming physics and engineering challenges that must be overcome from the viewpoint of incorporating nanophotonic technologies into commercially viable, fast, ultrathin and lightweight LiDAR systems.This Review highlights the technological challenges linked to the application of nanophotonics for light detection and ranging (LiDAR).

The use of oxide-supported isolated Pt-group metal atoms as catalytic active sites is of interest due to their unique reactivity and efficient metal utilization. However, relationships between the structure of these active sites, their dynamic response to environments and catalytic functionality have proved difficult to experimentally establish. Here, sinter-resistant catalysts where Pt was deposited uniformly as isolated atoms in well-defined locations on anatase TiO2 nanoparticle supports were used to develop such relationships. Through a combination of in situ atomic-resolution microscopy- and spectroscopy-based characterization supported by first-principles calculations it was demonstrated that isolated Pt species can adopt a range of local coordination environments and oxidation states, which evolve in response to varied environmental conditions. The variation in local coordination showed a strong influence on the chemical reactivity and could be exploited to control the catalytic performance.Oxide-supported isolated Pt-group metal atoms as catalytic active sites are of interest because of their unique reactivity. Isolated Pt species are now shown to adopt a range of local coordination environments and oxidation states in response to environmental conditions.

Integration of methanogens with semiconductors is an effective approach to sustainable solar-driven methanogenesis. However, the H 2 production rate by semiconductors largely exceeds that of methanogen metabolism, resulting in abundant H 2 as side product. Here, we report that binary metallic active sites (namely, NiCu alloys) are incorporated into the interface between CdS semiconductors and Methanosarcina barkeri . The self-assembled Methanosarcina barkeri -NiCu@CdS exhibits nearly 100% CH 4 selectivity with a quantum yield of 12.41 ± 0.16% under light illumination, which not only exceeds the reported biotic-abiotic hybrid systems but also is superior to most photocatalytic systems. Further investigation reveal that the Ni-Cu-Cu hollow sites in NiCu alloys can directly supply hydrogen atoms and electrons through photocatalysis to the Methanosarcina barkeri for methanogenesis via both extracellular and intracellular hydrogen cycles, effectively turning down the H 2 production. This work provides important insights into the biotic-abiotic hybrid interface, and offers an avenue for engineering the methanogenesis process. While the combination of synthetic and biological systems offers an appealing strategy for solar-to-fuel conversion, such hybrid systems typically suffer from low selectivity. Here, authors integrate a bimetallic alloy with a CdS-containing methanogen for selective CO 2 reduction to methane.

Fundamentally understanding the complex electrochemical reactions that are associated with energy devices (e.g., rechargeable batteries, fuel cells and electrolyzers) has attracted worldwide attention. In situ liquid cell transmission electron microscopy (TEM) offers opportunities to directly observe and analyze in-liquid specimens without the need for freezing or drying, which opens up a door for visualizing these complex electrochemical reactions at the nano scale in real time. The key to the success of this technique lies in the design and fabrication of electrochemical liquid cells with thin but strong imaging windows. This protocol describes the detailed procedures of our established technique for the fabrication of such electrochemical liquid cells (~110 h). In addition, the protocol for the in situ TEM observation of electrochemical reactions by using the nanofabricated electrochemical liquid cell is also presented (2 h). We also show and analyze experimental results relating to the electrochemical reactions captured. We believe that this protocol will shed light on strategies for fabricating high-quality TEM liquid cells for probing dynamic electrochemical reactions in high resolution, providing a powerful research tool. This protocol requires access to a clean room equipped with specialized nanofabrication setups as well as TEM characterization equipment. This protocol describes the procedure for the fabrication of electrochemical liquid cells for in situ liquid cell transmission electron microscopy. This allows direct visualization of complex electrochemical reactions at the nano scale in real time.