Creating 3D Nanoparticle Structural Space via Data Augmentation to Bidirectionally Predict Nanoparticle Mixture's Purity, Size, and Shape from Extinction Spectra.

Nanoparticle (NP) characterization is essential because diverse shapes, sizes, and morphologies inevitably occur in as-synthesized NP mixtures, profoundly impacting their properties and applications. Currently, the only technique to concurrently determine these structural parameters is electron microscopy, but it is time-intensive and tedious. Here, we create a three-dimensional (3D) NP structural space to concurrently determine the purity, size, and shape of 1000 sets of as-synthesized Ag nanocubes mixtures containing interfering nanospheres and nanowires from their extinction spectra, attaining low predictive errors at 2.

Achieving Molecular Recognition of Structural Analogues in Surface-Enhanced Raman Spectroscopy: Inducing Charge and Geometry Complementarity to Mimic Molecular Docking.

Molecular recognition of complex isomeric biomolecules remains challenging in surface-enhanced Raman scattering (SERS) spectroscopy due to their small Raman cross-sections and/or poor surface affinities. To date, the use of molecular probes has achieved excellent molecular sensitivities but still suffers from poor spectral specificity. Here, we induce "charge and geometry complementarity" between probe and analyte as a key strategy to achieve high spectral specificity for effective SERS molecular recognition of structural analogues.

Incorporating Chaotropic/Kosmotropic Chemistries onto Plasmonic Nanoheater to Boost Steam Generation Beyond its Photothermal Property.

Photothermal steam generation promises decentralized water purification, but current methods suffer from slow water evaporation even at high photothermal efficiency of ≈98%. This drawback arises from the high latent heat of vaporization that is required to overcome the strong and extensive hydrogen bonding network in water for steam generation. Here, light-to-vapor conversion is boosted by incorporating chaotropic/kosmotropic chemistries onto plasmonic nanoheater to manipulate water intermolecular network at the point-of-heating.

Incorporating plasmonic featurization with machine learning to achieve accurate and bidirectional prediction of nanoparticle size and size distribution.

Determination of nanoparticle size and size distribution is important because these key parameters dictate nanomaterials' properties and applications. Yet, it is only accomplishable using low-throughput electron microscopy. Herein, we incorporate plasmonic-domain-driven feature engineering with machine learning (ML) for accurate and bidirectional prediction of both parameters for complete characterization of nanoparticle ensembles.

Noninvasive and Point-of-Care Surface-Enhanced Raman Scattering (SERS)-Based Breathalyzer for Mass Screening of Coronavirus Disease 2019 (COVID-19) under 5 min.

Population-wide surveillance of COVID-19 requires tests to be quick and accurate to minimize community transmissions. The detection of breath volatile organic compounds presents a promising option for COVID-19 surveillance but is currently limited by bulky instrumentation and inflexible analysis protocol. Here, we design a hand-held surface-enhanced Raman scattering-based breathalyzer to identify COVID-19 infected individuals in under 5 min, achieving >95% sensitivity and specificity across 501 participants regardless of their displayed symptoms.

Surface-Enhanced Raman Scattering (SERS) Taster: A Machine-Learning-Driven Multireceptor Platform for Multiplex Profiling of Wine Flavors.

Integrating machine learning with surface-enhanced Raman scattering (SERS) accelerates the development of practical sensing devices. Such integration, in combination with direct detection or indirect analyte capturing strategies, is key to achieving high predictive accuracies even in complex matrices. However, in-depth understanding of spectral variations arising from specific chemical interactions is essential to prevent model overfit.

Enantiospecific Molecular Fingerprinting Using Potential-Modulated Surface-Enhanced Raman Scattering to Achieve Label-Free Chiral Differentiation.

Chiral differentiation is critical in diverse fields ranging from pharmaceutics to chiral synthesis. While surface-enhanced Raman scattering (SERS) offers molecule-specific vibrational information with high detection sensitivity, current strategies rely on indirect detection using additional selectors and cannot exploit SERS' key advantages for univocal and generic chiral differentiation. Here, we achieve direct, label-free SERS sensing of biologically important enantiomers by synergizing asymmetric nanoporous gold (NPG) nanoparticles with electrochemical-SERS to generate enantiospecific molecular fingerprints.

Modulating Orientational Order to Organize Polyhedral Nanoparticles into Plastic Crystals and Uniform Metacrystals.

In nanoparticle self-assembly, the current lack of strategy to modulate orientational order creates challenges in isolating large-area plastic crystals. Here, we achieve two orientationally distinct supercrystals using one nanoparticle shape, including plastic crystals and uniform metacrystals. Our approach integrates multi-faceted Archimedean polyhedra with molecular-level surface polymeric interactions to tune nanoparticle orientational order during self-assembly.

Applying a Nanoparticle@MOF Interface To Activate an Unconventional Regioselectivity of an Inert Reaction at Ambient Conditions.

Here we design an interface between a metal nanoparticle (NP) and a metal-organic framework (MOF) to activate an inert CO carboxylation reaction and in situ monitor its unconventional regioselectivity at the molecular level. Using a Kolbe-Schmitt reaction as model, our strategy exploits the NP@MOF interface to create a pseudo high-pressure CO microenvironment over the phenolic substrate to drive its direct C-H carboxylation at ambient conditions. Conversely, Kolbe-Schmitt reactions usually demand high reaction temperature (>125 °C) and pressure (>80 atm).

Multiplex Surface-Enhanced Raman Scattering Identification and Quantification of Urine Metabolites in Patient Samples within 30 min.

Successful translation of laboratory-based surface-enhanced Raman scattering (SERS) platforms to clinical applications requires multiplex and ultratrace detection of small biomarker molecules from a complex biofluid. However, these biomarker molecules generally exhibit low Raman scattering cross sections and do not possess specific affinity to plasmonic nanoparticle surfaces, significantly increasing the challenge of detecting them at low concentrations. Herein, we demonstrate a "confine-and-capture" approach for multiplex detection of two families of urine metabolites correlated with miscarriage risks, 5β-pregnane-3α,20α-diol-3α-glucuronide and tetrahydrocortisone.

Two-Photon-Assisted Polymerization and Reduction: Emerging Formulations and Applications.

Two-photon lithography (TPL) is an emerging approach to fabricate complex multifunctional micro/nanostructures. This is because TPL can easily develop various 2D and 3D structures on a variety of surfaces, and there has been a rapidly expanding pool of processable photoresists to create different materials. However, challenges in developing two-photon processable photoresists currently impede progress in TPL.

Three-Dimensional Surface-Enhanced Raman Scattering Platforms: Large-Scale Plasmonic Hotspots for New Applications in Sensing, Microreaction, and Data Storage.

Surface-enhanced Raman scattering (SERS) is a molecular-specific spectroscopic technique that provides up to 10-fold enhancement of signature Raman fingerprints using nanometer-scale 0D to 2D platforms. Over the past decades, 3D SERS platforms with additional plasmonic materials in the -axis have been fabricated at sub-micrometer to centimeter scale, achieving higher hotspot density in all , , and spatial directions and higher tolerance to laser misalignment. Moreover, the flexibility to construct platforms in arbitrary sizes and 3D shapes creates attractive applications besides traditional SERS sensing.

Designing surface-enhanced Raman scattering (SERS) platforms beyond hotspot engineering: emerging opportunities in analyte manipulations and hybrid materials.

Surface-enhanced Raman scattering (SERS) is a molecule-specific spectroscopic technique with diverse applications in (bio)chemistry, clinical diagnosis and toxin sensing. While hotspot engineering has expedited SERS development, it is still challenging to detect molecules with no specific affinity to plasmonic surfaces. With the aim of improving detection performances, we venture beyond hotspot engineering in this tutorial review and focus on emerging material design strategies to capture and confine analytes near SERS-active surfaces as well as various promising hybrid SERS platforms.

Shape-dependent thermo-plasmonic effect of nanoporous gold at the nanoscale for ultrasensitive heat-mediated remote actuation.

Nanoporous gold (NPG) promises efficient light-to-heat transformation, yet suffers limited photothermal conversion efficiency owing to the difficulty in controlling its morphology for the direct modulation of thermo-plasmonic properties. Herein, we showcase a series of shape-controlled NPG nanoparticles with distinct bowl- (NPG-B), tube- (NPG-T) and plate-like (NPG-P) structures for quantitative temperature regulation up to 140 °C in <1 s using laser irradiation. Notably, NPG-B exhibits the highest photothermal efficiency of 68%, which is >12 and 39 percentage points better than those of other NPG shapes (NPG-T, 56%; NPG-P, 49%) and Au nanoparticles (29%), respectively.

Creating two self-assembly micro-environments to achieve supercrystals with dual structures using polyhedral nanoparticles.

Organizing nanoparticles into supercrystals comprising multiple structures remains challenging. Here, we achieve one assembly with dual structures for Ag polyhedral building blocks, comprising truncated cubes, cuboctahedra, truncated octahedra, and octahedra. We create two micro-environments in a solvent evaporation-driven assembly system: one at the drying front and one at the air/water interface.

Favoring the unfavored: Selective electrochemical nitrogen fixation using a reticular chemistry approach.

Electrochemical nitrogen-to-ammonia fixation is emerging as a sustainable strategy to tackle the hydrogen- and energy-intensive operations by Haber-Bosch process for ammonia production. However, current electrochemical nitrogen reduction reaction (NRR) progress is impeded by overwhelming competition from the hydrogen evolution reaction (HER) across all traditional NRR catalysts and the requirement for elevated temperature/pressure. We achieve both excellent NRR selectivity (~90%) and a significant boost to Faradic efficiency by 10 percentage points even at ambient operations by coating a superhydrophobic metal-organic framework (MOF) layer over the NRR electrocatalyst.

Aluminum nanostructures with strong visible-range SERS activity for versatile micropatterning of molecular security labels.

The application of aluminum (Al)-based nanostructures for visible-range plasmonics, especially for surface-enhanced Raman scattering (SERS), currently suffers from inconsistent local electromagnetic field distributions and/or inhomogeneous distribution of probe molecules. Herein, we lithographically fabricate structurally uniform Al nanostructures which enable homogeneous adsorption of various probe molecules. Individual Al nanostructures exhibit strong local electromagnetic field enhancements, in turn leading to intense SERS activity.

Direct Metal Writing and Precise Positioning of Gold Nanoparticles within Microfluidic Channels for SERS Sensing of Gaseous Analytes.

We demonstrate a one-step precise direct metal writing of well-defined and densely packed gold nanoparticle (AuNP) patterns with tunable physical and optical properties. We achieve this by using two-photon lithography on a Au precursor comprising poly(vinylpyrrolidone) (PVP) and ethylene glycol (EG), where EG promotes higher reduction rates of Au(III) salt via polyol reduction. Hence, clusters of monodisperse AuNP are generated along raster scanning of the laser, forming high-particle-density, well-defined structures.

Quantitative prediction of the position and orientation for an octahedral nanoparticle at liquid/liquid interfaces.

Shape-controlled polyhedral particles and their assembled structures have important applications in plasmonics and biosensing, but the interfacial configurations that will critically determine their resultant assembled structures are not well-understood. Hence, a reliable theory is desirable to predict the position and orientation of a polyhedron at the vicinity of a liquid/liquid interface. Here we demonstrate that the free energy change theory can quantitatively predict the position and orientation of an isolated octahedral nanoparticle at a liquid/liquid interface, whose vertices and facets can play crucial roles in biosensing.

Driving CO to a Quasi-Condensed Phase at the Interface between a Nanoparticle Surface and a Metal-Organic Framework at 1 bar and 298 K.

We demonstrate a molecular-level observation of driving CO molecules into a quasi-condensed phase on the solid surface of metal nanoparticles (NP) under ambient conditions of 1 bar and 298 K. This is achieved via a CO accumulation in the interface between a metal-organic framework (MOF) and a metal NP surface formed by coating NPs with a MOF. Using real-time surface-enhanced Raman scattering spectroscopy, a >18-fold enhancement of surface coverage of CO is observed at the interface.

Dynamic Rotating Liquid Marble for Directional and Enhanced Mass Transportation in Three-Dimensional Microliter Droplets.

The ability of an artificial microdroplet to mimic the rotational behaviors of living systems is crucial for dynamic mass transportation but remains challenging to date. Herein, we report dynamic microdroplet rotation using a liquid marble (RLM) and achieve precise control over mass transportation and distribution in a three-dimensional (3D) microdroplet. RLM rotates synchronously with an external magnetic field, creating circular hydrodynamic flow and an outward centrifugal force.

Spinning Liquid Marble and Its Dual Applications as Microcentrifuge and Miniature Localized Viscometer.

Liquid marble offers an attractive droplet manipulation approach by isolating microdroplet in a nonstick encapsulating shell formed via the spontaneous coating of hydrophobic particles onto the liquid surface. While liquid marble prepared using magnetic nanoparticles enables precise spatiotemporal actuation of microdroplets, these manipulations are generally limited to simple and linear spatial maneuver of microdroplets. Herein, we demonstrate the unique and three-dimensional spinning of microliter-sized liquid marble (LM) and its subsequent dual applications as (1) the world's smallest centrifuge and (2) a miniature and localized viscometer.

Assembling substrate-less plasmonic metacrystals at the oil/water interface for multiplex ultratrace analyte detection.

Current substrate-less SERS platforms are limited to uncontrolled aggregation of plasmonic nanoparticles or quasi-crystalline arrays of spherical nanoparticles, with no study on how the lattice structures formed by nanoparticle self-assembly affect their detection capabilities. Here, we organize Ag octahedral building blocks into two large-area plasmonic metacrystals at the oil/water interface, and investigate their in situ SERS sensing capabilities. Amphiphilic octahedra assemble into a hexagonal close-packed metacrystal, while hydrophobic octahedra assemble into an open square metacrystal.

A Chemical Approach To Break the Planar Configuration of Ag Nanocubes into Tunable Two-Dimensional Metasurfaces.

Current plasmonic metasurfaces of nanocubes are limited to planar configurations, restricting the ability to create tailored local electromagnetic fields. Here, we report a new chemical strategy to achieve tunable metasurfaces with nonplanar nanocube orientations, creating novel lattice-dependent field localization patterns. We manipulate the interfacial behaviors of Ag nanocubes by controlling the ratio of hydrophilic/hydrophobic molecules added in a binary thiol mixture during the surface functionalization step.

Identifying Enclosed Chemical Reaction and Dynamics at the Molecular Level Using Shell-Isolated Miniaturized Plasmonic Liquid Marble.

Current microscale tracking of chemical kinetics is limited to destructive ex situ methods. Here we utilize Ag nanocube-based plasmonic liquid marble (PLM) microreactor for in situ molecular-level identification of reaction dynamics. We exploit the ultrasensitive surface-enhanced Raman scattering (SERS) capability imparted by the plasmonic shell to unravel the mechanism and kinetics of aryl-diazonium surface grafting reaction in situ, using just a 2-μL reaction droplet.