Inspired by aphids, liquid marbles have been studied extensively and have found application as isolated microreactors, as micropumps, and in sensing. However, current liquid‐marble‐based sensing ...methodologies are limited to qualitative colorimetry‐based detection. Herein we describe the fabrication of a plasmonic liquid marble as a substrate‐less analytical platform which, when coupled with ultrasensitive SERS, enables simultaneous multiplex quantification and the identification of ultratrace analytes across separate phases. Our plasmonic liquid marble demonstrates excellent mechanical stability and is suitable for the quantitative examination of ultratrace analytes, with detection limits as low as 0.3 fmol, which corresponds to an analytical enhancement factor of 5×108. The results of our simultaneous detection scheme based on plasmonic liquid marbles and an aqueous–solid–organic interface quantitatively tally with those found for the individual detection of methylene blue and coumarin.
Taking all the marbles: Plasmonic liquid marbles are used in conjunction with surface‐enhanced Raman spectroscopy for the simultaneous multiplex quantification and identification of ultratrace analytes across separate phases (see picture) with a detection limit as low as 0.3 fmol, which corresponds to an analytical enhancement factor of 5×108. The results quantitatively tally with those obtained for the individual detection of the analytes.
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. Our SERS-based breathalyzer harnesses key variations in vibrational fingerprints arising from interactions between breath metabolites and multiple molecular receptors to establish a robust partial least-squares discriminant analysis model for high throughput classifications. Crucially, spectral regions influencing classification show strong corroboration with reported potential COVID-19 breath biomarkers, both through experiment and in silico. Our strategy strives to spur the development of next-generation, noninvasive human breath diagnostic toolkits tailored for mass screening purposes.
Conspectus Surface-enhanced Raman scattering (SERS) is a molecular-specific spectroscopic technique that provides up to 1010-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 z-axis have been fabricated at sub-micrometer to centimeter scale, achieving higher hotspot density in all x, y, and z 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. In this Account, we introduce our library of substrate-based and substrate-less 3D plasmonic platforms, with an emphasis on their non-sensing applications as microlaboratories and data storage labels. We aim to provide a scientific synopsis on these high-potential yet currently overlooked applications of SERS and ignite new scientific discoveries and technology development in 3D SERS platforms to tackle real-world issues. One highlight of our substrate-based SERS platforms is multilayered platforms built from micrometer-thick assemblies of plasmonic particles, which can achieve up to 1011 enhancement factor. As an alternative, constructing 3D hotspots on non-plasmonic supports significantly reduces waste of plasmonic materials while allowing high flexibility in structural design. We then introduce our emerging substrate-less plasmonic capsules including liquid marbles and colloidosomes, which we further incorporate the latter within an aerosol to form centimeter-scale SERS-active plasmonic cloud, the world’s largest 3D SERS platform to date. We then discuss the various emerging applications arising only from these 3D platforms, in the fields of sensing, microreactions, and data storage. An important novel sensing application is the stand-off detection of airborne analytes that are several meters away, made feasible with aerosolized plasmonic clouds. We also describe plasmonic capsules as excellent miniature lab-in-droplets that can simultaneously provide in situ monitoring at the molecular level during reaction, owing to their ultrasensitive 3D plasmonic shells. We highlight the emergence of 3D SERS-based data storage platforms with 10–100-fold higher storage density than 2D platforms, featuring a new approach in the development of level 3 security (L3S) anti-counterfeiting labels. Ultimately, we recognize that 3D SERS research can only be developed further when its sensing capabilities are concurrently strengthened. With this vision, we foresee the creation of highly applicable 3D SERS platforms that excel in both sensing and non-sensing areas, providing modern solutions in the ongoing Fourth Industrial Revolution.
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. Experiments and simulations show that coiled surface polymer chains limit interparticle interactions, creating various geometrical configurations among Archimedean polyhedra to form plastic crystals. In contrast, brush‐like polymer chains enable molecular interdigitation between neighboring particles, favoring consistent particle configurations and result in uniform metacrystals. Our strategy enhances supercrystal diversity for polyhedra comprising multiple nondegenerate facets.
Gaining control over the orientational order of nanoparticles, and by extension the formation of plastic crystals over large areas, remains challenging. Molecular‐level polymeric surface interactions are now employed to modulate the orientational order of Archimedean nanoparticles. Two orientationally distinct supercrystals are formed using a single nanoparticle shape, including plastic crystals and uniform metacrystals.
Single-phase Cu2ZnSnS4 (CZTS) is an essential prerequisite toward a high-efficiency thin-film solar cell device. Herein, the selective phase formation of single-phase CZTS nanoparticles by ligand ...control is reported. Surface-enhanced Raman scattering (SERS) spectroscopy is demonstrated for the first time as a characterization tool for nanoparticles to differentiate the mixed compositional phase (e.g., CZTS, CTS, and ZnS), which cannot be distinguished by X-ray diffraction. Due to the superior selectivity and sensitivity of SERS, the growth mechanism of CZTS nanoparticle formation by hot injection is revealed to involve three growth steps. First, it starts with nucleation of Cu2–x S nanoparticles, followed by diffusion of Sn4+ into Cu2–x S nanoparticles to form the Cu3SnS4 (CTS) phase and diffusion of Zn2+ into CTS nanoparticles to form the CZTS phase. In addition, it is revealed that single-phase CZTS nanoparticles can be obtained via balancing the rate of CTS phase formation and diffusion of Zn2+ into the CTS phase. We demonstrate that this balance can be achieved by 1 mL of thiol with Cu(OAc)2, Sn(OAc)4, and Zn(acac)2 metal salts to synthesize the CZTS phase without the presence of a detectable binary/ternary phase with SERS.
NaYF(4):Yb,Er@SiO(2)@Ag core-shell nanocomposites were prepared to investigate metal-enhanced upconversion luminescence. Two sizes (15 and 30 nm) of Ag nanoparticles were used. The emission intensity ...of the upconversion nanocrystals was found to be strongly modulated by the presence of Ag nanoparticles (NPs) on the outer shell layer of the nanocomposites. The extent of modulation depended on the separation distance between Ag NPs and upconversion nanocrystals. The optimum upconversion luminescence enhancement was observed at a separation distance of 10 nm for Ag NPs with two different sizes (15 and 30 nm). A maximum upconversion luminescence enhancement of 14.4-fold was observed when 15 nm Ag nanoparticles were used and 10.8-fold was observed when 30 nm Ag NPs were used. The separation distance dependent emission intensity is ascribed to the competition between energy transfer and enhanced radiative decay rates. The biocompatibility of the nanocomposites was significantly improved by surface modification with DNA. The biological imaging capabilities of these nanocomposites were demonstrated using B16F0 cells.
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. Dynamic solvent flow concentrates the polyhedra at the drying front, generating hard particle behaviors and leading to morphology-dependent densest-packed bulk supercrystals. In addition, monolayers of nanoparticles adsorb at the air/liquid interface to minimize the air/liquid interfacial energy. Subsequent solvent evaporation gives rise to various structurally diverse dual-structure supercrystals. The topmost monolayers feature distinct open crystal structures with significantly lower packing densities than their densest-packed supercrystals. We further highlight a 3.3-fold synergistic enhancement of surface-enhanced Raman scattering efficiency arising from these dual-structure supercrystals as compared to a uniform one.
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. In this review, we critically discuss the importance of photoresist formulation in TPL. We begin by evaluating the commercial photoresists to design micro/nanostructures for promising applications in anti-counterfeiting, superomniphobicity, and micromachines with movable parts. Next, we discuss emerging hydrogel/organogel photoresists, focusing on customizing photoresist formulations to fabricate reconfigurable structures that can respond to changes in local pH, solvent, and temperature. We also review the development of metal salt-based photoresists for direct metal writing, whereby various formulations have been developed to enable applications in online sensing, catalysis, and electronics. Finally, we provide a critical outlook and highlight various outstanding challenges in formulating processable photoresists for TPL.
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 2.7–7.9 %. We first use plasmonically‐driven feature enrichment to extract localized surface plasmon resonance attributes from spectra and establish a lasso regressor (LR) model to predict purity, size, and shape. Leveraging the learned LR, we artificially generate 425,592 augmented extinction spectra to overcome data scarcity and create a comprehensive NP structural space to bidirectionally predict extinction spectra from structural parameters with <4 % error. Our interpretable NP structural space further elucidates the two higher‐order combined electric dipole, quadrupole, and magnetic dipole as the critical structural parameter predictors. By incorporating other NP shapes and mixtures′ extinction spectra, we anticipate our approach, especially the data augmentation, can create a fully generalizable NP structural space to drive on‐demand, autonomous synthesis‐characterization platforms.
Leveraging plasmonically‐driven feature enrichment and machine learning‐directed data augmentation to create a 3‐dimensional (3D) nanoparticle structural space for bidirectional predictions of silver nanocube's purity, size, and shape (corner radius) in as‐synthesized nanoparticle mixtures using extinction spectra and vice versa.
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