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Speedy, point-of-need detection and monitoring of small-molecule metabolites are vital across diverse applications ranging from biomedicine to agri-food and environmental surveillance. Nanomaterial-based sensor (nanosensor) platforms are rapidly emerging as excellent candidates for versatile and ultrasensitive detection owing to their highly configurable optical, electrical and electrochemical properties, fast readout, as well as portability and ease of use. To translate nanosensor technologies for real-world applications, key challenges to overcome include ultralow analyte concentration down to ppb or nM levels, complex sample matrices with numerous interfering species, difficulty in differentiating isomers and structural analogues, as well as complex, multidimensional datasets of high sample variability. In this Perspective, we focus on contemporary and emerging strategies to address the aforementioned challenges and enhance nanosensor detection performance in terms of sensitivity, selectivity and multiplexing capability. We outline 3 main concepts: (1) customization of designer nanosensor platform configurations via chemical- and physical-based modification strategies, (2) development of hybrid techniques including multimodal and hyphenated techniques, and (3) synergistic use of machine learning such as clustering, classification and regression algorithms for data exploration and predictions. These concepts can be further integrated as multifaceted strategies to further boost nanosensor performances. Finally, we present a critical outlook that explores future opportunities toward the design of next-generation nanosensor platforms for rapid, point-of-need detection of various smallmolecule metabolites. Agency for Science, Technology and Research (A*STAR) Nanyang Technological University National Medical Research Council (NMRC) Published version This research is supported by the Singapore National Medical Research Council COVID-19 Grant (MOH-000584) and A*STAR AME Individual Research Grant (A20E5c0082). S. X. L. and L. B. T. N. acknowledge Nanyang President's Graduate Scholarship support from Nanyang Technological University, Singapore.

Gas-phase surface-enhanced Raman scattering (SERS) remains challenging due to poor analyte affinity to SERS substrates. The reported use of capturing probes suffers from concurrent inconsistent signals and long response time due to the formation of multiple potential probe-analyte interaction orientations. Here, we demonstrate the use of multiple non-covalent interactions for ring complexation to boost the affinity of small gas molecules, SO2 and NO2 , to our SERS platform, achieving rapid capture and multiplex detection down to 100 ppm. Experimental and in-silico studies affirm stable ring complex formation, and kinetic investigations reveal a 4-fold faster response time compared to probes without stable ring complexation capability. By synergizing spectral concatenation and support vector machine regression, we achieve 91.7 % accuracy for multiplex quantification of SO2 and NO2 in excess CO2 , mimicking real-life exhausts. Our platform shows immense potential for on-site exhaust and air quality surveillance. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Submitted/Accepted version This research is supported by Singapore National Research Foundation Central Gap Fund (NRF2020NRF-CG001-010) and A*STAR AME Individual Research Grant (A20E5c0082).

Because of the versatility of plasmonic nanoparticles, there have been major improvements in tailoring the plasmonic effects for a plethora of applications. However, a major bottleneck of plasmonic...

Harnessing large hotspot volumes is key for enhanced gas-phase surface-enhanced Raman scattering (SERS) sensing. Herein, we introduce versatile, air-stable 3D 'Plasmonic bubbles' with bi-directional sensing capabilities. Our Plasmonic bubbles are robust, afford strong and homogenous SERS signals, and can swiftly detect both encapsulated and surrounding 4-methylbenzenethiol vapors. Published version

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. Using gold nanospheres as our model system, our ML approach achieves the lowest prediction errors of 2.3% and ±1.0 nm for ensemble size and size distribution respectively, which is 3-6 times lower than previously reported ML or Mie approaches. Knowledge elicitation from the plasmonic domain and concomitant translation into featurization allow us to mitigate noise and boost data interpretability. This enables us to overcome challenges arising from size anisotropy and small sample size limitations to achieve highly generalizable ML models. We further showcase inverse prediction capabilities, using size and size distribution as inputs to generate spectra with LSPRs that closely match experimental data. This work illustrates a ML-empowered total nanocharacterization strategy that is rapid (

Disease X is a hypothetical unknown disease that has the potential to cause an epidemic or pandemic outbreak in the future. Nanosensors are attractive portable devices that can swiftly screen disease biomarkers on site, reducing the reliance on laboratory-based analyses. However, conventional data analytics limit the progress of nanosensor research. In this Perspective, we highlight the integral role of machine learning (ML) algorithms in advancing nanosensing strategies toward Disease X detection. We first summarize recent progress in utilizing ML algorithms for the smart design and fabrication of custom nanosensor platforms as well as realizing rapid on-site prediction of infection statuses. Subsequently, we discuss promising prospects in further harnessing the potential of ML algorithms in other aspects of nanosensor development and biomarker detection. Nanyang Technological University Submitted/Accepted version S.X.L. and N.B.T.L. acknowledge Nanyang President’s Graduate Scholarship support from Nanyang Technological University, Singapore.

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. Agency for Science, Technology and Research (A*STAR) Nanyang Technological University National Medical Research Council (NMRC) Submitted/Accepted version This research is supported by National Medical Research Council, Singapore under COVID-19 Research Fund (MOH-COVID19RF-0007 and MOH-COVID19RF-0012), A*STAR Singapore, AME Individual Research Grant (A20E5c0082) and Max Planck Institute-Nanyang Technological University Joint Lab. S.X.L and L.B.T.N. acknowledge Nanyang Presidential scholarship support from Nanyang Technological University, Singapore.

Nanoplasmonic materials play a critical role in surface-enhanced Raman scattering (SERS) because they dictate the electromagnetic (EM) field confinement at the nanoscale and hence the SERS enhancements. These materials can be further engineered to maximize SERS sensitivity, even for analytes with no specific affinity to plasmonic surfaces. In this chapter, we discuss the various types and design strategies of nanoplasmonic materials and their platforms which are employed to boost SERS sensing performance. Four major approaches are outlined: (1) zero-dimensional to three-dimensional hotspot engineering for intense EM field confinement and interparticle plasmonic coupling, (2) physical confinement of liquid analytes on superhydrophobic SERS-active substrates, (3) concentration of gaseous analytes over hotspots using highly porous materials, and (4) development of unconventional nanoplasmonic materials including bimetallic configurations and hybrid systems. Finally, we finish this chapter by discussing current challenges in this research area.

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.

The electrochemical nitrogen reduction reaction (NRR) offers a sustainable solution towards ammonia production but suffers poor reaction performance owing to preferential catalyst–H formation and the consequential hydrogen evolution reaction (HER). Now, the Pt/Au electrocatalyst d-band structure is electronically modified using zeolitic imidazole framework (ZIF) to achieve a Faradaic efficiency (FE) of > 44% with high ammonia yield rate of > 161 mgmgcat @1 h @1 under ambient conditions. The strategy lowers electrocatalyst d-band position to weaken H adsorption and concurrently creates electron-deficient sites to kinetically drive NRR by promoting catalyst–N2 interaction. The ZIF coating on the electrocatalyst doubles as a hydrophobic layer to suppress HER, further improving FE by > 44-fold compared to without ZIF (ca. 1%). The Pt/Au-NZIF interaction is key to enable strong N2 adsorption over H atom. Ministry of Education (MOE) Nanyang Technological University This research is supported by the Ministry of Education, Singapore, under Tier 1 (RG11/18) and Tier 2 (MOE2016-T2- 1-043) grants, and Max Planck Institute-Nanyang Technological University Joint Lab. H.Y.F.S., C.S.L.K. and G.C.P.-Q. thank scholarship support from Nanyang Technological University, Singapore. J.R.T.C. and J.Y.P. thank CN Yang scholarship. H.K.L. thanks the International Postdoctoral Scholarship support from Nanyang Technological University, Singapore, and Singapore Ministry of Education. We thank Mr. Poh Chong Lim, A*STAR, for XRD analysis.

Probing changes of noncovalent interactions is crucial to study the binding efficiencies and strengths of (bio)molecular complexes. While surface-enhanced Raman scattering (SERS) offers unique molecular fingerprints to examine such interactions in situ, current platforms are only able to recognize hydrogen bonds because of their reliance on manual spectral identification. Here, we differentiate multiple intermolecular interactions between two interacting species by synergizing plasmonic liquid marble-based SERS platforms, chemometrics, and density functional theory. We demonstrate that characteristic 3-mercaptobenzoic acid (probe) Raman signals have distinct peak shifts upon hydrogen bonding and ionic interactions with tert-butylamine, a model interacting species. Notably, we further quantify the contributions from each noncovalent interaction coexisting in different proportions. As a proof-of-concept, we detect and categorize biologically important nucleotide bases based on molecule-specific interactions. This will potentially be useful to study how subtle changes in biomolecular interactions affect their structural and binding properties.

Here we design an interface between a metal nanoparticle (NP) and a metal-organic framework (MOF) to activate an inert CO₂ 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 CO₂ 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). Notably, we observe an unprecedented CO₂ meta-carboxylation of an arene that was previously deemed impossible in traditional Kolbe-Schmitt reactions. While the phenolic substrate in this study is fixed at the NP@MOF interface to facilitate spectroscopic investigations, free reactants could be activated the same way by the local pressurized CO₂ microenvironment. These valuable insights create enormous opportunities in diverse applications including synthetic chemistry, gas valorization, and greenhouse gas remediation. Ministry of Education (MOE) Nanyang Technological University X.Y.L. thanks the Singapore Ministry of Education for Tier 1 (RG11/18) and Tier 2 (MOE2016-T2-1-043) grants, and Max Planck Institute-Nanyang Technological University Joint Lab. C.-K.T. appreciates the funding support from Boston College and the NSF (CHE 1566445). H.K.L. thanks the Nanyang Technological University and the Ministry of Education, Singapore for the International Postdoctoral Scholarship. C.S.L.K. and G.C.P-Q. acknowledge scholarship support from Nanyang Technological University, Singapore.

Electrochemical nitrogen reduction reaction (NRR) offers sustainable ammonia production but suffers from poor performance owing to favorable water electrolysis. Recent designs achieve better efficiency by eradicating water but do not leverage on water as a readily available NRR proton source. Herein, we design a hydrophobic oleylamine-functionalized zeolitic-imidazolate framework coated over the electrocatalyst to achieve >18% NRR efficiency in the presence of water, an approximately fourfold boost compared to that without water. Our strategy kinetically regulates water availability at the electrocatalyst surface, suppresses direct water adsorption/electrolysis, and promotes preferential nitrogen adsorption to achieve water-assisted NRR. Conversely, control systems without hydrophobic modification experience a drastic decrease in efficiencies (

Stand-off Raman spectroscopy combines the advantages of both Raman spectroscopy and remote detection to retrieve molecular vibrational fingerprints of chemicals at inaccessible sites. However, it is currently restricted to the detection of pure solids and liquids and not widely applicable for dispersed molecules in air. Herein, we realize real-time stand-off SERS spectroscopy for remote and multiplex detection of atmospheric airborne species by integrating a long-range optic system with a 3D analyte-sorbing metal–organic framework (MOF)-integrated SERS platform. Formed via the self-assembly of Ag@MOF core–shell nanoparticles, our 3D plasmonic architecture exhibits micrometer thick SERS hotspot to allow active sorption and rapid detection of aerosols, gas, and volatile organic compounds down to parts-per-billion levels, notably at a distance up to 10 m apart. The platform is highly sensitive to changes in atmospheric content, as demonstrated in the temporal monitoring of gaseous CO2 in several cycles. Importantly, we demonstrate the remote and multiplex quantification of polycyclic aromatic hydrocarbon mixtures in real time under outdoor daylight. By overcoming core challenges in current remote Raman spectroscopy, our strategy creates an opportunity in the long-distance and sensitive monitoring of air/gaseous environment at the molecular level, which is especially important in environmental conservation, disaster prevention, and homeland defense. Ministry of Education (MOE) Nanyang Technological University Accepted version X.Y.L. thanks the Singapore Ministry of Education Tier 1 (RG11/18) and Tier 2 (MOE2016-T2-1-043) grants. G.C.P.-Q. and C.S.L.K. are thankful for Nanyang President’s Graduate Scholarships. N.Y. is thankful for the CN Yang scholarship. T.L. acknowledges the funding support from the National Natural Science Foundation of China (51433001).

Unraveling the role of transition-metal doping in affecting the native spinel-structured nanosheets' water splitting remains a grand challenge. In this work, a series of spinel-structured nanosheets wrapped hollow nitrogen-doped carbon polyhedrons were constructed, and doped transition-metal domains were deliberately introduced on the surface. Theoretical investigations show that their energy level can be finely tuned via direct transition-metal doping engineering. As a prototype, an Fe-doped NiCo₂O₄ nanosheets wrapped hollow nitrogen-doped carbon polyhedron (Fe–NiCo₂O₄@HNCP) exhibits outstanding bifunctional electrocatalytic performances with low overpotentials (η = 270 mV for OER, η = 84 mV for HER), low Tafel slopes (b = 42 mV dec⁻¹ for OER, b = 47 mV dec⁻¹ for HER), and high durability. The enhanced performance is attributed to the synergistic effects of energy level matching for electron transfer, and partial charge delocalization-induced rich active sites for reactant adsorption via thermodynamic and kinetic acceleration. This work may open a new pathway to design highly active and stable transition-metal doped electrocatalysts by manipulated energy levels for efficient overall water splitting. We are really grateful for the financial support from the National Natural Science Foundation of China (51433001, 21674019, 21604010), the Science and Technology Commission of Shanghai Municipality (16520722100), the Program of Shanghai Academic Research Leader (17XD1400100), the “Chenguang Program” supported by the Shanghai Education Development Foundation and Shanghai Municipal Education Commission (16CG39) and the Engineering and Physical Sciences Research Council (EPSRC, EP/L015862/1). The computational center of USTC is acknowledged for computational support.

Searching for an efficient and cost effective electrochemical catalyst is regarded as the key challenge for the hydrogen evolution reaction (HER). Both the active sites and electrical conductivity of the catalysts should be carefully engineered to improve their HER performance. In this work, S-doped MoSe2-decorated graphene/graphene nanoribbon aerogel (S-MoSe2@GGNR) hybrids have been fabricated as high-performance electrocatalysts for HER. The unique nanoribbon-interconnected-nanosheet structure of the graphene/graphene nanoribbon aerogel (GGNR) provides an open structure for fast ion diffusion and conductive channels for fast electron transport. GGNR as a substrate could prevent MoSe2 nanosheets from agglomeration and fully expose the active sites of MoSe2, while further S-doping can modify its electronic and crystalline structure, which can improve the activity of the catalytic sites. Consequently, the S-MoSe2@GGNR hybrids exhibit outstanding electrochemical activity with a potential of −153 mV vs. reversible hydrogen electrode to achieve a current density of 10.0 mA cm−2 and a small Tafel slope of 46 mV per decade. The good performance of the S-MoSe2@GGNR hybrids can be credited to synergistic effects between the unique hierarchical architecture of carbon aerogels and positive effect of S-doping, which makes them promising electrocatalysts for hydrogen production. The authors are grateful for the financial support from the National Natural Science Foundation of China (21704014, 51433001, and 21674019), Science and Technology Commission of Shanghai Municipality (16520722100), the Fundamental Research Funds for the Central Universities (2232017D-06), Shanghai Municipal Education Commission (17CG33), Shanghai Sailing Program (17YF1400200), and Program of Shanghai Academic Research Leader (17XD1400100).

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. We outline five major approaches to enhance SERS performance: (1) enlarging Raman scattering cross-sections of non-resonant molecules via chemical coupling reactions; (2) targeted chemical capturing of analytes through surface-grafted agents to localize them on plasmonic surfaces; (3) physically confining liquid analytes on non-wetting SERS-active surfaces and (4) confining gaseous analytes using porous materials over SERS hotspots; (5) synergizing conventional metal-based SERS platforms with functional materials such as graphene, semiconducting materials, and piezoelectric polymers. These approaches can be integrated with engineered hotspots as a multifaceted strategy to further boost SERS sensitivities that are unachievable using hotspot engineering alone. Finally, we highlight current challenges in this research area and suggest new research directions towards efficient SERS designs critical for real-world applications. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University Accepted version X. Y. L. thanks the financial support from Singapore Ministry of Education, Tier 1 (RG21/16) and Tier 2 (MOE2016-T2-1-043) grants. C. L. L. acknowledges the A*STAR Graduate Scholarship from A*STAR, Singapore. C. S. L. K. and G. C. P.-Q. acknowledge support from Nanyang Presidential Graduate Scholarship from Nanyang Technological University. Q. A. thanks the funding support from NSFC (21303169, 21673209, 51572246), the Fundamental Research Funds for the Central Universities (2652015295), and Beijing Nova Program (Z141103001814064).

Gas‐liquid reactions form the basis of our everyday lives, yet they still suffer poor reaction efficiency and are difficult to monitor in situ, especially at ambient conditions. Herein, we drive an inert gas‐liquid reaction between aniline and CO2 at 1 atm and 298 K by selectively concentrating these immiscible reactants at the interface between metal‐organic framework and solid nanoparticles (solid@MOF). Real‐time reaction SERS monitoring and simulation investigations affirm the formation of phenylcarbamic acid, which was previously undetectable because they are unstable for post‐reaction treatments. The solid@MOF ensemble gives rise to a >28‐fold improvement to reaction efficiency as compared to ZIF‐only and solid‐only platforms, emphasizing that the interfacial nanocavities in solid@MOF are the key to enhance gas‐liquid reaction. Our strategy can be integrated with other functional materials, hence opens up new opportunities for ambient‐operated gas‐liquid applications. MOE (Min. of Education, S’pore) Accepted version

Ramon A. Alvarez-Puebla, Jian-Feng Li and Xing Yi Ling introduce the Nanoscale themed collection on advances in plasmonics and its applications.

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. Herein, we design a machine-learning-driven "SERS taster" to simultaneously harness useful vibrational information from multiple receptors for enhanced multiplex profiling of five wine flavor molecules at parts-per-million levels. Our receptors employ numerous noncovalent interactions to capture chemical functionalities within flavor molecules. By strategically combining all receptor-flavor SERS spectra, we construct comprehensive "SERS superprofiles" for predictive analytics using chemometrics. We elucidate crucial molecular-level interactions in flavor identification and further demonstrate the differentiation of primary, secondary, and tertiary alcohol functionalities. Our SERS taster also achieves perfect accuracies in multiplex flavor quantification in an artificial wine matrix. Agency for Science, Technology and Research (A*STAR) Ministry of Health (MOH) This research is supported by the A*STAR AME Individual Research Grant (A20E5c0082), NMRC Grant (MOH-000503), and Max Planck Institute-Nanyang Technological University Joint Lab.

Photothermal materials are crucial for diverse heating applications, but it remains challenging to achieve high energy conversion efficiency due to the difficulty to concurrently improve light absorbance and suppress heat loss. Herein, a zeolitic imidazolate framework-isolated graphene (G@ZIF) nanohybrid is demonstrated that utilizes ultrathin, heat-insulating ZIF layers, and G@ZIF interfacial nanocavity to synergistically intensify light absorbance and heat localization. Under artificial sunlight illumination (≈1 kW m−2), the G@ZIF film attains a maximum temperature of 120 °C in an open environment with a 98% solar-to-thermal conversion efficiency. Importantly, the porous ZIF layer allows small molecules/media to enter and access the embedded hot graphene surface for targeted heat transfer in practical applications. As a proof-of-concept, the G@ZIF-based steam generator realizes 96% energy conversion from light to vapor with near-perfect desalination and water purification efficiencies (>99.9%). This design is generic and can be extended to other photothermal systems for advanced solar-thermal applications, including catalysis, water treatments, sterilization, and mechanical actuation. Ministry of Education (MOE) This research was supported by the Ministry of Education, Singapore, under Tier 1 (RG11/18 and RG97/19) and Tier 2 (MOE2016-T2-1-043) grants.

Gas reactions are prevalent in the industry and in our everyday lives. However, these processes are typically slow and difficult to monitor owing to the low molecular concentration of gas. While gas reactions and detections can be achieved at high temperatures and pressures, these operations are unsustainable because they demand a huge amount of energy input. Here, we achieve efficient gas-based reactions and sensing at ambient conditions by concentrating gas molecules at the interface formed between a functional solid and a metal-organic framework (MOF). Our strategy utilizes the excellent gas sorptivity of MOF to continuously accumulate gas molecules onto functional solid surfaces with plasmonic and/or catalytic properties. Using surface-enhanced Raman spectroscopy (SERS), we are able to directly observe the concentration of gas molecules into a quasi-condensed phase at the nanoscale solid@MOF interface, even at ambient operations.[1] We further leverage on this unique molecular phenomenon to activate a CO2 carboxylation of an arene that is otherwise inert at 1 atm and 298 K.[2] Our solid@MOF design thus offers enormous opportunities in relevant fields including chemistry, heterogeneous catalysis, greenhouse gases removal and gas-to-fuel conversions. Published version

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. To enhance SERS signals by 1012-fold, we use specific nanoscale surface chemistry for targeted metabolite capture from a complex urine matrix prior to confining them on a superhydrophobic SERS platform. We then apply chemometrics, including principal component analysis and partial least-squares regression, to convert molecular fingerprint information into quantifiable readouts. The whole screening procedure requires only 30 min, including urine pretreatment, sample drying on the SERS platform, SERS measurements, and chemometric analyses. These readouts correlate well with the pregnancy outcomes in a case-control study of 40 patients presenting threatened miscarriage symptoms. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Ministry of Health (MOH) Nanyang Technological University Accepted version X.Y.L. thanks the financial support from Singapore Ministry of Education, Tier 1 (RG11/18) and Tier 2 (MOE2016-T2-1-043) grants, and Max Planck Institute-Nanyang Technological University Joint Lab. C.W.K., T.C.T., and N.S.T. are thankful for the financial support from the Ministry of Health Singapore Industry Alignment Fund grant (MOHIAFCat1-11010). Y.C.K. and C.L.L. are thankful for scholarship support from A*STAR, Singapore. G.C.P.-Q. acknowledges scholarship support from Nanyang Technological University, Singapore. We wish to thank all the families who participated in our research.

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 remains challenging to detect small molecules with low Raman cross-section and/or no specific affinity to plasmonic surfaces. In this talk, I will discuss my group’s effort in improving SERS detection performances with focus on designing SERS platforms that can capture and confine analytes near SERS-active surfaces. Published version

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. Ministry of Education (MOE) Nanyang Technological University Accepted version X.Y.L. thanks Singapore Ministry of Education, Tier 1 (RG11/18) and Tier 2 (MOE2016-T2-1-043) grants, and Max PlanckInstitute−Nanyang Technological University Joint Lab for the financial support. C S.L.K., G.C.P.-Q., and S.X.L. thank the Nanyang President’s Graduate Scholarships.

There is a huge interest in developing superrepellent surfaces for antifouling and heat-transfer applications. To characterize the wetting properties of such surfaces, the most common approach is to place a millimetric-sized droplet and measure its contact angles. The adhesion and friction forces can then be inferred indirectly using Furmidge’s relation. While easy to implement, contact angle measurements are semiquantitative and cannot resolve wetting variations on a surface. Here, we attach a micrometric-sized droplet to an atomic force microscope cantilever to directly measure adhesion and friction forces with nanonewton force resolutions. We spatially map the micrometer-scale wetting properties of superhydrophobic surfaces and observe the time-resolved pinning–depinning dynamics as the droplet detaches from or moves across the surface.

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., Crystals with multiple structures often perform special functions in nature, inspiring the creation of synthetic analogues. Here, the authors subject polyhedral nanoparticles to two self-assembly micro-environments to realize supercrystals with dual structures, in which the order of the surface layer differs from the bulk structure.

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. The average SERS enhancement factor (EF) for individual nanostructures exceeds 104 for non-resonant probe molecules in the visible spectrum. These Al nanostructures also retain more than 70% of their original SERS intensities after one-month storage, displaying superb stability under ambient conditions. We further achieve tunable polarization-dependent SERS responses using anisotropic Al nanostructures, facilitating the design of sophisticated SERS-based security labels. Our micron-sized security label comprises two-tier security features, including a machine-readable hybrid quick-response (QR) code overlaid with a set of ciphertexts. Our work demonstrates the versatility of Al-based structures in low-cost modern chemical nano-analytics and forgery protection. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

Nanoporous gold (NPG) promises efficient light-to-heat transformation, yet suffers limited photothermal conversion efficiency owing to the difficulty in controlling their morphology for 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 oC in < 1 s using laser irradiation. Notably, NPG-B exhibits a highest photothermal efficiency of 68% which is >12 and 39 percentage points better than other NPG shapes (NPG-T, 56%; NPG-P, 49%) and Au nanoparticles (29%), respectively. We attribute NPG-B’s superior photothermal performance to its >13% enhanced light absorption cross section compared to other Au nanostructures. We further realize an ultrasensitive heat-mediated light-to-mechanical “kill switch” by integrating NPG-B with a heat-responsive shape-memory polymer (SMP/NPG-B). This SMP/NPG-B hybrid is analogous to a photo-triggered mechanical arm, and can be activated swiftly in

The local density of optical states governs an emitters lifetime and quantum yield through the Purcell effect. It can be modified by a surface plasmon electromagnetic field, but such a field has a spatial extension limited to a few hundreds of nanometers, which complicates the use of optical methods to spatially probe the emitter-plasmon coupling. Here we show that a combination of electron-based imaging, spectroscopies and photon-based correlation spectroscopy enables measurement of the Purcell effect with nanometer and nanosecond spatio-temporal resolutions. Due to the large variability of radiative lifetimes of emitters embedded in nanoparticles with inhomogeneous sizes we relied on a statistical approach to unambiguously probe the coupling between nitrogen-vacancy centers (NV^0) in nanodiamonds and surface plasmons in silver nanocubes. We quantified the Purcell effect by measuring the NV^0 excited state lifetimes in a large number of either isolated nanodiamonds or nanodiamond-nanocube dimers and demonstrated a statistically significant lifetime reduction for dimers.

To control the process of cation exchange (CE) in a multielemental system, a detailed understanding of structural changes at the microscopic level is imperative. However, the synthesis of a multielemental system has so far relied on the CE phenomenon of a binary system, which does not necessarily extend to the higher-order systems. Here, direct experimental evidence supported by theoretical calculations reveals a growth model of binary Cu–S to ternary Cu–Sn–S to quaternary Cu–Zn–Sn–S, which shows that cations preferentially diffuse along a specific lattice plane with the preservation of sulfuric anionic framework. In addition, we also discover that, unlike the commonly accepted structure (P63mc), the metastable crystal structure of Cu–Zn–Sn–S phase possesses fixed Sn occupancy sites. By revealing the preferential nature of cations diffusion and growth mechanism, our work provides insight into controlling the stoichiometry and phase purity of novel multielemental materials. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version We acknowledge financial support from National Research Foundation (NRF), Singapore, through the Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE) and Nanomaterials for Energy and Water Management (SHARE NEW) CREATE program. L.H.W. thanks the funding support from Singapore Ministry of Education, Tier 2 (2016-T2-1-030). S.L. acknowledges the funding support from Singapore Ministry of Education Tier 1 (107/15). H.Z. thanks the funding support from U.S. DOE BES Materials Sciences and Engineering Division Under Contract No. KC22ZH. X.Y.L. thanks the funding support from Singapore Ministry of Education, Tier 1 (RG21/16) and Tier 2 (MOE2016-T2-1- 043) grants.. The work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. We thank Fiona Doyle for lending us her synthetic laboratory in University of California Berkeley (UCB), Song Chengyu and Karen Bustilo for their help and assistance on TEM, and Matthew P. Sherburne for nanoparticle growth discussion.

Particle-assembled fluid-fluid interfaces give rise to soft substrate-less platforms with wide-ranging applications, including remote and on-demand manipulation, optical modulation, catalysis, and multiphase and multiplex sensing, as well as in situ reaction kinetics elucidation. Notably, these soft platforms are easy to fabricate and can exhibit long-range order, both of which are challenging to achieve using traditional solid-based substrates. In this perspective, we provide an overview of the latest research in the fabrication and applications of these soft platforms. We begin with a brief discussion on the formation mechanism of two- and three-dimensional substrate-less platforms, followed by highlighting the unique properties of these platforms. We also discuss the application of these particle-assembled interfaces to three specific research areas, including dynamic tuning of optical properties, multiplex molecular sensing, and small-volume reaction modulation and kinetics monitoring. We end our perspective with an outlook on the promising research frontiers that can be achieved using these soft substrate-less platforms. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Accepted version X.Y.L. is grateful for the financial support from National Research Foundation, Singapore (NRF-NRFF2012-04), Singapore Ministry of Education, Tier 1 (RG21/16) and Tier 2 (MOE2016-T2-1-043) grants. H.K.L. appreciates the A*STAR Graduate Scholarship support from A*STAR, Singapore. G.C.P.-Q. and C.S.L.K acknowledge support from Nanyang Presidential Graduate Scholarship from Nanyang Technological University.

Liquid marbles are emergent microreactors owing to their isolated environment and the flexibility of materials used. Plasmonic liquid marbles (PLMs) are demonstrated as the smallest spectroelectrochemical microliter‐scale reactor for concurrent spectro‐ and electrochemical analyses. The three‐dimensional Ag shell of PLMs are exploited as a bifunctional surface‐enhanced Raman scattering (SERS) platform and working electrode for redox process modulation. The combination of SERS and electrochemistry (EC) capabilities enables in situ molecular read‐out of transient electrochemical species, and elucidate the potential‐dependent and multi‐step reaction dynamics. The 3D configuration of our PLM‐based EC‐SERS system exhibits 2‐fold and 10‐fold superior electrochemical and SERS performance than conventional 2D platforms. The rich molecular‐level electrochemical insights and excellent EC‐SERS capabilities offered by our 3D spectroelectrochemical system are pertinent in charge transfer processes. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Accepted version X.Y.L. thanks the financial support from National Research Foundation, Singapore (NRF-NRFF2012-04), Singapore Ministry of Education, Tier 1(RG21/16) and Tier (MOE2016-T2-1-043 (S)) grants, and Nanyang Technological University.C.S.L.K.,G.C.P.-Q., and M.R.L. acknowledge support from Nanyang Presidential Graduate Scholarship. H.K.L. thanks the graduate scholarship from A*STAR, Singapore

3D plasmonic colloidosomes are superior SERS sensors owing to their high sensitivity and excellent tolerance to laser misalignment. Herein, we incorporate plasmonic colloidosomes in a microfluidic channel for online SERS detection. Our method resolves the poor signal reproducibility and inter-sample contamination in the existing online SERS platforms. Our flow system offers rapid and continuous online detection of 20 samples in less than 5 min with excellent signal reproducibility. The isolated colloidosomes prevent cross-sample and channel contamination, allowing accurate quantification of samples over a concentration range of five orders of magnitude. Our system demonstrates high-resolution multiplex detection with fully preserved signal and Raman features of individual analytes in a mixture. High-throughput multi-assay analysis is performed, which highlights that our system is capable of rapid identification and quantification of a sequence of samples containing various analytes and concentrations.

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. We focus on two limiting orientations of an octahedral nanoparticle, vertex up and facet up. Our proposed theory indicates that the surface wettability (hydrophilic/hydrophobic ratio) of the nanoparticle determines its most stable position and the preferred orientation at a water/oil interface. The surface wettability of an octahedron is adjusted from extremely hydrophobic to extremely hydrophilic by changing the amount of charge on the Ag surface in molecular dynamics (MD) simulations. The MD simulations results are in excellent agreement with our theoretical prediction for an Ag octahedral nanoparticle at a hexane/water interface. Our proposed theory bridges the gap between molecular-level simulations and equilibrium configurations of polyhedral nanoparticles in experiments, where insights from nanoparticle intrinsic wettability details can be used to predict macroscopic superlattice formation experimentally. This work advances our ability to precisely predict the final structures of the polyhedral nanoparticle assemblies at a liquid/liquid interface. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article., Funding is acknowledged from the European Research Council (ERC Advanced Grant No. 787510-4DBIOSERS to L.M.L.-M., ERC Advanced Grant No. 789104-eNANO to F.J.G.A., ERC Starting Grant No. 259432-MULTIBIOPHOT to J.K., ERC Consolidator Grant No. 772108-DarkSERS); the Department of Education of the Basque Government (Grant No. IT1164-19 to J.A.); the Spanish MINECO (CTQ2017-88648-R to R.A.-P., MAT2016-77809-R to I.P.-S. and J.P.-J.); the EPSRC (EP/P034063/1 to S.B., EP/L027151/1 to J.B., EP/L014165/1 to D.G. and K.F.); IDUN-Danish National Research Foundation (DNRF122) and Villum Fonden (Grant No. 9301) to A.B.; the National Research Foundation of Korea (Grant No. 2019R1A2C3004375 to J.B.); the German Science Foundation, DFG (SFB 1278 Polytarget (Project B4) to V.D., Grant No. SCHL 594/13-1 to S.S., Germany’s Excellence Strategy (EXC 2089/1-390776260) to S.M.); the Federal Ministry of Education and Research, Germany (BMBF) (Grant InfectoGnostics 13GW0096F to D.C.-M. and J.P.); DARPA-16-35-INTERCEPT-FP-018 to L.F.; the UK BBSRC (Grant No. BB/L014823/1 to R.G.); the Department of Science and Technology (DST Nanomission Project SR/NM/NS-23/2016 to K.G.T.); the U.S. National Science Foundation (Grant No. CHE-1707859 to A.J.H., Center for Sustainable Nanotechnology CHE-1503408 (Centers for Chemical Innovation Program) to C.L.H., Center for Chemical Innovation Chemistry at the Space-Time Limit (CaSTL) CHE-1414466 to G.C.S. and R.P.V.D., Grant No. CHE-1807269 to K.A.W.); the Knut and Alice Wallenberg Foundation to M.K.; the Office of Naval Research (Grant No. N00014-18-1-2876 to N.A.K.); Royal Society of New Zealand Te Apa̅rangi to E.L.R. and B.A.; Singapore Ministry of Education, Tier 1 (RG11/18) to X.Y.L.; the Photoexcitonix Project in Hokkaido Univ., Japan, to K.M.; BioNano Health-Guard Research Center funded by the Ministry of Science and ICT (MSIT) of Korea as Global Frontier Project (Grant No. H-GUARD_2013M3A6B2078947) to J.-M.N.; NSFC of P. R. China (Grant No. 21705015 to Y.O., Grant No. 21633005 to B.R.); National Key R&D Program (2017YFA0206902) to C.X. This work was coordinated under the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency—Grant No. MDM-2017-0720.

Hybrid materials of earth abundant transition metal dichalcogenides and noble metal nanoparticles, such as molybdenum sulfide (MoSx) and gold nanoparticles, exhibit synergistic effects that can enhance electrocatalytic reactions. However, most current hybrid MoSx-gold synthesis requires an energy intensive heat source of >500 °C or chemical plating to achieve deposition of MoSx on the gold surface. Herein, we demonstrate the direct overgrowth of MoSx over colloidal nanoporous gold (NPG), conducted feasibly under ambient conditions, to form hybrid particles with enhanced electrocatalytic performance toward hydrogen evolution reaction. Our strategy exploits the localized surface plasmon resonance-mediated photothermal heating of NPG to achieve >230 °C surface temperature, which induces the decomposition of the (NH4)2MoS4 precursor and direct overgrowth of MoSx over NPG. By tuning the concentration ratio between the precursor and NPG, the amount of MoSx particles deposited can be systematically controlled from 0.5% to 2% of the Mo/(Au + Mo) ratio. Importantly, we find that the hybrid particles exhibit higher bridging and an apical S to terminal S atomic ratio than pure molybdenum sulfide, which gives rise to their enhanced electrocatalytic performance for hydrogen evolution reaction. We demonstrate that hybrid MoSx-NPG exhibits >30 mV lower onset potential and a 1.7-fold lower Tafel slope as compared to pure MoSx. Our methodology provides an energy- and cost-efficient synthesis pathway, which can be extended to the synthesis of various functional hybrid structures with unique properties for catalysis and sensing applications. Ministry of Education (MOE) Nanyang Technological University Published version X. Y. Ling acknowledges Singapore Ministry of Education, Tier 1 (No. RG11/18) and Tier 2 (No. MOE2016-T2-1-043) grants. G. C. Phan-Quang, C. S. L. Koh, and S. X. Leong acknowledge the Nanyang President’s Graduate Scholarship.

We report on a novel way of performing stimulated electron energy-loss and energy-gain spectroscopy (sEELS/sEEGS) experiments that does not require a pulsed gun. In this scheme, a regular scanning transmission electron microscope (STEM) equipped with a conventional continuous electron gun is fitted with a modified EELS detector and a light injector in the object chamber. The modification of the EELS detector allows one to expose the EELS camera during tunable time intervals that can be synchronized with nanosecond laser pulses hitting the sample, therefore allowing us to collect only those electrons that have interacted with the sample under light irradiation. Using ∼ 5 ns laser pulses of ∼ 2 eV photon energy on various plasmonic silver samples, we obtain evidence of sEELS/sEEGS through the emergence of up to two loss and gain peaks in the spectra at ± 2 and ± 4 eV. Because this approach does not involve any modification of the gun, our method retains the original performances of the microscope in terms of energy resolution and spectral imaging with and without light injection. Compared to pulsed-gun techniques, our method is mainly limited to a perturbative regime (typically no more that one gain event per incident electron), which allows us to observe resonant effects, in particular when the plasmon energy of a silver nanostructure matches the laser photon energy. In this situation, EELS and EEGS signals are enhanced in proportion to n + 1 and n, respectively, where n is the average plasmon population due to the external illumination. The n term is associated with stimulated loss and gain processes, and the term of 1 corresponds to conventional (spontaneous) loss. The EELS part of the spectrum is therefore an incoherent superposition of spontaneous and stimulated EEL events. This is confirmed by a proper quantum-mechanical description of the electron/light/plasmon system incorporating light–plasmon and plasmon–electron interactions, as well as inelastic plasmon decay.

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. Ministry of Education (MOE) Accepted version This work was funded by Singapore Ministry of Education, Tier 1 (RG11/18) and Tier 2 (MOE2016-T2-1-043) grants, and Max Planck Institute-Nanyang Technological University Joint Lab, the Spanish Ministerio de Economia y Competitividad (CTQ2017-88648R and RYC-2015-19107), the Generalitat de Cataluña (2017SGR883), the Universitat Rovira i Virgili (2017PFR-URV-B2-02), and the Universitat Rovira i Virgili and Banco Santander (2017EXIT-08).

Bicontinuous nanoporous gold (NPG) is a high-performance catalyst characterized by its excellent electrochemical stability and immense active surface area with high electrolyte accessibility. However, the intrinsic catalytic activity of NPG is still lower compared to other metals (such as Pt), thus impeding its applicability in a commercial catalytic system. Herein, we incorporate secondary Pt metal with inherently strong catalytic activities into a zero-dimensional (0D) nanoporous gold bowl (NPGB) to develop Pt-NPGB bimetallic catalyst. Our strategy effectively exploits the highly accessible surface area of NPGB and the manipulative d-band electronic structure brought about by the synergistic intermetallic interaction for enhanced catalytic performance and durability. Deposition of Pt on the NPGB catalyst directly modulates its d-band electronic structure, with the electronic energy of Pt-NPGBs tunable between −3.93 to −4.24, approximating that of chemically resistant gold (−4.35 eV). This is vital to we...

To promote the effect of halide ions (Cl-, Br-, and I-) in facet-selective growth of {111} and {100} of shaped metal nanocrystals, we utilize PDADMAC, a hybrid cationic, polymeric stabilizer. SERS and synthesis experiments provide evidence supporting that the higher amount of PDADMA+ at surfaces promotes the local adsorption of halides, allowing the creation of Pd cubes, octahedra, and cuboctopods.

Miniaturized liquid–liquid interfacial reactors offer enhanced surface area and rapid confinement of compounds of opposite solubility, yet they are unable to provide in situ reaction monitoring at a molecular level at the interface. A picoreactor operative at the liquid–liquid interface is described, comprising plasmonic colloidosomes containing Ag octahedra strategically assembled at the water-in-decane emulsion interface. The plasmonic colloidosomes isolate ultrasmall amounts of solutions (

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. This reaction is a robust approach to generate covalently functionalized metallic surfaces, yet its kinetics remain unknown to date. Experiments and simulations jointly uncover a two-step sequential grafting process. An initial Langmuir chemisorption of sulfonicbenzene diazonium (dSB) salt onto Ag surfaces forms an intermediate sulfonicbenzene monolayer (Ag-SB), followed by subsequent autocatalytic multilayer growth of Ag-SB3. Kinetic rate constants reveal 19-fold faster chemisorption than multilayer growth. Our ability to precisely decipher molecular-level reaction dynamics creates opportunities to develop more efficient processes in synthetic chemistry and nanotechnology.