Plasmonic Hot-Electron-Painted Au@Pt Nanoparticles as Efficient Electrocatalysts for Detection of H2O2

Coupling plasmon and catalytic-active hotspots of Au@Pt core-satellite nanoparticles for in-situ spectroscopic observation of plasmon-promoted decarboxylation

Plasmon-induced hot carriers are a promising "active" energy source, attracting increasing attention for their potential applications in photocatalysis and photodetection. Here, we hybridize plasmonic Au spherical nanoparticles (SNPs) with catalytically active Pt nanocrystals to form Au@Pt core-satellite nanoparticles (CSNPs), which act as both an efficient catalyst for plasmon-promoted decarboxylation reaction and a robust surface-enhanced Raman scattering (SERS) substrate for plasmon-enhanced molecular spectroscopic detection. By regulating the coverage of Pt nanocrystals on the Au SNPs, we modulated the "hotspot" structures of the Au@Pt CSNPs to optimize the SERS detecting capability and catalytic decarboxylation performance. The coupling functionalities enable us with unique opportunities to in-situ SERS monitor universal reactions catalyzed by active catalysts (e.g. Pt, Pd) in the chemical industry in real-time. The decarboxylation rate of 4-mercaptophenylacetic acid was dynamically controlled by the surface catalytic decarboxylation step, following first-order overall reaction kinetics. Moreover, the reaction rate exhibited a strong correlation with the local field enhancement |E/E0|4 of the hotspot structure. This work provides spectroscopic insights into the molecule-plasmon interface under the plasmon-promoted catalytic reactions, guiding the rational design of the plasmonic interface of nanocatalysts to achieve desired functionalities.

An ultrasensitive sandwich-type electrochemical immunosensor based on rGO-TEPA/ZIF67@ZIF8/Au and AuPdRu for the detection of tumor markers CA72-4

Cancer antigen 72-4 (CA72-4) is an important marker of cancer detection, and accurate detection of CA72-4 is urgently required. Herein, a sandwich-type immunosensor was constructed for detection CA72-4 based on composite nanomaterial as the substrate material and trimetal nanoparticles as the nanoprobe. The composite nanomaterial rGO-TEPA/ZIF67@ZIF8/Au used as a selective bio-recognition element were modified on the glassy carbon electrode (GCE) surface. Meanwhile, the electrochemical nanoprobes were fabricated through the AuPdRu trimeric metal. After the target antigen 72-4 were captured, the nanoprobes were further assembled to form an antibody1 (Ab1)- antigen-antibody2 (Ab2) nanoprobes sandwich-like system on the electrode surface. Then, hybrid the substrate material rGO-TEPA/ZIF67@ZIF8/Au and the AuPdRu trimeric metal nanoprobes efficiently catalyzed the reduction of H2O2 and amplified the electrochemical signals. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and Chronoamperometry (I-T) methods were used to characterize the performance and detection capabilities for CA72-4 of the prepared immunosensors. The results showed that the detection limit was 1.8 × 10-5 U/mL (S/N = 3), and the linear range was 0.001-1000 U/mL. This study provides a new signal amplification strategy for electrochemical sensors and a theoretical basis for the clinical application of immunosensor to detect other tumor markers.

Single-Particle Fluorescence Spectroscopy for Elucidating Charge Transfer and Catalytic Mechanisms on Nanophotocatalysts

Photocatalysis is a cost-effective approach to producing renewable energy. A thorough comprehension of carrier separation at the micronano level is crucial for enhancing the photochemical conversion capabilities of photocatalysts. However, the heterogeneity of photocatalyst nanoparticles and complex charge migration processes limit the profound understanding of photocatalytic reaction mechanisms. By establishing the precise interrelationship between microscopic properties and photophysical behaviors of photocatalysts, single-particle fluorescence spectroscopy can elucidate the carrier separation and catalytic mechanism of the photocatalysts in situ, which provides perspectives for improving the photocatalytic efficiency. This Review primarily focuses on the basic principles and advantages of single-particle fluorescence spectroscopy and its progress in the study of plasmonic and semiconductor photocatalysis, especially emphasizing its importance in understanding the charge separation and photocatalytic reaction mechanism, which offers scientific guidance for designing efficient photocatalytic systems. Finally, we summarize and forecast the future development prospects of single-particle fluorescence spectroscopy technology, especially the insights into its technological upgrading.

In Situ Photoreversible Tuning of Chemical Interface Damping in Single Gold Nanorods Through Cucurbit[8]uril-Based Host-Guest Interactions

Chemical interface damping (CID) is a recently proposed plasmon-damping pathway based on the interfacial hot-electron transfer from metal to adsorbate molecules. However, the in situ reversible tuning of CID in single gold nanorods (AuNRs) has remained a considerable challenge. In this study, we used total internal reflection scattering microscopy and spectroscopy to investigate the CID induced by p-aminoazobenzene (p-AAB), which has fast photoisomerization characteristics, attached to single AuNRs. We demonstrated the in situ reversible tuning of CID in single AuNRs by switching between ultraviolet (UV, 365 nm) and visible (vis, 465 nm) irradiation to induce photoresponsive structural conversions between the cis and trans forms of p-AAB in ethanol, leading to different lowest unoccupied molecular orbital (LUMO) energies for both forms. The localized surface plasmon resonance (LSPR) line width was wide under vis irradiation but narrow under UV irradiation, indicating that hot electrons are more efficiently transferred to trans-p-AAB with a low LUMO energy level. We further investigated the in situ photoreversible tuning of CID by manipulating supramolecular host-guest interactions between cucurbit[8]uril (CB[8]) and p-AAB in the single AuNRs. Additionally, real-time in situ reversible tuning of CID in single AuNRs was achieved through photonic switching of the cis-trans forms of p-AAB inside CB[8]. The LSPR line width was narrow under vis irradiation but gradually widened under UV irradiation before narrowing again upon returning to vis irradiation, unlike the case with p-AAB only. These results can be ascribed to the fact that cis-p-AAB completely encapsulated within CB[8] in water is thermodynamically more favorable than trans-p-AAB. Therefore, we have discovered a new strategy for tuning the CID by performing p-AAB photoisomerization and adjusting the wavelength of incident light in single AuNRs. In addition, this study demonstrates that CID can be effectively applied to the development of biosensors to detect guest molecules and their structural changes inside the cavity of CB[8] in single AuNRs.

Unveiling the Dynamic Electrocatalytic Activity of Online Synthesized Bimetallic Nanocatalysts via Electrochemiluminescence Microscopy

Effective bimetallic nanoelectrocatalysis demands precise control of composition, structure, and understanding catalytic mechanisms. To address these challenges, we employ a two-in-one approach, integrating online synthesis with real-time imaging of bimetallic Au@Metal core-shell nanoparticles (Au@M NPs) via electrochemiluminescence microscopy (ECLM). Within 120 s, online electrodeposition and in situ catalytic activity screening alternate. ECLM captures transient faradaic processes during potential switches, visualizes electrochemical processes in real-time, and tracks catalytic activity dynamics at the single-particle level. Analysis using ECL photon flux density eliminates size effects and yields quantitative electrocatalytic activity results. Notably, a nonlinear activity trend corresponding to the shell metal to Au surface atomic ratio is discerned, quantifying the optimal surface component ratio of Au@M NPs. This approach offers a comprehensive understanding of catalytic behavior during the deposition process with high spatiotemporal resolution, which is crucial for tailoring efficient bimetallic nanocatalysts for diverse applications.

Electrogenerated chemiluminescence imaging of plasmon-induced electrochemical reactions at single nanocatalysts

This study explores plasmon-induced electrochemical reactions on single nanoparticles using electrogenerated chemiluminescence microscopy (ECLM). Under laser irradiation, real-time screening showed lower plasmon-induced reaction efficiency for bimetallic Au@Pt nanoparticles compared to monometallic Au nanoparticles. ECLM offers a high-throughput imaging and precise quantitative approach for analyzing photo-electrochemical conversion at single nanoparticle level, valuable for both theoretical exploration and optimization of plasmonic nanocatalysts.

Synergism of Holmium Orthovanadate/Phosphorus-Doped Carbon Nitride Nanocomposite: Nonenzymatic Electrochemical Detection of Hydrogen Peroxide

Developing efficient and robust electrode materials for electrochemical sensors is critical for real-time analysis. In this paper, a hierarchical holmium vanadate/phosphorus-doped graphitic carbon nitride (HoVO4/P-CN) nanocomposite is synthesized and used as an electrode material for electrochemical detection of hydrogen peroxide (H2O2). The HoVO4/P-CN nanocomposite exhibits superior electrocatalytic activity at a peak potential of -0.412 V toward H2O2 reduction in alkaline electrolytes while compared with other reported electrocatalysts. The HoVO4/P-CN electrochemical platform operated under the optimized conditions shows excellent analytical performance for H2O2 detection with a linear concentration range of 0.009-77.4 μM, a high sensitivity of 0.72 μA μM-1 cm-2, and a low detection limit of 3.0 nΜ. Furthermore, the HoVO4/P-CN-modified electrode exhibits high selectivity, remarkable stability, good repeatability, and satisfactory reproducibility in detecting H2O2. Its superior performance can be attributed to a large specific surface area, high conductivity, more active surface sites, unique structure, and synergistic action of HoVO4 and P-CN to benefit enhanced electrochemical activity. The proposed HoVO4/P-CN electrochemical platform is effectively applied to ascertain the quantity of H2O2 in food and biological samples. This work outlines a promising and effectual strategy for the sensitive electrochemical detection of H2O2 in real-world samples.

Gold Nanoparticle-Loaded Porous Poly(ethylene glycol) Nanosheets for Electrochemical Detection of H2O2

The effective detection of hydrogen peroxide (H2O2) in different environments and, above all, in biological media, is an important practical issue. To this end, we designed a novel electrochemical sensor for H2O2 detection by introducing gold nanoparticles (AuNPs) into the porous poly(ethylene glycol) (PEG) matrix formed by the thermally activated crosslinking of amino- and epoxy-decorated STAR-PEG precursors. The respective composite PEG-AuNP films could be readily prepared on oxidized Si substrates, separated from them as free-standing nanosheets, and transferred as H2O2 sensing elements onto the working electrode of the electrochemical cell, with the performance of the sensing element relied on the established catalytic activity of AuNPs with respect to H2O2 decomposition. The sensitivity, detection limit, and the operation range of the composite PEG-AuNP sensors were estimated at ~3.4 × 102 μA mM-1 cm-2, 0.17 μM of H2O2, and 20 μM-3.5 mM of H2O2, respectively, which are well comparable with the best values for other types of H2O2 sensors reported recently in literature. The particular advantages of the composite PEG-AuNP sensors are commercial source materials, a simple fabrication procedure, the bioinert character of the PEG matrix, the 3D character of the AuNP assembly, and the possibility of transferring the nanosheet sensing element to any secondary substrate, including the glassy carbon electrode of the electrochemical cell. In particular, the bioinert character of the PEG matrix can be of importance for potential biological and biomedical applications of the designed sensing platform.

Highly catalytic and stable Au@AuPt nanoparticles for visual and quantitative detection of E. coli O157:H7

A visual and quantitative ELISA-like method for Escherichia coli O157:H7 is developed based on highly catalytic and stable Au@AuPt nanoparticles. The proposed enhanced ELISA method can visually detect 100 CFU mL-1 O157:H7 with high specificity and without the need for strict low-temperature reagent storage, thereby increasing the utility. Moreover, it is applicable to spiked tap water and milk tea samples without additional treatments.

Plasmonic Nanomaterials in Dark Field Sensing Systems

Plasma nanoparticles offer promise in data storage, biosensing, optical imaging, photoelectric integration, etc. This review highlights the local surface plasmon resonance (LSPR) excitation mechanism of plasmonic nanoprobes and its critical significance in the control of dark-field sensing, as well as three main sensing strategies based on plasmonic nanomaterial dielectric environment modification, electromagnetic coupling, and charge transfer. This review then describes the component materials of plasmonic nanoprobes based on gold, silver, and other noble metals, as well as their applications. According to this summary, researchers raised the LSPR performance of composite plasmonic nanomaterials by combining noble metals with other metals or oxides and using them in process analysis and quantitative detection.

Iodide-Mediated Etching of Gold Nanostar for the Multicolor Visual Detection of Hydrogen Peroxide

A multicolor visual method for the detection of hydrogen peroxide (H₂O₂) was reported based on the iodide-mediated surface etching of gold nanostar (AuNS). First, AuNS was prepared by a seed-mediated method in a HEPES buffer. AuNS shows two different LSPR absorbance bands at 736 nm and 550 nm, respectively. Multicolor was generated by iodide-mediated surface etching of AuNS in the presence of H₂O₂. Under the optimized conditions, the absorption peak Δλ had a good linear relationship with the concentration of H₂O₂ with a linear range from 0.67~66.67 μmol L^-1, and the detection limit is 0.44 μmol L^-1. It can be used to detect residual H₂O₂ in tap water samples. This method offered a promising visual method for point-of-care testing of H₂O₂-related biomarkers.

Atomic layer deposition of Pt nanoparticles onto Co/MoN nanoarrays for improved electrochemical detection of H2O2

The design and preparation of advanced nanocatalysts for the sensitive electrochemical detection of H₂O₂ is of great significance. Herein, a facile Pt@Co/MoN sensing platform was fabricated by depositing Pt nanoparticles onto Co/MoN nanoarrays using atomic layer deposition (ALD) technology. Benefitting from the unique nanostructure and the strong interaction between Pt and the nitride support, the prepared Pt@Co/MoN exhibited excellent performance in the electrochemical detection of H₂O₂. This work provides an interesting strategy to fabricate low-Pt electrocatalysts on a nanoarray support for future applications in electroanalysis.

Dark-Field Imaging Monitoring of Adenosine Triphosphate in Live Cells by Au NBPs@ZIF-8 Nanoprobes

Monitoring the fluctuation of adenosine triphosphate (ATP) level in living cells could promote the understanding of metabolic pathways and cell biology. Here, we proposed a highly sensitive, selective, and biocompatible nanoprobe with core-shell structure, namely Au NBPs@ZIF-8 composed by gold nanobipyramids (Au NBPs) and zeolitic imidazolate framework-8 (ZIF-8), for monitoring intracellular ATP level fluctuation in living cells. Because the coordination between ATP and Zn²⁺ (the metal node of ZIF-8) was much stronger than that between 2-methylimidazole and Zn²⁺, which caused the decomposition of the ZIF-8 shell and the exposure of Au NBPs in the presence of ATP, it led to the change of the localized surface plasmon resonance scattering properties of nanoprobes under dark-field microscopy. Tricolor (RGB) analysis showed that R/G value had a good linear relationship with the ATP concentrations in the range of 10 μM to 4 mM (R² = 0.999) with a detection limit of 5.28 μM. This ATP sensing platform also exhibited excellent selectivity in complex intracellular interfering substances. Besides, we realized intracellular ATP real-time imaging in HeLa cells and observed the ATP level fluctuation under dark-field microscopy. The method mentioned here could be further applied for delivery of therapeutics for biomedical applications.