Spermine assumes a pivotal role in assessing food safety due to its potential to induce a spectrum of diseases upon excessive consumption. However, contemporary spermine detection methodologies, exemplified by high-performance liquid chromatography (HPLC), demand costly instrumentation and the expertise of skilled technicians. To address this challenge, the study introduces a portable fluorescence sensing platform. Ratiometric fluorescent probes were realized through the utilization of CdS quantum dots deeply doped with Ag⁺ (CdS:Ag QDs) and nitrogen-doped carbon quantum dots (N-CQDs). Hydrogen bonds formed between CdS:Ag QDs and spermine result in the formation of the assembly and the decreasing of the fluorescence intensity. In an effort to broaden the applicative scope and streamline deployment processes, fluorescent sensing hydrogels were meticulously engineered, capitalizing on the swelling properties inherent in polyvinyl alcohol (PVA) hydrogels. The systematic delineation of the correlation between 1 − R/B and spermine concentration facilitates the quantitative determination of spermine concentration. The incorporation of this composite construct serves to alleviate environmental influences on the probes, thereby augmenting their precision. The portable fluorescent sensing platform proves pivotal in expeditiously measuring spermine concentration within the fluorescent sensing hydrogel, enabling a quantitative assessment of pork freshness. The utilization of this platform for food freshness evaluation imparts the benefits of convenience, cost-effectiveness, and intuitive operation.

Single atom (SA) catalysts have achieved great success on highly selective heterogeneous catalysis due to their abundant and homogeneous active sites. The electronic structures of these active sites, restrained by their localized coordination environments, significantly determine their catalytic performances, which are difficult to manipulate. Here, we investigated the effect of localized surface plasmon resonance (LSPR) on engineering the electronic structures of single atomic sites. Typically, core–shell structures consisted of Au core and transition metal SAs loaded N-doped carbon (CN) shell were constructed, namely Au@M-SA/CN (M = Ni, Fe, and Co). It was demonstrated that plasmon-induced hot electrons originated from Au were directionally injected to the M-SAs under visible light irradiation, which significantly changed their electronic structures and meanwhile facilitated improved overall charge separation efficiency. The as-prepared Au@Ni-SA/CN exhibited highly efficient and selective photocatalytic CO₂ reduction to CO performance, which is 20.8, 17.5, and 6.9 times those of Au nanoparticles, Au@CN, and Ni-SA/CN, respectively. Complementary spectroscopy analysis and theoretical calculations confirmed that the plasmon enhanced Ni-SA/CN sites featured increased charge density for efficient intermediate activation, contributing to the superb photocatalytic performance. The work provides a new insight on plasmon and atomic site engineering for efficient and selective catalysis.

Carbon-based single-atom catalysts (SACs) have been widely studied in the field of biomedicine due to their excellent catalytic performance. However, carbon-based SACs usually aggregate during pyrolysis, which leads to the reduction of catalytic activity. Here, we describe a method to improve the monodispersion of SACs using silicon dioxide as a protective layer. The decoration of silicon dioxide serves as a buffer layer for individual nanoparticles, which is not destroyed during the pyrolysis process, ensuring the single-particle dispersion of the nanoparticles after etching. This approach increased the hydroxyl groups on the surface of Fe-SAC (Fe-SAC-SE) and improved its water solubility, resulting in a four times enhancement of the peroxidase (POD)-like activity of Fe-SAC-SE (58.4 U/mg) than that of non-protected SACs (13.9 U/mg). The SiO₂-protection approach could also improve the catalytic activities of SACs with other metals such as Mn, Co, Ni, and Cu, indicating its generality for SACs preparation. Taking advantage of the high POD-like activity, photothermal properties, and large specific surface area of Fe-SAC-SE, we constructed a synergistic therapeutic system (Fe-SAC-SE@DOX@PEG) for combining the photothermal therapy, catalytic therapy, and chemotherapy. It was verified that the photothermal properties of Fe-SAC-SE@DOX@PEG could effectively improve its POD-like activity, exhibiting excellent tumor-killing performance at the cellular level. This work may provide a general approach to improve the performances of SACs for disease therapy and diagnosis.

Active site exposure and intrinsic catalytic performance are considered important aspects of oxygen evolution reaction catalyst design. In this work, the coordination capacity of tributylphosphine is utilized to construct cationic vacancy defects on NiFe-LDH nanosheets. As-prepared defective NiFe-LDH nanosheets show not only the optimization of the exposure ability of the active site but also the intrinsic catalytic capacity is improved by construction of cationic vacancy defect to tune local electronic structure. The x-ray photoelectron spectroscopy results revealed that after reconstruction of the prepared d-NiFe-LDH, high-valence Ni and Fe can stably appear on the surface of the material. The presence of high-valence Ni and Fe is considered to be the main reason to improve the intrinsic catalytic capacity of catalysts. Finally, d-NiFe-LDH nanosheets show excellent catalytic performance (η₁₀ = 243 mV) and remarkable long-term stability.

The semiconductor-based photoanodes have shown great potential on photoelectrochemical (PEC) hydrogen generation. Compared to the pristine semiconductor, photoanodes fabricated with doped semiconductors exhibit modulated bandgap structure and enhanced charge separation efficiency, demonstrating improved optoelectronic properties. In this work, we develop a colloidal cation exchange (CE) strategy on versatile synthesis of heterovalent doped chalcogenide semiconductor thin films with high surface roughness. Using Ag-doped CdSe (CdSe:Ag) thin films as an example, the organized centimeter-scale CdSe:Ag films with nanometer-scale thickness (thickness around 80 nm, length × width around 1.5 cm × 1.2 cm) exhibit enhanced optical absorbance ability and charge carrier density by tuning the energy levels of conduction and valence bands as well as improved electrical conductivity by Ag dopants compared to the pristine CdSe film obtained by the vapor-phase vacuum deposition strategy. In the meantime, the surface roughness of the as-prepared semiconductor thin films is also increased with abundantly exposed active sites to facilitate accessibility to water for hydrogen generation and suppress photogenerated carrier recombination. The CdSe:Ag film photoanodes exhibit superb PEC hydrogen generation performance with a photocurrent density of 0.56 mA/cm² at 1.23 V versus reversible hydrogen electrode, which is nearly 3 times higher than the pristine CdSe film. This work provides a new strategy on colloidal synthesis of photoelectrodes with modulated heterovalent doping and surface roughness for PEC applications.

Oxidative stress and inflammation are central pathophysiological processes in a traumatic spinal cord injury (SCI). Antioxidant therapies that reduce the reactive oxygen and nitrogen species (RONS) overgeneration and inflammation are proved promising for improving the outcomes. However, efficient and long-lasting antioxidant therapy to eliminate multiple RONS with effective neuroprotection remains challenging. Here, a single-atom cobalt nanozyme (Co-SAzyme) with a hollow structure was reported to reduce the RONS and inflammation in the secondary injury of SCI. Among SAzymes featuring different single metal-N sites (e.g., Mn, Fe, Co, Ni, and Cu), this Co-SAzyme showed a versatile property to eliminate hydrogen peroxide (H₂O₂), superoxide anion (O₂^•−), hydroxyl radical (·OH), nitric oxide (·NO), and peroxynitrite (ONOO⁻) that overexpressed in the early stage of SCI. The porous hollow structure also allowed the encapsulation and sustained release of minocycline for neuroprotection in synergy. In vitro results showed that the Co-SAzyme reduced the apoptosis and pro-inflammatory cytokine levels of microglial cells under oxidative stress. In addition, the Co-SAzyme combined with minocycline achieved remarkable improved functional recovery and neural repairs in the SCI-rat model.

Electronic doped quantum dots (Ed-QDs), by heterovalent cations doping, have held promise for future device concepts in optoelectronic and spin-based technologies due to their broadband Stokes-shifted luminescence, enhanced electrical transport and tailored magnetic behavior. Considering their scale-up requirement and the low yielding of several current colloidal synthesis methods, a stable and efficient bulk synthesis strategy must be developed. Microreactors have long been recognized as an effective platform for producing nanomaterials and fabricating large-scale structures. Here, we chose microreactor platform for continuous synthesis of Ed-QDs in the air at low temperatures. By original reverse cation exchange reaction mechanism together with varying the kinetic conditions of microreactor platform, such as liquid flow rate, the Ag doped CdS (CdS:Ag) Ed-QDs with higher yield have been synthesized successfully due to the continuous synthesis advantages with a high degree of size selectivity. Enabled by microreactor engineering simulation, this research not only provides a new synthetic method towards scale-up production but also enables to improve chemical mass production of similar functional QDs for optical devices, bio-imaging and innovative information processing applications.

Here we report a synthetic strategy for controllable construction of yolk-shell and core-shell plasmonic metal@semiconductor hybrid nanocrystals through modulating the kinetics of sulfurization reaction followed by cation exchange. The yielded yolk-shell structured products feature exceptional crystallinity and more importantly, the intimately adjoined and sharp interface between plasmonic metal and semiconductor which facilitates efficient charge carrier communications between them. By exploiting the system composed of Au nanorods and p-type PbS as a demonstration, we show that the Au@PbS yolk-shell nanorods manifest notable improvement in visible and near infrared light absorption compared to the Au@PbS core-shell nanorods as well as hollow PbS nanorods. Moreover, the photocathode constituted by Au@PbS yolk-shell nanorods affords the highest photoelectrochemical activities both under simulated sunlight and λ > 700 nm light irradiation. The superior performance of Au@PbS yolk-shell nanorods is considered arising from the combination of the favorable structural advantages of yolk-shell configuration and the surface plasmon resonance enhancement effect. We envision that the reported synthetic strategy can offer a valuable means to create hybrid nanocrystals with desirable structures and functions that enable to harness the photogenerated charge carriers, including the plasmonic hot holes, in wide-range solar-to-fuel conversion.

Utilizing vacuum-tuned-atmosphere induced dip coating method, we achieve the cross-dimensional macroscopic diverse self-assemblies by using one building block with one chemical functionality. Coordinated modulating the vacuum degree, colloid concentration and evaporation atmosphere, Au@Ag core/shell nanocubes (NCs) can controllably assemble into diverse multi-dimensional superstructures. Under 0.08 MPa, we obtained the two-dimensional (2D) stepped superstructures with continuously tunable step width. In addition, we generated a series of tailorable nanoscale-roughened 2D Au@Ag NCs superstructures at 0.04 MPa, which exhibited the label-free ultrasensitive SERS detection for the different mutants of IAPP8-37 proteins. Under 0.01 MPa, we obtained the cross-dimensional tailorable Au@Ag NCs assemblies from random to macroscale 2D and three-dimensional (3D) densest superstructures by adjusting the capping ligand-environmental molecule interactions. This is a flexible method to generate as-prepared Au@Ag core/shell NCs into well-defined macroscopic diverse superstructures and to promote the exploitation into biological applications.

Control of surface structure at the atomic level can effectively tune catalytic properties of nanomaterials. Tuning surface strain is an effective strategy for enhancing catalytic activity; however, the correlation studies between the surface strain with catalytic performance are scant because such mechanistic studies require the precise control of surface strain on catalysts. In this work, a simple strategy of precisely tuning compressive surface strain of atomic-layer Cu₂O on Cu@Ag (AL-Cu₂O/Cu@Ag) nanoparticles (NPs) is demonstrated. The AL-Cu₂O is synthesized by structure evolution of Cu@Ag core-shell nanoparticles, and the precise thickness-control of AL-Cu₂O is achieved by tuning the molar ratio of Cu/Ag of the starting material. Aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) and EELS elemental mapping characterization showed that the compressive surface strain of AL-Cu₂O along the [111] and [200] directions can be precisely tuned from 6.5% to 1.6% and 6.6% to 4.7%, respectively, by changing the number of AL-Cu₂O layer from 3 to 6. The as-prepared AL-Cu₂O/Cu@Ag NPs exhibited excellent catalytic property in the synthesis of azobenzene from aniline, in which the strained 4-layers Cu₂O (4.5% along the [111] direction, 6.1% along the [200] direction) exhibits the best catalytic performance. This work may be beneficial for the design and surface engineering of catalysts toward specific applications.