Nanozymes, as a novel form of enzyme mimics, have garnered considerable interest. Despite overcoming the main disadvantages of their natural analogs, they still face challenges such as restricted mimic types and low substrate specificity. Herein, we introduce a reactive ligand modification strategy to diversify enzyme mimic types. Specifically, we have utilized helical plasmonic nanorods (HPNRs) modified with para-nitrothiophenol (4-NTP) to create an oxygen-sensitive nitroreductase (NTR) with light-controllability. HPNRs act as a light-adjustable source of nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NAD(P)H), providing photon-generated energetic electrons to adsorbed 4-NTP molecules. In the presence of O₂, the activated 4-NTP transfers the captured electron to the adsorbed O₂, mimicking the electron transfer process in its natural counterpart. This enhanced O₂ activation notably boosts the oxidative coupling of para-aminothiophenol (4-ATP). Density functional theory (DFT) calculations reveal that hot electrons injected into the lowest unoccupied molecular orbital (LUMO) energy level of 4-NTP can be transferred to that of molecular oxygen. In conclusion, our findings underline the potential of the reactive ligand modification strategy in developing new types of enzyme reactions, which opens up promising avenues for the enhancement and diversification of nanozyme functionalities.

Herein, a new strategy is proposed for achieving dynamic chiral controls in self-assembly systems of plasmonic nanorods based on temperature-modulation. Via enlarging Au{100} side facets of Au nanorod (AuNR) building block and changing surface ligand from often-used cetyltrimethylammonium bromide (CTAB) to cetylpyridinium chloride (CPC), inversion of chiroptical signal in side-by-side (SS) oligomers is realized. Under the guide of chiral cysteine (Cys), Au{100} side facet-linked SS rods twist in the opposite direction compared with Au{110} side facet-linked counterparts. At high CPC concentration, by controlling the incubation temperature of chiral Cys, the dominant twist mode can be regulated. Finite-difference time-domain (FDTD) simulations indicate the key role of the twisting dihedral angle of the oligomers in driving chiral signal inversion. At low CPC concentration, a temperature-sensitive chiral switching is observed owing to the conformation change of the CPC ligand layer. The temperature-modulated chiral responses are based on the interactions of chiral molecules, achiral surface ligands, and exposed facets of the building block. The rich dynamic tunability of chiroptical responses of plasmonic assemblies may find applications in stimulus-responsive nanodevices.

Photodynamic therapy (PDT), as a noninvasive therapeutic method, has been actively explored recently for cancer treatment. However, owing to the weak absorption in the optically transparent windows of biological tissues, most commercial photosensitizers (PSs) exhibit low singlet oxygen (¹O₂) quantum yields when excited by light within this window. Finding the best way to boost ¹O₂ production for clinical applications using light sources within this window is, thus, a great challenge. Herein, we tackle this problem using plasmon resonance energy transfer (PRET) from plasmonic nanoparticles (NPs) to PSs and demonstrate that the formation of plasmon quenching dips is an effective way to enhance ¹O₂ generation. The combination of the photosensitizer chlorin e6 (Ce6) and gold nanorods (AuNR) was employed as a model system. We observed a clear quenching dip in the longitudinal surface plasmon resonance (LSPR) band of the AuNRs when the LSPR band overlaps with the Q band of Ce6 and the spacing between Ce6 and the rods is within the acting distance of PRET. Upon irradiation with 660 nm continuous-wave laser light, we obtained a seven-fold enhancement in the ¹O₂ signal intensity compared with that of a non-PRET sample, as determined using the ¹O₂ electron spin resonance probe 2, 2, 6, 6-tetramethyl-4-piperidine (TEMP). Furthermore, we demonstrated that the PRET effect is more efficient in enhancing ¹O₂ yield than the often-employed local field enhancement effect. The effectiveness of PRET is further extended to the in vitro level. Considering the flexibility in manipulating the localized SPR properties of plasmonic nanoparticles/nanostructures, our findings suggest that PRET-based strategies may be a general way to overcome the deficiency of most commercial organic PSs in biological optically transparent windows and promote their applications in clinical tumor treatments.

Owing to the strong affinity of thiols to Au and Ag, they are often employed to modify the surfaces of nanoparticles (NPs). Recently, these strong ligand-interface interactions have been employed to control NP growth, and this technique has emerged as a unique modulation strategy for creating unconventional plasmonic hybrid nanostructures. In these systems, the roles of the non-mercapto components of the thiol molecules and their structures are still unknown. Therefore, we herein present our investigation into this phenomenon. Primary amino (–NH₂) groups in thiols are found to play a key role in regulating growth kinetics, i.e., in accelerating Ag deposition on Au NPs. The–NH₂ groups are thought to bring Ag ions to the particle surface by coordinating to them, and thereby assist their reduction. The effect of molecular structure is non-trivial and thus provides the possibility of selective thiol detection. Based on the dependence of kinetic modulation on the non-mercapto components and molecular structures of molecules, we demonstrate the highly sensitive and specific detection of cysteine (limit of detection: 6 nM) in a mixture of 19 natural amino acids based on Ag growth on Au nanospheres. In addition, based on this modulation effect, we reveal the entrapping of chiral thiols within the growth layer through their plasmonic circular dichroism (PCD) responses. We believe that thiol-based growth regulation has great potential for creating plasmonic nanostructures with novel functionalities.

Gold nanostructures are among the noble metal nanomaterials being intensely studied due to their good biocompatibility, tunable localized surface plasmon resonance (SPR), and ease of modification. These properties give gold nanostructures many potential chemical and biomedical applications. Herein, we demonstrate the critical role of oxygen activation during the decomposition of hydrogen peroxide (H₂O₂) in the presence of photoexcited gold nanorods (AuNRs) by using electron spin resonance (ESR) techniques. Upon SPR excitation, O₂ is activated first, and the resulting reactive intermediates further activate H₂O₂ to produce?OH. The reactive intermediates exhibit singlet oxygen-like (¹O₂-like) reactivity, indicated by ¹O₂-specific oxidation reaction, quenching behaviors, and the lack of the typical ¹O₂ ESR signal. In addition, by using the antioxidant sodium ascorbate (NaA) as an example, we show that hydroxyl radicals from H₂O₂ activation can induce much stronger NaA oxidation than that in the absence of H₂O₂. These results may have significant biomedical implications. For example, as oxidative stress levels are known to influence tumorigenesis and cancer progression, the ability to control redox status inside tumor microenvironments using noble metal nanostructures may provide new strategies for regulating the metabolism of reactive oxygen species and new approaches for cancer treatment.

Platinum nanoparticles (NPs) are reported to mimic various antioxidant enzymes and thus may produce a positive biological effect by reducing reactive oxygen species (ROS) levels. In this manuscript, we report Pt NPs as an enzyme mimic of ferroxidase by depositing platinum nanodots on gold nanorods (Au@Pt NDRs). Au@Pt NDRs show pH-dependent ferroxidase-like activity and have higher activity at neutral pH values. Cytotoxicity results with human cell lines (lung adenocarcinoma A549 and normal bronchial epithelial cell line HBE) show that Au@Pt NDRs are taken up into cells via endocytosis and translocate into the endosome/lysosome. Au@Pt NDRs have good biocompatibility at NDR particle concentrations lower than 0.15 nΜ. However, in the presence of H₂O₂, lysosomelocated NDRs exhibit peroxidase-like activity and therefore increase cytotoxicity. In the presence of Fe²⁺, the ferroxidase-like activity of the NDRs protects cells from oxidative stress by consuming H₂O₂. Thorough consideration should be given to this behavior when employing Au@Pt NDRs in biological systems.

Generation of circular dichroism (CD) beyond the UV region is of great interest in developing chiral sensors and chiroptical devices. Herein, we demonstrate a simple and versatile method for fabrication of plasmonic oligomers with strong CD response in the visible and near IR spectral range. The oligomers were fabricated by triggering the side-by-side assembly of cysteine-modified gold nanorods. The modified nanorods themselves did not exhibit obvious plasmonic CD signals; however, the oligomers show strong CD bands around the plasmon resonance wavelength. The sign of the CD band was dictated by the chirality of the absorbed cysteine molecules. By adjusting the size of the oligomers, the concentration of chiral molecules, and/or the aspect ratio of the nanorods, the CD intensity and spectral range were readily tunable. Theoretical calculations suggested that CD of the oligomers originated from a slight twist of adjacent nanorods within the oligomer. Therefore, we propose that the adsorbed chiral molecules are able to manipulate the twist angles between the nanorods and thus modulate the CD response of the oligomers.

In the light of the current problems of silver nanoparticles (Ag NPs) in terms of antibacterial performance, we have designed a novel trimetallic core/shell nanostructure with AgPt alloy nanodots epitaxially grown on gold nanorods (Au@PtAg NRs) as a potential antibacterial agent. Both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were studied. The antibacterial activity exhibits an obvious composition-dependence. On increasing the Ag fraction in the alloy shell up to 80%, the antibacterial activity gradually increases, demonstrating a flexible way to tune this activity. At 80% Ag, the antibacterial activity is better than that of a pure Ag shell. The improved antibacterial ability mainly results from the high exposure of silver on the shell surface due to the dot morphology. We thus demonstrate that forming alloys is an effective way to improve antibacterial activity while retaining high chemical stability for Ag-based nanomaterials. Furthermore, due to the tunable localized surface plasmonic response in the near-infrared (NIR) spectral region, additional control over antibacterial activity using light—such as photothermal killing and photo-triggered silver ion release—is expected. As a demonstration, highly enhanced antibacterial activity is shown by utilizing the NIR photothermal effect of the nanostructures. Our results indicate that such tailored nanostructures will find a role in the future fight against bacteria, including the challenge of the increasing severity of multidrug resistance.