Enhanced Catalytic Activity of Gold@Polydopamine Nanoreactors with Multi-compartment Structure Under NIR Irradiation

Cu-chelated polydopamine nanozymes with laccase-like activity for photothermal catalytic degradation of dyes

The industrial applications of enzymes are usually hindered by the high production cost, intricate reusability, and low stability in terms of thermal, pH, salt, and storage. Therefore, the de novo design of nanozymes that possess the enzyme mimicking biocatalytic functions sheds new light on this field. Here, we propose a facile one-pot synthesis approach to construct Cu-chelated polydopamine nanozymes (PDA-Cu NPs) that can not only catalyze the chromogenic reaction of 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AP), but also present enhanced photothermal catalytic degradation for typical textile dyes. Compared with natural laccase, the designed mimic has higher affinity to the substrate of 2,4-DP with Km of 0.13 mM. Interestingly, PDA-Cu nanoparticles are stable under extreme conditions (temperature, ionic strength, storage), are reusable for 6 cycles with 97 % activity, and exhibit superior substrate universality. Furthermore, PDA-Cu nanozymes show a remarkable acceleration of the catalytic degradation of dyes, malachite green (MG) and methylene blue (MB), under near-infrared (NIR) laser irradiation. These findings offer a promising paradigm on developing novel nanozymes for biomedicine, catalysis, and environmental engineering.

Polydopamine-Based Biomaterials in Orthopedic Therapeutics: Properties, Applications, and Future Perspectives

Polydopamine is a versatile and modifiable polymer, known for its excellent biocompatibility and adhesiveness. It can also be engineered into a variety of nanoparticles and biomaterials for drug delivery, functional modification, making it an excellent choice to enhance the prevention and treatment of orthopedic diseases. Currently, the application of polydopamine biomaterials in orthopedic disease prevention and treatment is in its early stages, despite some initial achievements. This article aims to review these applications to encourage further development of polydopamine for orthopedic therapeutic needs. We detail the properties of polydopamine and its biomaterial types, highlighting its superior performance in functional modification on nanoparticles and materials. Additionally, we also explore the challenges and future prospects in developing optimal polydopamine biomaterials for clinical use in orthopedic disease prevention and treatment.

Cancer Radiosensitization Nanoagent to Activate cGAS-STING Pathway for Molecular Imaging Guided Synergistic Radio/Chemo/Immunotherapy

Immunotherapy has emerged as an innovative strategy with the potential to improve outcomes in cancer patients. Recent evidence indicates that radiation-induced DNA damage can activate the cyclic-GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway to enhance the antitumor immune response. Even so, only a small fraction of patients currently benefits from radioimmunotherapy due to the radioresistance and the inadequate activation of the cGAS-STING pathway. Herein, this work integrates hafnium oxide (HfO2) nanoparticles (radiosensitizer) and 7-Ethyl-10-hydroxycamptothecin (SN38, chemotherapy drug, STING agonist) into a polydopamine (PDA)-coated core-shell nanoplatform (HfO2@PDA/Fe/SN38) to achieve synergistic chemoradiotherapy and immunotherapy. The co-delivery of HfO2/SN38 greatly enhances radiotherapy efficacy by effectively activating the cGAS-STING pathway, which then triggers dendritic cells maturation and CD8+ T cells recruitment. Consequently, the growth of both primary and abscopal tumors in tumor-bearing mice is efficiently inhibited. Moreover, the HfO2@PDA/Fe/SN38 complexes exhibit favorable magnetic resonance imaging (MRI)/photoacoustic (PA) bimodal molecular imaging properties. In summary, these developed multifunctional complexes have the potential to intensify immune activation to realize simultaneous cancer Radio/Chemo/Immunotherapy for clinical translation.

A graft-to strategy of poly(vinylphosphonates) on dopazide-coated gold nanoparticles using in situ catalyst activation

A modular synthetic pathway for poly(diethyl vinylphosphonates) grafting-to gold nanoparticles is presented. Utilising an azide-dopamine derivative as nanoparticle coating agent, alkyne-azide click conditions were used to covalently tether the polymer to gold nanoparticles leading to stable and well distributed colloids for different applications.

Photothermally Triggered Nanoreactors with a Tunable Catalyst Location and Catalytic Activity

Thermosensitive microgels based on poly(N-isopropylacrylamide) (PNIPAm) have been widely used to create nanoreactors with controlled catalytic activity through the immobilization of metal nanoparticles (NPs). However, traditional approaches with metal NPs located only in the polymer network rely on electric heating to initiate the reaction. In this study, we developed a photothermal-responsive yolk-shell nanoreactor with a tunable location of metal NPs. The catalytic performance of these nanoreactors can be controlled by both light irradiation and conventional heating, that is, electric heating. Interestingly, the location of the catalysts had a significant impact on the reduction kinetics of the nanoreactors; catalysts in the shell exhibited higher catalytic activity compared with those in the core, under conventional heating. When subjected to light irradiation, nanoreactors with catalysts loaded in the core demonstrated improved catalytic performance compared to direct heating, while nanoreactors with catalysts in the shell exhibited relatively similar activity. We attribute this enhancement in catalytic activity to the spatial distribution of the catalysts and the localized heating within the polydopamine cores of the nanoreactors. This research presents exciting prospects for the design of innovative smart nanoreactors and efficient photothermal-assisted catalysis.

Multi-functionalized carbon nanotubes towards green fabrication of heterogeneous catalyst platforms with enhanced catalytic properties under NIR light irradiation

Metal/carbon nanotubes (CNTs) have been attractive hybrid systems due to their high specific surface area and exceptional catalytic activity, but their challenging synthesis and dispersion impede their extensive applications. Herein, we report a facile and green approach towards the fabrication of metal/CNT composites, which utilizes a versatile glycopeptide (GP) both as a stabilizer for CNTs in water and as a reducing agent for noble metal ions. The abundant hydrogen bonds in GP endow the formed GP-CNTs with excellent plasticity, enabling the availability of polymorphic CNT species from dispersion to viscous paste, gel, and even to dough by increasing their concentration. The GP molecules can reduce metal precursors at room temperature without additional reducing agents, enabling the in situ immobilization of metal nanoparticles (e.g. Au, Ag, Pt, and Pd) on the CNT surface. The combination of the excellent catalytic properties of Pd particles with photothermal conversion capability of CNTs makes the Pd/CNT composite a promising catalyst for the fast degradation of organic pollutants, as demonstrated by a model catalytic reaction using 4-nitrophenol (4-NP). The conversion of 4-NP using the Pd/CNT composite as the catalyst has increased by 1.6-fold under near infrared light illumination, benefiting from the strong light-to-heat conversion effect of CNTs. Our proposed strategy opens a new avenue for the synthesis of CNT composites as a sustainable and versatile catalyst platform.

Template synthesis of dual-functional porous MoS2 nanoparticles with photothermal conversion and catalytic properties

Advanced catalysis triggered by photothermal conversion effects has aroused increasing interest due to its huge potential in environmental purification. In this work, we developed a novel approach to the fast degradation of 4-nitrophenol (4-Nip) using porous MoS₂ nanoparticles as catalysts, which integrate the intrinsic catalytic property of MoS₂ with its photothermal conversion capability. Using assembled polystyrene-b-poly(2-vinylpyridine) block copolymers as soft templates, various MoS₂ particles were prepared, which exhibited tailored morphologies (e.g., pomegranate-like, hollow, and open porous structures). The photothermal conversion performance of these featured particles was compared under near-infrared (NIR) light irradiation. Intriguingly, when these porous MoS₂ particles were further employed as catalysts for the reduction of 4-Nip, the reaction rate constant was increased by a factor of 1.5 under NIR illumination. We attribute this catalytic enhancement to the open porous architecture and light-to-heat conversion performance of the MoS₂ particles. This contribution offers new opportunities for efficient photothermal-assisted catalysis.

Surface-Functionalized Au-Pd Nanorods with Enhanced Photothermal Conversion and Catalytic Performance

Bimetallic nanostructures comprising plasmonic and catalytic components have recently emerged as a promising approach to generate a new type of photo-enhanced nanoreactors. Most designs however concentrate on plasmon-induced charge separation, leaving photo-generated heat as a side product. This work presents a photoreactor based on Au-Pd nanorods with an optimized photothermal conversion, which aims to effectively utilize the photo-generated heat to increase the rate of Pd-catalyzed reactions. Dumbbell-shaped Au nanorods were fabricated via a seed-mediated growth method using binary surfactants. Pd clusters were selectively grown at the tips of the Au nanorods, using the zeta potential as a new synthetic parameter to indicate the surfactant remaining on the nanorod surface. The photothermal conversion of the Au-Pd nanorods was improved with a thin layer of polydopamine (PDA) or TiO₂. As a result, a 60% higher temperature increment of the dispersion compared to that for bare Au rods at the same light intensity and particle density could be achieved. The catalytic performance of the coated particles was then tested using the reduction of 4-nitrophenol as the model reaction. Under light, the PDA-coated Au-Pd nanorods exhibited an improved catalytic activity, increasing the reaction rate by a factor 3. An analysis of the activation energy confirmed the photoheating effect to be the dominant mechanism accelerating the reaction. Thus, the increased photothermal heating is responsible for the reaction acceleration. Interestingly, the same analysis shows a roughly 10% higher reaction rate for particles under illumination compared to under dark heating, possibly implying a crucial role of localized heat gradients at the particle surface. Finally, the coating thickness was identified as an essential parameter determining the photothermal conversion efficiency and the reaction acceleration.

A binary carbon@silica@carbon hydrophobic nanoreactor for highly efficient selective oxidation of aromatic alkanes

Nanoreactors with a delimited void space and a large number of mesoporous structures have attracted great attention as potential heterogeneous catalysts. In this work, a cobalt and nitrogen co-doped binary carbon@silica@carbon hydrophobic nanoreactor was synthesized by an in situ synthesis method. Cobalt porphyrin was used as an active component to construct Co-N_x sites, and the purpose of the double carbon layer coating was to enhance the hydrophobicity of the surface of the nanoreactor. The optimal nanoreactor could achieve 96.9% ethylbenzene conversion and 99.1% acetophenone selectivity and showed outstanding universality to many other aromatic alkanes. The superior performance was mainly due to the presence of double carbon layers and the high content of Co-N_x sites. The double hydrophobic carbon layer coating could not only promote the adsorption of organic molecules, but also implant Co-N_x active sites on both the inner and outer surfaces of the nanoreactor. This work proposed a meaningful strategy to obtain a highly efficient nanoreactor for C-H bond oxidation.

Hyperporous magnetic catalyst foam for highly efficient and stable adsorption and reduction of aqueous organic contaminants

The facile and low-cost fabrication of free-standing magnetic catalysts with high catalytic efficiency, rapid reaction rate and excellent recoverability has been pursued for various catalysis applications, e.g., treating aqueous organic 4-nitrophenol pollutants. Here, we design and fabricate a free-standing nickel-coated hyperporous polymer foam (Ni-HPF) with adjustable shapes and sizes, hierarchical multiscale porous structures, abundant catalytical interfaces and excellent super-paramagnetic properties. Due to the synergistical effect of abundant binding sites and highly catalytic reduction, the as-prepared Ni-HPF has demonstrated high conversion efficiency (> 90% at extremely low concentration of 7.5 μM) and rapid reaction rate (2.58 × 10^-3 s^-1) for the reduction of organic 4-nitrophenol. Moreover, the magnetic catalyst also holds excellent recoverability (>80% conversion rate even after 1000 cycles) and good reproducibility (>80% conversion rate after 3 months of storage). As such, this work with novel material design and working principle could provide a wide range of potential applications in water purification, chemical catalysis and energy storage devices.

Artificial Melanogenesis by Confining Melanin/Polydopamine Production inside Polymersomes

Melanin and polydopamine are potent biopolymers for the development of biomedical nanosystems. However, applications of melanin or polydopamine-based nanoparticles are limited by drawbacks related to a compromised colloidal stability over long time periods and associated cytotoxicity. To overcome these hurdles, a novel strategy is proposed that mimics the confinement of natural melanin in melanosomes. Melanosome mimics are developed by co-encapsulating the melanin/polydopamine precursors L-DOPA/dopamine with melanogenic enzyme Tyrosinase within polymersomes. The conditions of polymersome formation are optimized to obtain melanin/polydopamine polymerization within the cavity of the polymersomes. Similar to native melanosomes, polymersomes containing melanin/polydopamine show long-term colloidal stability, cell-compatibility, and potential for cell photoprotection. This novel kind of artificial melanogenesis is expected to inspire new applications of the confined melanin/polydopamine biopolymers.

Polydopamine mediated modification of manganese oxide on melamine sponge for photothermocatalysis of gaseous formaldehyde

It is an urgent need to develop environmentally friendly strategies with low energy consumption for gaseous formaldehyde (HCHO) purification. Herein, a sponge based MS/PDA/MnO_x catalyst with plentiful 3D porosities was constructed. The dual-functional PDA layer not only promoted the MnO_x loading (25 wt% MnO_x in the composite), but also acted as a photothermal converter to absorb photo-irradiation to heat MnO_x catalyst (~80 °C after 10 min irradiation). Moreover, the 3D network structure favored the mass transfer and effectively reduced the catalyst agglomeration to expose more active sites. As a result, the obtained MS/PDA/MnO_x photothermocatalyst showed highly efficient performance for removal of HCHO within concentration of 40-320 ppm at room temperature under xenon light irradiation. This process followed a pseudo-second-order model, and the reaction rate of the MS/PDA/MnO_x was 4.82 times of the MS/MnO_x. Finally, a possible photothermocatalysis mechanism was proposed based on the intermediate examination via the in-situ DRIFTS investigation.

Polydopamine-based nanoreactors: synthesis and applications in bioscience and energy materials

Polydopamine (PDA)-based nanoreactors have shown exceptional promise as multifunctional materials due to their nanoscale dimensions and sub-microliter volumes for reactions of different systems. Biocompatibility, abundance of active sites, and excellent photothermal conversion have facilitated their extensive use in bioscience and energy storage/conversion. This minireview summarizes recent advances in PDA-based nanoreactors, as applied to the abovementioned fields. We first highlight the design and synthesis of functional PDA-based nanoreactors with structural and compositional diversity. Special emphasis in bioscience has been given to drug/protein delivery, photothermal therapy, and antibacterial properties, while for energy-related applications, the focus is on electrochemical energy storage, catalysis, and solar energy harvesting. In addition, perspectives on pressing challenges and future research opportunities regarding PDA-based nanoreactors are discussed.

Highly Dispersed RuOOH Nanoparticles on Silica Spheres: An Efficient Photothermal Catalyst for Selective Aerobic Oxidation of Benzyl Alcohol

Photothermal catalysis represents a promising strategy to utilize the renewable energy source (e.g., solar energy) to drive chemical reactions more efficiently. Successful and efficient photothermal catalysis relies on the availability of ideal photothermal catalysts, which can provide both large areas of catalytically active surface and strong light absorption power simultaneously. Such duplex requirements of a photothermal catalyst exhibit opposing dependence on the size of the catalyst nanoparticles, i.e., smaller size is beneficial for achieving higher surface area and more active surface, whereas larger size favors the light absorption in the nanoparticles. In this article, we report the synthesis of ultrafine RuOOH nanoparticles with a size of 2-3 nm uniformly dispersed on the surfaces of silica (SiOx) nanospheres of hundreds of nanometers in size to tackle this challenge of forming an ideal photothermal catalyst. The ultrasmall RuOOH nanoparticles exhibit a large surface area as well as the ability to activate adsorbed molecular oxygen. The SiOx nanospheres exhibit strong surface light scattering resonances to enhance the light absorption power of the small RuOOH nanoparticles anchored on the SiOx surface. Therefore, the RuOOH/SiOx composite particles represent a new class of efficient photothermal catalysts with a photothermal energy conversion efficiency of 92.5% for selective aerobic oxidation of benzyl alcohol to benzylaldehyde under ambient conditions.