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Ultrasmall nanoparticles (usNPs) have emerged as promising theranostic tools in cancer nanomedicine. With sizes comparable to globular proteins, usNPs exhibit unique physicochemical properties and physiological behavior distinct from larger particles, including lack of protein corona formation, efficient renal clearance, and reduced recognition and sequestration by the reticuloendothelial system. In cancer treatment, usNPs demonstrate favorable tumor penetration and intratumoral diffusion. Active targeting strategies, incorporating ligands for specific tumor receptor binding, serve to further enhance usNP tumor selectivity and therapeutic performance. Numerous preclinical studies have already demonstrated the potential of actively targeted usNPs, revealing increased tumor accumulation and retention compared to non-targeted counterparts. In this review, we explore actively targeted inorganic usNPs, highlighting their biological properties and behavior, along with applications in both preclinical and clinical settings.

High-entropy alloys (HEAs) are promising candidates for the electrocatalyst of hydrogen evolution reaction (HER) due to their unique properties such as cocktail electronic effect and lattice distortion effect. Herein, the ultrasmall (sub-2 nm) nanoparticles of PtRuCoNiCu HEA with uniform element distribution are highly dispersed on hierarchical N-doped carbon nanocages (hNCNC) via low-temperature thermal reduction, denoted as us-HEA/hNCNC. The optimal us-HEA/hNCNC exhibits excellent HER performance in 0.5 M H2SO4 solution, achieving an ultralow overpotential of 19 mV at 10 mA·cm−2 (without iR-compensation), high mass activity of 13.1 A·mgnoble metals−1 at −0.10 V and superb stability with a slight overpotential increase of 3 mV after 20,000 cycles of cyclic voltammetry scans, much superior to the commercial Pt/C (20 wt.%). The combined experimental and theoretical studies reveal that the Pt&Ru serve as the main active sites for HER and the CoNiCu species modify the electron density of active sites to facilitate the H* adsorption and achieve an optimum M-H binding energy. The hierarchical pore structure and N-doping of hNCNC support also play a crucial role in the enhancement of HER activity and stability. This study demonstrates an effective strategy to greatly improve the HER performance of noble metals by developing the HEAs on the unique hNCNC support. [ABSTRACT FROM AUTHOR]

Green synthesis of nanoparticles for catalytic applications remains of continued interest, especially for reactions that would occur on an industrial scale or that may be of environmental significance. Here, ultrasmall 2.1-nm copper nanoparticles were synthesized under ambient conditions using a copper sulfate pentahydrate precursor and lemongrass extract as a reducing and capping agent. Their potential to act as catalysts was tested using model reactions: the sodium borohydride reduction reactions of p-nitrophenol and Eosin Yellow. Kinetics measurements were obtained with visible time-course spectroscopy and showed that copper nanoparticles effectively catalyzed both reactions. Temperature dependence followed Arrhenius behavior, indicating the catalyst surface was accessible to reactants. Activation energies of 59.2 and 38.5 kJ/mol were obtained for the reduction reactions of p-nitrophenol and Eosin Yellow, respectively. Large frequency factors for both reactions were found, implying large numbers of catalytic sites and/or facilitation of reaction by capping agents. This copper nanoparticle catalyst prepared via green synthesis demonstrates reproducible reduction behavior for two model reactions and observed rate constants that compare favorably with other copper nanoparticle catalysts, particularly in terms of rate constants normalized for available surface area and including catalysts produced via traditional synthetic methods.

In this work, small trimetallic Au-PdPt nanoparticles (Au-PdPt NPs) with alloyed Pd–Pt layers composed of different ratios of Pd and Pt were successfully prepared by judiciously adjusting the ratio of Pd and Pt during the one-pot synthesis. Three types of Au-PdPt-NP/C catalysts were further prepared and named as ORR-A-Au52.4-Pd7.7Pt39.9-NP/C catalysts, HER-A-Au55.4-Pd14.5Pt30.1-NP/C catalysts, and ORR-B-Au55.6-Pd33.5Pt10.9-NP/C catalysts. Thanks to the different atomic ratios of Pd and Pt in their alloyed Pd–Pt layers, they can show excellent electrocatalytic performance toward the acidic ORR/HER and the alkaline ORR. For instance, (1) the ORR half-wave potential (E1/2) of ORR-A-Au52.4-Pd7.7Pt39.9-NP/C catalysts in the acidic media is 0.904 V, which is about 52 mV greater than that (0.852 V) of commercial Pt/C catalyst. (2) The HER overpotential at the current density of −10 mA cm–2 (η10) of HER-A-Au55.4-Pd14.5Pt30.1-NP/C catalysts in the acidic media is only 9 mV, which is superior to that (31 mV) of the commercial Pt/C catalyst. (3) The ORR E1/2 of ORR-B-Au55.6-Pd33.5Pt10.9-NP/C catalysts in the alkaline media is 0.935 V, which is 61 mV greater than that (0.874 V) of the commercial Pt/C catalyst. In addition, all of them exhibit excellent stability, compared with commercial Pt/C catalysts. This synthetic strategy can be further extended to improve the different catalytic activities of small Au-based NPs by alloying surface engineering. [ABSTRACT FROM AUTHOR]

Green synthesis of nanoparticles for catalytic applications remains of continued interest, especially for reactions that would occur on an industrial scale or that may be of environmental significance. Here, ultrasmall 2.1-nm copper nanoparticles were synthesized under ambient conditions using a copper sulfate pentahydrate precursor and lemongrass extract as a reducing and capping agent. Their potential to act as catalysts was tested using model reactions: the sodium borohydride reduction reactions of p-nitrophenol and Eosin Yellow. Kinetics measurements were obtained with visible time-course spectroscopy and showed that copper nanoparticles effectively catalyzed both reactions. Temperature dependence followed Arrhenius behavior, indicating the catalyst surface was accessible to reactants. Activation energies of 59.2 and 38.5 kJ/mol were obtained for the reduction reactions of p-nitrophenol and Eosin Yellow, respectively. Large frequency factors for both reactions were found, implying large numbers of catalytic sites and/or facilitation of reaction by capping agents. This copper nanoparticle catalyst prepared via green synthesis demonstrates reproducible reduction behavior for two model reactions and observed rate constants that compare favorably with other copper nanoparticle catalysts, particularly in terms of rate constants normalized for available surface area and including catalysts produced via traditional synthetic methods. [ABSTRACT FROM AUTHOR]

Liquid exfoliation can be considered as a viable approach for the scalable production of 2D materials due to its various benefits, although the polydispersity in the obtained nanosheet size hinders their straightforward incorporation. Size‐separation can help alleviate these concerns, however a correlation between nanosheet size and property needs to be established to bring about size‐specific applicability. Herein, size‐selected aqueous nanosheet dispersions have been obtained via centrifugation‐based protocols, and their chemical activity in the spontaneous reduction of chloroplatinic acid is investigated. Growth of ultrasmall Pt nanoparticles was achieved on nanosheet surfaces without a need for reducing agents, and stark differences in the nanoparticle coverage were observed as a function of nanosheet size. Defects in the nanosheets were probed via Raman spectroscopy, and correlated to the observed size‐activity. Additionally, the effect of reaction temperature during synthesis was investigated. The electrochemical activity of the ultrasmall Pt nanoparticle decorated MoS2 nanosheets was evaluated for the hydrogen evolution reaction, and enhancement in performance was observed with nanosheet size, and nanoparticle decoration density. These findings shine light on the significance of nanosheet size in controlling spontaneous reduction reactions, and provide a deeper insight to intrinsic properties of liquid exfoliated nanosheets. [ABSTRACT FROM AUTHOR]

Liquid‐liquid phase separation (LLPS) of biopolymers to form condensates is a widespread phenomenon in living cells. Agents that target or alter condensation can help uncover elusive physiological and pathological mechanisms. Owing to their unique material properties and modes of interaction with biomolecules, nanoparticles represent attractive condensate‐targeting agents. Our work focused on elucidating the interaction between ultrasmall gold nanoparticles (usGNPs) and diverse types of condensates of tau, a representative phase‐separating protein associated with neurodegenerative disorders. usGNPs attract considerable interest in the biomedical community due to unique features, including emergent optical properties and good cell penetration. We explored the interaction of usGNPs with reconstituted self‐condensates of tau, two‐component tau/polyanion and three‐component tau/RNA/alpha‐synuclein coacervates. The usGNPs were found to concentrate into condensed liquid droplets, consistent with the formation of dynamic client (nanoparticle) ‐ scaffold (tau) interactions, and were observable thanks to their intrinsic luminescence. Furthermore, usGNPs were capable to promote LLPS of a protein domain which is unable to phase separate on its own. Our study demonstrates the ability of usGNPs to interact with and illuminate protein condensates. We anticipate that nanoparticles will have broad applicability as nanotracers to interrogate phase separation, and as nanoactuators controlling the formation and dissolution of condensates. [ABSTRACT FROM AUTHOR]

Abstract Background Iron oxide nanoparticles have been approved by food and drug administration for clinical application as magnetic resonance imaging (MRI) and are considered to be a biocompatible material. Large iron oxide nanoparticles are usually used as transversal (T 2) contrast agents to exhibit dark contrast in MRI. In contrast, ultrasmall iron oxide nanoparticles (USPIONs) (several nanometers) showed remarkable advantage in longitudinal (T 1)-weighted MRI due to the brighten effect. The study of the toxicity mainly focuses on particles with size of tens to hundreds of nanometers, while little is known about the toxicity of USPIONs. Results We fabricated Fe3O4 nanoparticles with diameters of 2.3, 4.2, and 9.3 nm and evaluated their toxicity in mice by intravenous injection. The results indicate that ultrasmall iron oxide nanoparticles with small size (2.3 and 4.2 nm) were highly toxic and were lethal at a dosage of 100 mg/kg. In contrast, no obvious toxicity was observed for iron oxide nanoparticles with size of 9.3 nm. The toxicity of small nanoparticles (2.3 and 4.2 nm) could be reduced when the total dose was split into 4 doses with each interval for 5 min. To study the toxicology, we synthesized different-sized SiO2 and gold nanoparticles. No significant toxicity was observed for ultrasmall SiO2 and gold nanoparticles in the mice. Hence, the toxicity of the ultrasmall Fe3O4 nanoparticles should be attributed to both the iron element and size. In the in vitro experiments, all the ultrasmall nanoparticles (

This paper presents an extensive study carried out to understand the process of tailoring the morphology of solution processed nanostructured Ge23Sb7S70 Chalcogenide glass thin films and to analyze their microstructure dependent optical properties. To tailor the desired morphology of the solution processed ChG films different synthesis parameters have been optimized, step by step. It has been observed that the dissolution time and concentration of Chalcogenide glass precursor solution used for the deposition of solution processed films have the major role in determining their morphology. Annealing of solution processed chalcogenide glass film is an important step to get rid of residual solvent from the film. This study reveals that annealing may disturb the morphological uniformity of solution processed chalcogenide glass films and a careful optimization of annealing step is required to maintain the morphological uniformity. Microstructure dependent optical properties such as refractive index and optical bandgap of solution processed chalcogenide glass films have also been analyzed in this study. It has been observed the size of the microstructures insolution processed chalcogenide glass films greatly influences the optical properties of these films.

Pd-based nanostructures have potential use in optronics, sensing, organic catalysis, and gas-involved electrocatalysis. Despite the substantial advances made, controllable synthesis of amorphous-dominated Pd-based ternary alloy nanoparticles or related assemblies still faces challenges, and their uses for the hydrogen evolution reaction (HER) have not been fully studied. Here, the amorphous-dominated ultrasmall PdCuMo nanoparticle (2.58 nm) assemblies are fabricated under mild conditions via a polyether-assisted thermal reduction strategy, which possesses numerous amorphous/crystalline (a/c) heterophase interfaces, mesoporous structures, and a high specific surface area. Due to the presence of unique a/c heterophase interfaces, proper alloy constituents, and their strong interplay that can regulate the surface/interface electronic structure and optimize the Pd–H bonding intensity, the resultant amorphous-dominated PdCuMo assemblies manifest unprecedented HER performance with an ultralow overpotential of 15.6 mV at a current density of 10 mA cm–2 and a high mass activity of 390 A gPd–1 at a potential of −0.05 V vs reversible hydrogen electrode (RHE), outperforming their binary counterparts (PdCu and PdMo), PdCuMo control sample with a relatively high crystallinity (c-PdCuMo), benchmark Pt/C (commercial, 20%), and the state-of-the-art studied Pd-based electrocatalysts. Additionally, such amorphous-dominated PdCuMo assemblies exhibit outstanding durability and high faradic efficiency yet. This work may shed light on designing advanced amorphous-dominated or a/c heterophase Pd-based multicomponent alloy nanostructures or related assemblies for application in water splitting or other important technological fields. [ABSTRACT FROM AUTHOR]

During recent decades, ultrasmall inorganic nanoparticles have attracted considerable interest due to their favorable biodistribution, pharmacokinetics and theranostic properties. In particular, AGuIX nanoparticles made of polysiloxane and gadolinium chelates were successfully translated to the clinics. In an aqueous medium, these nanoparticles are in dynamic equilibrium with polysiloxane fragments due to the hydrolysis of Si–O–Si bonds. Thanks to high-performance liquid chromatography coupled with electrospray ionization mass spectrometry, all these fragments were separated and identified. [ABSTRACT FROM AUTHOR]

Background: Iron oxide nanoparticles have been approved by food and drug administration for clinical application as magnetic resonance imaging (MRI) and are considered to be a biocompatible material. Large iron oxide nanoparticles are usually used as transversal (T2) contrast agents to exhibit dark contrast in MRI. In contrast, ultrasmall iron oxide nanoparticles (USPIONs) (several nanometers) showed remarkable advantage in longitudinal (T1)-weighted MRI due to the brighten effect. The study of the toxicity mainly focuses on particles with size of tens to hundreds of nanometers, while little is known about the toxicity of USPIONs. Results: We fabricated Fe3O4 nanoparticles with diameters of 2.3, 4.2, and 9.3 nm and evaluated their toxicity in mice by intravenous injection. The results indicate that ultrasmall iron oxide nanoparticles with small size (2.3 and 4.2 nm) were highly toxic and were lethal at a dosage of 100 mg/kg. In contrast, no obvious toxicity was observed for iron oxide nanoparticles with size of 9.3 nm. The toxicity of small nanoparticles (2.3 and 4.2 nm) could be reduced when the total dose was split into 4 doses with each interval for 5 min. To study the toxicology, we synthesized different-sized SiO2 and gold nanoparticles. No significant toxicity was observed for ultrasmall SiO2 and gold nanoparticles in the mice. Hence, the toxicity of the ultrasmall Fe3O4 nanoparticles should be attributed to both the iron element and size. In the in vitro experiments, all the ultrasmall nanoparticles (< 5 nm) of Fe3O4, SiO2, and gold induced the generation of the reactive oxygen species (ROS) efficiently, while no obvious ROS was observed in larger nanoparticles groups. However, the ·OH was only detected in Fe3O4 group instead of SiO2 and gold groups. After intravenous injection, significantly elevated ·OH level was observed in heart, serum, and multiple organs. Among these organs, heart showed highest ·OH level due to the high distribution of ultrasmall Fe3O4 nanoparticles, leading to the acute cardiac failure and death. Conclusion: Ultrasmall Fe3O4 nanoparticles (2.3 and 4.2 nm) showed high toxicity in vivo due to the distinctive capability in inducing the generation of ·OH in multiple organs, especially in heart. The toxicity was related to both the iron element and size. These findings provide novel insight into the toxicology of ultrasmall Fe3O4 nanoparticles, and also highlight the need of comprehensive evaluation for their clinic application. [ABSTRACT FROM AUTHOR]

Ultrasmall metal–organic frameworks (MOFs) may generate unique properties to expand the scope of applications. However, the synthesis is still a great challenge. Herein, we propose a strategy to synthesize ultrasmall MOFs by high gravity technology. With the aid of tremendous intensification of molecular mixing and mass transfer in high‐gravity field, six typical MOFs were obtained instantaneously in a continuous way. These samples are monodispersed with sub‐5 nm in size, smaller than the previously reported values and even close to the length of one crystal unit cell. As a proof‐of‐concept, catalytic activity for Knoevenagel reaction can be significantly enhanced using ultrasmall ZIF‐8. Conversion time of benzaldehyde was decreased by 94 % or 75 % compared to those using conventional or hierarchically porous ZIF‐8. More importantly, this approach is readily scalable with the highest space‐time yield for nano‐MOFs, which may promote the convenient synthesis and practical applications of ultrasmall MOFs in large‐scale. [ABSTRACT FROM AUTHOR]

• Ultrasmall molybdenum carbide α − MoC 1 − x nanoparticles (1.6 nm) and a hybrid material composed of α − MoC 1 − x and reduced graphene oxide (rGO/ α − MoC 1 − x ) were synthesized by a one-pot oleylamine-mediated at a low temperature. • The materials were evaluated as electrocatalysts for the hydrogen evolution reaction (HER) in the acid medium, evidencing quite large activity for the HER. • The synthesis route is simple with low cost and energy consumption, showing a high potential to develop efficient and inexpensive catalysts for HER. Ultrasmall molybdenum carbide α − MoC 1 − x nanoparticles (1.6 nm) and the hybrid material rGO/ α − MoC 1 − x supported in reduced graphene oxide (rGO) were synthesized by a one-pot oleylamine-mediated route at low-temperature (613 K). They were evaluated as electrocatalysts for the hydrogen evolution reaction (HER) in the acid medium after surface cleaning with an ethanol-acetic acid solution. The electrocatalysts were also thermal treated (N 2 flow, 773 K/30 min) and compared with untreated ones. Quite large HER activity was observed for the α − MoC 1 − x compared with the rGO/ α − MoC 1 − x and rGO/ α − MoC 1 − x − 773. In addition, after cycling, all catalysts showed considerable performance improvement assigned to removing residual oleylamine molecules from the electrocatalyst's surface. Compared to the unsupported sample, the lower catalytic activity in the supported materials was attributed to the ultrasmall carbide nanoparticles oxidation increases. The route is simple, with low costs and energy consumption, showing a high potential to develop efficient electrocatalysts for HER. [Display omitted] [ABSTRACT FROM AUTHOR]

We describe here a method to synthesize ultrasmall nanocapsules with a diameter of 6 nm, exhibiting a well‐defined core–shell morphology. Remarkably, the nanocapules are synthesized in a miniemulsion process without the need of large amounts of surfactant as commonly used in the microemulsion process. Ultrasmall nanocapsules with an oil core and a silica shell are formed by the concurrent processes of a sol–gel reaction and Ostwald ripening. Using solvents with different water solubilities and alkoxysilanes with different reactivities, we demonstrate that sizes of obtained nanocapsules depend on the ripening rate and alkoxysilane conversion rate. The method can be also used for encapsulating natural oils such as peppermint oil and limonene. This work shows that the Ostwald ripening phenomenon can be employed beneficially for the preparation of very small colloids. [ABSTRACT FROM AUTHOR]

Hierarchical bottom‐up structuring in nature provides inspiration for the construction of self‐assembled complex with advanced properties out of simple building blocks. However, the development of self‐standing assemblies of ultrasmall metal nanoparticles using redox ligands is still challenging. Here, a molecule‐confined reduction strategy to prepare robust self‐organized superstructures through metal–ligand interfacial interactions and hydrogen bonding is reported. High‐density and well‐separated Pd nanoparticles and single atoms are embedded within organometallic matrixes (Pd@eFc) via in situ reduction of the Pd precursor by redox‐active ligands. Furthermore, these metal–organic networks can be disassembled into fragments with highly dispersed Pd nanoparticles and single atoms by solvent mediation. Strikingly, Pd@eFc disassembly delivers excellent oxygen reduction performance, while its assembly can act as a selective hydrogenation catalyst. This viable molecule‐confined reduction strategy can also be applied to other organometallic superstructures (e.g., Au@eFc, Ag@eFc). The findings thus encourage on‐going study to explore controlled hierarchically self‐assembled superstructures for a wide range of catalysis. [ABSTRACT FROM AUTHOR]

Composite polymer electrolytes (CPEs) decorated with ceramic fillers have emerged as appealing structures that exhibit coalesced merits of both inorganic and polymer solid electrolytes, but are currently challenged by the particle agglomeration that weakens ionic conductivity and electrochemical performances. Herein, a facile solvothermal method is proposed to fabricate the ultrasmall niobium(V) oxide (Nb 2 O 5) nanoparticle of average size being less than 3 nm, enabling the composite polymer electrolyte with homogenous dispersity (nano-CPE). Owning to the superior dispersity of ultrasmall Nb 2 O 5 nanoparticles, the polymer chains can be effectively disordered to enhance the local segmental motion through the physical interruption. Moreover, strong Lewis acid-based interactions between Nb 2 O 5 nanoparticles and lithium salts are formed, resulting in accelerating the dissociation of lithium salt and releasing more free charge carriers. Therefore, the 3D connected Li+ fast pathways along the amorphous region between the Nb 2 O 5 nanoparticles and polymer chains are constructed, ensuring the improved ionic conductivity. In addition, the homogenous Li deposition can also be simultaneously achieved through the intimate interfacial contact, which can efficiently suppress the growth of lithium dendrite in the metal anode. The fabricated nano-CPE presents a high ionic conductivity of 6.6 × 10−5 S/cm at room temperature and wide anti-oxidative potential of 5.1 V. The lithium symmetric battery using nano-CPE delivers a decent lithium plating/stripping performance for 200 h at 0.5 mA/cm2. The solid-sate LiFePO 4 battery achieves long stable cycling performances (151mAh/g and 140 mAh/g after 230 cycles at 0.5C and 1.0C, respectively). This work may offer a facile and efficient synthesized method of highly dispersed ultrasmall nanoparticles for advancing the CPE with improved ionic conductivity, interfacial contact and cell performances. [ABSTRACT FROM AUTHOR]

High-entropy alloys nanoparticles (HEAs NPs) have gained considerable attention due to their extensive compositional tunability and intriguing catalytic properties. However, the synthesis of highly dispersed ultrasmall HEAs NPs remains a formidable challenge due to their inherent thermodynamic instability. In this study, highly dispersed ultrasmall (ca. 2 nm) PtCuGaFeCo HEAs NPs are synthesized using a one-pot solution-based method at 160 °C and atmospheric pressure. The PtCuGaFeCo NPs exhibit good catalytic activity for the oxygen reduction reaction (ORR). The half-wave potential relative to the reversible hydrogen electrode (RHE) reaches 0.88 V, and the mass activity and specific activity are approximately six times and four times higher than that of the commercial Pt/C catalyst. Based on X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analyses, the surface strain and optimized coordination environments of PtCuGaFeCo have led to high ORR activities in acidic media. Moreover, the ultrasmall size also plays an important role in enhancing catalytic performance. The work presents a facile and viable synthesis strategy for preparing the ultrasmall HEAs NPs, offering great potential in energy and electrocatalysis applications through entropy engineering., (© 2024 Wiley‐VCH GmbH.)

Ensuring high catalytic activity and durability at low iridium (Ir)usage is still a big challenge for the development of electrocatalysts toward oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE). Here, a rapid liquid-reduction combined with surface galvanic replacement strategy is reported to synthesize the sub 2 nm high-entropy alloy (HEA) nanoparticles featured with Ir-rich IrRuNiMo medium-entropy oxide shell (Ir-MEO) and a IrRuCoNiMo HEA core (HEA@Ir-MEO). Advanced spectroscopies reveal that the Ir-rich MEO shell inhibits the severe structural evolution of transition metals upon the OER, thus guaranteeing the structural stability. In situ differential electrochemical mass spectrometry, activation energy analysis and theoretical calculations unveil that the OER on HEA@Ir-MEO follows an adsorbate evolution mechanism pathway, where the energy barrier of rate-determining step is substantially lowered. The optimized catalyst delivers the excellent performance (1.85 V/3.0 A cm -2 @80 °C), long-term stability (>500 h@1.0 Acm -2 ), and low energy consumption (3.98 kWh Nm -3 H 2 @1.0 A cm -2 ) in PEMWE with low Ir usage of ≈0.4 mg cm -2 , realizing the dramatical reduction of hydrogen (H 2 ) production cost to 0.88 dollar per kg (H 2 )., (© 2024 Wiley‐VCH GmbH.)

Although tremendous efforts have been devoted to the structural and functional tailoring of natural polyphenol-functionalized nanoparticles, preparing ultrasmall sized (< 6 nm) particles with precisely-defined structures has remained a grand challenge. In this work, we reported the preparation of ultra-small and precisely structured polyhedral oligomeric silsesquioxanes (POSS)-based polyphenol nanoparticles (T8-, T10-, and T12-GAPOSS) by accurately functionalizing the POSS surface with plant polyphenol gallic acid units via thiol-Michael "click" reactions. Those polyphenol nanoparticles exhibited strong free radical scavenging capacity, good biocompatibility and ability to resist cell oxidative damage, which demonstrated great potentials in inhibiting oxidative stress induced pathologies. [ABSTRACT FROM AUTHOR]

Ultrasmall particle size (<10 nm) and rich oxygen vacancies are two sought‐after characteristics for titanium dioxide (TiO2) to achieve high performance, namely, high rate and high storage capacity, when being used as an anode in lithium‐ion batteries (LIBs). However, free TiO2 particles simultaneously possessing both characteristics have not been reported, owing to the synthetic challenges. In this study, we report novel TiO2 nanoparticles with ultrasmall size (ca. 5–8 nm) as well as rich oxygen vacancies synthesized through a simple strategy. Specifically, porous carbon nanoparticles were used to confine the TiO2 precursor in the nanosized pores in the carbon nanoparticles, which were annealed at a high temperature in argon to produce the TiO2 nanoparticles with ultrasmall size and rich oxygen vacancies and subsequently annealed in air to burn away the carbon nanoparticles to afford the so‐called TiOx nanoparticles in a quantitative yield. The obtained anatase TiOx nanoparticles showed an exceptional ultrahigh‐rate lithium storage capability. A record reversible specific capacity of 235 mAh g−1 was achieved at the current density of 0.1 A g−1. Even at an ultrahigh rate of 10 A g−1 (ca. 59 C), it still delivered a specific capacity of 90 mAh g−1, which is five times that of the electrode made with the commercial anatase TiO2 nanoparticles. Furthermore, this electrode also showed an excellent cycling performance with capacity retentions of 87 % and 90 % at high rates of 1 A g−1 and 5 A g−1, respectively, after 1000 cycles. The strategy reported in this work can potentially be a universal method for synthesis of other metal oxides with ultrasmall particle size and rich oxygen vacancies. [ABSTRACT FROM AUTHOR]

Nanoparticle-polymer composites exhibit unusual mechanical properties and chain dynamics when the nanoparticle size is smaller than the entanglement mesh size of the matrix polymer chains, corresponding to the ultrasmall regime defined by de Gennes. However, the mechanism is still ambiguous due to the lack of suitable model systems. Here, we develop an ultrasmall nanoparticle system by using a bimodal grafting strategy to graft both short alkyl chains and long polystyrene chains onto the polyoxometalate molecular nanoparticles with a tunable repulsive potential between the nanoparticles, thus facilitating their uniform dispersion in polystyrene matrices. Linear viscoelasticity of the resultant nanocomposites changes with increasing the filler content, which shows a decrease in both plateau modulus and terminal relaxation time, indicative of a dilution effect of the nanoparticles. Namely, the entanglement network becomes sparser with increasing the filler content. [ABSTRACT FROM AUTHOR]

Studies into the interactions of serum proteins with nanoparticles are typically performed using nanoparticles that are larger than the size of proteins. Due to this size discrepancy, adsorbed proteins are commonly depicted as a globular structure surrounding a nanoparticle. Here, we asked how we should view nanoparticle–protein complexes when the nanoparticles are of similar size or smaller than the proteins with which they interact. We showed that nanoparticles can serve as a cargo on a protein rather than as a carrier of the protein in a size-dependent manner. This can occur when nanoparticles are below 10 nm in diameter. We discovered that when the nanoparticle is a cargo on the protein, the binding of the protein to the receptor target is minimally affected in contrast to the nanoparticle serving as a carrier. Our study should change how we view and describe nanoparticle–protein complexes when the nanoparticles involved are equal in size or smaller than proteins. Unlabelled Image • Ultrasmall nanoparticles act as cargo on large serum proteins. • These ultrasmall nanoparticle–protein complexes have the size and shape of proteins. • Size and surface chemistry of particles determine whether they are cargo or carrier. [ABSTRACT FROM AUTHOR]

Abstract Herein, graphite nanosheets (GN) were first prepared through simple liquid-phase exfoliation of graphite powder in N, N -dimethylacetamide (DMAC). After then, ultrasmall Cu-based metal organic frame (HKUST-1) nanoparticles (less than 5 nm) were in-situ anchored on the surface of graphite nanosheets with high degree of dispersion. Due to the intrinsic structural advantages of the as-synthesized HKUST-1 nanoparticles decorated graphite nanosheets (HKUST-1/GN) hybrids, including superior electron transfer ability and the greatly enhanced adsorption property, HKUST-1/GN shows excellent electrochemical sensing performance toward DNA damage biomarker 8-hydroxy-2'-deoxyguanosine with fast detection speed (∼240 s), wide linear window (10 nM–1 μM), high sensitivity (346857 μA mM−1 cm−2), low detection limit (∼2.5 nM), and good reproducibility. As a result, a highly sensitive electrochemical sensing platform for the detection of DNA damage biomarker 8-hydroxy-2'-deoxyguanosine was fabricated basing the as-prepared HKUST-1/GN hybrids. What is more, the developed electrochemical method was successfully used for the detection of real samples and exhibited satisfied result. Graphical abstract Image 1 Highlights • HKUST-1 decorated graphite nanosheets (HKUST-1/GN) hybrids are easily in-situ prepared. • HKUST-1/GN hybrids show remarkably enhanced adsorption property. • High sensitivity and selectivity is achieved toward 8-hydroxy-2'-deoxyguanosine sensing. • The strategy provides guidance for the synthesis of other electrode materials. [ABSTRACT FROM AUTHOR]

Ultrasmall nanoparticles, with sizes in the 1–3 nm range, exhibit unique properties distinct from those of free molecules and larger-sized nanoparticles. Demonstrating that the hydrothermal method can serve as a facile method for the synthesis of platinum nanoparticles, we successfully synthesized ultrasmall Pt nanoparticles with an average size of 2.45 nm, with the aid of poly(vinyl pyrrolidone) (PVP) as reducing agents and capping agents. Because of the size effect, these ultrasmall Pt nanoparticles exhibit a high activity toward the methanol oxidation reaction.

As a bridge between individual atoms and large plasmonic nanoparticles, ultrasmall (core size <3 nm) noble metal nanoparticles (UNMNPs) have been serving as model for us to fundamentally understand many unique properties of noble metals that can only be observed at an extremely small size scale. With decades’ efforts, many significant breakthroughs in the synthesis, characterization and functionalization of UNMNPs have laid down a solid foundation for their future applications in the healthcare. In this review, we aim to tightly correlate these breakthroughs with their biomedical applications and illustrate how to utilize these breakthroughs to address long-standing challenges in the clinical translation of nanomedicines. In the end, we offer our perspective on the remaining challenges and opportunities at the frontier of biomedical-related UNMNPs research. [ABSTRACT FROM AUTHOR]

We report a solvothermal synthesis of ultrasmall platinum nanoparticles (USPtNPs) with an average size of 0.204 (± 0.008) nm using reline deep eutectic solvent (DES) as a stabilizing medium at a temperature of 80 ºC. SEM and EDS were used to morphologically characterize the USPtNPs. These revealed approximately spherical shapes with emission lines characteristic of platinum. DES was characterized by FT-IR and NMR, which indicated its formation through hydrogen bonds between the precursors. DSC was also used to characterize the precursors and the formed DES. Furthermore, an electrochemical sensor for determining riboflavin (RB) in commercial energy drinks and biological fluids was developed using the USPtNPs together with multiwalled carbon nanotubes (MWCNT). The USPtNPs-DES/MWCNT/GCE film was characterized by SEM, which demonstrated the characteristic tubular morphology of MWCNT. The RB voltammetric response was studied, and a significant enhanced on the current response was observed, especially due to the USPtNPs. This sensor displayed a linear response for RB in the range of 0.02–1.2µmol L−1, with a limit of detection of 1.8 nmol L−1. Besides detectability at nanomolar range, excellent performance was verified for repeatability and anti-interference features. The sensor based on extraordinary USPtNPs synthesized in DES in a simpler and environmentally friendly way was successfully applied to determine RB in different matrices. • First synthesis of USPtNPs using deep eutectic solvent as stabilizing medium. • USPtNPs with an average size of 0.208 nm obtained in a solvothermal synthesis. • First sensor based on USPtNPs and MWCNTs to detect RB in biological and food samples. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries are potential low-cost alternatives to current lithium-ion technology, yet their performances still fall short of expectation due to the lack of suitable electrode materials with large capacity, long-term cycling stability, and high-rate performance. In this work, we demonstrated that ultrasmall (∼5 nm) iron selenide (FeSe2) nanoparticles exhibited a remarkable activity for sodium-ion storage. They were prepared from a high-temperature solution method with a narrow size distribution and high yield and could be readily redispersed in nonpolar organic solvents. In ether-based electrolyte, FeSe2 nanoparticles exhibited a large specific capacity of ∼500 mAh/g (close to the theoretical limit), high rate capability with ∼250 mAh/g retained at 10 A/g, and excellent cycling stability at both low and high current rates by virtue of their advantageous nanosizing effect. Full sodium-ion batteries were also constructed from coupling FeSe2 with NASICON-type Na3V2(PO4)3 cathode and demonstrated impressive capacity and cycle ability. [ABSTRACT FROM AUTHOR]

The fast renal clearance of hydrophilic small molecular anticancer drugs and ultrasmall nanoparticles (NPs) results in the low utilization rate and certain side effects, thus improving the tumor targeting is highly desired but faces great challenges. A novel and general β-cyclodextrin (CD) aggregation-induced assembly strategy to fabricate doxorubicin (DOX) and CD-coated NPs (such as Au) co-encapsulated pH-responsive nanocomposites (NCs) is proposed. By adding DOX×HCl and reducing pH in a reversed microemulsion system, hydrophilic CD-coated AuNPs rapidly assemble into large NCs. Then in situ polymerization of dopamine and sequentially coordinating with Cu 2+ on the surface of NCs provide extra weak acid responsiveness, chemodynamic therapy (CDT), and improved biocompatibility as well as stability. The subsequent tumor microenvironment responsive dissociation notably improves their passive tumor targeting, bioavailability, imaging, and therapeutic capabilities, as well as facilitates their internalization by tumor cells and metabolic clearance, thereby reducing side effects. The combination of polymerized dopamine and assembled AuNPs reinforces photothermal capability, thus further boosting CDT through thermally amplifying Cu-catalyzed Fenton-like reaction. Both in vitro and in vivo studies confirm the desirable outcomes of these NCs as photoacoustic imaging guided trimodal (thermally enhanced CDT, photothermal therapy, and chemotherapy) synergistic tumor treatment agents with minimal systemic toxicity., (© 2023 Wiley-VCH GmbH.)

The misfolding and aggregation of α-synuclein is one of the key pathogeneses in Parkinson's disease (PD). Development of innovative and effective approaches to eliminate α-synuclein aggregates is crucial for PD treatment. Herein, we report that quercetin-modified ultrasmall Cu 2- x Se antioxidative nanoparticles (abbreviated as CSPQ) can promote neurons to efficiently scavenge α-synuclein aggregates and boost PD therapy by activating their nuclear factor-erythroid 2-related factor 2 (Nrf2) to enhance the SQSTM1/p62-dependent selective autophagy. We reveal that CSPQ nanoparticles can promote the degradation of Kelch-like ECH-associated protein 1 (Keap1) and thus activate Nrf2/p62 pathway of neurons by stimulating their nuclear translocation of transcription factor EB (TFEB). Moreover, these nanoparticles can successfully reduce α-synuclein associated pathology to alleviate neuronal damage in vivo and improve motor disorder and exploration ability of α-synuclein preformed fibrils (PFFs)-induced PD mice. Our work demonstrates the importance and novelty of modulating the selective autophagy of neurons by nanoparticles in clearance of α-synuclein aggregates for PD therapy, and highlights the great potential of CSPQ nanoparticles in PD therapy. [Display omitted] • Quercetin-modified Cu 2-x Se nanoparticles promote neurons to scavenge α-synuclein aggregates and boost PD therapy. • The nanoparticles activate the Nrf2 of neurons to regulate their SQSTM1/p62-dependent selective autophagy. • The activation of Nrf2 is due to the nuclear translocation of transcription factor EB. [ABSTRACT FROM AUTHOR]

The biological properties of spherical nucleic acids (SNAs) are largely independent of nanoparticle core identity but significantly affected by oligonucleotide surface density. Additionally, the payload-to-carrier (i.e., DNA-to-nanoparticle) mass ratio of SNAs is inversely proportional to core size. While SNAs with many core types and sizes have been developed, all in vivo analyses of SNA behavior have been limited to cores >10 nm in diameter. However, "ultrasmall" nanoparticle constructs (<10 nm diameter) can exhibit increased payload-to-carrier ratios, reduced liver accumulation, renal clearance, and enhanced tumor infiltration. Therefore, we hypothesized that SNAs with ultrasmall cores exhibit SNA-like properties, but with in vivo behavior akin to traditional ultrasmall nanoparticles. To investigate, we compared the behavior of SNAs with 1.4-nm Au 102 nanocluster cores (AuNC-SNAs) and SNAs with 10-nm gold nanoparticle cores (AuNP-SNAs). Significantly, AuNC-SNAs possess SNA-like properties (e.g., high cellular uptake, low cytotoxicity) but show distinct in vivo behavior. When intravenously injected in mice, AuNC-SNAs display prolonged blood circulation, lower liver accumulation, and higher tumor accumulation than AuNP-SNAs. Thus, SNA-like properties persist at the sub-10-nm length scale and oligonucleotide arrangement and surface density are responsible for the biological properties of SNAs. This work has implications for the design of new nanocarriers for therapeutic applications., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

A simple strategy for making nanoparticles by sonofragmentation of high‐aspect‐ratio 1D substrates is introduced. With common laboratory equipment, ultrathin nanowires are fragmented into nanoparticles of size determined by the nanowire width, resulting within hours in monodisperse, crystalline nanoparticles of <10 nm. This strategy is applicable to a diversity of semiconductor, oxide, and metal nanowires. [ABSTRACT FROM AUTHOR]

An ultrasmall Fe2O3 nanoparticle/three-dimensional hierarchical porous graphene-like (Fe2O3/3D HPG) composite has been synthesized by a facile hydrothermal method, which is investigated as a high performance electrode material for supercapacitors. In the composite, the ultra-small-sized Fe2O3 nanoparticles, with an average size of approximately 5 nm, are uniformly distributed on the 3D HPG substrate. The as-prepared Fe2O3/3D HPG composite electrode exhibits good electrochemical performance with a maximum specific capacitance of 967 F g−1 at 1.0 A g−1 in the three-electrode system in 2.0 mol L−1 KOH aqueous solution, and an outstanding rate capability (74 % capacitance retention at 30 A g−1). In addition, the composite electrode also exhibits an excellent cycling performance with 92 % capacitance retention of the initial capacity after 5000 cycles at 1.0 A g−1. [ABSTRACT FROM AUTHOR]

Water soluble luminescent gold nanoparticles with average size 2.3 nm were for the first time synthesized by completely green method of Au(III) reduction using chitosan derivative—biocompatible nontoxic N -(4-imidazolyl)methylchitosan (IMC) as both reducing and stabilizing agent. Reduction of Au(III) to gold nanoparticles in IMC solution is a slow process, in which coordination power of biopolymer controls both reducing species concentration and gold crystal growth rate. Gold nanoparticles formed in IMC solution do not manifest surface plasmon resonance, but exhibit luminescence at 375 nm under UV light excitation at 230 nm. Due to biological activity of imidazolyl-containing polymers and their ability to bind proteins and drugs, the obtained ultra-small gold nanoparticles can find an application for biomolecules detection, bio-imaging, drug delivery, and catalysis. Very high catalytic activity (as compared to gold nanoparticles obtained by other green methods) was found for Au/IMC nanoparticles in the model reaction of p -nitrophenol reduction providing complete conversion of p -nitrophenol to p -aminophenol within 180–190 s under mild conditions. [ABSTRACT FROM AUTHOR]

Ultrasmall nanoparticulate materials with core sizes in the 1-3 nm range bridge the gap between single molecules and classical, larger-sized nanomaterials, not only in terms of spatial dimension, but also as regards physicochemical and pharmacokinetic properties. Due to these unique properties, ultrasmall nanoparticles appear to be promising materials for nanomedicinal applications. This review overviews the different synthetic methods of inorganic ultrasmall nanoparticles as well as their properties, characterization, surface modification and toxicity. We moreover summarize the current state of knowledge regarding pharmacokinetics, biodistribution and targeting of nanoscale materials. Aside from addressing the issue of biomolecular corona formation and elaborating on the interactions of ultrasmall nanoparticles with individual cells, we discuss the potential diagnostic, therapeutic and theranostic applications of ultrasmall nanoparticles in the emerging field of nanomedicine in the final part of this review. [ABSTRACT FROM AUTHOR]

Lanthanide-doped upconversion nanoparticles (UCNPs) have been widely exploited as nanoprobes or energy transducers in traditional as well as emerging biological applications, such as bioimaging, photodynamic therapy, optogenetics, gene editing. However, the breadth and depth of their utility in the biomedical areas are still not comparable to conventional luminescent probes, such as fluorescent dyes and semiconductor quantum dots. Their application is largely limited by their large size, typically > 20 nm, to ensure a sufficient luminescence brightness. In order to enhance the brightness of UCNPs without exceeding the critical size limitations for biomedical applications, we employ here a transient energy trapping effect as a nanoprobe surface passivation strategy to prevent deleterious distant energy migration in the host lattice, which is particularly prevalent in ultrasmall UCNPs and leads to luminescence quenching. We demonstrate this strategy by incorporating Tm3+ ions as energy trapping centers near the surface of sub-10 nm NaYF 4 : Yb, Er UCNPs and obtain an emission enhancement by almost one order of magnitude without any increment on the nanoparticle size. Our work presents a promising strategy for the preparation of ultrasmall and bright upconversion nanoprobes that are less vulnerable to surface quenching and that potentially minimize the interference with the object. This facilitates their biomedical applications as here demonstrated by unprecedented high-quality cell labeling and imaging, featured with very uniform nanoparticle distribution in the outer nuclear region. [Display omitted] • Energy trapping ions are used to inhibit energy migration, preventing surface quenching of upconversion nanoparticles. • This energy-trapping strategy was applied to sub-10 nm UCNPs, and significant luminescence enhancement was obtained. • The improved ultrasmall bright UCNPs exhibit excellent water-quenching resistance. • The ultrasmall bright UCNPs enabled unprecedented high-quality cell labeling and imaging. [ABSTRACT FROM AUTHOR]

An efficient mediated electrosynthesis of the spherical (85 nm) nanocomposite material Pd@p(MVCA-co-St) was carried out in an aqueous medium. Ultrasmall palladium nanoparticles (3-8 nm) are stabilized in nanocapsules of water-soluble nanoparticles of the copolymer p(MVCA-co-St) consisting of tetraviologen calix[4]resorcinol (MVCA) with styrene (St). The role of the mediator is played by viologen units of a polymer nanoparticle at potentials of the MV/MV redox couple. The high catalytic activity of the nanocomposite material in the reduction of nitrophenol with sodium borohydride is shown. [ABSTRACT FROM AUTHOR]

This paper reports the effect of different concentrations of Rosa ‘Andeli’ double delight petals aqueous extract (PERA) in the synthesis of silver nanoparticles (Ag-NPs), using an easy green chemistry method. Its kinetics study and photocatalytic activity were also evaluated. The Ag-NPs were obtained using an aqueous silver nitrate solution (AgNO 3 ) with 9.66% w/v, 7.25% w/v, and 4.20% w/v PERA as both reducing–stabilizing agent. The formation of the Ag-NPs was demonstrated by analysis of UV–vis spectroscopy, scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) and transmission electron microscopy (TEM). TEM analysis shows spherical nanoparticles in shape and size between ∼0.5 and 1.4 nm. A comparative study was done to determine which concentration was the best reducing–stabilizing agent, and we found out that “ultra-small” nanoparticles (0.5–1.1 nm) were obtained with 9.66% w/v of PERA. The size of the Ag-NPs depends on the concentration of PERA and Ag(I). The reaction of formation of “ultra-small” Ag-NPs, proved to be first order for metallic precursor (silver) and second order for reducing–stabilizing agent (PERA). The Ag-NPs showed photocatalytic activity, in degradation of commercial dye with an efficiency of 95%. [ABSTRACT FROM AUTHOR]

In order to further improve the stability and biocompatibility of magnetic fluids (MFs), we report a one-step protocol for the preparation of ultrasmall superparamagnetic iron oxide MFs. Four kinds of MFs (n % L -Cysteine-S-branched polymethacrylic acid-coated Fe 3 O 4 nanoparticles MFs, n %Cys-PMAA@Fe 3 O 4 MFs) with ultrasmall particle size (< 5 nm) were obtained using the different molecular weight of polymer ligands as the outer layer. Among them, 2 %Cys-PMAA@Fe 3 O 4 MFs show the best performance in the apparent particle size (4.10 ± 0.90 nm), hydrodynamic size (< 50 nm), and magnetic weight gain (67 mg), and stability index (I = 99 %). In addition, 2 %Cys-PMAA@Fe 3 O 4 MFs exhibit excellent stability for 180 days under different salt concentrations (up to 3 mol/L) and pH (2−12). Importantly, the 2 %Cys-PMAA@Fe 3 O 4 MFs show good biocompatibility in vitro that HEK293T and MCF-7 cells viability are higher than 90 % in 24 h when the iron concentration is 250 μg·mL−1. Furthermore, the hemolysis test and H&E tissue section staining demonstrate that the MFs are non-toxic in vivo. Finally, the value of 2 %Cys-PMAA@Fe 3 O 4 MFs at 1.5 T (r 2 = 57.48 mM−1·s−1, r 1 = 8.61 mM−1·s−1, r 2 /r 1 = 6.68) is slightly less than Combidex for r 2 (r 2 = 65 mM−1·s−1), and 2.5-folds higher than Gd-DTPA for r 1 (r 1 = 3.5 mM−1·s−1), so the tumor area can be clearly observed with dual-mode imaging at 3.0 T in vivo by the tail vein injection. This study contributes to the rationalized design and development of a clinical dual-modulus contrast agent. [Display omitted] • The different ratios of polymer ligands L -Cysteine-S-branched polymethacrylic acid (Cys-PMAA) were successfully synthesized. • The branching of degrees for Cys-PMAA was discussed. • Magnetic fluids owned ultra-small particle size (< 5 nm) and hydrodynamic particle size (< 50 nm). • Excellent stability within 180 days in pH (2−12) and 0–3 mol/L NaCl solution. • 2 % samples showed excellent dual-mode imaging effect in Vitro and in Vivo. [ABSTRACT FROM AUTHOR]

Supported bimetallic nanoparticles (NPs) with ultrasmall sizes and homogeneous alloying are attractive for catalysis. However, facile synthesis of this type of material remains very challenging. Here, the aerosol drying impregnation method for rapid, scalable, and general synthesis of silica-supported bimetallic NPs is proposed. The method relies on aerosol spray drying to promote the mixing and dispersing of binary metal precursors on SiO 2 . It is capable of controlling the composition and size of bimetallic NPs and avoids the use of expensive metal complex salts and complicated experiment procedures. Twelve permutations combining a noble metal (Pd, Ru, and Pt) and a base one (Fe, Co, Ni, and Cu) with ultrasmall sizes (1.4-2.2 nm in average size), uniform dispersion, and good alloying are synthesized. Interesting activity and selectivity trends in catalytic semihydrogenation of phenylacetylene over the supported Pd-based NPs can be observed. The silica-supported PdNi NPs deliver both high activity and styrene selectivity. Spectroscopic and density functional theory calculation results reveal the improved chemoselectivity originated from the suitably down-shifted d-band center of the PdNi NPs inducing an increased energy barrier for overhydrogenation and a weakened styrene adsorption., (© 2022 Wiley-VCH GmbH.)

Ultrasmall nanoparticles (NPs) are a promising platform for the diagnosis and therapy of cancer, but the particles in sizes as small as several nanometers have an ability to translocate across biological barriers, which may bring unpredictable health risks. Therefore, it is essential to develop workable cell-based tools that can deliver ultrasmall NPs to the tumor in a safer manner. Here, this work uses macrophages as a shuttle to deliver sub-5 nm PEGylated gold (Au) NPs to tumors actively or passively, while reducing the accumulation of Au NPs in the brain. This work demonstrates that sub-5 nm Au NPs can be rapidly exocytosed from live macrophages, reaching 45.6% within 24 h, resulting in a labile Au NP-macrophage system that may release free Au NPs into the blood circulation in vivo. To overcome this shortcoming, two straightforward methods are used to engineer macrophages to obtain "half-dead" and "dead" macrophages. Although the efficiency of engineered macrophages for delivering sub-5 nm Au NPs to tumors is 2.2-3.8% lower than that of free Au NPs via the passive enhanced permeability and retention effect, this safe-by-design approach can dramatically reduce the accumulation of Au NPs in the brain by more than one order of magnitude. These promising approaches offer an opportunity to expand the immune cell- or stem cell-mediated delivery of ultrasmall NPs for the diagnosis and therapy of diseases in a safer way in the future., (© 2022 Wiley-VCH GmbH.)

Highlights: [•] A synthetic method for ultrasmall Pt nanoparticles (∼1nm) is developed. [•] Compared to bulk Pt, structural relaxation is observed in the Pt nanoparticles. [•] The Pt 4f core level energy shifts positively by +1eV compared with bulk Pt. [Copyright &y& Elsevier]