Luminescent Gold Nanoparticles with Size-Independent Emission

Origin of the Photoluminescence of Metal Nanoclusters: From Metal-Centered Emission to Ligand-Centered Emission

Recently, metal nanoclusters (MNCs) emerged as a new class of luminescent materials and have attracted tremendous interest in the area of luminescence-related applications due to their excellent luminous properties (good photostability, large Stokes shift) and inherent good biocompatibility. However, the origin of photoluminescence (PL) of MNCs is still not fully understood, which has limited their practical application. In this mini-review, focusing on the origin of the photoemission emission of MNCs, we simply review the evolution of luminescent mechanism models of MNCs, from the pure metal-centered quantum confinement mechanics to ligand-centered p band intermediate state (PBIS) model via a transitional ligand-to-metal charge transfer (LMCT or LMMCT) mechanism as a compromise model.

P band intermediate state (PBIS) tailors photoluminescence emission at confined nanoscale interface

The availability of a range of excited states has endowed low dimensional quantum nanostructures with interesting luminescence properties. However, the origin of photoluminescence emission is still not fully understood, which has limited its practical application. Here we judiciously manipulate the delicate surface ligand interactions at the nanoscale interface of a single metal nanocluster, the superlattice, and mesoporous materials. The resulting interplay of various noncovalent interactions leads to a precise modulation of emission colors and quantum yield. A new p-band state, resulting from the strong overlapping of p orbitals of the heteroatoms (O, N, and S) bearing on the targeting ligands though space interactions, is identified as a dark state to activate the triplet state of the surface aggregated chromophores. The UV-Visible spectra calculated by time-dependent density functional theory (TD-DFT) are in quantitative agreement with the experimental adsorption spectra. The energy level of the p-band center is very sensitive to the local proximity ligand chromophores at heterogeneous interfaces.

Facile in situ synthesis of ultrasmall near-infrared-emitting gold glyconanoparticles with enhanced cellular uptake and tumor targeting

The simultaneous possession of high tumor-targeting efficiency, long blood circulation, and low normal-tissue retention is critical for future clinically translatable nanomedicines. Herein, we reported a facile in situ glycoconjugation strategy for the synthesis of near-infrared (NIR)-emitting gold glyconanoparticles (AuGNPs, ∼2.4 nm) using 1-thio-β-d-glucose as both the surface ligand and the reducing agent in the presence of a gold precursor. The ultrasmall AuGNPs showed similar low healthy organ retention to that of the renal-clearable ultrasmall nonglyconanoparticles, but ∼10 and 2.5 times higher in vitro and in vivo tumor-targeting efficiencies, respectively, were observed. This facile glycoconjugation strategy of ultrasmall AuGNPs was found to show activity towards glucose transporters in the cancer cells and prolonged blood circulation with both renal and hepatobiliary clearance pathways, which synergistically enhanced the tumor targeting of the ultrasmall AuGNPs. This discovery provides a smart strategy for the improvement in tumor targeting by ultrasmall NPs and further strengthens our understanding of glycoconjugation in designing future clinically translatable nanomedicines.

Core-in-cage structure regulated properties of ultra-small gold nanoparticles

Understanding the structure-property relationships of novel materials is pivotal for the advances in science and technology. Thiolate ligand protected ultra-small gold nanoparticles (AuNPs; diameter below 3 nm) constitute an emerging class of nanomaterials with molecule-like properties that make them distinct from their larger counterparts. Here we provide new insights into the structure-property relationships of these nanomaterials by developing a series of ultra-small AuNPs, having comparable size and surface functionalities, but with different core-in-cage structures. We identified the density of metallic core and cage containing Au(i)-thiolate motifs, as well as cage rigidity as crucial factors that can significantly modulate the optical and biological properties of these AuNPs. In particular, AuNPs having a longer motif with a more rigid cage structure exhibited stronger luminescence while those containing a high percentage of loosely bound oligomeric Au(i)-thiolate motifs in the cage (semi-rigid structure) had better antibacterial activity. We also studied for the first time the inflammatory response to these NPs and revealed the importance of cage structure. We envisage that the finding reported in this paper can be applied not only to ultra-small AuNPs but also to other nanomaterials to develop new pathways to exciting future applications in electronics, sensing, imaging and medicine.

Probing the biological obstacles of nanomedicine with gold nanoparticles

Despite massive growth in nanomedicine research to date, the field still lacks fundamental understanding of how certain physical and chemical features of a nanoparticle affect its ability to overcome biological obstacles in vivo and reach its intended target. To gain fundamental understanding of how physical and chemical parameters affect the biological outcomes of administered nanoparticles, model systems that can systematically manipulate a single parameter with minimal influence on others are needed. Gold nanoparticles are particularly good model systems in this case as one can synthetically control the physical dimensions and surface chemistry of the particles independently and with great precision. Additionally, the chemical and physical properties of gold allow particles to be detected and quantified in tissues and cells with high sensitivity. Through systematic biological studies using gold nanoparticles, insights toward rationally designed nanomedicine for in vivo imaging and therapy can be obtained. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Renal Clearable Luminescent Gold Nanoparticles: From the Bench to the Clinic

With more and more engineered nanoparticles (NPs) being translated to the clinic, the United States Food and Drug Administration (FDA) has recently issued the latest draft guidance on nanomaterial-containing drug products with an emphasis on understanding their in vivo transport and nano-bio interactions. Following these guidelines, NPs can be designed to target and treat diseases more efficiently than small molecules, have minimum accumulation in normal tissues, and induce minimum toxicity. In this Minireview, we integrate this guidance with our ten-year studies on developing renal clearable luminescent gold NPs. These gold NPs resist serum protein adsorption, escape liver uptake, target cancerous tissues, and report kidney dysfunction at early stages. At the same time, off-target gold NPs can be eliminated by the kidneys with minimum accumulation in the body. Additionally, we identify challenges to the translation of renal clearable gold NPs from the bench to the clinic.

Surface Coverage-Regulated Cellular Interaction of Ultrasmall Luminescent Gold Nanoparticles

Investigations for accurately controlling the interaction between functional nanoparticles (NPs) and living cells set a long-thought benefit in nanomedicine and disease diagnostics. Here, we reveal a surface coverage-dependent cellular interaction by comparing the membrane binding and uptake of three ultrasmall luminescent gold NPs (AuNPs) with different surface coverages. Lower surface coverage leads to fast cellular interaction and strong membrane binding but low cellular uptake, whereas high surface coverage induces slow cellular interaction and low membrane binding but major cellular uptake. The slight number increase of cell-penetrating peptide on the surface of AuNPs shows improved cellular interaction dynamics and internalization through direct cellular membrane penetration. Furthermore, the different intrinsic emissions resulted from the surface coverage variation, especially the pH-responsive dual emissions, make the AuNPs powerful optical probes for subcellular imaging and tracking. The findings advance the fundamental understanding of the cellular interaction mechanisms of ultrasmall AuNPs and provide a feasible strategy for the design of functional NPs with tunable cellular interaction by surface regulation.

Light-responsive nanomedicine for biophotonic imaging and targeted therapy

Nanoparticles (NPs) play a key role in nanomedicine in multimodal imaging, drug delivery and targeted therapy of human diseases. Consequently, due to the attractive properties of NPs including high stability, high payload, multifunctionality, design flexibility, and efficient delivery to target tissues, nanomedicine employs various types of NPs to enhance targeting and treatment efficacy. In this review, we primarily focus on light-responsive materials, such as fluorophores, photosensitizers, semiconducting polymers, carbon structures, gold particles, quantum dots, and upconversion crystals, for their biomedical applications. Armed with these nanomaterials, NPs represent a growing potential in biophotonic imaging (luminescence, photoacoustic, surface enhanced Raman scattering, and optical coherence tomography) as well as targeted therapy (photodynamic therapy, photothermal therapy, and light-responsive drug release).

Surface Dynamics and Ligand-Core Interactions of Quantum Sized Photoluminescent Gold Nanoclusters

Quantum-sized metallic clusters protected by biological ligands represent a new class of luminescent materials; yet the understanding of structural information and photoluminescence origin of these ultrasmall clusters remains a challenge. Herein we systematically study the surface ligand dynamics and ligand-metal core interactions of peptide-protected gold nanoclusters (AuNCs) with combined experimental characterizations and theoretical molecular simulations. We show that the peptide sequence plays an important role in determining the surface peptide structuring, interfacial water dynamics and ligand-Au core interaction, which can be tailored by controlling peptide acetylation, constituent amino acid electron donating/withdrawing capacity, aromaticity/hydrophobicity and by adjusting environmental pH. Specifically, emission enhancement is achieved through increasing the electron density of surface ligands in proximity to the Au core, discouraging photoinduced quenching, and by reducing the amount of surface-bound water molecules. These findings provide key design principles for understanding the surface dynamics of peptide-protected nanoparticles and maximizing the photoluminescence of metallic clusters through the exploitation of biologically relevant ligand properties.

Probing Ligand-Induced Cooperative Orbital Redistribution That Dominates Nanoscale Molecule-Surface Interactions with One-Unit-Thin TiO2 Nanosheets

Understanding the general electronic principles underlying molecule-surface interactions at the nanoscale is crucial for revealing the processes based on chemisorption, like catalysis, surface ligation, surface fluorescence, etc. However, the electronic mechanisms of how surface states affect and even dominate the properties of nanomaterials have long remained unclear. Here, using one-unit-thin TiO₂ nanosheet as a model surface platform, we find that surface ligands can competitively polarize and confine the valence 3d orbitals of surface Ti atoms from delocalized energy band states to localized chemisorption bonds, through probing the surface chemical interaction at the orbital level with near-edge X-ray absorption fine structure (NEXAFS). Such ligand-induced orbital redistributions, which are revealed by combining experimental discoveries, quantum calculations, and theoretical analysis, are cooperative with ligand coverages and can enhance the strength of chemisorption and ligation-induced surface effects on nanomaterials. The model and concept of nanoscale cooperative chemisorption reveal the general physical principle that drives the coverage-dependent ligand-induced surface effects on regulating the electronic structures, surface activity, optical properties, and chemisorption strength of nanomaterials.

DNA-Encoded Morphological Evolution of Bimetallic Pd@Au Core-shell Nanoparticles from a High-indexed Core

DNA-mediated synthesis of nanoparticles with different morphologies has proven to be a powerful method to synthesize and access many exclusive shapes and surface properties. While previous studies employ seeds that contain relatively low-energy facets, such as a simple cubic palladium seed in the synthesis of Pd-Au bimetallic nanoparticles, few studies have investigated whether DNA molecules can still exert their influence when the synthesis uses a seed that contains high-energy facets. Seeds that are enclosed by such high-energy facets or sites are known to act as easy nucleation sites in nanoparticles growth and could potentially suppress the effect of DNA. To answer this question, we herein report DNA-encoded control of morphological evolution of bimetallic Pd@Au core-shell nanoparticles from a concave palladium nanocube seed that contains high indexed facets. Based on detailed spectroscopic and SEM studies of time-dependent growth of the bimetallic nanoparticles, we found that each of 10-mer DNA molecules (T10, G10, C10 and A10) has a unique way of interacting with both the seed's surface and the precursor. Among them, the most important factor is the binding affinity of the nucleobase to the Pd surface, with the A10 possessing the highest binding affinity and thus capable of stabilizing the seed's high energy surfaces. Furthermore, for bases with lower binding affinity (T10, G10 and C10) than A10, the growth is completely dictated by the seed's surface energy initially, but the later growth can still be influenced by the different DNA sequences, resulting in four unique morphologically different Pd@Au bimetallic nanoparticles. The effect of these DNA molecules with medium binding affinity can only be observed when there is more deposition of Au. Based on the above results, a scheme for the DNA controlled growth is proposed. Together these results have provided insights into factors governing DNA-mediated growth of core-shell structures using seeds with high-energy sites, and the insights can readily be applied to other bimetallic systems that adopt seed-mediated synthesis.

Near-infrared light triggered drug release from mesoporous silica nanoparticles

Stimuli triggered drug delivery systems enable controlled release of drugs at the optimal space and time, thus achieving optimal therapeutic effects. As one of the most important stimuli used in bioapplications, near-infrared (NIR) light possesses unique advantages such as deep tissue penetration with minimum auto-fluorescence & tissue scattering and high biosafety. Mesoporous silica nanoparticles (MSNs) are one of the most studied nanocarriers; apart from having a high surface area and large pore volume for loading of drugs, they can be easily functionalized with inorganic nanomaterials and stimuli responsive polymers or organic switch molecules, creating possibilities for designing complex stimuli triggered drug delivery systems. Considering the high tissue penetration depth of NIR light and the unique mesoporous structure of MSNs, NIR responsive inorganic nanoparticle functionalized MSNs can be further combined with stimuli responsive materials to form smart "nano-devices" for controlled drug delivery toward tumors, and to date much progress has been made. In this article, recent advances in the design of NIR triggered mesoporous silica drug delivery systems are systematically summarized and some outstanding studies are highlighted. We will also discuss the shortcomings, challenges and opportunities in the field.

Revealing isoelectronic size conversion dynamics of metal nanoclusters by a noncrystallization approach

Atom-by-atom engineering of nanomaterials requires atomic-level knowledge of the size evolution mechanism of nanoparticles, which remains one of the greatest mysteries in nanochemistry. Here we reveal atomic-level dynamics of size evolution reaction of molecular-like nanoparticles, i.e., nanoclusters (NCs) by delicate mass spectrometry (MS) analyses. The model size-conversion reaction is [Au₂₃(SR)₁₆]⁻ → [Au₂₅(SR)₁₈]⁻ (SR = thiolate ligand). We demonstrate that such isoelectronic (valence electron count is 8 in both NCs) size-conversion occurs by a surface-motif-exchange-induced symmetry-breaking core structure transformation mechanism, surfacing as a definitive reaction of [Au₂₃(SR)₁₆]⁻ + 2 [Au₂(SR)₃]⁻ → [Au₂₅(SR)₁₈]⁻ + 2 [Au(SR)₂]⁻. The detailed tandem MS analyses further suggest the bond susceptibility hierarchies in feed and final Au NCs, shedding mechanistic light on cluster reaction dynamics at atomic level. The MS-based mechanistic approach developed in this study also opens a complementary avenue to X-ray crystallography to reveal size evolution kinetics and dynamics.

How metal nanoclusters evolve in size is poorly understood, particularly at the atomic level. Here, the authors use mass spectrometry to study the size conversion dynamics between two isoelectronic gold nanoclusters with atomic resolution, revealing that the growth reaction proceeds through a distinct balanced equation.

Luminescence mechanisms of ultrasmall gold nanoparticles

The past decade has witnessed a burst of study on ultrasmall gold nanoparticles. Unlike semiconductor quantum dots, ultrasmall gold nanoparticles have very diverse emission mechanisms, which are often involved in many structural factors such as size, valence state, surface ligands and crystallinity. In this frontier, we summarize our latest advancement in the fundamental understanding of emission mechanisms of ultrasmall gold nanoparticles, which are expected to help us more precisely control their emissions and broaden their applications from energy technologies to disease detection.

NIR-emitting and photo-thermal active nanogold as mitochondria-specific probes

We report a bioinspired multifunctional albumin derived polypeptide coating comprising grafted poly(ethylene oxide) chains, multiple copies of the HIV TAT derived peptide enabling cellular uptake as well as mitochondria targeting triphenyl-phosphonium (TPP) groups. Exploring these polypeptide copolymers for passivating gold nanoparticles (Au NPs) yielded (i) NIR-emitting markers in confocal microscopy and (ii) photo-thermal active probes in optical coherence microscopy. We demonstrate the great potential of such multifunctional protein-derived biopolymer coatings for efficiently directing Au NP into cells and to subcellular targets to ultimately probe important cellular processes such as mitochondria dynamics and vitality inside living cells.

Reactivity Toward Ag+: A General Strategy to Generate a New Emissive Center from NIR-Emitting Gold Nanoparticles

We report a facile strategy for the transformation of single NIR-emitting AuNPs to dual-NIR-emitting bimetallic Ag@AuNPs based on the robust reactivity toward Ag(I) ions under mild conditions. The reactivities toward Ag(I) ions were found to be significantly different between visible- and NIR-emitting glutathione (GSH)-coated AuNPs: the high GSH surface coverage on the 610 nm-emitting AuNPs resulted in a reversible interaction due to enough surface steric hindrance to resist Ag(I) ions from interaction with the Au(0) core, whereas the low GSH surface coverage on the 810 nm-emitting AuNPs led to both antigalvanic reaction and Ag(I)-carboxylate shell formation on the surface of the AuNPs, which were responsible for the formation of a new emissive center at 705 nm. This strategy was also demonstrated to exhibit excellent generalization toward various NIR-emitting AuNPs with surface chemistries containing carboxyl groups, opening a new pathway of tailoring the optical properties of metallic NPs through surface reactivity.

Synthesis of Fluorescent Au Nanocrystals-Silica Hybrid Nanocomposite (FLASH) with Enhanced Optical Features for Bioimaging and Photodynamic Activity

Fluorescent Au nanocrystals (AuNCs)-silica hybrid nanocomposite (FLASH) was synthesized by co-condensation of surface-modified AuNCs. Present FLASH nanocomposite exhibited four times the enhanced photoluminescence and photocatalytic activity compared to single nanocrystals. On the basis of these enhanced optical features, we successfully demonstrated in vitro fluorescence bioimaging of introduced FLASH to human cervical cancer cell line (HeLa). Beyond the confirmation of photocatalytic activity from the photodegradation of methylene blue as a model compound, the regional selective photodynamic therapy of HeLa cells under UV irradiation was also presented. Taken together the enhanced optical features and further potential in theranostic applications, we expect that the present FLASH can be a promising tool for nanobiotechnology field.

Mercaptosuccinic acid-coated NIR-emitting gold nanoparticles for the sensitive and selective detection of Hg2

A sensitive fluorescent detection platform for Hg²⁺ was constructed based on mercaptosuccinic acid (MSA) coated near-infrared (NIR)-emitting gold nanoparticles (AuNPs). The thiolated mercaptosuccinic acid was employed as both reducing agent and surface coating ligand in a one-step synthesis of NIR-emitting AuNPs (MSA-AuNPs), which exhibited stable fluorescence with the maximum wavelength at 800nm and a wide range of excitation (220-650nm) with the maxima at 413nm. The MSA coated NIR-emitting AuNPs showed a rapid fluorescence quenching toward Hg²⁺ over other metal ions with a limit of detection (LOD, 3δ) as low as 4.8nM. The sensing mechanism investigation revealed that the AuNPs formed aggregation due to the "recognition" of Hg²⁺ from the MSA, and the resultant strong coupling interaction between Hg²⁺ and Au (I) to further quench the fluorescence of the AuNPs, which synergistically resulted in a highly sensitive and selective fluorescence response toward Hg²⁺. This proposed strategy was also demonstrated the possibility to be used for Hg²⁺ detection in water samples.

Dose Dependencies and Biocompatibility of Renal Clearable Gold Nanoparticles: From Mice to Non-human Primates

While dose dependencies in pharmacokinetics and clearance are often observed in clinically used small molecules, very few studies have been dedicated to the understandings of potential dose-dependent in vivo transport of nanomedicines. Here we report that the pharmacokinetics and clearance of renal clearable gold nanoparticles (GS-AuNPs) are strongly dose-dependent once injection doses are above 15 mg kg^-1 : high dose expedited the renal excretion and shortened the blood retention. As a result, the no-observed-adverse-effect-level (NOAEL) of GS-AuNPs was >1000 mg kg^-1 in CD-1 mice. The efficient renal clearance and high compatibility can be translated to the non-human primates: no adverse effects were observed within 90 days after intravenous injection of 250 mg kg^-1 GS-AuNPs. These fundamental understandings of dose effect on the in vivo transport of ultrasmall AuNPs open up a pathway to maximize their biomedical potentials and minimize their toxicity in the future clinical translation.

Precise control of alloying sites of bimetallic nanoclusters via surface motif exchange reaction

Precise control of alloying sites has long been a challenging pursuit, yet little has been achieved for the atomic-level manipulation of metallic nanomaterials. Here we describe utilization of a surface motif exchange (SME) reaction to selectively replace the surface motifs of parent [Ag₄₄(SR)₃₀]^4- (SR = thiolate) nanoparticles (NPs), leading to bimetallic NPs with well-defined molecular formula and atomically-controlled alloying sites in protecting shell. A systematic mass (and tandem mass) spectrometry analysis suggests that the SME reaction is an atomically precise displacement of SR-Ag(I)-SR-protecting modules of Ag NPs by the incoming SR-Au(I)-SR modules, giving rise to a core-shell [Ag₃₂@Au₁₂(SR)₃₀]^4-. Theoretical calculation suggests that the thermodynamically less favorable core-shell Ag@Au nanostructure is kinetically stabilized by the intermediate Ag₂₀ shell, preventing inward diffusion of the surface Au atoms. The delicate SME reaction opens a door to precisely control the alloying sites in the protecting shell of bimetallic NPs with broad utility.

Physiological stability and renal clearance of ultrasmall zwitterionic gold nanoparticles: Ligand length matters

Efficient renal clearance has been observed from ultrasmall zwitterionic glutathione-coated gold nanoparticles (GS-AuNPs), which have broad preclinical applications in cancer diagnosis and kidney functional imaging. However, origin of such efficient renal clearance is still not clear. Herein, we conducted head-to-head comparison on physiological stability and renal clearance of two zwitterionic luminescent AuNPs coated with cysteine and glycine-cysteine (Cys-AuNPs and Gly-Cys-AuNPs), respectively. While both of them exhibited similar surface charges and the same core sizes, additional glycine slightly increased the hydrodynamic diameter of the AuNPs by 0.4 nm but significantly enhanced physiological stability of the AuNPs as well as altered their clearance pathways. These studies indicate that the ligand length, in addition to surface charges and size, also plays a key role in the physiological stability and renal clearance of ultrasmall zwitterionic inorganic NPs.

pH-Guided Self-Assembly of Copper Nanoclusters with Aggregation-Induced Emission

We here report a facile pH-guided strategy for the fabrication of water-soluble protein/copper nanoclusters (CuNCs) hybrid nanostructures with stable and bright luminescence resulted from aggregation-induced emission. Using l-cysteine as both the reducing and capping agents, the synthesized CuNCs showed a good reversible pH-responsive aggregation and dispersion in the solution. The CuNCs formed insoluble macroscopic aggregates with stable red-colored emission (620 nm) at pH 3.0 but became soluble with weak luminescence at pH <1.5 or pH >4.0. The highly reversible pH-responsive properties of the CuNCs made it feasible to achieve water-soluble protein/CuNCs hybrid nanostructures in the presence of protein without any external forces (e.g., sonication). The weak luminescent CuNCs were first mixed with protein under neutral condition (e.g., pH 7.0), followed by tuning of the pH to acidic conditions (e.g., pH 3.0) to form luminescent protein/CuNCs hybrid nanostructures, the sizes of which were much smaller than those of the protein-free macroscopic CuNC aggregates. This strategy was easily applicable to other dispersing agents (e.g., glucose oxidase), opening a new pathway for the construction of many other smart water-soluble luminescent biomolecule/nanocluster hybrid nanostructures with various applications.

Renal clearable noble metal nanoparticles: photoluminescence, elimination, and biomedical applications

Metal nanoparticles have demonstrated broad and promising biomedical applications in research laboratories, but how to fulfill their promises in the clinical practices demands extensive effort to minimize their non-specific accumulation in the body. In the past 6 years, we have developed a class of renal clearable noble metal nanoparticles with tunable visible and near-infrared emission, which can behave like small molecular contrast agents to be effectively eliminated through the kidneys. By taking advantage of the unique clearance pathway, we were able to gain some fundamental understanding of how engineering nanoparticles cleared out of the body through urinary system. Moreover, they also provided unique opportunities in early cancer detection and kidney functional imaging that were often challenging to be achieved with non-renal clearable nanoparticles and small molecular probes. In this review, we summarize key factors that govern in the renal clearance of luminescent noble metal nanoparticles and their strengths in cancer targeting and kidney functional imaging. At the end, we also outline several key challenges that need to be addressed before they can be considered in the clinical practices. WIREs Nanomed Nanobiotechnol 2017, 9:e1453. doi: 10.1002/wnan.1453 For further resources related to this article, please visit the WIREs website.

Bioapplications of renal-clearable luminescent metal nanoparticles

This review summarizes the recent synthetic strategies of the renal-clearable luminescent metal nanoparticles, and discusses the biological behaviors and current disease-related applications of this type of biomaterials in tumor targeting, kidney disease and antimicrobial investigations.

The effect of ligand–ligand interactions on the formation of photoluminescent gold nanoclusters embedded in Au(i)–thiolate supramolecules

Photoluminescence of cysteine-capped gold nanoclusters obtained via the reduction of –[Cys–Au(i)]_n– supramolecules is highly dependent on the degree of supramolecular aggregation.

Tailoring Renal Clearance and Tumor Targeting of Ultrasmall Metal Nanoparticles with Particle Density

Identifying key factors that govern the in vivo behavior of nanomaterials is critical to the clinical translation of nanomedicines. Overshadowed by size-, shape-, and surface-chemistry effects, the impact of the particle core density on clearance and tumor targeting of inorganic nanoparticles (NPs) remains largely unknown. By utilizing a class of ultrasmall metal NPs with the same size and surface chemistry but different densities, we found that the renal-clearance efficiency exponentially increased in the early elimination phase while passive tumor targeting linearly decreased with a decrease in particle density. Moreover, lower-density NPs are more easily distributed in the body and have shorter retention times in highly permeable organs than higher-density NPs. The density-dependent in vivo behavior of metal NPs likely results from their distinct margination in laminar blood flow, which opens up a new path for precise control of nanomedicines in vivo.