Currently available gold nanoparticles (GNPs) typically accumulate in the liver and spleen, leading to concerns for their long-term biosafety. To address this long-standing problem, we developed ultraminiature chain-like gold nanoparticle clusters (GNCs). Via self-assembly of 7-8 nm GNP monomers, GNCs provide red-shifted optical absorption and scattering contrast in the near-infrared window. After disassembly, GNCs turn back to GNPs with a size smaller than the renal glomerular filtration size cutoff, allowing their excretion via urine. Our one-month longitudinal study in a rabbit eye model demonstrated that GNCs facilitate multimodal molecular imaging of choroidal neovascularization (CNV) in vivo, non-invasively, with excellent sensitivity and spatial resolution. GNCs targeting αv β3  integrins enhanced photoacoustic and OCT signals from CNV by 25.3-fold and 150%, respectively. With excellent biosafety and biocompatibility demonstrated, GNCs render a first-of-its-kind nanoplatform for biomedical imaging. This article is protected by copyright. All rights reserved.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/adma.202302069

Renal Clearable Ultraminiature Chain-like Gold Nanoparticle Clusters for Multimodal Molecular Imaging of Choroidal Neovascularization.

The localized surface plasmon resonance (LSPR) of metal nanoparticles is strongly dependent on geometrical and environmental factors, as well as the nanoparticle aggregation phenomena, which are exploited in a range of applications. In this work we investigate the LSPR of gold nanoparticles, produced by laser ablation in liquid (LAL), and their agglomeration induced by halides after LAL. We study the aggregation process under a range of factors like bromide concentration, temperature, and different halides. By absorption spectroscopy and electron microscopy we show that increasing bromide concentration leads to longer and more complex aggregates, with consequent red-shift and broadening of the LSPR. Simulations, in agreement with experiments, show that a red-shift of the LSPR is expected as AuNP linear chains become longer and validate this trend for different particle size and gap between particles. By using real-time absorption spectroscopy, we observe immediate growth of nanoparticles after salt addition. We also demonstrate that higher temperatures tend to suppress the aggregation process, while lower temperatures promote it. We then observe that a heavier halide like iodide tends to form a very broad LSPR indicating complex nanoparticle architectures. Finally, we show that the aggregates are disrupted by re-irradiating the colloid. These findings provide an expanded understanding into the factors ruling the aggregation phenomena, and will help developing existing applications while stimulating new ones. 

Surface plasmon resonance of gold nanoparticle aggregates induced by halide ions

A synthesis of two metaiodobenzylguanidine (MIBG) derivatives is reported: N-[4-(guanidinomethyl)-2-iodophenyl]-3-mercaptopropanamide (MIBG-3-MPAM) and N-[4-(guanidinomethyl)phenyl]-3-mercaptopropanamide (BG-3-MPAM). The design of these molecules allows for their conjugation to a wide range of nanocarriers, such as pulsed-laser ablation (PLA)-synthesized gold nanoparticles (AuNPs), which are utilized here to assess uptake into neuroblastoma (NB), HeLa, and HEK cell lines. Through dark-field imaging and quantitative inductively coupled plasma mass spectrometry (qICP-MS), the MIBG derivatives are found to enhance total AuNP uptake in vitro by over 100× at sufficiently high molar ratios across cell lines, and the iodine atom is found to play an important role in further enhancing the uptake efficiency. 

Flexible Synthesis Scheme and Application of AuNP Surface-Conjugatable Metaiodobenzylguanidine Derivatives for Enhanced Cellular Internalization

In-Situ Synthesis of Size-Controllable Biocompatible Au@COF Nanosensor for SERS and Dark-Field Scattering Dual-Mode Detecting Intracellular Metabolite

Hydrogen peroxide is widely involved in intracellular physiological activities, playing vital roles in regulating various intracellular metabolite and physiological events. Surface enhanced Raman spectroscopy (SERS) may serve as a promising technique to efficiently sensing metabolites in living cells owing to its non-invasiveness, low autofluorescence, and rapid detection capability. Herein, a size-controllable core-shell structure was constructed by covering 2D covalent organic frameworks (COFs) on Au nanoparticles (Au@COF), and the cellular hydrogen peroxide were detected by Raman spectroscopy/Dark-field scattering imaging dual-mode technique. The introduction of COFs endows Au@COF with perfect enrichment capacity as well as high stability and good biocompatibility. Combining the superior fingerprint identification of SERS and the imaging capability of dark-field microscopy, the present method exhibits high applicability for hydrogen peroxide detection in living cells. Results show that when the living MCF-7 cells were treated by different drugs, the level of H 2 O 2 metabolite can be monitored in real-time. This study provides a simple but sensitive and facile platform for biosensing hydrogen peroxide and cellular metabolites. • A biocompatible core-shell structure was constructed by covering ultrathin 2D covalent organic frameworks (COFs) on Au nanoparticles (Au@COF). • Intracellular Hydrogen Peroxide was successfully detected by Au@COF using SERS and Dark-Field Scattering Dual-Mode technique. • This study provides a simple and sensitive platform for biosensing hydrogen peroxide and cellular metabolites. 

SERS and Dark-Field Scattering Dual-Mode Detection of Intracellular Hydrogen Peroxide Using Biocompatible Au@COF Nanosensor

The development of optically tunable and intensely scattering materials is of wide interest in biophotonics and medicine, provided they are biocompatible. Highly linear, tunable, narrow-gap, and in...

Au Nanobead Chains with Tunable Plasmon Resonance and Intense Optical Scattering: Scalable Green Synthesis, Monte Carlo Assembly Kinetics, Discrete Dipole Approximation Modeling, and Nano-Biophotonic Application

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Au Nanobead Chains with Tunable Plasmon Resonance and Intense Optical Scattering: Scalable Green Synthesis, Monte Carlo Assembly Kinetics, Discrete Dipole Approximation Modeling, and Nano-Biophotonic Application