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1. Probing Protein Corona Formation around Gold Nanoparticles: Effects of Surface Coating

   https://doi.org/10.1021/acsnano.3c08005  

   Dridi, Narjes; Jin, Zhicheng; Perng, Woody; Mattoussi, Hedi (March 2024, ACS Nano)

   none (Ed.)

   There has been much interest in integrating various inorganic nanoparticles (nanoscale colloids) in biology and medicine. However, buildup of a protein corona around the nanoparticles in biological media, driven by nonspecific interactions, remains a major hurdle for the translation of nanomedicine into clinical applications. In this study, we investigate the interactions between gold nanoparticles and serum proteins using a series of dihydrolipoic acid (DHLA)-based ligands. We employed gel electrophoresis combined with UV−vis absorption and dynamic light scattering to correlate protein adsorption with the nature and size of the ligand used. For instance, we found that AuNPs capped with DHLA alone promote nonspecific protein adsorption. In comparison, capping AuNPs with polyethylene glycol- or zwitterion-appended DHLA essentially prevents corona formation, regardless of ligand charge and size. Our results highlight the crucial role of surface chemistry and core material in protein corona formation and offer valuable information for the design of colloidal nanomaterials for biological applications. 

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2. Thermodynamics of Protein-Surface Binding- the Model Makes all the Difference

   Nicholas C. Fitzkee, Kayla D (February 2020, Biophysical journal)

   null (Ed.)

   Gold nanoparticles (AuNPs) are now being used in such areas as diagnostics, drug delivery, and biological sensing. In these applications, AuNPs are frequently exposed to biological fluids. These fluids contain many different proteins, any of which may interfere with the intended function of the nanoparticle. In this work, we examine the thermodynamic consequences of proteinnanoparticle binding using a combined spectroscopic and calorimetric approach. We monitored binding using UV-Vis spectroscopy, differential scanning calorimetry (DSC), and isothermal titration calorimetry (ITC). Six proteins were studied based on their differing chemical properties, and both 15 nm and 30 nm citrate-coated AuNPs were investigated. We interpreted the UV-Vis data using two different models: the commonly-used Langmuir isotherm model and a more complex mass transport model. Both models can be used to determine Kd values for the 30 nm AuNP data; however, the mass transport model is more appropriate for 15 nm AuNPs. This is because, when fitting the Langmuir model, it is commonly assumed that most proteins are not surface-associated, and this assumption fails for 15 nm AuNPs. The DSC thermograms show two transitions for a globular protein adsorbed to a 15 nm AuNP: one high-temperature transition that is similar to global protein unfolding (68 C), and one low-temperature transition that may correspond to unfolding at the surface (56 C). Conversely, ITC experiments show no net heat of adsorption for GB3, even at high protein/AuNP concentrations. Together, the spectroscopic and calorimetric data suggest a complex, multi-step process for protein-nanoparticle adsorption. Moreover, for the proteins studied, both AuNP curvature and protein chemistry contribute to protein adsorption, with proteins generally binding more weakly to the larger nanoparticles. In the future, this work may lead to principles for improving the design of AuNPbased therapeutics and sensors. 

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3. Core size does not affect blinking behavior of dye-doped Ag@SiO ₂ core–shell nanoparticles for super-resolution microscopy

   https://doi.org/10.1039/c9ra10421f  

   Thompson, S.; Pappas, Dimitri (February 2020, RSC Advances)

   Dye-doped nanoparticles have been investigated as bright, luminescent labels for super-resolution microscopy via localization methods. One key factor in super-resolution is the size of the luminescent label, which in some cases results in a frame shift between the label target and the label itself. Ag@SiO 2 core–shell nanoparticles, doped with organic fluorophores, have shown promise as super-resolution labels. One key aspect of these nanoparticles is that they blink under certain conditions, allowing super-resolution localization with a single excitation source in aqueous solution. In this work, we investigated the effects of both the Ag core and the silica (SiO 2 ) shell on the self-blinking properties of these nanoparticles. Both core size and shell thickness were manipulated by altering the reaction time to determine core and shell effects on photoblinking. Size and shell thickness were investigated individually under both dry and hydrated conditions and were then doped with a 1 mM solution of Rhodamine 110 for analysis. We observed that the cores themselves are weakly luminescent and are responsible for the blinking observed in the fully-synthesized metal-enhanced fluorescence nanoparticles. There was no statistically significant difference in photoblinking behavior—both intensity and duty cycle—with decreasing core size. This observation was used to synthesize smaller nanoparticles ranging from approximately 93 nm to 110 nm as measured using dynamic light scattering. The blinking particles were localized via super-resolution microscopy and show single particle self-blinking behavior. As the core size did not impact blinking performance or intensity, the nanoparticles can instead be tuned for optimal size without sacrificing luminescence properties. 

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4. Ultrafast photoinduced charge carrier dynamics of L-cysteine and oleylamine stabilized CsPbBr3 perovskite quantum dots coupled with gold nanoparticles

   https://doi.org/10.1063/5.0222815  

   Khvichia, Mariam; Chou, Kai-Chun; Lee, Sidney; Zeitz, David C; Zou, Shengli; Li, Yan; Zhang, Jin Z (September 2024, The Journal of Chemical Physics)

   We have synthesized L-cysteine and oleylamine stabilized CsPbBr3 perovskite quantum dots (PQDs) and coupled them with gold nanoparticles (AuNPs). The PQDs and AuNPs, as well as their hybrid nanostructures (HNS), were characterized using UV–visible (UV–vis) and photoluminescence (PL) spectroscopy. The UV–vis spectra show absorption bands of the HNS at 503 and 520 nm, attributed mainly to PQDs and AuNPs, respectively. The PQDs show a strong excitonic PL band peaked at 513 nm from PQDs. The HR-TEM results show the formation of hybrid structures between PQDs and AuNPs, which is also supported by the PL quenching of the PQDs by the coupled AuNPs. Ultrafast dynamics of the exciton and charge carriers in the HNS and pristine PQD were studied using femtosecond transient absorption. Multiexponential fitting of the dynamic data revealed the existence of shallow and deep trap states in pristine PQDs and ultrafast electron transfer from PQDs to AuNPs in the HNS. A kinetic model was proposed to account for the key dynamic processes involved and to extract the time for electron transfer from PQDs to AuNPs in the HNS, found to be ∼2 ps. Dynamic processes in pristine PQDs are largely unchanged by HNS formation with AuNPs. 

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5. Mechanism of Cationic Peptide-Induced Assembly of Gold Nanoparticles: Modulation of Electrostatic Repulsion

   Lam, B; Ramji, R; Mullooly, M; Closser, K D; Pascal, T A; Jokerst, J V (April 2025, Aggregate)

   The aggregation of plasmonic nanoparticles can lead to new and controllable properties useful for numerous applications. We recently showed the reversible aggregation of gold nanoparticles (AuNPs) via a small, cationic di-arginine peptide; however, the mechanism underlying this aggregation is not yet comprehensively understood. Here, we seek insights into the intermolecular interactions of cationic peptide-induced assembly of citrate-capped AuNPs by empirically measuring how peptide identity impacts AuNP aggregation. We examined the nanoscale interactions between the peptides and the AuNPs via UV-vis spectroscopy to determine the structure-function relationship of peptide length and charge on AuNP aggregation. Careful tuning of the sequence of the di-arginine peptide demonstrated that the mechanism of assembly is driven by a reduction in electrostatic repulsion. We show that acetylated N-terminals and carboxylic acid C-terminals decrease the effectiveness of the peptide in inducing AuNP aggregation. The increase in peptide size through the addition of glycine or proline units hinders aggregation and leads to less redshift. Arginine-based peptides were also found to be more effective in assembling the AuNPs than cysteine-based peptides of equivalent length. We also illustrate that aggregation is independent of peptide stereochemistry. Finally, we demonstrate the modulation of peptide-AuNP behavior through changes to the pH, salt concentration, and temperature. Notably, histidine-based and tyrosine-based peptides could reversibly aggregate the AuNPs in response to the pH. 

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