James Chen Yong Kah

Exploiting the Protein Corona around Gold Nanorods for Loading and Triggered Release

We form coronas of serum proteins on gold nanorods (NRs) coated with cetyltrimethylammonium bromide (CTAB). These coronas can be exploited for their ability to hold small molecular therapeutics at a capacity much higher (~5-10×) than what covalent conjugation strategies can achieve. Coronas are loaded with DNA oligonucleotides and Doxorubicin, showing that they can hold species of either negative or positive charge. Payload capacity varies with assembly strategy, ionic strength, and loading concentration. Payload release can be achieved by increasing the temperature or by ultrafast laser excitation of the NRs at their longitudinal surface plasmon resonance. DNA leakage from the corona is minimal within the first 3 days of preparation, although Dox leakage was more significant. The coronas also stabilize the NRs in buffer and biological media. This study demonstrates the biological utility of the protein corona around nanomaterials, contrasting the common view of the corona as an undesirable biological response.

Critical parameters in the pegylation of gold nanoshells for biomedical applications: An in vitro macrophage study

Pegylation of gold nanoshells provides an effective means to reduce their reticuloendothelial system (RES) clearance in body. In this study, we perform a parametric investigation on the factors that would affect the macrophage uptake of gold nanoshells with the aim to optimize their pegylation and minimize their macrophage uptake. We synthesized and pegylated the gold nanoshells using methoxy-poly(ethylene glycol)-thiol and employed an in vitro macrophage assay to examine the effect of surface density of poly(ethylene glycol) (PEG), chain length of the PEG, and size of the gold nanoshells on their macrophage uptake. We have shown that a saturated surface density would minimize macrophage uptake, which could be obtained by experimental titration-based Ellman’s reagent. Our results suggest that the chain length of PEG and size of gold nanoshells influence the surface density of PEG. We have also shown that PEG with molecular weight of around 2000 Da and a size range larger than 186 nm would be appropriate for facilitating a high surface density. Our in vitro macrophage system thus provides a good model to accurately predict the RES response to different pegylation parameters.

Optimizing the Properties of the Protein Corona Surrounding Nanoparticles for Tuning Payload Release

We manipulate the passive release rates of DNA payloads on protein coronas formed around nanoparticles (NPs) by varying the corona composition. The coronas are prepared using a mixture of hard and soft corona proteins. We form coronas around gold nanorods (NRs), nanobones (NBs), and carbon nanotubes (CNTs) from human serum (HS) and find that tuning the amount of human serum albumin (HSA) in the NR-coronas (NR-HS-DNA) changes the payload release profile. The effect of buffer strength, HS concentration, and concentration of the cetyltrimethylammonium bromide (CTAB) passivating the NP surfaces on passive release is explored. We find that corona properties play an important role in passive release, and concentrations of CTAB, HS, and phosphate buffer used in corona formation can tune payload release profiles. These advances in understanding protein corona properties bring us closer toward developing a set of basic design rules that enable their manipulation and optimization for particular biological applications.

Synthesis of Contiguous Silica−Gold Core−Shell Structures: Critical Parameters and Processes

A direct process for preparing contiguous gold shells (15-25 nm thick) over amorphous silica spheres (200 nm) is described. In this method, gold seeds are synthesized from HAuCl(4) in a dilute NaOH solution using deposition-precipitation with subsequent metallization by sodium borohydride (NaBH(4)). The ease of dispersing gold nanocrystals on spheres of bare silica and spheres after grafting with ammonia was studied as a function of pH (4-8), reaction temperature (65-96 degrees C), and time (5-30 min). Additional parameters requiring optimization included the quantity of NaBH4 and the HAuCl(4) in K(2)CO(3) solution to silica volume ratio. The evolution of gold nanocrystal growth was monitored by transmission electron microscopy, and the bathochromic shift of ultraviolet-visible absorption was correlated with shell perfection and thickness.

Combinatorial treatment of photothermal therapy using gold nanoshells with conventional photodynamic therapy to improve treatment efficacy: An in vitro study

Both photodynamic (PDT) and photothermal (PTT) therapy have proven to be effective treatment strategies for cancer, but the approach of combining them into a single treatment modality may offer better treatment efficacy. We compare the treatment efficacy of such combined treatment with the individual treatment.

Synthesis of gold nanoshells based on the depositionprecipitation process

The synthesis of gold nanoshells involves the preparation of precursor seed particles consisting of nanoparticulate gold loaded on a dielectric core as scaffolds on which the layer of gold shell can be grown. The common route in preparing these seed particles involves a two-step technique of synthesizing colloidal gold particles followed by attaching them to amine functionalized dielectric core. In this paper, we present the use of a singlestep deposition-precipitation (DP) process, commonly used in the catalytic field, as a feasible alternative route to seeding gold hydroxide nanoparticles onto a silica core and growing a layer of gold shell around the core without the need for prior synthesis of colloidal gold. The various factors such as pH, temperature and time of reaction, as well as the effect of amine functionalization of silica on the deposition of gold were investigated. Compared to bare silica nanoparticles whose low isoelectric point render the DP process of seeding nanoparticulate gold unfavorable, amine functionalization of the silica surface is able to alter its isoelectric point to facilitate the deposition of gold hydroxide nanoparticles and increase the uniformity and density of seeding. We have also established that by varying the pH and time of reaction, it is possible to control the size of the gold hydroxide nanoparticles and density of seeding. The highest seeding density was achieved at pH 8 where the surface charge on the amine terminated silica surface favored the attraction of complex gold anions and the hydrolysis of these complex anions at elevated temperature produced the insoluble gold hydroxide precipitate which was readily deposited on the silica. As the time of reaction was increased from 3 min to 60 min, these gold hydroxide nanoparticles also increased in size from 2 nm to 7 nm. We have also shown the progressive growth of the gold hydroxide seeds to eventually form gold nanoshells with a complete layer of gold shell with tunable optical response.

Control of optical contrast using gold nanoshells for optical coherence tomography imaging of mouse xenograft tumor model in vivo

The control of image contrast is essential toward optimizing a contrast enhancement procedure in optical coherence tomography (OCT). In this study, the in vivo control of optical contrast in a mouse tumor model with gold nanoshells as a contrast agent is examined. Gold nanoshells are administered into mice, with the injected dosage and particle surface parameters varied and its concentration in the tumor under each condition is determined using a noninvasive theoretical OCT modeling technique. The results show that too high a concentration of gold nanoshells in the tumor only enhances the OCT signal near the tissue surface, while significantly attenuating the signal deeper into the tissue. With an appropriate dosage, IV delivery of gold nanoshells allows a moderate concentration of 6.2 x 10(9) particles/ml in tumor to achieve a good OCT signal enhancement with minimal signal attenuation with depth. An increase in the IV dosage of gold nanoshells reveals a corresponding nonlinear increase in their tumor concentration, as well as a nonlinear reduction in the fractional concentration of injected gold nanoshells. Furthermore, this fractional concentration is improved with the use of antiepodermal growth factor receptor (EGFR) surface functionalization, which also reduces the time required for tumor delivery from 6 to 2 h.

Protein coronas on gold nanorods passivated with amphiphilic ligands affect cytotoxicity and cellular response to penicillin/streptomycin.

We probe how amphiphilic ligands (ALs) of four different types affect the formation of protein coronas on gold nanorods (NRs) and their impact on cellular response. NRs coated with cetyltrimethylammonium bromide were ligand exchanged with polyoxyethylene[10]cetyl ether, oligofectamine, and phosphatidylserine (PS). Protein coronas from equine serum (ES) were formed on these NR-ALs, and their colloidal stability, as well as cell uptake, proliferation, oxidative stress, and gene expression, were examined. We find that the protein corona that forms and its colloidal stability are affected by AL type and that the cellular response to these NR-AL-coronas (NR-AL-ES) is both ligand and corona dependent. We also find that the presence of common cell culture supplement penicillin/streptomycin can impact the colloidal stability and cellular response of NR-AL and NR-AL-ES, showing that the cell response is not necessarily inert to pen/strep when in the presence of nanoparticles. Although the protein corona is what the cells see, the underlying surface ligands evidently play an important role in shaping and defining the physical characteristics of the corona, which ultimately impacts the cellular response. Further, the results of this study suggest that the cellular behavior toward NR-AL is mediated by not only the type of AL and the protein corona it forms but also its resulting colloidal stability and interaction with cell culture supplements.

Stability of Gold Nanorods Passivated with Amphiphilic Ligands

The stability of gold nanorods (NRs) coated with amphiphilic ligands (ALs) was investigated. NRs coated with cetyltrimethylammonium bromide (CTAB) were ligand exchanged with polyoxyethylene [10] cetyl ether (Brij56), Oligofectamine (OF), and phosphatidylserine (PS). An aggregation index based on the longitudinal surface plasmon resonance peak broadening was used to measure stability of the NR-ALs under different conditions including the number of washes, pH, ionic concentration, and temperature. The aggregation index was also used to measure the stability of the NR-ALs under ultrafast laser irradiation and in the presence of proteins commonly used in cell culture. Differences in NR-AL stability were found, which were due to differences in the physical and chemical properties of the ALs. Apart from the charge on the AL headgroup, we suggest the Gibbs free energy of passivation (ΔG(p)) and enthalpy of passivation (ΔH(p)) of the AL could potentially aid in the selection of amphiphiles that can effectively passivate NRs for stability and optimize their properties and desired biological impact.

Component-Specific Analysis of Plasma Protein Corona Formation on Gold Nanoparticles Using Multiplexed Surface Plasmon Resonance.

At the nano-bio interface, human plasma differentially interacts with engineered nanomaterials through the creation of protein coronas, which in turn become primary determinants of both the pharmacokinetics and pharmacodynamics of circulating nanoparticles. Here, for the first time, the specific binding kinetics of the four major corona forming proteins (human serum albumin, fibrinogen, ApoA1, and polyclonal IgG) are determined for gold nanoparticles (AuNPs). Using a multiplexed surface plasmonic assay, highly reproducible measurements of on rate (k(on)), off rate (k(off)), and disassociation constant (K(D)), in addition to relative amounts of protein binding, are obtained. Dramatic differences in k(on) for individual components are shown as primary determinants of protein affinities, with k(on) ranging over nearly two orders of magnitude for the proteins studied, while k(off) remains within a factor of two for the set. The effect of polyethylene glycol (PEG) modification on plasma component binding is also studied and the effect of PEG length on human serum interaction is characterized through systematic screening of PEG molecular weight (2-30k). The effect of nanoparticle modification on particle targeting is also characterized through study of a hybrid AuNP system.