Jasmine M. Tam

Small multifunctional nanoclusters (Nanoroses) for targeted cellular imaging and therapy

The ability of 20-50 nm nanoparticles to target and modulate the biology of specific types of cells will enable major advancements in cellular imaging and therapy in cancer and atherosclerosis. A key challenge is to load an extremely high degree of targeting, imaging, and therapeutic functionality into small, yet stable particles. Herein we report approximately 30 nm stable uniformly sized near-infrared (NIR) active, superparamagnetic nanoclusters formed by kinetically controlled self-assembly of gold-coated iron oxide nanoparticles. The controlled assembly of nanocomposite particles into clusters with small primary particle spacings produces collective responses of the electrons that shift the absorbance into the NIR region. The nanoclusters of approximately 70 iron oxide primary particles with thin gold coatings display intense NIR (700-850 nm) absorbance with a cross section of approximately 10(-14) m(2). Because of the thin gold shells with an average thickness of only 2 nm, the r(2) spin-spin magnetic relaxivity is 219 mM(-1) s(-1), an order of magnitude larger than observed for typical iron oxide particles with thicker gold shells. Despite only 12% by weight polymeric stabilizer, the particle size and NIR absorbance change very little in deionized water over 8 months. High uptake of the nanoclusters by macrophages is facilitated by the dextran coating, producing intense NIR contrast in dark field and hyperspectral microscopy, both in cell culture and an in vivo rabbit model of atherosclerosis. Small nanoclusters with optical, magnetic, and therapeutic functionality, designed by assembly of nanoparticle building blocks, offer broad opportunities for targeted cellular imaging, therapy, and combined imaging and therapy.

Controlled Assembly of Biodegradable Plasmonic Nanoclusters for Near-Infrared Imaging and Therapeutic Applications

Metal nanoparticles with surface plasmon resonance (SPR) in the near-infrared region (NIR) are of great interest for imaging and therapy. Presently, gold nanoparticles with NIR absorbance are typically larger than 50 nm, above the threshold size of approximately 5 nm required for efficient renal clearance. As these nanoparticles are not biodegradable, concerns about long-term toxicity have restricted their translation into the clinic. Here, we address this problem by developing a flexible platform for the kinetically controlled assembly of sub-5 nm ligand-coated gold particles to produce metal/polymer biodegradable nanoclusters smaller than 100 nm with strong NIR absorbance for multimodal application. A key novel feature of the proposed synthesis is the use of weakly adsorbing biodegradable polymers that allows tight control of nanocluster size and, in addition, results in nanoclusters with unprecedented metal loadings and thus optical functionality. Over time, the biodegradable polymer stabilizer degrades under physiological conditions that leads to disassembly of the nanoclusters into sub-5 nm primary gold particles which are favorable for efficient body clearance. This synthesis of polymer/inorganic nanoclusters combines the imaging contrast and therapeutic capabilities afforded by the NIR-active nanoparticle assembly with the biodegradability of a polymer stabilizer.

High bioavailability from nebulized itraconazole nanoparticle dispersions with biocompatible stabilizers

A nebulized dispersion of amorphous, high surface area, nanostructured aggregates of itraconazole (ITZ):mannitol:lecithin (1:0.5:0.2, w/w) yielded improved bioavailability in mice. The ultra-rapid freezing (URF) technique used to produce the nanoparticles was found to molecularly disperse the ITZ with the excipients as a solid solution. Upon addition to water, ITZ formed a colloidal dispersion suitable for nebulization, which demonstrated optimal aerodynamic properties for deep lung delivery and high lung and systemic levels when dosed to mice. The ITZ nanoparticles produced supersaturation levels 27 times the crystalline solubility upon dissolution in simulated lung fluid. A dissolution/permeation model indicated that the absorption of 3 microm ITZ particles is limited by the dissolution rate (BCS Class II behavior), while absorption is permeation-limited for more rapidly dissolving 230 nm particles. The predicted absorption half-life for 230 nm amorphous ITZ particles was only 15 min, as a result of the small particle size and high supersaturation, in general agreement with the in vivo results. Thus, bioavailability may be enhanced, by decreasing the particle size to accelerate dissolution and increasing permeation with (1) an amorphous morphology to raise the drug solubility, and (2) permeability enhancers.

Kinetic assembly of near-IR-active gold nanoclusters using weakly adsorbing polymers to control the size.

Clusters of metal nanoparticles with an overall size of less than 100 nm and high metal loadings for strong optical functionality are of interest in various fields including microelectronics, sensors, optoelectronics, and biomedical imaging and therapeutics. Herein we assemble approximately 5 nm gold particles into clusters with controlled size, as small as 30 nm and up to 100 nm, that contain only small amounts of polymeric stabilizers. The assembly is kinetically controlled with weakly adsorbing polymers, PLA(2K)-b-PEG(10K)-b-PLA(2K) or PEG (MW = 3350), by manipulating electrostatic, van der Waals (VDW), steric, and depletion forces. The cluster size and optical properties are tuned as a function of particle volume fractions and polymer/gold ratios to modulate the interparticle interactions. The close spacing between the constituent gold nanoparticles and high gold loadings (80-85 w/w gold) produce a strong absorbance cross section of approximately 9 x 10(-15) m(2) in the NIR at 700 nm. This morphology results from VDW and depletion attractive interactions that exclude the weakly adsorbed polymeric stabilizer from the cluster interior. The generality of this kinetic assembly platform is demonstrated for gold nanoparticles with a range of surface charges from highly negative to neutral with the two different polymers.

Amorphous cyclosporin nanodispersions for enhanced pulmonary deposition and dissolution

Aqueous colloidal dispersions of amorphous cyclosporin A (CsA) nanoparticles, intended for pulmonary delivery, were formed by antisolvent precipitation and stabilized with 10% polysorbate 80. Dissolution of the dispersion of CsA nanoparticles produced supersaturation values 18 times the aqueous equilibrium solubility. Nebulization of the dispersion to mice produced therapeutic lung levels and systemic concentrations below toxic limits. The sizes of the aerosolized aqueous droplets are optimal for deep lung deposition, whereas the amorphous drug nanoparticles facilitate rapid dissolution. A dissolution/permeation model was developed to characterize the effects of particle size, solubility, and drug dose on the absorption half-lives of poorly water soluble drugs in the alveolar epithelium. For crystalline 3 microm particles with a solubility of 1 microg/mL, the half-life for absorption was estimated to be 500 min. The half-life may be reduced to less than 1 min by increasing the solubility by a factor of 100 with an amorphous form as well as by decreasing the particle size 10-fold. The in vitro and in vivo data, as well as the dissolution/permeation model, indicate that nebulization of amorphous nanoparticle suspensions has the potential to enhance lung epithelial absorption markedly for poorly water soluble drugs, relative to respiratory delivery of crystalline, micron-sized particles.

Utility of biodegradable plasmonic nanoclusters in photoacoustic imaging

Plasmonic metal nanoparticles are used in photoacoustic imaging as contrast agents because of their resonant optical absorption properties in the visible and near-IR regions. However, the nanoparticles could accumulate and result in long-term toxicity in vivo, because they are generally not biodegradable. Recently, biodegradable plasmonic gold nanoclusters, consisting of sub-5 nm primary gold nanoparticles and biodegradable polymer stabilizer, were introduced. In this Letter, we demonstrate the feasibility of biodegradable nanoclusters as a photoacoustic contrast agent. We performed photoacoustic and ultrasound imaging of a tissue-mimicking phantom with inclusions containing nanoclusters at various concentrations. The results indicate that the biodegradable gold nanoclusters can be used as effective contrast agents in photoacoustic imaging.

Templated Open Flocs of Anisotropic Particles for Pulmonary Delivery with Pressurized Metered Dose Inhalers

The challenges in forming stable drug suspensions in hydrofluoroalkane (HFA) propellants have limited drug dosages and efficiency of drug delivery with pressurized metered dose inhalers (pMDI). Herein, stable suspensions of weakly flocculated particles, in the shape of thin plates or needles, of a poorly water-soluble drug, itraconazole (Itz), are efficiently delivered by pMDI at high doses, up to 2.4 mg/actuation. These anisotropic particles pack inefficiently and form low-density flocs that stack upon each other to prevent settling. In contrast, spherical particles formed dense aggregates that settled within minutes. Upon actuation of the pMDI, atomized propellant droplets shear apart and thus template the highly friable flocs. Evaporation of the HFA compacts the flocs to yield porous particles with optimal aerodynamic properties. High fine particle fractions (49-64%) were achieved with the stable suspensions for drug loadings up to 50 mg/mL. Furthermore, the micron-sized particles, ideal for pulmonary delivery, are composed of nanoparticles that dissociate and facilitate rapid dissolution of poorly water-soluble drugs. Pulmonary delivery of stable suspensions of templated, open flocs is broadly applicable to a range of anisotropic particle morphologies for poorly water-soluble drugs and proteins for efficient delivery of high doses, up to several milligrams, using minimal amounts of excipients.

Cancer imaging and therapy with metal nanoparticles

Nanotechnology offers unique opportunities for cancer detection, therapy and the ability to monitor therapeutic interventions. This potential has to be analyzed in context of challenges that need to be overcome in translation of nanoparticles to clinical applications including specific delivery in tissues and clearance from the body. Here, we will present a case study of plasmonic nanoparticles in cancer imaging and therapy.

Biodegradable plasmonic nanoclusters as contrast agent for photoacoustic imaging

Metallic nanoparticles have been widely used in a variety of imaging and therapeutic applications due to their unique optical properties in the visible and near-infrared (NIR) regions - for example, various plasmonic nanoparticles are used for molecular photoacoustic imaging and photothermal therapy. However, there are concerns that these agents may not be safe under physiological conditions, because these nanoparticles are not biodegradable, could accumulate and, therefore, could be toxic long-term. We investigate the feasibility of using biodegradable gold nanoclusters as a contrast agent for highly sensitive photoacoustic imaging. The size of these biodegradable nanoclusters, consisting of sub-5 nm primary gold particles and a biodegradable polymer binder, is less than 100 nm. Due to plasmon coupling, these nanoclusters are characterized by a broad extinction spectrum that extends to the near infrared (NIR) spectral range. Photoacoustic imaging of tissue models containing inclusions with different concentrations of nanoparticles was performed using a tunable pulsed laser system. The results indicate that the biodegradable nanoclusters, comprised of small gold nanoparticles, can be used as contrast agents in photoacoustic imaging.

Photoacoustic imaging with biodegradable plasmonic nanoclusters

Plasmonic nanoparticles have been widely used for various biomedical applications such as biological imaging, sensing, and cancer therapy. Specifically, gold nanospheres, nanorods, and nanoshells are used as contrast agents for photoacoustic imaging due to their strong absorptive property. However, there are concerns about using these nanoparticles in-vivo because they are not biodegradable and cannot be cleared from the body. Recently, biodegradable nanoclusters have been reported. The biodegradable nanoparticles are composed of primary 4-nm gold nanoparticles and stabilized by a biodegradable polymer binder. In this study, we demonstrated the utility of biodegradable nanoclusters as a contrast agent in photoacoustic imaging. The tissue mimicking phantoms were used for ultrasound and photoacoustic imaging. The results show that the biodegradable plasmonic nanoclusters can be used as photoacoustic contrast agent.