Andrew P. Goodwin

PEG branched polymer for functionalization of nanomaterials with ultralong blood circulation.

Nanomaterials have been actively pursued for biological and medical applications in recent years. Here, we report the synthesis of several new poly(ethylene glycol) grafted branched polymers for functionalization of various nanomaterials including carbon nanotubes, gold nanoparticles (NPs), and gold nanorods (NRs), affording high aqueous solubility and stability for these materials. We synthesize different surfactant polymers based upon poly(gamma-glutamic acid) (gammaPGA) and poly(maleic anhydride-alt-1-octadecene) (PMHC18). We use the abundant free carboxylic acid groups of gammaPGA for attaching lipophilic species such as pyrene or phospholipid, which bind to nanomaterials via robust physisorption. Additionally, the remaining carboxylic acids on gammaPGA or the amine-reactive anhydrides of PMHC18 are then PEGylated, providing extended hydrophilic groups, affording polymeric amphiphiles. We show that single-walled carbon nanotubes (SWNTs), Au NPs, and NRs functionalized by the polymers exhibit high stability in aqueous solutions at different pH values, at elevated temperatures, and in serum. Moreover, the polymer-coated SWNTs exhibit remarkably long blood circulation (t(1/2) = 22.1 h) upon intravenous injection into mice, far exceeding the previous record of 5.4 h. The ultralong blood circulation time suggests greatly delayed clearance of nanomaterials by the reticuloendothelial system (RES) of mice, a highly desired property for in vivo applications of nanomaterials, including imaging and drug delivery.

Supramolecular Stacking of Doxorubicin on Carbon Nanotubes for In Vivo Cancer Therapy

Doxorubicin (DOX) is a member of the anthracycline class of chemotherapeutic agents that are used for the treatment of many common human cancers, including aggressive non-Hodgkin’s lymphoma.[1,2] However, DOX is highly toxic in humans and can result in severe suppression of hematopoiesis, gastrointestinal toxicity,[3] and cardiac toxicity.[4] To date, several approaches, including delivery using liposomes (DOXIL),[5] have been developed to reduce the toxicity and enhance the clinical utility of this highly active antineoplastic agent.

Protein microarrays with carbon nanotubes as multicolor Raman labels

The current sensitivity of standard fluorescence-based protein detection limits the use of protein arrays in research and clinical diagnosis. Here, we use functionalized, macromolecular single-walled carbon nanotubes (SWNTs) as multicolor Raman labels for highly sensitive, multiplexed protein detection in an arrayed format. Unlike fluorescence methods, Raman detection benefits from the sharp scattering peaks of SWNTs with minimal background interference, affording a high signal-to-noise ratio needed for ultra-sensitive detection. When combined with surface-enhanced Raman scattering substrates, the strong Raman intensity of SWNT tags affords protein detection sensitivity in sandwich assays down to 1 fM—a three-order-of-magnitude improvement over most reports of fluorescence-based detection. We use SWNT Raman tags to detect human autoantibodies against proteinase 3, a biomarker for the autoimmune disease Wegeners granulomatosis, diluted up to 107-fold in 1% human serum. SWNT Raman tags are not subject to photobleaching or quenching. By conjugating different antibodies to pure 12C and 13C SWNT isotopes, we demonstrate multiplexed two-color SWNT Raman-based protein detection.

Two-photon degradable supramolecular assemblies of linear-dendritic copolymers

Micelles of dendritic-linear copolymers have been developed to release a payload after infrared stimulus.

Phospholipid-Dextran with a Single Coupling Point: a Useful Amphiphile for Functionalization of Nanomaterials

Nanomaterials hold much promise for biological applications, but they require appropriate functionalization to provide biocompatibility in biological environments. For noncovalent functionalization with biocompatible polymers, the polymer must also remain attached to the nanomaterial after removal of its excess to mimic the high-dilution conditions of administration in vivo. Reported here are the synthesis and utilization of singly substituted conjugates of dextran and a phospholipid (dextran-DSPE) as stable coatings for nanomaterials. Suspensions of single-walled carbon nanotubes were found not only to be stable to phosphate buffered saline (PBS), serum, and a variety of pHs after excess polymer removal, but also to provide brighter photoluminescence than carbon nanotubes suspended by poly(ethylene glycol)-DSPE. In addition, both gold nanoparticles (AuNPs) and gold nanorods (AuNRs) were found to maintain their dispersion and characteristic optical absorbance after transfer into dextran-DSPE and were obtained in much better yield than similar suspensions with PEG-phospholipid and commonly used thiol-PEG. These suspensions were also stable to PBS, serum, and a variety of pHs after removal of excess polymer. dextran-DSPE thus shows great promise as a general surfactant material for the functionalization of a variety of nanomaterials, which could facilitate future biological applications.

Aptamer‐Crosslinked Microbubbles: Smart Contrast Agents for Thrombin‐Activated Ultrasound Imaging

Thrombosis, or malignant blood clotting, is associated with numerous cardiovascular diseases and cancers. A microbubble contrast agent is presented that produces ultrasound harmonic signal only when exposed to elevated thrombin levels. Initially silent microbubbles are activated in the presence of both thrombin-spiked and freshly clotting blood in three minutes with detection limits of 20 nM thrombin and 2 aM microbubbles.

High‐contrast in vivo visualization of microvessels using novel FeCo/GC magnetic nanocrystals

FeCo‐graphitic carbon shell nanocrystals are a novel MRI contrast agent with unprecedented high per‐metal‐atom‐basis relaxivity (r1 = 97 mM‐1 sec‐1, r2 = 400 mM‐1 sec‐1) and multifunctional capabilities. While the conventional gadolinium‐based contrast‐enhanced angiographic magnetic MRI has proven useful for diagnosis of vascular diseases, its short circulation time and relatively low sensitivity render high‐resolution MRI of morphologically small vascular structures such as those involved in collateral, arteriogenic, and angiogenic vessel formation challenging. Here, by combining FeCo‐graphitic carbon shell nanocrystals with high‐resolution MRI technique, we demonstrate that such microvessels down to ∼100 μm can be monitored in high contrast and noninvasively using a conventional 1.5‐T clinical MRI system, achieving a diagnostic imaging standard approximating that of the more invasive X‐ray angiography. Preliminary in vitro and in vivo toxicity study results also show no sign of toxicity. Magn Reson Med, 2009.

DNA‐Coated Microbubbles with Biochemically Tunable Ultrasound Contrast Activity

Changing the mechanical properties of the microbubble shell in response to a biochemical stimulus leads to vast changes in both ultrasound-induced bubble dynamics and contrast-enhanced ultrasound imaging. Here, DNA-coated microbubbles are shown to be a simple and highly versatile platform that can silence and re-activate contrast activity in response to the introduction and removal of biochemical stimuli.

Characterization of individual ultrasound microbubble dynamics with a light-scattering system

Ultrasound microbubbles are contrast agents used for diagnostic ultrasound imaging and as carriers for noninvasive payload delivery. Understanding the acoustic properties of individual microbubble formulations is important for optimizing the ultrasound imaging parameters for improved image contrast and efficient payload delivery. We report here a practical and simple optical tool for direct real-time characterization of ultrasound contrast microbubble dynamics based on light scattering. Fourier transforms of raw linear and nonlinear acoustic oscillations, and microbubble cavitations are directly recorded. Further, the power of this tool is demonstrated by comparing clinically relevant microbubble cycle-to-cycle dynamics and their corresponding Fourier transforms.

Stable Encapsulation of Air in Mesoporous Silica Nanoparticles: Fluorocarbon-Free Nanoscale Ultrasound Contrast Agents.

While gas-filled micrometer-sized ultrasound contrast agents vastly improve signal-to-noise ratios, microbubbles have short circulation lifetimes and poor extravasation from the blood. Previously reported fluorocarbon-based nanoscale contrast agents are more stable but their contrast is generally lower owing to their size and dispersity. The contrast agents reported here are composed of silica nanoparticles of ≈100 nm diameter that are filled with ≈3 nm columnar mesopores. Functionalization of the silica surface with octyl groups and resuspension with Pluronic F127 create particles with pores that remain filled with air but are stable in buffer and serum. Administration of high intensity focused ultrasound (HIFU) allows sensitive imaging of the silica nanoparticles down to 10(10) particles mL(-1) , with continuous imaging for at least 20 min. Control experiments with different silica particles supported the hypothesis that entrapped air could be pulled into bubble nuclei, which can then in turn act as acoustic scatterers. This process results in very little hemolysis in whole blood, indicating potential for nontoxic blood pool imaging. Finally, the particles are lyophilized and reconstituted or stored in PBS (phosphate-buffered saline, at least for four months) with no loss in contrast, indicating stability to storage and reformulation.