Andrew Burns

Multimodal silica nanoparticles are effective cancer-targeted probes in a model of human melanoma

Nanoparticle-based materials, such as drug delivery vehicles and diagnostic probes, currently under evaluation in oncology clinical trials are largely not tumor selective. To be clinically successful, the next generation of nanoparticle agents should be tumor selective, nontoxic, and exhibit favorable targeting and clearance profiles. Developing probes meeting these criteria is challenging, requiring comprehensive in vivo evaluations. Here, we describe our full characterization of an approximately 7-nm diameter multimodal silica nanoparticle, exhibiting what we believe to be a unique combination of structural, optical, and biological properties. This ultrasmall cancer-selective silica particle was recently approved for a first-in-human clinical trial. Optimized for efficient renal clearance, it concurrently achieved specific tumor targeting. Dye-encapsulating particles, surface functionalized with cyclic arginine-glycine-aspartic acid peptide ligands and radioiodine, exhibited high-affinity/avidity binding, favorable tumor-to-blood residence time ratios, and enhanced tumor-selective accumulation in αvβ3 integrin-expressing melanoma xenografts in mice. Further, the sensitive, real-time detection and imaging of lymphatic drainage patterns, particle clearance rates, nodal metastases, and differential tumor burden in a large-animal model of melanoma highlighted the distinct potential advantage of this multimodal platform for staging metastatic disease in the clinical setting.

Fluorescent Silica Nanoparticles with Efficient Urinary Excretion for Nanomedicine

The development of molecularly targeted probes that exhibit high biostability, biocompatibility, and efficient clearance profiles is key to optimizing biodistribution and transport across biological barriers. Further, coupling probes designed to meet these criteria with high-sensitivity, quantitative imaging strategies is mandatory for ensuring early in vivo tumor detection and timely treatment response. These challenges have often only been examined individually, impeding the clinical translation of fluorescent probes. By simultaneously optimizing these design criteria, we created a new generation of near-infrared fluorescent core-shell silica-based nanoparticles (C dots) tuned to hydrodynamic diameters of 3.3 and 6.0 nm with improved photophysical characteristics over the parent dye. A neutral organic coating prevented adsorption of serum proteins and facilitated efficient urinary excretion. Detailed particle biodistribution studies were performed using more quantitative ex vivo fluorescence detection protocols and combined optical-PET imaging. The results suggest that this new generation of C dots constitutes a promising clinically translatable materials platform which may be adapted for tumor targeting and treatment.

Materials and transducers toward selective wireless gas sensing.

Wireless sensors are devices in which sensing electronic transducers are spatially and galvanically separated from their associated readout/display components. The main benefits of wireless sensors, as compared to traditional tethered sensors, include the non-obtrusive nature of their installations, higher nodal densities, and lower installation costs without the need for extensive wiring.1–3 These attractive features of wireless sensors facilitate their development toward measurements of a wide range of physical, chemical, and biological parameters of interest. Examples of available wireless sensors include devices for sensing of pH, pressure, and temperature in medical, pharmaceutical, animal health, livestock condition, automotive, and other applications.4–7 Some implementations of wireless gas sensors can be already found in monitoring of analyte gases (e.g. carbon dioxide, water vapor, oxygen, combustibles) in relatively interference-free industrial and indoor environments.8,9 However, unobtrusive wireless gas sensors are urgently needed for many more diverse applications ranging from wearable sensors at the workplace, urban environment, and battlefield, to monitoring of containers with toxic industrial chemicals while in transit, to medical monitoring of hospitalized and in-house patients, to detection of food freshness in individual packages, and to distributed networked sensors over large areas (also known as wireless sensor networks, WSNs). Unfortunately, in these and numerous other practical applications, the available wireless gas sensors fall short of meeting emerging measurement needs in complex environments. In particular, existing wireless gas sensors cannot perform highly selective gas detection in the presence of high levels of interferences and cannot quantitate several components in gas mixtures. 1.1. Diversity Of Monitoring Needs Of Volatiles The monitoring of numerous gases of environmental, industrial, and homeland security concern is needed over the broad range of their regulated exposure concentrations. Figure 1 illustrates the relationships between several regulated exposure levels spanning several orders of magnitude of gas concentrations. Typical examples of concentrations of regulated exposure are presented in Table 110–14 for three groups of toxic volatiles such as volatile organic compounds (VOCs), toxic industrial chemicals (TICs), and chemical warfare agents (CWAs). These examples demonstrate the need for gas sensing capabilities with broad measurement dynamic ranges to cover 2 – 4 orders of magnitude in gas concentrations. Figure 1 Examples of regulated vapor-exposure limits established by different organizations: GPL: General Population Limit, established by USACHPPM – U.S. Army Center for Health Promotion and Preventative Medicine; PEL: Permissible Exposure Limit, established ... Table 1 Examples of regulated concentration levels (in ppm by volume) from three representative classes of toxic gases: VOCs, TICs, and CWAs.10–14 Additional needs for detection of volatiles originate from medical diagnostics, food safety, process monitoring, and other areas.15–17 In those applications, the types and levels of detected volatiles can provide the needed information for further control actions.

Core-shell silica nanoparticles as fluorescent labels for nanomedicine

Progress in biomedical imaging depends on the development of probes that combine low toxicity with high sensitivity, resolution, and stability. Toward that end, a new class of highly fluorescent core-shell silica nanoparticles with narrow size distributions and enhanced photostability, known as C dots, provide an appealing alternative to quantum dots. Here, C dots are evaluated with a particular emphasis on in-vivo applications in cancer biology. It is established that C dots are nontoxic at biologically relevant concentrations, and can be used in a broad range of imaging applications including intravital visualization of capillaries and macrophages, sentinel lymph node mapping, and peptide-mediated multicolor cell labeling for real-time imaging of tumor metastasis and tracking of injected bone marrow cells in mice. These results demonstrate that fluorescent core-shell silica nanoparticles represent a powerful novel imaging tool within the emerging field of nanomedicine.

A silica sol–gel design strategy for nanostructured metallic materials

Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol-gel process built around a multifunctional sol-gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate. This approach allows a wide range of biological functionalities and metals--including noble metals--to be combined into a library of sol-gel materials with a high degree of control over composition and structure. We demonstrate that the sol-gel process based on these precursors is compatible with block-copolymer self-assembly, colloidal crystal templating and the Stöber process. As a result of the exceptionally high metal content, these materials can be thermally processed to make porous nanocomposites with metallic percolation networks that have an electrical conductivity of over 1,000 S cm(-1). This improves the electrical conductivity of porous silica sol-gel nanocomposites by three orders of magnitude over existing approaches, opening applications to high-current-density devices.

Functional tomographic fluorescence imaging of pH microenvironments in microbial biofilms by use of silica nanoparticle sensors.

ABSTRACT Attached bacterial communities can generate three-dimensional (3D) physicochemical gradients that create microenvironments where local conditions are substantially different from those in the surrounding solution. Given their ubiquity in nature and their impacts on issues ranging from water quality to human health, better tools for understanding biofilms and the gradients they create are needed. Here we demonstrate the use of functional tomographic imaging via confocal fluorescence microscopy of ratiometric core-shell silica nanoparticle sensors (C dot sensors) to study the morphology and temporal evolution of pH microenvironments in axenic Escherichia coli PHL628 and mixed-culture wastewater biofilms. Testing of 70-, 30-, and 10-nm-diameter sensor particles reveals a critical size for homogeneous biofilm staining, with only the 10-nm-diameter particles capable of successfully generating high-resolution maps of biofilm pH and distinct local heterogeneities. Our measurements revealed pH values that ranged from 5 to >7, confirming the heterogeneity of the pH profiles within these biofilms. pH was also analyzed following glucose addition to both suspended and attached cultures. In both cases, the pH became more acidic, likely due to glucose metabolism causing the release of tricarboxylic acid cycle acids and CO2. These studies demonstrate that the combination of 3D functional fluorescence imaging with well-designed nanoparticle sensors provides a powerful tool for in situ characterization of chemical microenvironments in complex biofilms.

Integrating Structure Control over Multiple Length Scales in Porous High Temperature Ceramics with Functional Platinum Nanoparticles

High temperature ceramics with porosity on multiple length scales offer great promise in high temperature catalytic applications for their high surface area and low flow resistance in combination with thermal and chemical stability. We have developed a bottom-up approach to functional, porous, high-temperature ceramics structured on eight distinct length scales integrating functional Pt nanoparticles from the near-atomic to the macroscopic level. Structuring is achieved through a combination of micromolding and multicomponent colloidal self-assembly. The resulting template is filled with a solution containing a solvent, a block copolymer, a ceramic precursor, and a nanoparticle catalyst precursor as well as a radical initiator. Heat treatment results in three-dimensionally interconnected, high-temperature ceramic materials functionalized with well-dispersed 1-2 nm Pt catalyst nanoparticles and very high porosity.

Dye structure–optical property correlations in near-infrared fluorescent core-shell silica nanoparticles

In this paper we report on dye structure–optical property correlations for a range of near-infrared emitting (NIR, 650–900 nm) fluorescent dyes in a 9–14 nm diameter core-shell silica particle architecture (C dots), including Cy5, Alexa Fluor 700, DY730, Alexa Fluor 750, and DY780. For each dye an apparent per-dye enhancement in fluorescence is observed over free dye in aqueous solution ranging from 1.2× to 6.6×, highlighting the versatility of the silica encapsulation approach. For the Cy5 and DY730 dye/particle sample pairs photobleaching was undertaken and revealed that the particles photobleach slower than the dyes. For a particular NIR dye series with identical chemical backbone, DY730, DY731, DY732, and DY734, we demonstrate that with increasing number of sulfonated substituent groups the per-dye brightness enhancement decreases. Finally, we show that in special cases, like Cy5, brightness enhancement of dyes in dots over free dye may be a combination of effects from dye conjugation chemistry and immobilization in the silica matrix. These results provide powerful design criteria for next generation optical probes for applications ranging from bioimaging to security.

Large stokes-shift fluorescent silica nanoparticles with enhanced emission over free dye for single excitation multiplexing.

We describe a polycondensation reaction of silica precursors in a modified Stober-type basic ethanol solution to produce graded Stokes-shift core-shell silica nanoparticles providing bright and spectrally multiplexed sets of fluorescent tags that are excitable using a single excitation source. Dynamic light scattering and scanning electron microscopy demonstrate particle sizes in the sub-10 nm regime. Absorption matched emission comparisons between encapsulated and free dyes in aqueous solution reveal about an order of magnitude per-dye brightness enhancements that are apparent by simply looking at the solutions under laser illumination conditions.

Site-specific labeling of surface proteins on living cells using genetically encoded peptides that bind fluorescent nanoparticle probes.

We report a highly specific, robust, and generic method for noncovalent labeling of cellular proteins with highly fluorescent core-shell silica nanoparticles termed C dots. Our approach uses short genetically engineered peptides with affinity for silica (GEPS) that are site-specifically introduced at the termini or in loops of cellular proteins. Because GEPS are absent from native cell surface proteins, GEPS-tagged recombinant proteins can be selectively and rapidly labeled with fluorescent C dots. To demonstrate the versatility of our method, we targeted 30 nm C dots to two structurally distinct integral outer membrane proteins in Escherichia coli, FhuA and OmpX. Efficient labeling was achieved in 15 min or less and was observed to be highly sensitive and specific. This strategy provides a powerful technique, comparable to other chemical and biological labeling strategies, for efficient and quantitative investigation of protein function in live biological cells.