Hans C. Fischer

Mediating Tumor Targeting Efficiency of Nanoparticles Through Design

Here we systematically examined the effect of nanoparticle size (10-100 nm) and surface chemistry (i.e., poly(ethylene glycol)) on passive targeting of tumors in vivo. We found that the physical and chemical properties of the nanoparticles influenced their pharmacokinetic behavior, which ultimately determined their tumor accumulation capacity. Interestingly, the permeation of nanoparticles within the tumor is highly dependent on the overall size of the nanoparticle, where larger nanoparticles appear to stay near the vasculature while smaller nanoparticles rapidly diffuse throughout the tumor matrix. Our results provide design parameters for engineering nanoparticles for optimized tumor targeting of contrast agents and therapeutics.

In vivo Quantum‐Dot Toxicity Assessment

Quantum dots have potential in biomedical applications, but concerns persist about their safety. Most toxicology data is derived from in vitro studies and may not reflect in vivo responses. Here, an initial systematic animal toxicity study of CdSe-ZnS core-shell quantum dots in healthy Sprague-Dawley rats is presented. Biodistribution, animal survival, animal mass, hematology, clinical biochemistry, and organ histology are characterized at different concentrations (2.5-15.0 nmol) over short-term (<7 days) and long-term (>80 days) periods. The results show that the quantum dot formulations do not cause appreciable toxicity even after their breakdown in vivo over time. To generalize the toxicity of quantum dots in vivo, further investigations are still required. Some of these investigations include the evaluation of quantum dot composition (e.g., PbS versus CdS), surface chemistry (e.g., functionalization with amines versus carboxylic acids), size (e.g., 2 versus 6 nm), and shape (e.g., spheres versus rods), as well as the effect of contaminants and their byproducts on biodistribution behavior and toxicity. Combining the results from all of these studies will eventually lead to a conclusion regarding the issue of quantum dot toxicity.

Exploring Primary Liver Macrophages for Studying Quantum Dot Interactions with Biological Systems

2010 WILEY-VCH Verlag Gmb Nanomaterial toxicity is currently a major concern and could potentially hamper the advancement of nanotechnology development. The nanotoxicology field is active and many researchers have reported on the biological responses of nanoparticles. Responses vary with nanoparticle type, properties and experimental methods. A diversity of cell types to test the toxicity of nanoparticles in vitro has also been reported. Bregoli et al. recently compared primary cells with multiple immortalized cell lines and found differences in cytotoxicity between the primary cells and the cell lines. Furthermore, toxicity results may differ between those of cell culture studies and in vivo animal studies. Therefore, the type of cells used for toxicity testing will impact the results and conclusions drawn regarding nanomaterial toxicity and its subsequent clinical use. Another current research focus is to develop high-throughput in vitro testing platforms as a first step in nanotoxicity evaluation. Although in vivo toxicity characterization is the most accurate method as it takes into account all possible intracellular effects, this strategy is expensive, labor intensive, and time consuming. Cell varieties used for in vitro nanoparticle testing are intended to mirror cell types encountered in vivo. Different in vivo exposure or administration routes result in different cell types being primarily responsible for uptake. However, many in vivo studies have shown that the non-specific interactions occur with phagocytic cells that are associated with the reticuloendothelial systems. For example, resident liver macrophages, commonly called Kupffer cells (KC), are primarily responsible for in vivo uptake of intravenously dosed nanoparticles including semiconductor quantum dots (QDs), nanotubes, and polymer nanobeads. Our aim in this study is to qualify or verify primary KCs as a suitable in vitro model by characterizing interactions of QDs with KCs freshly isolated from Sprague–Dawley rats and compare our results to previously published in vivo QD studies. Our study has two main aspects. The first involved preparing and characterizing QDs, and isolating and culturing primary macrophages. The second was studying QD interactions with macrophages, studying the uptake and release kinetics, metabolism, cytokine release, and cellular response to microbes. We selected diverse QD types to conduct these studies (Fig. 1A). The physical, electrophoretic, and optical properties of the QDs were characterized (Table S1, Supporting Information). Dynamic light scattering (DLS) determined the hydrodynamic radius. Both zeta potential and gel electrophoresis verified that polyethylene glycol (PEG) and bovine serum albumin (BSA) were successfully conjugated to the blode co-polymer-coated QD (PQD) surface. QD core size measured with transmission electron microscopy (TEM) agreed with absorbance based size determination. KCs were isolated (Fig. 1; Fig. S3, Supporting Information) and plated at 800 cells per mm density, exposed to QD at a concentration of 0.3 nmol mL . This was equivalent to the QD concentration in vivo in a previously published study,

Visualizing quantum dots in biological samples using silver staining.

Quantum dot (QD) based contrast agents are currently being developed as probes for bioimaging and as vehicles for drug delivery. The ability to detect QDs, regardless of fluorescence brightness, in cells, tissues, and organs is imperative to their development. Traditional methods used to visualize the distribution of QDs in biological samples mainly rely on fluorescence imaging, which does not account for optically degenerate QDs as a result of oxidative quenching within the biological environment. Here, we demonstrate the use of silver staining for directly visualizing the distribution of QDs within biological samples under bright field microscopy. This strategy involves silver deposition onto the surface of QDs upon reduction by hydroquinone, effectively amplifying the size of QDs until visible for detection. The method can be used to detect non-fluorescent QDs and is fast, simple, and inexpensive.

Engineering Biocompatible Quantum Dots for Ultrasensitive, Real-Time Biological Imaging and Detection

Advances in the design of optical probes have played a central role in the emergence of photon-based microscopy techniques for biological imaging and detection [1, 2, 3, 4, 5, 6]. These advances have led to the elucidation of the biological function and activity of many proteins, nucleic acids, and other molecules in living cells, tissues, and animals. Currently, the molecular architecture of greater than 70% of all optical probes consists of an “optical emitter” attached to a “targeting molecule” [4]. The targeting molecule directs the optical emitter to specific biological sites where the optical emitter can then be used to detect the activities of biomolecules. The most popular optical probes have been traditionally designed from organic-based molecules; for instance, probes for the imaging of cellular cytoskeleton are based on the conjugation of red-fluorescent molecule Texas Red to the small targeting organic molecule phalloidin (for labeling actin fibers) and green-fluorescent Alexa Fluor 488 to a recognition antibody (for labeling microtubules) [4]. Hundreds of different types of organic-based fluorescent probes are commercially available. These probes can be used in numerous applications, including the staining of DNA and proteins, detection of subtle differences in the ionic content in living cells, or detection of protein structures [4, 7, 8, 9, 10]. Due to their complex molecular structures, however, organic fluorophores often exhibit unfavorable absorption and emission properties, such as photobleaching, environmental quenching, broad and asymmetric emission spectra, and the inability to excite multiple fluorophores of more than 2–3 colors at a single wavelength [10, 11].

Preliminary results: exploring the interactions of quantum dots with whole blood components

Biocompatible ZnS capped CdSe fluorescent semiconductor nanocrystals (quantum dots, QDs) exhibit great potential as imaging agents with biomedical and clinical relevance. However, little is known about the fate of the quantum dots in vivo, and the importance of chemical and physical composition that may influence their behavior in vivo. When the QDs are introduced in vivo, the first interactions with blood components will dictate their kinetic behavior in vivo. We present some preliminary results that demonstrate the interactions of the quantum dots with plasma proteins and that quantum dots can be trapped in fibrous networks.

Biomedical Applications of Semiconductor Quantum Dots

In recent decades‚ the exquisite sensitivity and versatility of optical technologies have led to numerous breakthroughs in biological research‚ including real-time imaging of live cells‚ gene expression profiling‚ cell sorting‚ and clinical diagnostics. A key component in optical detection schemes is the probe design. These probes are constructed from organic fluorophores‚ such as fluorescein and tetramethylrhodamine (TMR)‚ and recognition molecules. The optical emission of fluorophores is used to visualize the activities of biomolecules‚ while the recognition molecules direct the fluorophores to specific cells‚ tissues‚ or organs. Although optical probes are widely used‚ most organic fluorophores exhibit unfavourable properties that have hampered their applications in single-protein tracking in living cells‚ molecular pathology‚ and other research areas. These properties include photobleaching‚ sensitivity to environmental conditions‚ and inability to excite multiple fluorophores using a single wavelength. A new generation of probes has emerged in the last five years that overcomes many of the limitations associated with organic fluorophores. These probes employ fluorophores that are sub-100 nm in size and composed of inorganic atoms. Unlike organic-only fluorophores‚ the optical and electronic properties of inorganic fluorophores can be tuned during the synthesis process by changing their size‚ shape‚ or composition. In this chapter‚ we will describe the use of one type of inorganic fluorophore‚ semiconductor nanocrystals‚ for the development of “custom-designed” probes for biomedical detection. Semiconductor nanocrystals‚ also known as “quantum dots” (qdots)‚ are typically composed of atoms from groups II-VI (CdSe‚ CdS‚ ZnSe) and III-V (InP and InAs)‚ and are defined as particles with physical dimensions smaller than the Bohr exciton radius. The Bohr exciton radius of prototypical CdSe qdots‚ as illustrated in Fig. 1‚ is ~10 nm. The unique optical and electronic properties of qdots have spurred a great deal of research into their potential applications in the design of novel biological probes‚ light emitting diodes‚ photovoltaic cells‚ among other devices.