Leo Y. T. Chou

DNA assembly of nanoparticle superstructures for controlled biological delivery and elimination

The assembly of nanomaterials using DNA can produce complex nanostructures, but the biological applications of these structures remain unexplored. Here we describe the use of DNA to control the biological delivery and elimination of inorganic nanoparticles by organizing them into colloidal superstructures. The individual nanoparticles serve as building blocks, whose size, surface chemistry, and assembly architecture dictate overall superstructure design. These superstructures interact with cells and tissues as a function of their design, but subsequently degrade into building blocks that can escape biological sequestration. We demonstrate that this strategy reduces nanoparticle retention by macrophages and improves their in vivo tumour accumulation and whole-body elimination. Superstructures can be further functionalized to carry and protect imaging or therapeutic agents against enzymatic degradation. These results suggest a new strategy to engineer nanostructure interactions with biological systems and highlight new directions in the design of biodegradable and multifunctional nanomedicine.

Fluorescence‐Tagged Gold Nanoparticles for Rapidly Characterizing the Size‐Dependent Biodistribution in Tumor Models

Nanoparticle vehicles may improve the delivery of contrast agents and therapeutics to diseased tissues, but their rational design is currently impeded by a lack of robust technologies to characterize their in vivo behavior in real-time. This study demonstrates that fluorescent-labeled gold nanoparticles can be optimized for in vivo detection, perform pharmacokinetic analysis of nanoparticle designs, analyze tumor extravasation, and clearance kinetics in tumor-bearing animals. This optical imaging approach is non-invasive and high-throughput. Interestingly, these fluorescent gold nanoparticles can be used for multispectral imaging to compare several nanoparticle designs simultaneously within the same animal and eliminates the host-dependent variabilities across measured data. Together these results describe a novel platform for evaluating the performance of tumor-targeting nanoparticles, and provide new insights for the design of future nanotherapeutics.

Nanotoxicology: No signs of illness

Quantum dots that contain cadmium, selenium and zinc are not toxic to monkeys for periods of up to 90 days, but longer-term studies are needed to determine the ultimate fate of the heavy metals that accumulate in the organs.

Tuning the Drug Loading and Release of DNA-Assembled Gold-Nanorod Superstructures

The use of DNA to assemble inorganic nanoparticles into superstructures is an emerging strategy to build non-toxic delivery vehicles for targeting diseases in the body. The impact of the core-satellite nanosystem design in mediating drug storage, drug release (via heat), and killing of HeLa cells in culture is investigated.

Oligolysine-based coating protects DNA nanostructures from low-salt denaturation and nuclease degradation

DNA nanostructures have evoked great interest as potential therapeutics and diagnostics due to ease and robustness of programming their shapes, site-specific functionalizations and responsive behaviours. However, their utility in biological fluids can be compromised through denaturation induced by physiological salt concentrations and degradation mediated by nucleases. Here we demonstrate that DNA nanostructures coated by oligolysines to 0.5:1 N:P (ratio of nitrogen in lysine to phosphorus in DNA), are stable in low salt and up to tenfold more resistant to DNase I digestion than when uncoated. Higher N:P ratios can lead to aggregation, but this can be circumvented by coating instead with an oligolysine-PEG copolymer, enabling up to a 1,000-fold protection against digestion by serum nucleases. Oligolysine-PEG-stabilized DNA nanostructures survive uptake into endosomal compartments and, in a mouse model, exhibit a modest increase in pharmacokinetic bioavailability. Thus, oligolysine-PEG is a one-step, structure-independent approach that provides low-cost and effective protection of DNA nanostructures for in vivo applications.

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 the Structure and Properties of DNA-Nanoparticle Superstructures Using Polyvalent Counterions

DNA assembly of nanoparticles is a powerful approach to control their properties and prototype new materials. However, the structure and properties of DNA-assembled nanoparticles are labile and sensitive to interactions with counterions, which vary with processing and application environment. Here we show that substituting polyamines in place of elemental counterions significantly enhanced the structural rigidity and plasmonic properties of DNA-assembled metal nanoparticles. These effects arose from the ability of polyamines to condense DNA and cross-link DNA-coated nanoparticles. We further used polyamine wrapped DNA nanostructures as structural templates to seed the growth of polymer multilayers via layer-by-layer assembly, and controlled the degree of DNA condensation, plasmon coupling efficiency, and material responsiveness to environmental stimuli by varying polyelectrolyte composition. These results highlight counterion engineering as a versatile strategy to tailor the properties of DNA-nanoparticle assemblies for various applications, and should be applicable to other classes of DNA nanostructures.

A strategy to assemble nanoparticles with polymers for mitigating cytotoxicity and enabling size tuning

AIM We aim to develop a facile strategy for assembling nanoparticles within cross-linked polymer micelles that enables tuning of their overall hydrodynamic size and surface charge and to mitigate toxicity. MATERIALS & METHODS Hydrophobic nanoparticles and amphiphilic co-polymers self-assembled upon solvent-selective precipitation. Size-tunability of the assembled nanostructure was achieved by controlling both the nanoparticle and polymer ratio and the kinetics of the assembly process. RESULTS & CONCLUSION We were successful in creating polymer shells on the surface of inorganic nanoparticles. The shell thickness could be tuned, and protect the nanoparticles from environmental degradation and minimize the cytotoxicity of inorganic nanoparticles. This strategy provides a method to engineer the interactions of nanoparticles with biological systems, including their targeted delivery to diseased tissues and their safety of use without significantly altering their original materials properties.

Controlling DNA-nanoparticle serum interactions.

Significance DNA-mediated nanoparticle assembly is an emerging concept to design drug delivery vehicles that can modify their structure or function in response to the in vivo environment. However, better understanding of their interactions with different tissues and organs is needed to establish specific design criteria. Here, we perform a systematic investigation of the molecular properties and mechanisms responsible for serum degradation of DNA-assembled structures. We show that the degradation process is determined by the combined contributions of the surface chemistry of nanoparticles and their supramolecular arrangement. The results also present a strategy for using physiological fluid degradation as the mechanism of controlled drug release. Our findings provide a general framework to study biological interactions of DNA nanostructures. Understanding the interaction of molecularly assembled nanoparticles with physiological fluids is critical to their use for in vivo delivery of drugs and contrast agents. Here, we systematically investigated the factors and mechanisms that govern the degradation of DNA on the nanoparticle surface in serum. We discovered that a higher DNA density, shorter oligonucleotides, and thicker PEG layer increased protection of DNA against serum degradation. Oligonucleotides on the surface of nanoparticles were highly resistant to DNase I endonucleases, and degradation was carried out exclusively by protein-mediated exonuclease cleavage and full-strand desorption. These results enabled the programming of the degradation rates of the DNA-assembled nanoparticle system from 0.1 to 0.7 h−1 and the engineering of superstructures that can release two different preloaded dye molecules with distinct kinetics and half-lives ranging from 3.3 to 9.8 h. This study provides a general framework for investigating the serum stability of DNA-containing nanostructures. The results advance our understanding of engineering principles for designing nanoparticle assemblies with controlled in vivo behavior and present a strategy for storage and multistage release of drugs and contrast agents that can facilitate the diagnosis and treatment of cancer and other diseases.