The LuoLabs nanoparticle subgroup has developed a new and versatile DNA-based strategy for organizing nanoparticle superlattices without the use of any base-pairing. Some of their current research directions include:
Real-time dynamical self-organization of nanoparticle superlattices,
Patterning superlattices into nanoscale features with micromolds,
Assembly of nanoparticle crystals at 1D, 2D and 3D levels.
The group believes their DNA-based systems will find a plethora of applications in high-efficiency solar cells, novel nanocatalysis and ultra-sensitive sensors.
The group has developed a simple approach for patterning highly-ordered arrays of nanoparticles (both 2D and 3D) that uses a soft stamp for to regulate the drying process of microdroplets containing DNA-capped nanoparticles. This technique provides rational control over the local nucleation and growth of the nanoparticle superlattices. Using DNA-capped gold nanoparticles as a model system, they have patterned nanoparticle superlattices over large areas into a number of versatile structures by varying the stamp pattern and applied pressure, including single-particle-width corrals, single particle-thick microdiscs and submicrometre-sized 'supra-crystals'. They believe that this technique is versatile enough to be applied to other types of nanoparticles for plasmonic applications as well as for the patterning of proteins and large macromolecules.
The group has developed the first DNA-based route towards monolayered free-standing nanoparticle superlattices (suspended highly-ordered nanoparticle arrays), which have potential applications as optoelectronic materials that are free from substrate-induced interference. DNA-conjugated gold nanoparticles were utilized in a microhole-confined, drying-mediated self-assembly process. Without using Watson–Crick base-pairing, they produced discrete, free-standing superlattice membranes that were stabilized by physical interactions between the DNA ligands. In addition, both structure (inter-particle spacings) and functional properties (plasmonic and mechanical) can be rationally controlled by adjusting DNA length. Their method opens a simple yet efficient avenue towards the assembly of artificial nanoparticle solids in their ultimate thickness limit—a promising step that may enable the integration of free-standing superlattices into solid-state nanodevices.
The team studies how nanoparticles arrange can into highly-ordered crystals, and how attaching DNA to the nanoparticles provides control over the crystallization process. They have been able to produce three-dimensional crystals simply by drying a solution containing DNA-capped nanoparticles. The spacing within the 3D crystals could also be controlled by changing the DNA length, but could also adjust dynamically to their environmental conditions. For example, varying the humidity or salt concentrations within the crystals produced reversible shrinkage and expansion. These studies suggest that it may be possible in the future to develop "smart", environmentally-adaptable nanoscale materials based on DNA-nanoparticle assemblies. Studies of the crystal formations were performed using small-angle x-ray scattering spectroscopy at CHESS, which is a technique typically used to investigate the partially ordered materials on the nanoscale and the physical characteristics of large macromolecules.
The LuoLabs group has developed DNA hydrogels that are made entirely from DNA. Biological components can be easily encapsulated in these gels during the enzymatic gelation process which is performed under physiological conditions. The DNA hydrogels can be easily tuned by adjusting initial concentrations and using different types of branched DNA monomers, allowing them to be tailored for specific applications such as controlled drug delivery, tissue engineering, 3D cell culture, cell transplant therapy and other biomedical applications.
Their DNA hydrogels provided the foundation for the newly developed cell free expression system which they call the P-gel system. In this system, a linear expression plasmid is incorporated into a DNA hydrogel by using branched DNA monomers as croslinkers. The resulting P-gel is molded into micropads which are used in place of plasmid DNA during coupled transcription/translation cell free expression. The P-gel system can produce up to 5 mg/ml of protein in a single expression, a vast improvement over commercially available solution phase systems.
The labs has developed novel DNA-based "fluorescence nanobarcodes" that can rapidly identify multiple pathogens simultaneously in a single assay. These DNA nanobarcodes are formed from branched DNA via a novel self-assembly process. Each DNA nanobarcode carries a unique fluorescence color ratio – for example, 1 green dye and 2 red dyes (1G2R), or 4 green dyes and 1 red dye (4G1R). This allows us to distinguish among a large number of different targets using only two colors. Since the nanobarcodes are made entirely from DNA, they can be easily interfaced with biological systems.
DNA nanobarcodes are formed via a novel self-assembly process. Each DNA nanobarcode carries a unique fluorescence color ratio to identify a specific pathogen biomarker.
The group has also developed branched DNA structures with photo-crosslinkable capabilities – termed Anisotropic, Branched, Crosslinkable monomers (ABC monomers). These ABC monomers achieve highly sensitive detection via light-driven amplification. After brief UV exposure, monomers form large polymeric aggregates that are easy to detect. Each ABC monomer can also be labeled with fluorescence dyes, quantum dots, or nanoparticles for added functionality.
Visit the LuoLabs website for more information.
Dan Luo is the Biomaterials representative for Materials Today, and a member of the Editorial Board.