Semi-Biosynthesis of DNA Nanostructures

Nanotechnology refers to all technologies aiming to build objects, make measurements, and carry out processes on the nanometer length scale. In particular molecular nanotechnology exemplifies the so-called bottom up approach, which is briefly defined as the ability to build useful nanostructures with molecular precision, such as molecular machinery. Such capability for controlling matter at the molecular scale has always been the dream of scientists. All living things are nanofoundries. Billions of years ago, nature perfectly provided all living things with the most accurate biological nanotechnology systems. Cellular internal dynamics, communicative resonance in protein conformational states, viruses as microreplicators, nanoscale life mechanisms, (e.g. repairing and replication) and nanoscale energy exchanges are examples of these systems. It is clear that learning and using some biological techniques (DNA replication), or even using some of the molecular tools provided by nature (enzymes) will be most relevant to nanotechnology development. In this project we demonstrate how we can derive benefit from employing biological techniques, such as Rolling Circle Amplification, Polymerase Chain Reaction, and cloning to address the challenge of emplacing DNA nanoarrays at pre-determined locations on a surface. In vitro, rolling Circle amplification (RCA) driven by DNA polymerization was first reported by Eric T. Kool and coworkers in 1995. DNA products resulting from RCA are repeating head-to-tail multimeric copies of the DNA template. We report the design and synthesis of both single stranded circular DNA (used as a template) and a multimeric product. Using the RCA technique, long tandem repeats, consisting of multiple copies of a 95 base pair sequence have been produced. We incorporated two specific, unique sequences at each end of these synthesized DNA strands, which can be used as recognition sites for surface hybridization. For the first time, heterogeneity has been introduced into a repetitive system to yield a modular nanostructured macromolecule. This product was further cloned into bacterial host cells. The DNA fragments were extracted and sequenced. The results not only confirm success in these particular experiments, but they also verify the general validity of this technique for generating nano-constructs semi- biosynthetically. In order to demonstrate applicability of the RCA product to nanotechnology, we used these strands as scaffolds for gold nanoparticle patterning

Gold nanoshells for surface enhanced Raman spectroscopy and drug delivery

Gold nanoshells are tunable plasmonic nanostructures consisting of spherical silica cores wrapped with thin layer of Au. Based on the size of the Au layer with respect to the silica core, gold nanoshells can resonantly absorb or scatter light at any wavelength on the visible or infrared. On resonance, gold nanoshells interact strongly with light to give rise to collective oscillations of the free electrons against the background of the ionic core, phenomena known as localized surface plasmons. The free electron oscillation creates surface plasmon multimodes of various orders. As a result, the average local near field surrounding the Au nanoshell is enhanced. The local field enhancement has been extensively used in different applications. In this work, the local near-field is used to enhance the Raman spectroscopy of DNA and explore the different modes attributed to the base composition and structure of the DNA sequence. We showed that urface enhanced Raman spectroscopy of DNA is dominated by the adenine modes regardless of the base composition of the DNA sequence, a property that we have used to develop a DNA label-free detection system. As absorbers, plasmon-resonant Au nanoshells can convert absorbed light into heat. As a consequence, the temperature on the Au nanoshell surface increases dramatically. This property is used to light-trigger the release of variety of therapeutic molecules such as single stranded DNA, siRNA and small molecules. We demonstrated that the local heat can be used to dehybridize double stranded DNA attached to the Au surface via a thiol moiety on one of the DNA strands. The complementary sequence (therapeutic sequence) is released at temperature lower than the standard melting temperature of same DNA sequence. Moreover, small molecules (DAPI) which were initially intercalated on the double stranded DNA attached to the Au surface were successfully released due to the heat generated around the nanoshell surface. Finally, siRNA molecules were also released using a different system made of PLL (polylysine) attached to Au nanoshells. The electrostatic interaction between the negatively charged siRNA and the positively charged PLL was overcome by the thermal perturbation causing the siRNA to be released. In vitro experiments successfully showed the release of siRNA, single stranded DNA and small molecules

Experimental and theoretical studies of condensation on a horizontal tube row with vapour shear

SIGLEAvailable from British Library Document Supply Centre- DSC:DX97907 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Experimental and theoretical studies on condensation on a horizontal tube row with vapour shear

SIGLEAvailable from British Library Document Supply Centre- DSC:DX97907 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Photothermally targeted thermosensitive polymer-masked nanoparticles

The targeted delivery of therapeutic cargos using noninvasive stimuli has the potential to improve efficacy and reduce off-target effects (toxicity). Here, we demonstrate a targeting mechanism that uses a thermoresponsive copolymer to mask a peptide ligand that binds a widely distributed receptor (integrin β1) on the surface of silica core-gold shell nanoparticles. The nanoparticles convert NIR light into heat, which causes the copolymer to collapse, exposing the ligand peptide, allowing cell binding. The use of NIR light could allow targeting of plasmonic nanoparticles deep within tissues. This approach could be extended to a variety of applications including photothermal therapy and drug delivery. © 2014 American Chemical Society.Link_to_subscribed_fulltex