Gold Nanoparticles Optimize the Specificity of DNA Binding
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Gold Nanoparticles Optimize the Specificity of DNA Binding The polymerase chain reaction (PCR) has revolutionized biology since its invention in the 1980s. Commonly used for DNA amplification, it is also employed in DNA detection in optoelectronic DNA biosensors. However, PCR specificity is still unsatisfactory. In a study reported in the August 12 issue of Angewandte Chemie International Edition (p. 4989; DOI: 10.1002/anie. 200590108), H. Li of Shanghai Jiao Tong University, J. Lv of the
Chinese Academy of Sciences, and their colleagues have used gold nanoparticles to avoid nonspecific PCR reactions and enhance the binding of single-stranded DNA while preventing the binding of double-stranded DNA. Gold nanoparticles were studied due to their wide use in the field of biomaterials because of their nontoxic, biocompatible properties, and their ability to undergo surface functionalization. Gold nanoparticles also have unique optoelectronic properties. According to J. Hu of Shanghai Jiao
Tong University, he and his co-workers tested 10 nm gold nanoparticles free of additives in concentrations of 0.2–1.0 nM. The researchers used colloidal gold nanoparticles synthesized with a citrate stabilization process. They performed PCR with a 283 base-pair target sequence from a λ-DNA template, and the products were examined using agarose gel electrophoresis. The researchers found that nonspecific binding of DNA was enhanced at concentrations of 0.2–0.8 nM, but was inhibited at concentrations of 1.0 nM. This high speci-
Carbon Nanotubes Used for Cancer Cell Destruction and Drug Delivery Biological cells are transparent to nearinfrared light (NIR) in the wavelength range of 700–1100 nm. However, singlewalled carbon nanotubes (SWNTs) show strong optical absorption in this spectral window. Furthermore, SWNTs have been used to safely deliver cargos across cellular membranes without cytotoxicity. Tying these facts together, Nadine Wong Shi Kam, Hongjie Dai, and co-workers at Stanford University have shown how SWNTs can be used to deliver molecular cargos as well as selectively destroy cancer cells inside living cells by optically stimulating them. The optical stimulation can be used to release the cargos, which can then destroy cancer cells, or to kill the cancer cells by heat transfer from bare optically-stimulated SWNTs. They report their results in the August 16 issue of the Proceedings of the National Academy of Sciences (p. 11600; DOI: 10.1073/pnas.0502680102). SWNTs functionalized with a fluorescent-labeled DNA, functionalized by various phospholipids (PL), and functionalized with one or two PL-polyethylene glycol-folic acid (PL-PEG-FA) molecules acting as cargos were used in the study. HeLa cells (an adherent cell line) were used for the cell cultures and were subjected to incubation treatment in SWNT solutions. An 808-nm diode laser source (beam size ~3 cm and power density up to 3.5 W/cm2) was used for the optical stimulation in the NIR regime. It was shown that SWNTs internalized within living cells a
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