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We investigate the efficiency of incorporation of boranephosphonate-modified nucleotides by phi29 DNA polymerase and present a simple method for forming large defined silver nanostructures by rolling circle amplification (RCA) using boranephosphonate internucleotide linkages. RCA is a linear DNA amplification technique that can use specifically circularized DNA probes for detection of target nucleic acids and proteins. The resulting product is a collapsed single-stranded DNA molecule with tandem repeats of the DNA probe. By substituting each of the natural nucleotides with the corresponding 5'-(α-P-borano)deoxynucleosidetriphosphate, only a small reduction in amplification rate is observed. Also, by substituting all four natural nucleotides, it is possible to enzymatically synthesize a micrometer-sized, single-stranded DNA molecule with only boranephosphonate internucleotide linkages. Well-defined silver particles are then readily formed along the rolling circle product.

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Single-walled carbon nanotubes (SWNTs), when dispersed in DMSO with boranephosphonate DNA (bpDNA), were efficiently metalized with silver, gold, and palladium nanoparticles (NPs). This was possible by first adsorbing boranephosphonate DNA onto the surface of SWNTs and then bathing with silver, gold, and palladium metal salts, which form the corresponding nanoparticles by reduction of their respective ions without addition of any external reducing agent. Reduction of a redox dye, 2,6-dichlorophenolindophenol (DCPIP), by Pd nanoparticle conjugates (PdNP/bpDNA/SWNT) disclosed the efficient electron transfer properties of these metallized SWNTs. These PdNP/bpDNA/SWNT conjugates were also successfully used to catalyze Heck and Suzuki coupling reactions. Boranephosphonate DNA-mediated metallization of SWNTs therefore provides a new method for fabricating well-defined SWNT-based nanostructures. This discovery should reveal unexpected applications in various research areas ranging from nanoelectronic devices to nanoscale SWNT supported multimetallic catalysts having different compositions.

In this work, we report that not only do gold nanorods coated with hydrophobically modified mesoporous silica shells enhance the photoacoustic (PA) signal over unmodified mesoporous silica-coated gold nanorods but also that the relationship between the PA amplitude and the input laser fluence is strongly nonlinear. Mesoporous silica shells of ∼14 nm thickness with ∼3 nm pores were grown on gold nanorods showing nearinfrared absorption. The silica shell was rendered hydrophobic with addition of dodecyltrichlorosilane and then resuspended in aqueous media with a lipid monolayer. Analysis of the PA signal revealed not only an enhancement of the PA signal compared to mesoporous silica-coated gold nanorods at lower laser fluences but also a nonlinear relationship between the PA signal and the laser fluence. We attribute each effect to the entrapment of solvent vapor in the mesopores: the vapor has both a larger expansion coefficient and a larger thermal resistance than silica that enhances conversion to acoustic energy, and the hydrophobic porous surface is able to promote a phase transition at the surface, leading to a nonlinear PA response even at fluences as low as 5 mJ cm −2 . At 21 mJ cm −2 , the highest laser fluence tested, the PA enhancement was >12-fold over mesoporous silica-coated gold nanorods.