Bin Sun

Carbon-on-metal films for surface plasmon resonance detection of DNA arrays.

Surface plasmon resonance (SPR) imaging affords label-free monitoring of biomolecule interactions in an array format. A surface plasmon conducting metal thin film is required for SPR measurements. Gold thin films are traditionally used in SPR experiments as they are readily functionalized with thiol-containing molecules through formation of a gold-sulfur bond. The lability of this gold-thiol linkage upon exposure to oxidizing conditions and ultraviolet light renders these surfaces incompatible with light-directed synthetic methods for fabricating DNA arrays. It is shown here that applying a thin carbon overlayer to the gold surface yields a chemically robust substrate that permits light-directed synthesis and also supports surface plasmons. DNA arrays fabricated on these carbon-metal substrates are used to analyze two classes of biomolecular interactions: DNA-DNA and DNA-protein. This new strategy allows the combinatorial study of binding interactions directly from native, unmodified biomolecules of interest and offers the possibility of discovering new ligands in complex mixtures such as cell lysates.

Azlactone-functionalized polymers as reactive templates for parallel polymer synthesis: synthesis and screening of a small library of cationic polymers in the context of DNA delivery.

Azlactone-functionalized polymers are used as reactive templates for the synthesis of a library of amine-functionalized polymers of interest in the context of DNA delivery and other applications.

Characterization of pH-induced changes in the morphology of polyelectrolyte multilayers assembled from poly(allylamine) and low molecular weight poly(acrylic acid).

We report characterization of pH-dependent behavior in polyelectrolyte multilayers (PEMs) fabricated from poly(allylamine) (PAH) and low molecular weight poly(acrylic acid) (PAA) synthesized by living/controlled polymerization. Exposure of these films to solutions of low pH (e.g. pH 2.0-3.2) resulted in transformations from films that were smooth and uniform to films with porous morphologies, as characterized by scanning electron microscopy (SEM). We observed large differences in both the extent of this transformation and the sizes of the pores that resulted compared to films fabricated using higher molecular weight PAA used in past studies. Whereas transformations reported in past studies generally lead to pores with sizes in the range of 0.3-2 μm, we observed larger-scale transformations and films with cell-like internal structures comprised of networks of closed pores, interconnected pores, and through-pores with sizes as large as 10-15 μm depending on pH and the manner in which the films were incubated. Films fabricated using fluorescently end-labeled samples of PAA permitted real-time imaging of changes in internal structure using confocal microscopy (LSCM). The results of these studies also revealed large differences in the nature of these transformations when films were placed in contact with surfaces as opposed to when dipped into aqueous solutions. Our results reveal approaches that can be used to fabricate films with large pores (e.g., pores with sizes on the order of 10-15 μm) and suggest methods that could potentially be used to generate PEMs having controlled gradients in pore size.

Detection of DNA hybridisation on a functionalised diamond surface using reflection anisotropy spectroscopy

The analysis of single-stranded DNA attached to a polycrystalline diamond surface by reflection anisotropy spectroscopy (RAS) demonstrates that the DNA is oriented essentially vertically to the surface. RAS is able to detect the hybridisation between the attached strand and the homologous sequence.

Photo-induced surface functionalization of carbon surfaces: The role of photoelectron ejection

Carbon-based materials are attractive for a wide range of applications, from biomaterials to fuel cells; however, their effective use often requires controlling the surface chemistry to incorporate recognition moieties or reactive centers. The high stability of carbon also makes it a challenging material to functionalize; recently, the use of ultraviolet light (254nm) to initiate functionalization of carbon surfaces has emerged as a way to obtain carbon/organic interfaces with tailored properties. The authors have investigated the mechanism of covalent grafting of amorphous carbon surfaces with functional organic molecules using the photochemical reaction of terminal alkenes. Measurements comparing the reactivity of different n-alkenes bearing different terminal groups at the terminus opposite the olefin showed pronounced differences in reactivity. They characterized the rate and final coverage of the resulting organic layers using x-ray photoelectron spectroscopy and infrared reflection-absorption spectroscopy. Ultraviolet photoelectron spectroscopy and photocurrent measurements suggested that the reaction involves photoelectron emission from the carbon surface into the liquid phase. Density functional calculations show a strong correlation between the electron affinity of the alkenes and the observed reactivity. The specific terminal group opposite to the olefin was found to play an important role in the stabilization of excess negative charges on the molecule, thus explaining the strong dependence of reactivity on the particular terminal group. These findings suggest that the reaction involves injection of photoelectrons into the alkene acceptor levels, leading to the formation of radical anions in the liquid phase. Finally, the authors demonstrate that the grafting of marginally reactive alkenes can be enhanced by seeding the surface with a small amount of good electron accepting groups. These results provide fundamental new insights into the role of electronic excitations in controlling rates and mechanisms of olefin reactions at surfaces. While demonstrated here for amorphous carbon, these results may also be significant for the UV initiated grafting of olefins on other semiconductors.Carbon-based materials are attractive for a wide range of applications, from biomaterials to fuel cells; however, their effective use often requires controlling the surface chemistry to incorporate recognition moieties or reactive centers. The high stability of carbon also makes it a challenging material to functionalize; recently, the use of ultraviolet light (254nm) to initiate functionalization of carbon surfaces has emerged as a way to obtain carbon/organic interfaces with tailored properties. The authors have investigated the mechanism of covalent grafting of amorphous carbon surfaces with functional organic molecules using the photochemical reaction of terminal alkenes. Measurements comparing the reactivity of different n-alkenes bearing different terminal groups at the terminus opposite the olefin showed pronounced differences in reactivity. They characterized the rate and final coverage of the resulting organic layers using x-ray photoelectron spectroscopy and infrared reflection-absorption spectr...