Yong Man Lee

Electrochemical analysis of copper ion using a Gly-Gly-His tripeptide modified poly(3-thiopheneacetic acid) biosensor.

A novel biosensor harnessing a conducting polymer functionalized with a copper ion specific peptide proved to be highly effective for electrochemical analysis of copper ions. The developed sensor comprised a transducer based on a conducting polymer (poly(3-thiopheneacetic acid)) electrode and a probe (tripeptide, Gly-Gly-His) selectively cognitive of copper ions. For functionalization of the electrode, the carboxylic group of the polymer was covalently coupled with the amine group of the tripeptide, and its structural features were confirmed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared (ATR-IR) spectroscopy. The peptide modified polythiophene biosensor was used for the electrochemical analysis of various trace metal ions by square wave voltammetry. The electrode was found to be highly sensitive and selective to Cu(2+) in the range of 0.02-20 microM with almost no cross binding to other metal ions such as Ni(2+) and Pb(2+). Furthermore, the developed sensor exhibited a high stability and reproducibility despite the repeated use of the sensor electrode and probe. With the advent of more diverse affinity bioprobes specific towards a broad range of analytes, the demonstrated strategy harnessing peptide modified polythiophene biosensor is likely to provide an excellent platform for the selective determination of trace amount of analytes whose detection is otherwise cumbersome.

Nanomesh‐Structured Ultrathin Membranes Harnessing the Unidirectional Alignment of Viruses on a Graphene‐Oxide Film

DOI: 10.1002/adma.201305862 However, strong van der Waals interactions and subsequent irreversible aggregation of the nanomaterials makes it unlikely for the assembled system to exhibit unidirectional alignment. This limitation can be overcome by employing “intelligent” (i.e., responsive) and fl exible one-dimensionally structured biomaterials. [ 11,12 ] The self-assembled structures of M13 viruses are an example; their mechanical stiffness and structural characteristics are readily controlled by manipulating the environmental pH or the type of bonding with the underlying substrate. [ 13,14 ]

Hierarchical nanoflake surface driven by spontaneous wrinkling of polyelectrolyte/metal complexed films.

A mechanical or physical change observed in nanocomposite thin films has recently offered new opportunities to generate intriguing nanostructures. In this study, we present a novel means of creating a hierarchically developed nanoflake structure by exploiting surface wrinkles that occur during the incorporation process of metallic nanoparticles into layer-by-layer assembled polyelectrolyte multilayer (PEM) thin films. The PEM film composed with linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) allows for facilitated cationic exchange reaction within the film even after the electrostatic complexation and chemical cross-linking reaction. The subsequent reduction process induces an in situ complexation of metallic nanoparticles with a PEM matrix, causing an accumulation of lateral compressive stress for surface wrinkling. The wrinkling characteristics of the complexed films can be theoretically interpreted by employing the gradationally swollen film model, whereby a gradual change in the elastic property along the axial direction of the film can be appropriately reflected. In addition, wrinkled surfaces are further processed to form vertically aligned and hierarchically ordered nanoflakes after selective removal of the PEM matrix with plasma ashing. Consequently, superhydrophobic surface properties (water contact angle = 170°, sliding angle <1°) can be attained from the hierarchical nanoflake structure. The method presented here is advantageous in that large-scale preparation can be readily implemented by a stepwise dipping process without resorting to specific patterning or a serially applied complex structuring process, which can provide a promising platform technique for various surface engineering applications.

Nanoparticles of conjugated polymers prepared from phase-separated films of phospholipids and polymers for biomedical applications.

Phase separation in films of phospholipids and conjugated polymers results in nanoassemblies because of a difference in the physicochemical properties between the hydrophobic polymers and the polar lipid heads, together with the comparable polymer side-chain lengths to lipid tail lengths, thus producing nanoparticles of conjugated polymers upon disassembly in aqueous media by the penetration of water into polar regions of the lipid heads.

Spontaneous surface flattening via layer-by-layer assembly of interdiffusing polyelectrolyte multilayers.

We report a facile means to achieve planarization of nonflat or patterned surfaces by utilizing the layer-by-layer (LbL) assembly of highly diffusive polyelectrolytes. The polyelectrolyte pair of linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) is known to maintain intrinsic diffusive mobility atop or even inside ionically complexed films prepared by LbL deposition. Under highly hydrated and swollen conditions during the sequential film buildup process, the LbL-assembled film of LPEI/PAA undergoes a topological self-deformation for minimizing surface area to satisfy the minimum-energy state of the surface, which eventually induces surface planarization along with spontaneous filling of surface textures or nonflat structures. This result is clearly different from other cases of applying nondiffusive polyelectrolytes onto patterned surfaces or confined structures, wherein surface roughening or incomplete filling is developed with the LbL assembly. Therefore, the approach proposed in this study can readily allow for surface planarization with the deposition of a relatively thin layer of polyelectrolyte multilayers. In addition, this strategy of planarization was extended to the surface modification of an indium tin oxide (ITO) substrate, where surface smoothing and enhanced optical transmittance were obtained without sacrificing the electronic conductivity. Furthermore, we investigated the potential applicability of surface-treated ITO substrates as photoelectrodes of dye-sensitized solar cells prepared at room temperature. As a result, an enhanced photoconversion efficiency and improved device characteristics were obtained because of the synergistic role of polyelectrolyte deposition in improving the optical properties and acting as a blocking layer to prevent electron recombination with the electrolytes.

A simple one-step assay platform based on fluorescence quenching of macroporous silicon

We synthesized 3D macroporous silicon through a simple electrochemical dissolution process and systematically estimated its protein adsorption and effect on fluorescence emission. Compared with conventional 2D polystyrene plate, the macroporous silicon showed a superior protein adsorption capacity and significant fluorescence quenching effect. We developed a 3D macroporous silicon-based adenosine assay system through the following fabrication process: streptavidin molecules that have been immobilized on the surface of macroporous silicon are attached with biotin-linked and adenosine-specific DNA aptamer, followed by hybridization between the attached aptamer and fluorescent chemical (carboxytetramethylrhodamine/CTMR) that is conjugated with a short complementary DNA sequence. In the absence of adenosine, the aptamer-CTMR complexes remain closely attached to the surface of porous silicon, hence fluorescence being significantly quenched. Upon binding to adenosine, the DNA aptamer is subject to structure switching that leads to dissociation of CTMR from DNA aptamer, and consequently the CTMR fluorescence is restored, indicating a simple one-step assay of adenosine. Compared to the conventional 2D PS and ZnO nanorods-based assays, adenosine at much lower (sub-micromolar) concentration was successfully detected through the 3D macroporous silicon-based assay. The three-dimensionally and densely immobilized aptamer probes and effective fluorescence quenching on the surface of macroporous silicon enables adenosine to be detected at lower levels. Although the adenosine detection is reported here as a proof-of-concept, the developed macroporous silicon-based simple one-step assay platform can be applied in general to fluorescence quenching -based detection of many other biomolecules.

Multiscale Porous Interconnected Nanocolander Network with Tunable Transport Properties

A nanocolander network is developed by embedding mesoporous block copolymers inside the structural frame of a macroporous inverse-opal structure. Spontaneously formed macroconduits interconnecting the macropores are utilized as internal bypasses for enhancing the bulk transport properties. A demonstrative application for the membrane of the nanocolander network is of perfect size-selectivity for nanoparticle separation without compromising the high permeability of the transporting medium.

Incorporation of a Metal Oxide Interlayer using a Virus-Templated Assembly for Synthesis of Graphene-Electrode-Based Organic Photovoltaics.

UNLABELLED Transition metal oxide (TMO) thin films have been exploited as interlayers for charge extraction between electrodes and active layers in organic photovoltaic (OPV) devices. Additionally, graphene-electrode-based OPVs have received considerable attention as a means to enhance device stability. However, the film deposition process of a TMO thin-film layer onto the graphene electrode is highly restricted owing to the hydrophobic nature of the graphene surface; thus, the preparation of the device should rely on a vacuum process that is incompatible with solution processing. In this study, we present a novel means for creating a thin tungsten oxide (WO3 ) interlayer on a graphene electrode by employing an engineered biotemplate of M13 viruses, whereby nondestructive functionalization of the graphene and uniform synthesis of a WO3 thin interlayer are concurrently achieved. As a result, the incorporated virus-templated WO3 interlayer exhibited solar-conversion efficiency that was 20 % higher than that of conventional OPVs based on the use of a (3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) interlayer. Notably, bilayer-structured OPVs with synergistically integrated WO3 /PEDOT:PSS achieved >60 % enhancement in device performance.