Ilsun Yoon

Patterned Multiplex Pathogen DNA Detection by Au Particle-on-Wire SERS Sensor

A Au particle-on-wire system that can be used as a specific, sensitive, and multiplex DNA sensor is developed. A pattern formed by multiple Au nanowire sensors provides positional address and identification for each sensor. By using this system, multiplex sensing of target DNAs was possible in a quantitative manner with a detection limit of 10 pM. Target DNAs from reference bacteria and clinical isolates were successfully identified by this sensor system, enabling diagnostics for infectious diseases.

Single nanowire on a film as an efficient SERS-active platform.

Fabricating well-defined and highly reproducible platforms for surface-enhanced Raman scattering (SERS) is very important in developing practical SERS sensors. We report a novel SERS platform composed of a single metallic nanowire (NW) on a metallic film. Optical excitation of this novel sandwich nanostructure provides a line of SERS hot spots (a SERS hot line) at the gap between the NW and the film. This single nanowire on a film (SNOF) architecture can be easily fabricated, and the position of hot spots can be conveniently located in situ by using an optical microscope during the SERS measurement. We show that high-quality SERS spectra from benzenethiol, brilliant cresyl blue, and single-stranded DNA can be obtained on a SNOF with reliable reproducibility, good time stability, and excellent sensitivity, and thus, SNOFs can potentially be employed as effective SERS sensors for label-free biomolecule detection. We also report detailed studies of polarization- and material-dependent SERS enhancement of the SNOF structure.

Au Nanowire‐on‐Film SERRS Sensor for Ultrasensitive Hg2+ Detection

We report an ultrasensitive and selective single nanowire-on-film (SNOF) surface-enhanced resonance Raman scattering (SERRS) sensor for Hg(2+) detection based on structure-switching double stranded DNAs (dsDNAs). Binding of Hg(2+) induces conformational changes of the dsDNAs and let a Raman reporter get close to the SNOF structure, thereby turning on SERRS signal. The well-defined SNOF structure provides a detection limit of 100 pM with improved accuracy in Hg(2+) detection. This sensor is stable over a considerable amount of time and reusable after simple treatment. Since this SNOF sensor is composed of a single Au NW on a film, development of a multiplex sensor would be possible by employing NWs modified by multiple kinds of aptamers.

Self-Assembly of Semiconducting Photoluminescent Peptide Nanowires in the Vapor Phase†

The self-assembly of bioorganic molecules, which are ubiquitous in nature, is an attractive route for fabricating functional supramolecular architectures. It also facilitates the preparation of highly ordered nanostructures by the organization of molecular building blocks through the combination of noncovalent interactions including hydrogen bonds, electrostatic interactions, p–p stacking, hydrophobic interactions, and dipole–dipole interactions. The fabrication of nanostructures through the self-assembly of peptides has attracted interest because of the unique properties of peptides, such as their functional flexibility and molecular recognition capability. In particular, the self-assembly of an aromatic dipeptide consisting of two covalently linked phenylalanine units (namely, diphenylalanine, FF), which is a key structural motif in Alzheimer s b-amyloid polypeptides, serves as an excellent model because it can spontaneously form various nanostructures in aqueous or organic environments. Herein, we report the first synthesis of semiconducting, single-crystalline, peptide-based nanowires (NWs) through a simple vapor-transport process as well as the characterization of their molecular arrangement. Single-crystalline NWs were synthesized through a simple vapor-transport process in which the linear FF peptide was used as the starting material. Powdered FF was vaporized at 250 8C in an argon atmosphere and transported downstream in a horizontal tube (see Figure S1 in the Supporting Information). Thermogravimetric analysis (TGA) shows that the peptide powder begins to vaporize at approximately 250 8C (Figure S2a). Peptide NWs were grown on a silicon substrate located downstream at 180 8C. The as-synthesized peptide NWs were well-faceted with a smooth surface and an average diameter of approximately 90 nm (Figure 1a). A gradual growth of peptide NWs occurs during the vapor-transport process (Figure S3): after the formation of nuclei on the substrate, short peptide fibrils grow into peptide NWs that are longer than 10 mm. No additional mass loss was observed by TGAup to 250 8C, which indicates a high thermal stability of the synthesized peptide NWs (Figure S2b). Figure 1b shows a selected-area electrondiffraction (SAED) pattern of a representative single peptide NW. The SAED pattern of the NW exhibits a regular spot pattern, thus indicating that the peptide NW is singlecrystalline. To investigate the crystal structure of the peptide NW a finely ground sample of the peptide NW was analyzed by powder X-ray diffraction (PXRD) at room temperature (Figure S4). Most reports previously suggested that the crystal structure of self-assembled FF nanostructures consisted of an ordered hexagonal array of normal linear dipeptide molecules. According to our results, the vapor-transport process converted linear FF into cyclo-FF, in which the terminal carboxylic acid and amine groups fused together during evaporation to form a cyclic amide bond—namely, 3,6-bis(phenylmethyl)-2,5-piperazinedione (cyclo-FF)—and with aromatic stacking between the side chains. According to the literature, dipeptides can lose water and form cyclic analogues upon heating. To unravel the molecular arrangement of NWs we performed Pawley refinement to optimize the lattice parameters and, subsequently, carried out Rietveld refinements (Figure S4) using the single-crystal structure of cyclo-FF and considering all the possible geometrical degrees of freedom. The simulated pattern fits well with the experimental PXRD pattern (Rwp= 8.82%, and RP= 6.81%, respectively) collected by using synchrotron radiation (Pohang Accelerator Laboratory, Korea); the refined lattice parameters [a= 6.18517(17) , b= 10.38349(29) , c= 23.85128(62) ] from Rietveld refinement are consistent with the SAED pattern (Figure S4). While TGA showed that the FF powder lost water at around 100 8C, the peptide NWs did not show such a water loss, which indicates that the as-synthesized peptide NWs did not contain water (Figure S2b). The NWs in this study were assembled by a vapor-transport process, with no water molecules involved. The FF molecules in the previously reported linear FF based nanotubes (NTs) assemble around central water clusters through hydrogen bonds to form a hexagonal unit cell in an aqueous environment. Vapor-phase processes often pro[*] J. S. Lee, Prof. C. B. Park Department of Materials Science and Engineering, KAIST Daejeon 305-701 (Korea) E-mail: parkcb@kaist.ac.kr

Polymorph-Tuned Synthesis of α- and β-Bi2O3 Nanowires and Determination of Their Growth Direction from Polarized Raman Single Nanowire Microscopy

We report polymorph-tuned synthesis of α- and β-Bi(2)O(3) nanowires and their single nanowire micro-Raman study. The single crystalline Bi(2)O(3) nanowires in different phases (α and β) were selectively synthesized by adjusting the heating temperature of Bi precursor in a vapor transport process. No catalyst was employed. Furthermore, at an identical precursor evaporation temperature, α- and β- phase Bi(2)O(3) nanowires were simultaneously synthesized along the temperature gradient at a substrate. The growth direction of α-Bi(2)O(3) nanowires was revealed by polarized Raman single nanowire spectra. For thin β-Bi(2)O(3) nanowires with a very small diameter, the polarized Raman single nanowire spectrum was strongly influenced by the shape effect.

Au Nanowire–Au Nanoparticles Conjugated System which Provides Micrometer Size Molecular Sensors

We report a new type of molecular sensor using a Au nanowire (NW)-Au nanoparticles (NPs) conjugated system. The Au NW-NPs structure is fabricated by the self-assembly of biotinylated Au NPs on a biotinylated Au NW through avidin; this creates hot spots between NW and NPs that strongly enhance the Raman signal. The number of the Au NPs attached to the NW is reproducibly proportional to the concentration of the avidin, and is also proportional to the measured surface-enhanced Raman scattering (SERS) signals. Since this well-defined NW-NPs conjugated sensor is only a few micrometer long, we expect that development of multiplex nanobiosensor of a few tens micrometer size would become feasible by combining individually modified multiple Au NWs together on one substrate.

Pattern-selective epitaxial growth of twin-free Pd nanowires from supported nanocrystal seeds.

We report that twin-free single-crystalline Pd nanowire (NW) arrays grow epitaxially in a selected pattern on a substrate. Parallel aligned Pd NWs are synthesized on a SrTiO(3) (110) substrate in a very high density. On a SrTiO(3) (001) substrate, Pd NWs grow horizontally in two perpendicular directions. Vertical Pd NWs are synthesized instead of horizontal NWs when a c-cut sapphire substrate is employed. We reveal that the atomic structure of the substrate surface determines the geometry and orientation of seeds, which in turn direct the growth patterns of the NWs. The interface energy between the NW material and the substrate is also critical in determining the NW growth pattern. Polarization-dependent localized surface plasmon resonance of as-synthesized epitaxial Pd NW arrays is investigated for application as a plasmonic platform.

Rainbow Radiating Single-Crystal Ag Nanowire Nanoantenna

Optical antennas interface an object with optical radiation and boost the absorption and emission of light by the objects through the antenna modes. It has been much desired to enhance both excitation and emission processes of the quantum emitters as well as to interface multiwavelength channels for many nano-optical applications. Here we report the experimental implementation of an optical antenna operating in the full visible range via surface plasmon currents induced in a defect-free single-crystalline Ag nanowire (NW). With its atomically flat surface, the long Ag NW reliably establishes multiple plasmonic resonances and produces a unique rainbow antenna radiation in the Fresnel region. Detailed antenna radiation properties, such as radiating near-field patterns and polarization states, were experimentally examined and precisely analyzed by numerical simulations and antenna theory. The multiresonant Ag NW nanoantenna will find superb applications in nano-optical spectroscopy, high-resolution nanoimaging, photovoltaics, and nonlinear signal conversion.

Nanofibre optic force transducers with sub-piconewton resolution via near-field plasmon–dielectric interactions

Ultrasensitive nanomechanical instruments, including the atomic force microscope (AFM)1-4 and optical and magnetic tweezers5-8, have helped shed new light on the complex mechanical environments of biological processes. However, it is difficult to scale down the size of these instruments due to their feedback mechanisms9, which, if overcome, would enable high-density nanomechanical probing inside materials. A variety of molecular force probes including mechanophores10, quantum dots11, fluorescent pairs12,13 and molecular rotors14-16 have been designed to measure intracellular stresses; however, fluorescence-based techniques can have short operating times due to photo-instability and it is still challenging to quantify the forces with high spatial and mechanical resolution. Here, we develop a compact nanofibre optic force transducer (NOFT) that utilizes strong near-field plasmon-dielectric interactions to measure local forces with a sensitivity of <200 fN. The NOFT system is tested by monitoring bacterial motion and heart-cell beating as well as detecting infrasound power in solution.

Gap controlled plasmon-dielectric coupling effects investigated with single nanoparticle-terminated atomic force microscope probes

Precise positioning of a plasmonic nanoparticle (NP) near a small dielectric surface is not only necessary for understanding gap-dependent interactions between a metal and dielectric but it is also a critical component in building ultrasensitive molecular rulers and force sensing devices. In this study we investigate the gap-dependent scattering of gold and silver NPs by controllably depositing them on an atomic force microscope (AFM) tip and monitoring their scattering within the evanescent field of a tin dioxide nanofiber waveguide. The enhanced distance-dependent scattering profiles due to plasmon-dielectric coupling effects show similar decays for both gold and silver NPs given the strong dependence of the coupling on the decaying power in the near-field. Experiments and simulations also demonstrate that the NPs attached to the AFM tips act as free NPs, eliminating optical interference typically observed from secondary dielectric substrates. With the ability to reproducibly place individual plasmonic NPs on an AFM tip, and optically monitor near-field plasmon-dielectric coupling effects, this approach allows a wide-variety of light-matter interactions studies to be carried out on other low-dimensional nanomaterials.