Near-Infrared Dye Immobilized in Porous Silica Layer on Gold Nanorod and Its Fluorescence Enhancement by Strengthened Electromagnetic Field Based on Surface Plasmon Resonance

We report immobilizing Nile Blue A, which is a cationic fluorescent dye emitting in the near-infrared region, in the porous silica layer on gold nanorod and its fluorescence enhancement by strengthened electromagnetic field based on surface plasmon resonance. The effect of the spacer corresponding to the silica layer on the metal-enhanced fluorescence effect is also discussed in detail. Hollow silica nanorod was in advance prepared, and then the silica layer was partly etched to increase the porosity for the improvement of the mass transfer. Subsequently, gold nanorod was fabricated in the restricted space of hollow silica nanorod. Finally, Nile Blue A was physically immobilized in the porous silica layer on gold nanorod through electrostatic interactions. The fluorescence enhancement of Nile Blue A based on surface plasmon resonance was semi-quantified by comparative experiments using hollow silica nanorod, which is exactly the same structure except for gold as silica-coated gold nanorod. Since our results demonstrated that the porosity degree of the silica layer significantly affected the fluorescence enhancement of Nile Blue A, it is hopeful that our design concept, distinct from the conventional one, can lay a foundation for further development of near-infrared fluorescence nanomaterials.

     

A quantitative explanation of the effects of some alcohols on gramicidin single-channel lifetime

The effects of n-decanol, n-hexadecanol, n-octyl(oxyethylene)3 alcohol and cholesterol on gramicidin single-channel lifetime in planar lipid bilayers have been determined. The bilayers used were formed from a solution of monoolein in squalene. Measurements have also been made of the above compounds' effects on membrane thickness (as measured by electrical capacity and optical reflectance technique) and surface tension (as derived from bulk interfacial tension and bilayer-lens contact angle measurements). The reduction in single-channel lifetime caused by the n-alkanols may be accounted for quantitatively in terms of the effects of these compounds on bilayer thickness and surface tension. The n-octyl(oxyethylene)3 alcohol caused an increase in single-channel lifetime which is also consistent with the thickness/tension theory. The reduction in channel lifetime caused by cholesterol, however, was much larger than would be predicted from its effects on bilayer thickness and surface tension.     

Detection of insulin-antibody binding on a solid surface using imaging ellipsometry

Imaging ellipsometry (IE) was used to detect the binding of insulin to its antibody on a solid surface. The modification of a gold surface with 11-mecaptoundecanoic acid (11-MUA), the adsorption of protein G, and antibody immobilization onto the protein G layer were confirmed by surface plasmon resonance. Ellipsometric images and ellipsometric angles of the surface antibody were acquired using the IE system by off-null ellipsometry. Ellipsometric images of antigen binding to the antibody were acquired, and their mean optical intensities estimated. Changes in mean optical intensity indicated that the detection range for insulin was from 10 ng/ml to 100 microg/ml.     

A label-free optical sensor based on nanoporous gold arrays for the detection of oligodeoxynucleotides

Interest in using nanoporous materials for sensing applications has increased. The present study reports a method of preparing well-ordered nanoporous gold arrays using a porous silicon (PSi) template. Gold nanolayer could be electrodeposited on the surface of the PSi template at low electrolysis currents in low concentration of chloroauric acid (HAuCl₄) solution. Surface morphology characterizations and optical measurements revealed that a PSi-templated nanoporous gold (Au–PSi) array well replicated the nanoporous structure and retained the optical properties of PSi. Fourier transform reflectometric interference spectra showed that a characteristic blue-shifted effective optical thickness (EOT) was observed due to the low refractive index of the gold film. An optical DNA biosensor was then fabricated via the self-assembly of single-stranded DNA (ssDNA) with a specific sequence on the surface of Au–PSi. The attachment of ssDNA and its hybridization with target oligonucleotides (ODNs) persistently caused the blue shift of the EOT. Consequently, a relationship between the EOT shift and the ODN concentration was established. The mechanism of the optical response caused by DNA hybridization on the Au–PSi surface was qualitatively explained by the electromagnetic theory and electrochemical impedance spectroscopy (EIS). The lowest detection limit for target ODNs was estimated at around 10⁻¹⁴ mol L⁻¹, when the baseline noise, a variation in the value of EOT is around 5 nm. The fabricated Au–PSi based optical biosensor has potential use in the discovery of new ODN drugs because it will be able to detect the binding event between ODNs and the target DNA.     

Monitoring the assembly of antibody-binding membrane protein arrays using polarised neutron reflection

Protein arrays are used in a wide range of applications. The array described here binds IgG antibodies, produced in rabbit, to gold surfaces via a scaffold protein. The scaffold protein is a fusion of the monomeric E. coli porin outer membrane protein A (OmpA) and the Z domain of Staphylococcus aureus protein A. The OmpA binds to gold surfaces via a cysteine residue in a periplasmic turn and the Z domain binds immunoglobulins via their constant region. Polarised Neutron Reflection is used to probe the structure perpendicular to the gold surface at each stage of the assembly of the arrays. Polarised neutrons are used as this provides a means of achieving extra contrast in samples having a magnetic metal layer under the gold surface. This contrast is attained without resorting to hydrogen/deuterium exchange in the biological layer. Polarised Neutron Reflection allows for the modelling of many and complex layers with good fits. The total thickness of the biological layer immobilised on the gold surface is found to be 187 A and the layer can thus far be separated into its lipid, protein and solvent parts.     

Improvement of Transparent Metal Top Electrodes for Organic Solar Cells by Introducing a High Surface Energy Seed Layer

We present highly transparent and conductive silver thin films in a thermally evaporated dielectric/metal/dielectric (DMD) multilayer architecture as top electrode for efficient small molecule organic solar cells. DMD electrodes are frequently used for optoelectronic devices and exhibit excellent optical and electrical properties. Here, we show that ultrathin seed layers such as calcium, aluminum, and gold of only 1 nm thickness strongly influence the morphology of the subsequently deposited silver layer used as electrode. The wetting of silver on the substrate is significantly improved with increasing surface energy of the seed material resulting in enhanced optical and electrical properties. Typically thermally evaporated silver on a dielectric material forms rough and granular layers which are not closed and not conductive below thicknesses of 10 nm. With gold acting as seed layer, the silver electrode forms a continuous, smooth, conductive layer down to a silver thickness of 3 nm. At 7 nm silver thickness such an electrode exhibits a sheet resistance of 19 Ω/□ and a peak transmittance of 83% at 580 nm wavelength, both superior compared to silver electrodes without seed layer and even to indium tin oxide (ITO). Top‐illuminated solar cells using gold/silver double layer electrodes achieve power conversion efficiencies of 4.7%, which is equal to 4.6% observed in bottom‐illuminated reference devices employing conventional ITO. The top electrodes investigated here exhibit promising properties for semitransparent solar cells or devices fabricated on opaque substrates.     

Multilayer DNA/poly(allylamine hydrochloride) microcapsules: assembly and mechanical properties

We report the preparation, characterization, and mechanical properties of DNA/poly(allylamine hydrochloride) (PAH) multilayer microcapsules. The DNA/PAH multilayers were first constructed on a planar support to examine their layer-by-layer buildup. Surface plasmon resonance spectroscopy (SPR) showed a nonlinear growth of the assembly upon each bilayer deposited independently on a concentration of salt. A weak increase in the film thickness with the DNA concentration was, however, detected. A post-treatment of the multilayers in the salt solutions has shown a thinning of the film. The optimal conditions of the planar film growth were used to deposit the same multilayers on the surface of colloidal templates and to study their roughness and morphology with the atomic force microscope (AFM) imaging. When an outer layer is formed by DNA, we observe large domains of oriented parallel DNA loops, while an outer layer formed by PAH shows highly porous morphology. The dissolution of colloidal templates led to a formation of highly porous DNA/PAH microcapsules. We probe their mechanical properties by measuring force-deformation curves with the AFM-related setup. The experiment suggests that the DNA/PAH capsules are softer than capsules made from the flexible polyelectrolytes studied before. The softening is due to both higher permeability and smaller Young's modulus of the shell material. The Young's modulus of the DNA/PAH shells increases after post-treatment in salt solutions of relatively low concentration.     

Search of Extremely Sensitive Near-Infrared Plasmonic Interfaces: A Theoretical Study

The sensitivity of the wavelength position of localized surface plasmon resonance (LSPR) in metal nanostructures to local changes in the refractive index has been widely used for label-free detection strategies. Tuning the optical properties of the nanostructures from the visible to the infrared region is expected to have a drastic effect on the refractive index sensitivity. Here, we theoretically investigate the optical response of a newly designed plasmonic interface to changes in the bulk refractive index by the finite difference time domain method. It consists of a structured interface, where the planar interface is superposed with dielectric pillars 30 nm in height and 125 nm in length with a separation distance of 15 nm. The pillars are covered with U-shaped gold nanostructures of 50 nm in height, 125 nm in length, and 5 nm of gold base thickness. The whole structure is finally covered with a 5-nm thick dielectric layer of n ₂?=?2.63. This plasmonic structure shows bulk refractive index sensitivities up to 1750 nm/RIU (RIU : refractive index unit) in the near infrared (λ?=?2621 nm). The enhanced sensitivity is a consequence of the extremely enhanced electrical field between the gold nanopillars of the plasmonic interface.     

Influence of Plasma Polymerized Dielectric Buffer Layer and Gold Film on the Excitation of Long-Range Surface Plasmon Resonance

Recently, long-range surface plasmon resonance (LRSPR) sensor has attracted a great deal of attention as a potentially non-destructive and label-free technique for cellular studies in real time. Thus, much effort has been placed on the fabrication and optimization of multilayered structure required for the excitation of LRSPR. In this work, a detailed study about the influence of both plasma polymerized dielectric buffer layer (DBL) and thin gold film on the excitation of LRSPR was performed. The DBLs of different thicknesses were deposited directly onto SF11 glass slides by radio frequency plasma polymerization (pp) of perfluorooctyl ethylene (PFOE). Thereafter, Au films of different thicknesses were thermally evaporated onto the ppPFOE layers. Atomic force microscopy (AFM) results suggest that the resulting SF11/ppPFOE/Au structure has a smooth surface regardless of Au film’s thickness. LRSPR measurements indicate that the excitation of LRSPR relies not only on the thickness of the ppPFOE buffer layer, but also on the thickness and optical property of thin Au film. Theoretical simulation based on Fresnel’s equation allows for the determination of both the thickness and optical constant of each layer supporting the LRSPR, and also enables us to predict the optimum combination of ppPFOE and Au film in a LRSPR sensor. The performance of various LRSPR sensors to monitor the bulk refractive index variation has also been investigated.     

Tuning Plasmonic Properties of Truncated Gold Nanospheres by Coating

The influence of TiO₂ coating on resonant properties of gold nanoisland films deposited on silica substrates was studied numerically and in experiments. The model describing plasmonic properties of a metal truncated nanosphere placed on a substrate and covered by a thin dielectric layer has been developed. The model allows calculating a particle polarizability spectrum and, respectively, its surface plasmon resonance (SPR) wavelength for any given cover thickness, particle radius and truncation parameter, and dielectric functions of the particle, the substrate, the coating layer, and the surrounding medium. Dependence of the SPR position calculated for truncated gold nanospheres has coincided with the measured one for the gold nanoisland films covered with titania of different thicknesses. In the experiments, gold films with thickness of 5 nm were deposited on a silica glass substrate, annealed at 500 °C to form nanoislands of 20 nm in diameter, and covered with amorphous titania layers using atomic layer deposition technique. The resulting structures were characterized with scanning electron microscopy and optical absorption spectroscopy. The measured dependence of the SPR position on titania film thickness corresponded to the one calculated for truncated sphere-shaped nanoparticles with the truncation angle of ~50°. We demonstrated the possibility of tuning the SPR position within ~100 nm range by depositing to 30 nm thick titania layer.

     

光学蛋白芯片技术在噬菌体M13KO7检测中的应用

将亲和素共价固定在表面改性后的硅片上,通过亲和素与生物素相互作用将生物素标记的噬菌体抗体GP3固定在亲和素膜层表面,当含有M13KO7噬菌体的样品经过抗体表面时,通过噬菌体与抗体之间的相互作用噬菌体就会被抗体捕获,生物学信号可以通过芯片上的膜层厚度变化表现出来,这种膜层厚度变化可以被椭偏生物传感器技术识别。结果表明,GP3抗体在芯片表面形成了饱和的抗体膜层,厚度为6.9nm;M13KO7噬菌体与芯片上固定的抗体会发生特异性相互作用,噬菌体被抗体捕获后形成的复合物膜层厚度为17.5nm,并且随着噬菌体浓度升高膜层厚度增加,检测含有M13KO7噬菌体的样品灵敏度为109pfu/mL。与其它研究病毒与抗体相互作用方法相比光学蛋白芯片技术具有简便快捷、无需标记待检样品和结果直观等优点,为研究病毒与其抗体相互作用以及疾病早期临床诊断提供了一个新的方法。     

Immobilization of biocomponents for immune optical sensors

Immobilisation of both human immunoglobulin(IgG) and antiimmunoglobulin (anti-IgG) was performed by means of polyelectrolyte self-assembly. This technique was compared with direct immobilisation of the immune components on bare gold and their covalent binding via glutaraldehyde as a bifunctional reagent. Additionally, the immune components were properly oriented during their immobilisation by using a predeposited layer of the protein A. Methods of the surface plasmon resonance (SPR) and planar interferometry were employed for monitoring the immobilisation as well as specific immune reaction. It was shown that in case of the use of polyelectrolyte self-assembly it is possible to achieve the sensitivity of the analysis up to 30 ng/ml for SPR and up to 1 ng/ml for planar interferometer based immune sensors.     

Adsorption properties of proteins at and near the air/water interface from IRRAS spectra of protein solutions

A detailed study is performed using infrared reflection absorption spectroscopy (IRRAS) to characterize the molecular behaviour of proteins at and near the air/water interface of protein solutions. IRRAS spectra of beta-casein solutions in H2O and D2O show spectral shifts and derivative-like features not commonly observed in monomolecular layer systems. They can be fully understood using optical theory. Fair agreement between experimental and simulated IRRAS spectra over a broad spectral range (4000-1000 cm(-1)) is obtained using a stratified layer model. An attenuated total reflection and transmission spectrum is used to represent the protein extinction coefficient in H2O and D2O, respectively. It is shown that the derivative-like features observed result from the reflective properties of the proteins themselves. Furthermore, both concentration and film thickness could be fitted. At high protein concentrations (100 mg/mL) the spectrum is that of a single homogeneous protein solution. At 0.1 mg/mL, beta-casein is accumulated at the surface in a thin layer of approximately 10 nm thickness, with a concentration about 2500 times higher than in the sub-phase. At an initial concentration of 10 mg/mL, the concentration in the surface layer is about 15 times higher than in the subphase, while the thickness is about 30 nm.     

Characterization of biomimetic surfaces formed from cell membranes

A method for fabricating biomimetic surfaces from intact cell membranes is described. A monolayer of alkanethiol on gold is covered by a second layer derived from the components of erythrocyte membranes either by self-assembly or by Langmuir-Blodgett methods. The resulting asymmetric hybrid layer was characterized by ellipsometry, surface plasmon resonance (SPR), contact angle, capacitance, voltammetry, and electron and atomic force microscopy. The erythrocyte membrane layer was measured to be approximately 30-40 A in thickness. Using SPR, the presence of erythrocyte components on the surface was demonstrated by their selective removal by enzymatic action. The uniform deposition of membranous material on the substrate was shown by electron and atomic force microscopy. Demonstration of acetylcholinesterase (AChase) activity, a membrane-anchored enzyme, on the surface for at least 8 days, suggests that the outer leaflet of the erythrocyte membrane is present in its native form. Cyclic voltammetry demonstrates that enhanced electron transport from a solution redox species accompanies formation of the erythrocyte layer at the surface. This enhanced electron transport is blocked by 4,4'-diisothiocyanate stilbene-2,2'-disulfonic acid, a well known blocker of anion transport, suggesting that an erythrocyte anion transporter protein is incorporated into the surface layer in an active conformation.     

Analysis of recombinant protein expression using localized surface plasmon resonance (LSPR)

The localized surface plasmon resonance (LSPR)-based optical biosensor using nano-structures of noble metals has been considered as a useful tool for label-free detection of DNA hybridization and protein-protein interactions. We fabricated LSPR-based optical biosensors using gold nano-islands (nominal thickness; 75 A) on glass substrates that were easily made using the conventional fabrication methods. The formation of gold nano-islands on glass substrates was realized by heat treatment of thin gold film deposited with a low deposition rate (approximately 0.05 A/s). The morphologies of sensor surfaces composed of gold nano-islands were observed using an atomic force microscope (AFM) with a non-contact mode. To investigate the sensing capacity of the gold nano-island sensor for the binding of proteins by affinity interactions, the streptavidin and biotin interaction was used as a model system. In addition, detection of recombinant glutathione-S-transferase (GST)-tagged human interleukin-6 (hIL6) expressed in Escherichia coli was carried out by LSPR. It is expected that the LSPR sensors composed of gold nano-islands can be an alternative to traditional methods such as SDS-polyacrylamide gel electrophoresis (SDS-PAGE) for fast analysis of protein expression.     

Porous silicon-based biosensor for pathogen detection

A porous silicon-based biosensor for rapid detection of bacteria was fabricated. Silicon (0.01 ohmcm, p-type) was anodized electrochemically in an electrochemical Teflon cell containing ethanoic hydrofluoric acid solution to produce sponge-like porous layer of silicon. Anodizing conditions of 5 mA/cm2 for 85 min proved best for biosensor fabrication. A single-tube chemiluminescence-based assay, previously developed, was adapted to the biosensor for detection of Escherichia coli. Porous silicon chips were functionalized with a dioxetane-Polymyxin B (cell wall permeabilizer) mixture by diffusion and adsorption on to the porous surface. The reaction of beta-galactosidase enzyme from E. coli with the dioxetane substrate generated light at 530 nm. Light emission for the porous silicon biosensor chip with E. coli was significantly greater than that of the control and planar silicon chip with E. coli (P<0.01). Sensitivity of the porous silicon biosensor was determined to be 101-102 colony forming units (CFU) of E. coli. The porous silicon-based biosensor was fabricated and functionalized to successfully detect E. coli and has potential applications in food and environmental testing.     

Analysis and Modeling of Lithium Flows in Porous Materials

One of the primary conditions necessary for the success of magnetic fusion reactors is the ability to mitigate damage to the first wall during ELMs and plasma disruptions. A potential solution involves the use of flowing liquid metals such as lithium as a first wall, but ensuring its stability under the extreme environments in the reactor would be imperative. The conditions leading to instabilities on the free surface of flowing liquid lithium (LL) layers on a substrate and in a porous material are investigated using both analytical methods and computational modeling, with consideration for the effects of LL velocity, LL layer thickness, substrate porosity, LL permeability, and hydrogen (H) plasma velocity. Linear stability analysis is used to predict the critical velocity and wavelength-dependence of wave growth, as well as the onset of instability. The modeling of LL flows is performed on a flat substrate and in a porous material for various LL thicknesses, LL and H plasma velocities to analyze the conditions leading to droplet formation and ejection.     

Ligand density effect on biorecognition by PEGylated gold nanoparticles: regulated interaction of RCA120 lectin with lactose installed to the distal end of tethered PEG strands on gold surface

PEGylated gold nanoparticles (diameter: 20 nm) possessing various functionalities of lactose ligand on the distal end of tethered PEG ranging from 0 to 65% were prepared to explore the effect of ligand density of the nanoparticles on their lectin binding property. UV-visible spectra of the aqueous solution of the nanoparticles revealed that the strong steric stabilization property of the PEG layer lends the nanoparticles high dispersion stability even under the physiological salt concentration (ionic strength, I = 0.15 M). The number of PEG strands on a single particle was determined to be 520 from thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) observation under controlled acceleration voltage revealed the thickness of the PEG layer on the nanoparticle to be approximately 7 nm. The area occupied by a single lactose molecule on the surface of PEGylated gold nanoparticles was then calculated based on TGA and SEM results and was varied in the range of 10-34 nm2 depending on the lactose functionality (65 approximately 20%). PEGylated gold nanoparticles with 40% and 65% lactose functionality showed a selective and time-dependent aggregation in phosphate buffer with the addition of Ricinus communis agglutinin (RCA120) lectin, a bivalent galactose-specific protein. The aggregates can be completely redispersed by adding an excess amount of galactose. Time-lapse monitoring of UV-visible spectra at 600-750 nm revealed that the aggregation of PEGylated gold nanoparticles was accelerated with an increase in both RCA120 concentration in the solution and the lactose density of the nanoparticles. Furthermore, the sensitivity of lectin detection could be controlled by the regulation of lactose density on the particle surface. Interestingly, there was a critical lactose density (>20%) observed to induce detectable particle aggregation, indicating that the interaction between the particles is triggered by the multimolecular bridging via lectin molecules.     

Solid and Hollow Gold Nanostructures for Nanomedicine: Comparison of Photothermal Properties

The photothermal properties of solid and hollow gold nanostructures represented by colloidal solutions of spherical nanoparticles, nanoshells, and nanocages upon irradiation with a 100 mW 808 nm continuous-wave laser for the first time were experimentally compared under identical optical density and nanoparticle concentration conditions. Accompanying computer modeling of light absorption by the studied gold nanostructures revealed the general parameters influencing the photothermal efficiency, which is of significance for nanomedical applications. The spectral position of localized plasmonic excitations of the studied nanostructures ranged from 518 nm for solid gold nanoparticles to 718 nm for gold nanocages, which provided a possibility to observe a direct influence of the wavelength proximity between the localized surface plasmon resonance and laser line on the heat generation capability of the nanostructures. As a result, the best photothermal efficiency was registered for gold nanocages, which proves them as an efficient photothermal treatment agent and a possible candidate to build a nanocarrier platform for drug delivery with a controlled release. Light absorption modeling demonstrated an existence of optimal wall thickness for gold nanoshells that should lead to the maximum photothermal efficiency when irradiated with 808 nm light, which varied from about 0.1 to 0.4 in units of external nanoshell radius with an increase of the wall porosity. Additionally, computer modeling results show that increased wall porosity should lead to enhanced photothermal efficiency of polydisperse colloidal solutions of hollow gold nanostructures.     

Three-dimensional structure of the surface protein layer (MW layer) of Bacillus brevis 47

The three-dimensional (3D) structure of one surface protein layer from Bacillus brevis 47, the middle wall (MW) layer, has been reconstructed from tilted-view electron micrographs after correlation averaging to a resolution of 2 nm. The MW layer has p6 symmetry with a center-to-center spacing of 18.3 nm and a minimum thickness of 5.5 nm. The reconstruction reveals a distinct domain structure: the heavier domain of six monomers jointly forms a massive core centered at the sixfold symmetry axis, and lighter domains interconnect adjacent unit cells. In addition, the larger domains collectively form a pore by making contact with each other towards the inner surface, while the smaller domains establish a second connectivity towards the outer surface of the S layer. The MW layer of B. brevis resembles the S layer of Acetogenium kivui in various aspects: they have very similar lattice parameters and highly reminiscent 3D structures; the pores penetrate through the whole core and appear to determine the porosity of the S layers.