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3D nanoporous Ag microstructures (np-AgMSs) were successfully fabricated from AgCl microcrystal templates by a galvanic replacement approach using sacrificial Zn metal. This simple, rapid, and stabilizer-free protocol preserves the initial morphologies of AgCl microcrystal templates. The chloride ion is proven to be an essential ingredient in electrolytes as it facilitates the liberation of electrons from the sacrificial Zn metal. The formation mechanism of np-AgMSs via the reduction, at the AgCl/metal interfaces, of the mobile Ag+ dissolved from AgCl is proposed. The concerted reaction between oxidative etching of np-AgMSs (by Cl− and Cl−/O2) and re-deposition of Ag atoms converts large grains to small grains. The grain size of np-AgMSs can be tuned by adjusting the concentration of Cl−. The np-AgMSs also show efficient catalytic activity for the reduction of p-nitrophenol by NaBH4 within 6 minutes for at least 10 cycles.

An interaction between the incident light and the structural architecture within the shell of Asian green mussel (Perna viridis) induces observable pearlescent colors. In this paper, we investigate the influence of the structural architecture on the expressed colors. After a removal of the organic binder, small flakes from crushed shells show vivid rainbow reflection under an optical microscope. An individual flake expresses vivid color under a bright-field illumination while become transparent under a dark-field illumination. The expressed colors of the aragonite flakes are directly associated with its structural architecture. The flakes with aragonite thickness of 256, 310, and 353 nm, respectively, appear blue, green, and red under an optical microscope. The spectral simulation corroborates the experimentally observed optical effects as the flakes with thicker aragonite layers selectively reflected color with longer wavelengths. Flakes with multiple aragonite thicknesses expressed multi-color as the upper aragonite layers allow reflected colors from the lower layers to be observed.

In this paper we demonstrate a simple and rapid shape transformation of silver nanospheres (AgNSs) to silver nanoplates (AgNPls) using the oxidation and reduction capabilities of hydrogen peroxide. AgNPls having tunable surface plasmon resonance across the visible region with average size of 40–100 nm and thickness of 10–15 nm can be fabricated within 2 min simply by adding H2O2 into a colloid of AgNSs with average particle size of 7 nm. The efficiency of H2O2 as a shape-transforming agent depends strongly on its concentration, pH of the AgNS colloid, and the employed stabilizers. H2O2 oxidizes AgNSs to silver ions while concertedly reduces silver ions to silver atom necessary for the growth of AgNPls. The shape transformation reaction was conducted at a relatively low concentration of H2O2 in order to minimize the oxidative dissolution while facilitating kinetically controlled growth of AgNPls under a near neutral pH. Polyvinyl-pyrrolidone is an effective steric stabilizer preventing aggregation while assisting the growth of AgNPls. Trisodium citrate inhibits the formation of AgNPls under the H2O2 reduction as it forms a stable complex with silver ions capable of withstanding the weakly reducing power of H2O2. After a complete consumption of AgNSs, large nanoplates grows with an expense of smaller nanoplates. The growth continues until H2O2 is exhausted. A high concentration H2O2 promotes catalytic decomposition of H2O2 on the surface of AgNSs and oxidative dissolution of AgNSs without a formation of AgNPls.

The potential of a nanoporous Ag microstructure (np-AgMs) for use as a single particle for surface-enhanced Raman scattering spectroscopy (SERS), with the added advantages of being easy to manipulate and reusable, was successfully demonstrated. The np-AgMs with interconnected pore and controllable pore size were fabricated from symmetric hexapod AgCl via a galvanic replacement reaction in NaCl solution with zinc (Zn) as the sacrificed metal. The clean surface of np-AgMs enables rapid surface functionalization with easy handling and sample preparation as no particle aggregation occurs. The SERS acquisition spots on the np-AgMs can be visually selected using a normal Raman microscope. SERS spectra of p-aminothiophenol (PATP) with a concentration range of 10−8–10−3 M can be achieved. The position-dependent enhancement of np-AgMs was expendably evaluated. The signal-position correlation was confirmed by electric filed enhancement obtained from Finite-difference time-domain (FDTD) calculation. In addition, the highly stable substrate showed insignificant loss of the enhanced Raman signal after several cycles of chemical re-generation. Finally, the potential application of np-AgMs in label-free detection of biomolecules including hemoprotein, protein without chromophore and DNA strains at low concentration of 500 μg mL−1 was demonstrated.

Morphologically controlled micro-/nanostructures have gained considerable interest as they offer unique properties associated with size, shape, and crystallographic facets. In this paper, we report a simple yet rapid protocol for large scale synthesis of silver microplates (AgMPls) from a silver ammine complex ([Ag(NH3)2]+) under an etching environment containing O2/Cl−, NH4OH/H2O2, and H2O2 capable of dissolving silver crystals except plate structures. H2O2 is employed as the sole reducing agent. Chloride ions are essential for creating an etching environment capable of selective dissolution of singly and multiply twinned crystals, while leaving plate structures unaffected. Without chloride ions, H2O2 reduces the [Ag(NH3)2]+ complex to silver microparticles containing truncated cubes, icosahedra, pentagonal rods, and plate microstructures with icosahedra as the major product. The developed protocol enables environmentally friendly fabrication of highly pure AgMPls and AgMPs directly from the AgCl precipitate.

A novel technique for the fabrication of nano/microporous gold (Au) microsheets using an ultrasonic-assisted cyclic galvanic replacement reaction between a sacrificial silver (Ag) plate and gold ions (AuCl4−) is reported. First of all, AuCl4− is reduced on the surface of sacrificial Ag via a galvanic replacement reaction. Then, the epitaxial growth of the Au film on the Ag surface is disturbed by the precipitated AgCl by-product of this galvanic replacement reaction. The co-precipitated AgCl and galvanic-generated Au nanostructures induce the formation of an interpenetrated Au/AgCl nanocomposite film on the surface of the sacrificial Ag plate. Finally, ultrasonic radiation enables auto-detachment of the galvanic-generated film along the AgCl/Ag interface. The galvanic replacement and auto-detachment processes continuously occur as a cycle until the scarified Ag is totally consumed. The coral-like Au nanostructures with nano/microporous morphologies are realized after removing AgCl by NH3 treatment. The hierarchical nano/microporous structures have micropores and nanopores with sizes of 0.15–0.30 μm and 30–60 nm, respectively, separated by chain-like Au structures. The complex porous structures, through which liquids can easily flow, can potentially be used in applications such as high-efficiency free-standing catalysts, super capacitors, electrochemical sensors and surface-enhanced Raman scattering (SERS) substrates. A SERS application of the Au microsheets is also demonstrated.

In this work, ATR FT-IR spectra of single human hair and cosmetic residues on hair surface are successfully collected using a homemade dome-shaped Ge μIRE accessary installed on an infrared microscope. By collecting ATR spectra of hairs from the same person, the spectral patterns are identical and superimposed while different spectral features are observed from ATR spectra of hairs collected from different persons. The spectral differences depend on individual hair characteristics, chemical treatments, and cosmetics on hair surface. The “Contact-and-Collect” technique that transfers remarkable materials on the hair surface to the tip of the Ge μIRE enables an identification of cosmetics on a single hair. Moreover, the differences between un-split and split hairs are also studied in this report. These highly specific spectral features can be employed for unique identification or for differentiation of hairs based on the molecular structures of hairs and cosmetics on hairs.

In this research, a sensitive and selective method for detecting one of the most toxic insecticides, "carbofuran", in rice and soybean is presented. This method is based on the coupling reaction of diazonium ion combined with a surface-enhanced Raman scattering technique. Diazonium ion produced from p-aminothiophenol reacts specifically with carbofuran phenol from the hydrolysis of carbofuran. The generated azo compounds attach to the surface of silver nanoparticles via the Ag-S bond. Therefore, a strong Raman intensity can be obtained. The concentration of carbofuran can be determined by following the intensity of the peak at 1201 cm-1, attributed to the C-N stretching vibration of the azo compound. The result shows a good linear correlation (R2 = 0.9786) against carbofuran concentrations (0.1 - 5 ppm) with a detection limit of 0.452 ppm. Our proposed protocol is insignificantly influenced by various common interferences. Moreover, this method has been successfully validated to determine carbofuran concentrations in rice and soybean with detection limits of 0.446 and 0.520 ppm, respectively.

Pearlescent effect is a unique optical phenomenon originated by an interference of visible light with biomaterial having periodic structure such as pearls, mother-of-pearls, mollusk shells, beetle wings, and butterfly wings. The pearlescent effect exhibits series of vivid colors at a particular spot as an angle of observation is changed. In this paper, the pearlescent effect in Asian green mussel (Perna viridis) shell was investigated. The nacreous layer of the shells is an assembly of stratified bilayers of alternate aragonite calcium carbonate and organic matrix. A consecutive chemical/thermal treatment was employed to remove the organic layer. The enhanced pearlescent effect, indicated by more vivid and brighter colors, was due to a greater refractive index difference within the treated structure as the organic layers were replaced by air gaps of the same thickness. The modified transfer matrix method developed for the stratified bilayers system was employed to verify enhanced pearlescent effect. The results from theoretical simulation corroborated the visual observation as a 4-time full-width-at-half-maximum increment of the reflectance peak, and a broader spectral coverage was achieved after the replacement of organic layers by air gaps.

In this study, we achieved an enhancement of the transmission surface plasmon resonance (T-SPR) intensity by depositing silver nanoparticles (AgNPs) onto a gold grating substrate. The T-SPR spectrum of the gold grating substrate with AgNPs showed a strong and narrow SPR peak located between 650 and 800 nm; the maximum SPR excitation was observed at a 35° angle of incidence. We controlled the distance between the gold grating surface and the AgNPs by using layer-by-layer (LbL) ultrathin films of poly(diallydimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) to study the distance dependence of the coupling effect between the AgNPs and the gold grating substrate. The distance-dependent T-SPR response of peak position and intensity showed distinctive changes when the intermediate layer was 10 bilayers (∼17 nm) thick. The strongest coupling surface plasmon excitation between the AgNPs and the gold grating substrate was obtained at this layer spacing. Furthermore, we explored the potential of the developed system as a switchable pH sensor. The T-SPR spectrum sensitively changed as the pH switched from acidic (pH 2) to alkaline (pH 12) conditions by the swelling/shrinking of the poly(allylamine hydrochloride) (PAH)/PSS LbL film, respectively, which was deposited between the AgNPs and the gold grating.

A novel colorimetric method with image colour analysis for highly sensitive and accurate detection of hydrogen peroxide using starch-stabilized silver nanoprisms (AgNPrs) is proposed. AgNPrs were morphologically decomposed by a low concentration of hydrogen peroxide revealed by UV-visible absorption spectroscopy and transmission electron microscopy (TEM). The morphological changes of AgNPrs led to an appreciable colour change in the AgNPr solution from red to orange, and finally yellow. A good linear relationship between the wavelength shift of AgNPrs and the H2O2 concentration can be obtained. The solution phase detection of H2O2 by the direct morphological change can be accomplished without any surface modification of AgNPrs. In addition to the conventional determination of the H2O2 concentration utilizing spectroscopic data, a new and simple colorimetric strategy based on the chromaticity analysis of AgNPr solution was demonstrated. The strategy can be employed not only for visual detection of H2O2 by the naked eye but also for reliable and convenient methods for quantification of H2O2. The hydrogen peroxide concentration at 1.57 μM can be recognized by naked-eye observation with good accuracy, stability and reproducibility. Furthermore, the proposed protocol can be applied to determine the glucose concentration through the glucose-oxidase system. A good linearity between the red chromaticity of the solution colour and the glucose concentrations was observed. The new colorimetric determination of hydrogen peroxide utilizing digital image analysis on colour changes from AgNPr shape decomposition will open up an alternative method for simple, rapid and reliable detection of hydrogen peroxide and can realize its future applications in biochemical analysis or clinical diagnosis.

Herein various AgCl microstructures including octapods, octapods with fishbone pods, hexapods, hexapods with 4-blade arrowhead pods, concave octahedra, and octahedra are selectively precipitated from a [Ag(NH3)2]+ solution by addition of Cl−. The microstructures were rapidly formed and precipitated within 5 min. In a Cl−-rich environment, the octapod grew from cubic seeds as the growth along the 〈111〉 directions was favorable. The hexapod grew from octahedral seeds in an NH4OH-rich environment as the growth along the 〈100〉 directions dominated. By manipulating the seed morphology and the growth environment, complex AgCl microstructures of thermodynamically unfavorable structures (hexapods and octahedra) can be selectively fabricated. A potential application of AgCl microstructures as photocatalysts was explored by partial photo-reduction of the surface AgCl into isolated AgNPs. The fabricated AgCl microstructures were turned into efficient Ag@AgCl visible-light photocatalysts as complete decomposition of methyl orange was achieved within 20 min. This work not only explores a method to control the preferential growth of AgCl microstructures along the 〈100〉 and 〈111〉 directions but also provides an in-depth understanding on the crystal growth mechanisms and how to manipulate them efficiently.

An easy-to-perform colorimetric analysis of protein content in milk based on aggregation-induced color change of starch-stabilized gold nanoparticles (AuNPs) has been developed. The synthesized AuNPs were employed without further surface modification. The assay relies on the additional stabilization power of proteins that inhibits the aggregation of AuNPs induced by hydrochloric acid. In the presence of milk proteins, the assay shows red to blue color shift as the total protein concentration decreases. Since the localized surface plasmon resonance (LSPR) expresses correlation with protein concentration, the protein content can be quantified. With an optimized condition, the assay is so sensitive that it can accurately determine protein content from 2.93 × 10 −1 to 2.93 × 10 −3 mg/mL via naked eye observation based on color change. Moreover, an extra accuracy can be achieved via the corresponding UV–visible spectra. Adulterating substance study showed that starch, lactose, table sugar, melamine, and sodium chloride cannot deceive the assay. The developed assay is very simple, requires only 6 min of analysis time without any extraction process. This technique provides a great potential for on-site milk analysis, milk adulteration detection as well as in-house use.

The ubiquity of high quality smartphones at affordable prices not only accelerated the social penetration in the global population but also promoted nontraditional usage of smartphones as point-of-care medical diagnostic devices, sensors, and portable digital microscopes. This paper reveals a simple, rapid, cost-effective, and template-free technique for mass-scale production of an elastomeric PDMS (ePDMS) planoconvex lens capable of converting a smartphone into a portable digital microscope. By taking advantage of the resistance to spreading of liquid by a sharp edge, highly stable spherical cap of viscous liquid PDMS (lPDMS) on a smooth PMMA circular disk was fabricated. The axisymmetric spreading of lPDMS under the gravitational force and interfacial tension force enable the formation of spherical cap with a certain radius of curvature. A thermal treatment at 80 °C for 30 min cured the spherical cap lPDMS into a bubble-free ePDMS planoconvex lens. Lenses with focal lengths of 55.2-3.4 mm could be reproducibly fabricated by adjusting the volume of dispensed lPDMSs and diameter of PMMA disks. High-resolution panoramic microscope images without a distortion of small cylindrical object could be constructed on-the-fly using the imbedded smartphone app. Applications of the smartphone digital microscope equipped with an ePDMS planoconvex lens for imaging of micro printings, gun shot residues, cylindrical objects, and bullet toolmarks were explored.

In this study, urchin-like gold nanoparticles (UL-AuNPs) are used in the fabrication of organic thin-film solar cells (OSCs). UL-AuNPs, which have gold nanothorns on their surface, enhance light accumulation by acting as light-trapping materials. This is due to the enhanced electric field and light scattering attributed to the nanothorns on the surface of the nanoparticles. UL-AuNPs were incorporated into a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) thin-film layer of organic thin-film solar cells (OSCs). UV-vis spectra, atomic force microscopy (AFM) images, current density versus voltage properties, and the impedance spectra of the fabricated devices were recorded at various concentrations of UL-AuNPs. We found that the efficiency of the OSCs with UL-AuNPs was not only higher than that of a reference cell without nanoparticles but also higher than that of OSCs with spherical AuNPs. Finite-difference time-domain (FDTD) simulation indicated that the electric field around the UL-AuNPs increased due to the presence of nanothorns.

Hydrotalcite-supported platinum nanoparticles (Pt NPs/HT) prepared by the immobilization method with soluble starch as a reducing and a stabilizing agent were applied as catalysts for the selective oxidation of glycerol using atmospheric molecular oxygen as an oxidant in water. The Pt NPs/HT catalyst achieved a high selectivity (68%) toward glyceric acid (GA) in base-free aqueous solution. The catalyst was removed from the solution by simple filtration after the reaction and could be reused up to three times with a high selectivity (71% in third recycled).

A green synthesis of size-controllable, uniform gold nanospheres is reported. The size of the gold particles can be selectively tuned from nanometer to submicrometer regimes with narrow size distribution through pH adjustment of the solution. Based on the employed green chemical reduction method, soluble starch is used as both reducing agent and stabilizer. Soluble starch is generally a very weak reducing agent. However, under an alkaline condition, its reducing efficiency is enhanced by the concomitant generation of reducing species as the starch molecules are alkaline degraded. The in situ generated reducing species nucleate and grow gold nanoparticles. The growth mechanism of gold particles is systematically investigated and proposed. The synthesized gold colloid is very stable and can be kept over 4 months without precipitation, aggregation, or any significant changes. Moreover, all processes of this method are simple and environmentally friendly, and no complex instrument is needed.

Imprinted solution-processible gold nanoparticle (AuNP) grating films were fabricated for use as a grating-coupled surface plasmon resonance (SPR) excitation substrate. The imprinted AuNP grating pattern, which consists of a 1.72 μm grating pitch, was fabricated on flat glass substrates by imprinting AuNP on silicon grating templates. In this study, the SPR measurements were carried out on an SPR device in the grating-coupling configuration with a He–Ne laser ( λ = 632.8 nm) as the excitation source, and multimode surface plasmon excitations were observed upon irradiation with white light. SPR excitation of our substrate was observed at the incident angle of 47.1°. For SPR measurements using white light irradiation, multimode surface plasmon excitation resulting from several diffraction orders was observed in the wavelength region of 500–850 nm. The surface plasmon dispersion branches were calculated to obtain the diffraction order in this region. SPR excitation of the imprinted AuNP grating substrate was further studied by fabrication of a layer-by-layer ultrathin film of iron containing bis(terpyridine) polymer (Fe(II)-BTP) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). A shift of the SPR excitation spectrum was observed when the ultrathin film was deposited on the imprinted AuNP grating surface. Thus, this substrate should be a useful SPR substrate in a variety of applications such as photoelectric conversions and sensors.

We developed a novel technique for increasing the sensitivity of transmission surface plasmon resonance (T-SPR) signals. T-SPR spectroscopy was performed by irradiating, with white light, a gold grating substrate whose surface was nanostructured by growing gold nanoparticles (AuNPs). AuNPs were grown directly on the substrate surface by alcohol reduction and their growth was observed at various stages by UV–visible spectroscopy and standard Kretschmann-type SPR spectroscopy. For comparison, normal gold film with smooth surface was examined under similar condition. The T-SPR results show a possibility of hybrid excitation of both localized and propagating surface plasmon. Significantly, T-SPR spectra of the gold grating substrate obtained during AuNP growth show stronger and narrower peaks in the range 650–800 nm. The maximum T-SPR excitation was at an incident angle of 35°. A layer-by-layer system of 5,10,15,20-tetrakis (1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) molecules and sodium copper chlorophyllin molecules was used to verify the enhancement of the developed system. We believe that the AuNPs/Au grating for T-SPR devices will provide enhanced signals for detecting nanometer order materials and for high-sensitive sensor applications.

Tests for acute oral toxicity, eye irritation, corrosion and dermal toxicity of colloidal silver nanoparticles (AgNPs) were conducted in laboratory animals following OECD guidelines. Oral administration of AgNPs at a limited dose of 5,000 mg/kg produced neither mortality nor acute toxic signs throughout the observation period. Percentage of body weight gain of the mice showed no significant difference between control and treatment groups. In the hematological analysis, there was no significant difference between mice treated with AgNPs and controls. Blood chemistry analysis also showed no differences in any of the parameter examined. There was neither any gross lesion nor histopathological change observed in various organs. The results indicated that the LD(50) of colloidal AgNPs is greater than 5,000 mg/kg body weight. In acute eye irritation and corrosion study, no mortality and toxic signs were observed when various doses of colloidal AgNPs were instilled in guinea pig eyes during 72 hr observation period. However, the instillation of AgNPs at 5,000 ppm produced transient eye irritation during early 24 hr observation time. No any gross abnormality was noted in the skins of the guinea pigs exposed to various doses of colloidal AgNPs. In addition, no significant AgNPs exposure relating to dermal tissue changes was observed microscopically. In summary, these findings of all toxicity tests in this study suggest that colloidal AgNPs could be relatively safe when administered to oral, eye and skin of the animal models for short periods of time.

Aims: To isolate a biosurfactant (BS)-producing bacterium, to characterize the BS properties and to evaluate its ability to enhance pesticide solubilization for further application in environmental remediation. Methods and Results: Five BS-producing bacteria were isolated from fuel oil-contaminated soil. Among them, Burkholderia cenocepacia BSP3 exhibited the highest emulsification index and was chosen for further study. Glucose-containing medium supplemented with nitrate or sunflower seed oil provided suitable conditions for growth and BS production. The BS was identified as a glucolipid, having a critical micelle concentration (CMC) of 316 mg l−1. It could lower the surface tension of deionized water to 25 ± 0·2 mN m−1 and exhibited good emulsion stability. Finally, the application of the BS to facilitate pesticide solubilization demonstrated that this BS at the concentration below and above its CMC could enhance the apparent water solubility of three pesticides, i.e. methyl parathion, ethyl parathion and trifluralin. Conclusions: Burkholderia cenocepacia BSP3 is a BS-producing bacterium isolated from oil-contaminated soil. The BS was identified as a glucolipid having a molecular mass of 550·4 g mol−1. An apparent yield of the BS was 6·5 ± 0·7 g l−1. This glucolipid-type BS noticeably enhanced pesticide solubilization suggesting its role in environmental remediation. Significance and Impact of the Study: A glucolipid type BS normally found in marine micro-organisms was isolated from a soil-bacterium. Due to its surface active properties and good performance in enhancement of pesticide solubilization, it could be used as a solubilizing agent for environmental remediation and synergistic treatment with bioremediation of pesticide-contaminated soil.

Photoisomerization and photodimerization of a widely used UVB filter, 2-ethylhexy-4-methoxycinnamate (EHMC) on a ZnSe surface and baby mouse ( Mus musculus Linn.) skin were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR). Differentiation between the E- and the Z-EHMC could be achieved by examining the infrared (IR) peak at 981 cm−1 (b peak), which corresponds to the CH rocking deformation vibration of Ph-CH=CH- detected only in the E configuration. By plotting the ratios of the peak area of the b peak and an internal standard peak (1060–998 cm−1) against mole percentage of Z-isomer in the E-Z mixtures, a linear calibration plot was obtained. Thus, a simple estimation of the mole percentage of each configuration in a sample was obtained. At the same UVB exposure, photostationary equilibrium of the E/Z isomerization on the surface varied with the applied amounts of EHMC. Photoisomerizations on ZnSe and on baby mouse skin were comparable. Less than 10% of E-EHMC changed configuration when the mouse skins applied with 1.0–4.0 mg/cm2 E-EHMC were exposed to sunlight for 60 min (UVB radiant exposure of ∼0.30 J/cm2). This corresponded to less than 5% loss in UV filtering efficiency. However, at a typical EHMC skin coverage (∼0.2 mg/cm2), 0.30 J/cm2 UVB exposure induced ∼50% photoisomerization resulting in 25% loss of UV filtering efficiency. No photodimerization was detected even at the extreme EHMC coverage of 4.0 mg/cm2 after a UVB exposure of 0.90 J/cm2.

A novel and facile green synthetic method for creating flowerlike palladium microstructures (FPdµSTs) using hydrogen peroxide (H2O2) as a sole reducing and shape-controlling agent was developed. FPdµSTs with particle size in the range of 1–5 μm were successfully synthesized. Morphology (size and shape) and complexity of the FPdµSTs could be tuned through the synthetic conditions (i.e., concentrations of H2PdCl4 and H2O2). H2O2 played an important role in creating palladium microstructures by reduction of H2PdCl4 under acidic condition. The time-dependent investigation on the particle growth suggested that the FPdµSTs evolved from spherical palladium nanoparticles with a particle size of 3 nm. The small particles, which were formed at the early stage of the reaction, aggregated and grew into complex flowerlike microstructures.

We fabricated plasmonic gold nanoparticle (AuNP)–TiO2 nanocomposite films and measured the photocurrent that originates from the water-splitting reaction catalyzed by the AuNP–TiO2 nanocomposite photoelectrocatalytic (PEC) electrode. The localized surface plasmon resonance (LSPR) of the gold nanoparticles affected the generation of photocurrent by TiO2 upon illumination with visible light. Electrochemical impedance spectroscopy (EIS) revealed that the improvement in the photocurrent generation originates from an enhancement in electron–hole pair generation induced by the SPR of the plasmonic gold nanoparticles rather than the extension of the electron lifetime. Moreover, we introduced a novel method to enhance the photocurrent of TiO2 by a multiple plasmonic effect, i.e., LSPR of plasmonic gold nanoparticles and the grating-coupled propagating SP on a gold grating. We fabricated the AuNP–TiO2 nanocomposites on a gold-coated Blu-ray disc recordable (BD-R). The enhancement of the photocurrent due to the combination of LSPR and the grating-coupled SP was investigated.

Uniform spherical palladium nanoparticles with an average particle size of 4.3±0.5 nm were successfully synthesized by reducing H2PdCl4 with intermediates in situ generated during a successive acidic/alkaline treatment of sucrose. A successive acidic/alkaline treatment plays an important role on converting the non-reducing sucrose into efficient reducing species containing aldehyde functionality. The Benedict's test corroborates the development and vanishing of the in situ generated reducing species upon prolonged degradation. An increase in alkalinity drastically improves the reduction efficiency. ATR FT-IR spectroscopy indicated spontaneous development of carboxylate after the alkaline treatment. Under the employed condition, small organic species with carbonyl groups (aldehyde, acid, and acid salt) were generated through the sucrose degradation before being oxidized to carbonate after an hour of the treatment. Sucrose was completely decomposed into carbonate after a 24-h successive acidic/alkaline treatment. The synthesized palladium nanoparticles express a good catalytic activity in the decolorization process of Congo red by sodium borohydride.

The study on the shape evolution of metal nanoparticles (MNPs) is crucial to gain an understanding on controlling the shape and size of metal nanostructures. In this work, a detailed study on shape evolution of silver (Ag) nanospheres to nanoplates induced by hydrogen peroxide (H2O2) was performed. According to the growth mechanism of Ag nanoplates, the spectrophotometric method combined with chemometric analysis has potential to reveal the structural evolution process as observed by surface plasmon resonance phenomena. The extinction spectra of the evolving nanostructures were analyzed by factor analysis and error indicator functions. Five major components attributed to the different particle shapes and sizes were theoretically predicted. Furthermore, the concentration profiles and pure spectra of these components were resolved using multivariate curve resolution–alternative least squares (MCR–ALS) analysis. The evolution profiles show that the spherical Ag particles systematically evolved into plate structures of different sizes. Larger nanoplates were obtained when higher concentrations of H2O2 were employed. An evidence of nanoplate disintegration was observed when a large amount of H2O2 was employed. The predicted structural morphologies of each component given by chemometric calculation were in excellent agreement with those observed by transmission electron microscope (TEM) images.

In this work, the efficiency of soluble starch as a reducing and a stabilizing agent in the synthesis of platinum nanoparticles under acidic–alkaline treatment is systematically studied. The degraded intermediates with reducing potential (i.e., small molecules containing aldehyde and α-hydroxy ketone moieties) are concomitantly generated when the alkaline concentration is greater than 0.025 M. The in situ generated species could completely reduce platinum ions (20 mM) and sufficiently stabilize the obtained platinum nanoparticles (5 mM) of uniform particle size (2–4 nm). The reduction is efficient and rapid as a complete conversion is achieved within 5 min. In a stronger alkaline condition, the platinum nanoparticles tend to aggregate and form a bigger domain because extensive degradation generates small starch fragments with less stabilization efficiency. This observation suggests that starch is a promising green material which could be chemically treated and transformed to a powerful reducing agent and stabilizer for the synthesis of metal nanoparticles.

Gold nanoparticles (AuNPs) have a unique property called localized surface plasmon resonance (LSPR). LSPR excitation wavelength is strongly dependent on size of gold nanoparticles. At the LSPR wavelength, gold nanoparticles exhibit an enormous electric field enhancement extended from their surface. We have been synthesized gold nanoparticles using chemical reduction of hydrogen tetrachloroaurate (HAuCl4) with sodium borohydride (NaBH4). The soluble starch was used as a stabilizer. The pH of gold salt solution and concentration of stabilizer were varied to investigate the change of the size and stability of gold nanoparticles. Under basic condition, the gold ion was easily reduced to gold nanoparticles. Then, the smaller size of gold nanoparticles could be observed. The concentration of starch solution also affected on the size and stability of gold nanoparticles. The size of gold nanoparticles was increased with the decreasing of starch concentration. In this work, grating pattern of gold nanoparticles was prepared by imprinting method. There is a possibility to use the grating pattern of gold nanoparticles in SPR grating-coupling method.

Surface contaminants, such as powder and thin film on various solid surfaces, were analyzed by ATR FT-IR microspectroscopy. An ATR accessory consisting of a miniature-Ge IRE with contact area smaller than 50 microm, in diameter was fabricated and employed for a non-destructive characterization. The IRE was pre-aligned and fixed onto a 15x Schwarzschild-Cassegrain infrared objective. Easy maneuvering of the microscope stage enabled an accumulative collection of the contaminant at the tip of a miniature-Ge IRE, where the contaminants were analyzed under the ATR condition. By making a gentle contact between the Ge tip and selected area on the surface, any removable contaminants were transferred onto the Ge tip where its molecular information was acquired without any interference from the solid substrate. A thin organic film (i.e., mineral oil or fluorolube) was coated at the tip of the IRE in order to enhance the collecting efficiency of the removable contaminants.

The influence of the metal film thickness (i.e., the chromium adhesion promoting film and the gold film) on the sensitivity of surface plasmon resonance (SPR) signals (i.e., resonance angle shift and reflectance change) towards the thickness variation of the nonabsorbing dielectric film is investigated. The sensitivity of reflectance change decreases when a thick chromium film or a thin gold film is employed. Its linear range becomes narrower as the thickness of the metal films increases. The sensitivity and linear range of the resonance angle shift are not affected by the thickness variation of the metal films. The phenomena were theoretically explained based on the attenuated total reflection (ATR) generated evanescent field at the prism/metal interface and the SPR-generated evanescent field at the metal/dielectric interface.

The highly sensitive nature of surface plasmon resonance (SPR) spectroscopy and surface plasmon field-enhanced fluorescence spectroscopy (SPFS) are governed by the strong surface plasmon resonance-generated evanescent field at the metal/dielectric interface. The greatest evanescent field amplitude at the interface and the maximum attenuation of the reflectance are observed when a nonabsorbing dielectric is employed. An absorbing dielectric decreases the evanescent field enhancement at the interface. The SPR curve of an absorbing dielectric is characterized by a greater reflectance minimum and a broader curve, as compared to those of the nonabsorbing dielectric with the same refractive index. For a weakly absorbing dielectric, such as nanometer-thick surface-confined fluorophores, the absorption is too small to induce a significant change in the SPR curve. However, the presence of a minute amount of the fluorophore can be detected by the highly sensitive SPFS. The angle with the maximum fluorescence intensity of an SPFS curve is always smaller than the resonance angle of the corresponding SPR curve. This discrepancy is due to the differences of evanescent field distributions and their decay characteristics within the metal film and the dielectric medium. The fluorescence intensity in an SPFS curve can be expressed in terms of the evanescent field amplitude. Excellent correlations between the experimentally measured fluorescence intensities and the evanescent field amplitudes are observed.

The reflectance in a surface plasmon resonance (SPR) curve can be expressed in terms of the integration of the product between the evanescent electric field and the imaginary part of the dielectric constant of all absorbing media. The evanescent field in the metal film consists of two fields, one originating at the prism/metal interface and the other at the metal/dielectric interface. Near the resonance angle, the evanescent field strength at the metal/dielectric interface is much greater than that at the prism/metal interface. The evanescent field in dielectric medium has a single origin at the metal/dielectric interface. Due to the optical enhancement at the interface, the amplitude of the evanescent electric field in the dielectric medium is much greater than that in the metal film. This field, however, is not being utilized in conventional SPR where changes in the refractive index of the nonabsorbing dielectric media are of interest. In a system with an absorbing dielectric medium, the absorption of the medium is enhanced by the strong evanescent electric field. The evanescent field distributions in the metal film and in the dielectric medium are significantly altered by the absorbing dielectric, which results in shifting of the resonance angle, increasing of the reflectance, and broadening of the SPR curve. Since the absorption contribution from the absorbing dielectric can be separated from that of the metal film via knowledge of evanescent field distribution, an in-depth analysis of the SPR curve of an absorbing medium and its relationship with the material characteristics are possible.

We report here a simple yet efficient approach for fabricating large gold nanosheets using H2O2 as the reducing agent with starch as the stabilizer and shape-controlling agent. The weak reducing capability of H2O2 enables a kinetically controlled growth of nanosheets out of flower-like nanostructures formed at the early stage. Small nanosheets with starch-bound {111} facet undergo oriented attachment and become large nanosheets having lateral size as large as 50 μm with 20–50 nm thickness. Without starch, gold quasi-microspheres with diameters of 5–10 μm become the dominant product as they also grow out of the flower-like nanostructures by filling gold atoms in the gaps between nano-petals. This starch-enable selective formation of large nanosheets is rapid and efficient as a 100% conversion could be attained even at a high concentration of gold ions (25.4 mM). A large-scale production of 2.5 g glittering gold nanosheets with a 5-L batch 10 h synthesis was demonstrated. The synthetic protocol was not only achieving atomic economy using an environmental friendly reducing reagent and renewable stabilizer, the mass-scale production prototype was accomplished at room temperature without a need for extensive waste treatment. The slightly acidic starch solution obtained after the reaction was recycled for the next synthesis or neutralized before discharging.

A novel approach for the synthesis of colloidal silver nanoprisms (AgNPrs) with controllable localized surface plasmon resonance (LSPR) via a chemical shape transformation of silver nanospheres (AgNSs) is presented. The shape conversion is carried out by feeding hydrogen peroxide (H2O2) solution into a starch-stabilized AgNS colloid under ambient conditions. Oxidative dissolution and the mild reducing action of H2O2 under alkaline conditions serve as the principal reactions for the shape transformation process. After addition of H2O2, the instantaneous shape transformation events can be visualized by the naked eye through the color change of the colloid. Initial concentration of AgNSs, molar ratio of H2O2:AgNSs, H2O2 injection rate, and mixing efficiency are the key parameters for controlling the LSPR wavelengths of AgNPrs as the in-plane dipole plasmon resonance can be selectively tuned across visible and near infrared regions (i.e., 460–850 nm). The obtained AgNPrs exhibited mixed geometries e.g. hexagonal, truncated triangular, rounded-tip triangular prisms, and circular disks with average bisector lengths of 30 to 120 nm and the thickness of 10 to 20 nm. A colloid of highly concentrated AgNPrs having a final concentration up to 11 mM can be produced within 10 min.

In this report, we propose a novel starch-mediated photochemical reduction method for synthesizing micrometer-sized gold nanoplates and the possibility of using them as a tip-enhanced Raman scattering (TERS) substrate. To reduce gold ions, a starch chain firstly forms a complex with AuCl(4)(-), and the gold ion is subsequently reduced by receiving an electron from a chloride ion and generating a chloride radical when the [AuCl(4)(-)-starch] complex is irradiated by sunlight. Due to the slow reaction rate and the capability of starch as a template, gold structure can thermodynamically grow along the (111) facet which is the lowest energy facet of the gold face-centered cubic (fcc) crystal. This method can provide various shapes of gold plates such as triangle, truncated triangle, hexagon, polygon, etc. The plate size can be controlled in the range from a few micrometers to more than one hundred micrometers by increasing the acidity of solution while the plate thickness is less than 100 nm. Potential application of the gold plates as TERS substrates is demonstrated by collecting Raman signals while approaching a silver-coated tungsten tip to the surface of the micrometer-sized gold nanoplate covered by crystal violet (CV) molecules. The results show that less than one hundred CV molecules can be detected in our study.