Spectroscopy on the wing: Naturally inspired SERS substrates for biochemical analysis

We show that naturally occurring chitinous nanostructures found on the wings of the Graphium butterfly can be used as substrates for surface‐enhanced Raman scattering when coated with a thin film of gold or silver. The substrates were found to exhibit excellent biocompatibility and sensitivity, making them ideal for protein assaying. An assay using avidin/biotin binding showed that the substrates could be used to quantify protein binding directly from changes in the surface‐enhanced Raman scattering (SERS) spectra and were sensitive over a concentration range comparable with a typical enzyme‐linked immunosorbent assays (ELISA) assay. A biomimetic version of the wing nanostructures produced using a highly reproducible, large‐scale fabrication process, yielded comparable enhancement factors and biocompatibility. The excellent biocompatibility of the wings and biomimetic substrates is unparalleled by other lithographically produced substrates, and this could pave the way for widespread application of ultrasensitive SERS‐based bioassays. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Egg‐Derived Mesoporous Carbon Microspheres as Bifunctional Oxygen Evolution and Oxygen Reduction Electrocatalysts

A bifunctional evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts are developed, based on codoped mesoporous carbon microspheres from ecofriendly biomass of eggs without the introduction of extrinsic dopants, via a facile and high‐throughput spray‐drying process. The obtained egg‐derived mesoporous carbon microspheres (egg‐CMS) present large specific surface area and high pore volume, as well as abundant dopant types including nitrogen, phosphorous, and iron that are originated from the innate protein and small organic molecule contents. When fabricated as OER or ORR catalysts, these egg‐CMS exhibit low onset potentials, high current densities, small Tafel slopes, and excellent stabilities. As a proof‐of‐concept, a rechargeable Zn‐air battery is demonstrated using the high‐active egg‐CMS as a bifunctional OER and ORR catalyst, suggesting the capability of utilizing full biomass materials for efficient energy storage and utilization.     

Elucidation of the Sodium‐Storage Mechanism in Hard Carbons

Hard carbons (HCs) are the most promising candidate anode materials for emerging Na‐ion batteries (NIBs). HCs are composed of misaligned graphene sheets with plentiful nanopores and defects, imparting a complex correlation between its structure and sodium‐storage behavior. The currently debated mechanism of Na⁺‐ion insertion in HCs hinders the development of high‐performance NIBs. In this article, ingenious and reliable strategies are used to elaborate the correlation between the structure and electrochemical performance and further illuminate the sodium‐storage mechanism in HCs. First, filling sulfur into the micropores of HCs can remove the low‐voltage plateau, providing solid evidence for its association with the pore‐filling mechanism. Along with the decreased concentration of defects/heteroatoms at higher treatment temperature, the reduced sloping capacity confirms the adsorption mechanism in the sloping region. Finally, the similar sodium‐insertion behaviors of HCs with ether‐based and ester‐based electrolytes indicate that no Na⁺ ions intercalate between the graphene layers. The determined adsorption‐pore‐filling mechanism encourages the design of more efficient HC anode materials with high capacity for high‐energy NIBs.     

Enhanced Cathodic Oxygen Reduction and Power Production of Microbial Fuel Cell Based on Noble‐Metal‐Free Electrocatalyst Derived from Metal‐Organic Frameworks

Microbial fuel cell (MFC) can generate electricity from organic substances based on anodic electrochemically active microorganisms and cathodic oxygen reduction reaction (ORR), thus exhibiting promising potential for harvesting electric energy from organic wastewater. The ORR performance is crucial to both power production efficiency and overall cost of MFC. A new type of metal‐organic‐framework‐derived electrocatalysts containing cobalt and nitrogen‐doped carbon (CoNC) is developed, which is effective to enhance activity, selectivity, and stability toward four‐electron ORR in pH‐neutral electrolyte. When glucose is used as the substrate, the maximum power density of 1665 mW m^?2 is achieved for the optimized CoNC pyrolyzed at 900 °C, which is 39.8% higher than that of 1191 mW m^?2 for commercial Pt/C catalyst in the single‐chamber MFC. The improved performance of CoNC catalyst can be attributed to large surface area, microporous nature, and the involvement of nitrogen‐coordinated cobalt species. These properties enable the efficient ORR by increasing the active sites and enhancing mass transfer of oxygen and protons at “water‐flooding” three‐phase boundary where ORR occurs. This work provides a proof‐of‐concept demonstration of a noble‐metal‐free high‐efficiency and cost‐effective ORR electrocatalyst for effective recovery of electricity from biomass materials and organic wastewater in MFC.     

Statistically quantified measurement of an Alzheimer's marker by surface‐enhanced Raman scattering

Fibrillar forms of the Amyloid‐β (Aβ) protein have been implicated in the early stages of Alzheimer's disease (AD), however there are no standardised assays for soluble Aβ oligomer biomarkers that provide the best indication of the disease progression [1,2]. As a step towards a fast and label‐free method for testing different AD biomarkers, we have combined laser nano‐textured substrates with a SERS mapping technique and validated it using soluble Aβ‐40 oligomers [3‐5]. The nano‐textured SERS substrates provide fast (&5 min), label‐free spectra associated with soluble Aβ‐40 oligomers down to a concentration of 10 nM. Statistical analysis of the spectral intensities mapped over the substrate surface shows a quantitative correlation with the oligomer concentration.

Schematics of experiments: SERS mapping of Aβ‐40 (left figure: measured SERS intensity overlayed with an SEM image of ripples) was carried out on the laser nano‐textured (ripple) surface of sapphire and statistical analysis of the SERS intensity was carried out for qualitative (a high SERS intensity at low probability) and quantitative (a moderate SERS intenisty at the highest probability) measures. Quantitative statistical analysis of SERS mapping data can be performed off line for cross correlations with other known SERS signatures.     

NiFe Layered Double Hydroxide Nanoparticles on Co,N‐Codoped Carbon Nanoframes as Efficient Bifunctional Catalysts for Rechargeable Zinc–Air Batteries

The future large‐scale deployment of rechargeable zinc–air batteries requires the development of cheap, stable, and efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this work, a highly efficient bifunctional electrocatalyst is prepared by depositing 3–5 nm NiFe layered double hydroxide (NiFe‐LDH) nanoparticles on Co,N‐codoped carbon nanoframes (Co,N‐CNF). The NiFe‐LDH/Co,N‐CNF electrocatalyst displayed an OER overpotential of 0.312 V at 10 mA cm^?2 and an ORR half‐wave potential of 0.790 V. The outstanding performance of the electrocatalyst is attributable to the high electrical conductivity and excellent ORR activity of Co,N‐CNF, together with the strong anchoring of 3–5 nm NiFe‐LDH nanoparticles, which preserves active sites. Inspired by the excellent OER and ORR performance of NiFe‐LDH/Co,N‐CNF, a prototype rechargeable zinc–air battery is developed. The battery exhibited a low discharge–charge voltage gap (1.0 V at 25 mA cm^?2) and long‐term cycling durability (over 80 h), and superior overall performance to a counterpart battery constructed using a mixture of IrO₂ and Pt/C as the cathode. The strategy developed here can easily be adapted to synthesize other bifunctional CNF‐based hybrid electrodes for ORR and OER, providing a practical route to more efficient rechargeable zinc–air batteries.     

Surface‐enhanced Raman spectroscopy for on‐site analysis: A review of recent developments

On‐site identification and quantification of chemicals is critical for promoting food safety, human health, homeland security risk assessment, and disease diagnosis. Surface‐enhanced Raman spectroscopy (SERS) has been widely considered as a promising method for on‐site analysis due to the advantages of nondestructive, abundant molecular information, and outstanding sensitivity. However, SERS for on‐site application has been restricted not only by the cost, performance, and portability of portable Raman instruments, but also by the sampling ability and signal enhancing performance of the SERS substrates. In recent years, the performance of SERS for on‐site analysis has been improved through portable Raman instruments, SERS substrates, and other combined technologies. In this review, popular commercial portable Raman spectrometers and the related technologies for on‐site analysis are compared. In addition, different types of SERS substrates for on‐site application are summarized. SERS combined with other technologies, such as electrochemical and microfluidics are also presented. The future perspective of SERS for on‐site analysis is also discussed.     

Metal‐Organic Framework‐Derived Non‐Precious Metal Nanocatalysts for Oxygen Reduction Reaction

By virtue of diverse structures and tunable properties, metal‐organic frameworks (MOFs) have presented extensive applications including gas capture, energy storage, and catalysis. Recently, synthesis of MOFs and their derived nanomaterials provide an opportunity to obtain competent oxygen reduction reaction (ORR) electrocatalysts due to their large surface area, controllable composition and pore structure. This review starts with the introduction of MOFs and current challenges of ORR, followed by the discussion of MOF‐based non‐precious metal nanocatalysts (metal‐free and metal/metal oxide‐based carbonaceous materials) and their application in ORR electrocatalysis. Current issues in MOF‐derived ORR catalysts and some corresponding strategies in terms of composition and morphology to enhance their electrocatalytic performance are highlighted. In the last section, a perspective for future development of MOFs and their derivatives as catalysts for ORR is discussed.     

Cu,Co‐Embedded N‐Enriched Mesoporous Carbon for Efficient Oxygen Reduction and Hydrogen Evolution Reactions

Rational synthesis of hybrid, earth‐abundant materials with efficient electrocatalytic functionalities are critical for sustainable energy applications. Copper is theoretically proposed to exhibit high reduction capability close to Pt, but its high diffusion behavior at elevated fabrication temperatures limits its homogeneous incorporation with carbon. Here, a Cu, Co‐embedded nitrogen‐enriched mesoporous carbon framework (CuCo@NC) is developed using, a facile Cu‐confined thermal conversion strategy of zeolitic imidazolate frameworks (ZIF‐67) pre‐grown on Cu(OH)₂ nanowires. Cu ions formed below 450 °C are homogeneously confined within the pores of ZIF‐67 to avoid self‐aggregation, while the existence of Cu? N bonds further increases the nitrogen content in carbon frameworks derived from ZIF‐67 at higher pyrolysis temperatures. This CuCo@NC electrocatalyst provides abundant active sites, high nitrogen doping, strong synergetic coupling, and improved mass transfer, thus significantly boosting electrocatalytic performances in oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). A high half‐wave potential (0.884 V vs reversible hydrogen potential, RHE) and a large diffusion‐limited current density are achieved for ORR, comparable to or exceeding the best reported earth‐abundant ORR electrocatalysts. In addition, a low overpotential (145 mV vs RHE) at 10 mA cm^?2 is demonstrated for HER, further suggesting its great potential as an efficient electrocatalyst for sustainable energy applications.     

Defective Carbon–CoP Nanoparticles Hybrids with Interfacial Charges Polarization for Efficient Bifunctional Oxygen Electrocatalysis

The development of efficient catalysts for both oxygen reduction and evolution reactions (oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)) is central to regenerative fuel cells and rechargeable metal–air batteries. It is highly desirable to achieve the efficient integration of dual active components into the catalysts and to understand the interaction between the dual components. Here, a facile approach is demonstrated to construct defective carbon–CoP nanoparticle hybrids as bifunctional oxygen electrocatalysts, and further probe the interfacial charge distribution behavior. By combining multiple synchrotron‐based X‐ray spectroscopic characterizations with density functional theory calculations, the interfacial charge polarization with the electrons gathering at the defective carbon surface and the holes gathering at the CoP surface due to strong interfacial coupling is revealed, which simultaneously facilitates the ORR and OER with remarkable bifunctional oxygen electrode activities. This work not only offers a bifunctional oxygen catalyst with outstanding performance, but also unravels the promoting factor of the hybrids from the view of interfacial charge distribution.     

Apically Dominant Mechanism for Improving Catalytic Activities of N‐Doped Carbon Nanotube Arrays in Rechargeable Zinc–Air Battery

The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in zinc–air batteries (ZABs) require highly efficient, cost‐effective, and stable electrocatalysts as alternatives to high cost and low poison resistant platinum group metals (PGM) catalysts. Although nitrogen‐doped carbon nanotube (NCNT) arrays are now capable of catalyzing ORR efficiently, their hydrophobic surface and base‐growth mode are found to limit the catalytic performance in the practical ZABs. Here, the concept of an apically dominant mechanism in improving the catalytic performance of NCNT by precisely encapsulating CoNi nanoparticles (NPs) within the apical domain of NCNT on the Ni foam (denoted as CoNi@NCNT/NF) is demonstrated. The CoNi@NCNT/NF exhibits a more excellent catalytic performance toward both ORR and OER than that of traditional NCNT derived from the base‐growth method. The ZAB coin cell using CoNi@NCNT/NF as an air electrode shows a peak power density of 127 mW cm^?2 with an energy density of 845 Wh kg_Zn^?1 and rechargeability over 90 h, which outperforms the performance of PGM catalysts. Density functional theory calculations reveal that the ORR catalytic performance of the CoNi@NCNT/NF is mainly attributed to the synergetic contributions from NCNT and the apical active sites on NCNT near to CoNi NPs.     

Highly sensitive fluorescence and SERS detection of azide through a simple click reaction of 8‐chloroquinoline and phenylacetylene

In 0.19 mol/L acetic acid (HAc), a click reaction of 8‐chloroquinoline/azide/phenylacetylene take places in aqueous solution without Cu(I) as a catalyst. 8‐Chloroquinoline (CQN) exhibited a strong fluorescence peak at 430 nm that was quenched linearly as the concentration of azide increased from 20 to 1000 ng/mL. This quenching was due to consumption of CQN in the click reaction and a decrease in the number of efficiently excited photons due to the presence of triazole–quinoline ramification molecules with strong hydrophobicity. Using blue nanosilver sol as the substrate, CQN absorbed onto the surface of nanosilver particles, showing a strong surface‐enhanced Raman scattering (SERS) peak at 1585 cm^‐1 that decreased linearly as the azide concentration increased from 8 to 500 ng/mL; the detection limit was 4 ng/mL. Thus, two new, simple and sensitive fluorescence and SERS methods have been developed for the determination of azide via the click reaction. Copyright © 2014 John Wiley & Sons, Ltd.     

Sandwich‐Like Reduced Graphene Oxide/Carbon Black/Amorphous Cobalt Borate Nanocomposites as Bifunctional Cathode Electrocatalyst in Rechargeable Zinc‐Air Batteries

The inhibitively high cost of the noble‐metal‐containing materials has become a major obstacle for the large‐scale application of rechargeable zinc‐air batteries (ZABs). To solve this problem in a practical way, a green and scalable method to prepare sandwich‐like reduced graphene oxide /carbon black/amorphous cobalt borate nanocomposites (rGO/CB/Co‐B_i) is reported. These composites are shown to be a highly efficient and robust bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this system, the spontaneous assembly of the GO sheet and CB nanoparticles is demonstrated by noncovalent interactions to build the sandwich‐like structure with hierarchical pore distribution. The impressive ORR and OER activities of the obtained nanocomposite are attributed to the high conductivity, large surface area, and the hierarchically porous channels. With room‐temperature synthesis and significant activities shown in the demonstrative battery test, the prepared nanocomposite can potentially serve as an alternative for noble‐metal‐based rechargeable ZAB cathode materials.     

A new silver nanochain SERS analytical platform to detect trace hexametaphosphate with a rhodamine S molecular probe

Using AgNO₃ as the precursor, stable silver nanochain (AgNC) sols, orange‐red in color, were prepared using hydrazine hydrate. A strong surface plasmon resonance Rayleigh scattering (RRS) peak occurred at 420 nm plus two surface plasmon resonance (SPR) absorption peaks at 410 nm and 510 nm. Rhodamine S (RhS) cationic dye was absorbed on the as‐prepared AgNC substrate to obtain a RhS–AgNC surface‐enhanced Raman scattering (SERS) nanoprobe that exhibited a strong SERS peak at 1506 cm^–1 and a strong RRS peak at 375 nm. Upon addition of the analyte sodium hexametaphosphate (HP), it reacted with RhS, which resulted in a decrease in the SERS and RRS peaks that was studied in detail. The decreased SERS and RRS intensities correlated linearly with HP concentration in the range of 0.0125–0.3 µmol/L and 0.05–1.0 µmol/L, with a detection limit of 6 nmol/L and 20 nmol/L HP respectively. Due to advantages of high sensitivity, good selectivity and simple operation, the RhS molecular probes were used to determine HP concentration in real samples. Copyright © 2015 John Wiley & Sons, Ltd.     

A simple gold nanoplasmonic SERS method for trace Hg2+ based on aptamer‐regulating graphene oxide catalysis

The as‐prepared graphene oxide (GO) exhibited a strong catalytic effect on reduction of HAuCl₄ by trisodium citrate to form gold nanoplasmons (AuNPs) with a strong surface‐enhanced Raman scattering (SERS) effect at 1615 cm^?1 in the presence of molecular probe Victoria blue 4R (VB4r). SERS intensity increased with nanocatalyst GO concentration due to the formation of more AuNP substrates. The aptamer (Apt) of Hg²⁺ can bind to GO to form Apt–GO complexes, which can strongly inhibit nanocatalysis. When target Hg²⁺ is present, the formed stable Hg²⁺–Apt complexes are separated from the GO surface, which leads to GO catalysis recovery. The enhanced SERS signal was linear to Hg²⁺ concentration in the range 0.25–10 nmol/L, with a detection limit of 0.08 nmol/L Hg²⁺. Thus, a new gold nanoplasmon molecular spectral analysis platform was established for detecting Hg²⁺, based on Apt regulation of GO nanocatalysis.     

A sensitive SERS quantitative analysis method for Ni2+ by the dimethylglyoxime reaction regulating a graphene oxide nanoribbon catalytic gold nanoreaction

The nanogold reaction between HAuCl₄ and trisodium citrate (TCA) proceeded very slowly at 60°C in a water bath. The as‐prepared graphene oxide nanoribbons (GONRs) exhibited strong catalysis during the reaction to form gold nanoparticles (Au NPs) and appeared as a strong surface‐enhanced Raman scattering (SERS) peak at 1616 cm^?1 in the presence of the molecular probe Victoria blue 4R (VB4r). With increase in GONR concentration, the SERS peak increased due to increased formation of Au NPs. Upon addition of dimethylglyoxime (DMG) ligand, which was adsorbed onto the GONR surface to inhibit GONR catalysis, the SERS peak decreased. When Ni²⁺ was added, a coordination reaction between DMG and Ni²⁺ took place to form stable complexes of [Ni (DMG)₂]²⁺ and the release of free GONR catalyst that resulted in the SERS peak increasing linearly. A SERS quantitative analysis method for Ni²⁺ was therefore established, with a linear range of 0.07–2.8 μM, and a detection limit of 0.036 μM Ni²⁺.     

Structural properties of bombesin-like peptides revealed by surface-enhanced Raman scattering on roughened silver electrodes

This work presents a Fourier-transform absorption infrared, Fourier-transform Raman, and surface-enhanced Raman scattering (SERS) study of the following peptides belonging to the bombesin-like family: phyllolitorin, [Leu(8)]phyllolitorin, NMB, NMC, and PG-L. The SERS study was undertaken to understand the adsorption mechanism of bombesin-like peptides on an electrochemically roughened silver electrode surface and to show changes in the adsorption mechanism with alterations in amino acids and small tertiary structures. The SERS spectra presented here shows bands mainly associated with the Trp(8) residue vibrations. The presence of mainly pyrrole coring vibrations for phyllolitorin and [Leu(8)]phyllolitorin and mainly benzene coring modes for NMB and NMC indicated that these groups interact with the roughened silver electrode surface. Furthermore, N(1)--C(8) and C(3)--C(9) bonds of the PG-L indole ring seemed to have nearly a vertical orientation on the electrode surface. In addition, distinct vibrations of the C--S fragment were observed in the SERS spectra of [Leu(8)]phyllolitorin and PG-L. The strong enhancement of the nu(C==O) vibration in the [Leu(8)]phyllolitorin SERS spectrum yielded evidence that the intact C==O bond(s) bind strongly to the silver electrode surface, whereas NMC, phyllolitorin, and NMB were located near the silver surface. This finding was supported by the presence of the nu(C--C(==O)) mode. The amide I band observed at 1642 and 1634 cm(-1) for NMB and NMC, respectively, and the Raman amide III band seen in the 1282-1249 cm(-1) range for all peptides except PG-L, indicate that the strongly hydrogen-bonded alpha-helical conformation and random-coil structure are favored for binding to the surface. (c) 2008 Wiley Periodicals, Inc. Biopolymers 89: 980-992, 2008.This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com.     

Efficient Oxygen Reduction Catalysts of Porous Carbon Nanostructures Decorated with Transition Metal Species

Developing substitutes of noble metal catalysts toward oxygen reduction reaction (ORR) at the cathode is of vital importance for promoting low‐temperature polymer electrolyte membrane fuel cells. Transition metal species have been one of the hot areas of interest due to their low cost, high activity, and long‐term stability. The design of porous carbon nanostructures decorated with transition metal species plays a vital role in enhancing ORR catalytic performance. Here, the recent breakthroughs in porous carbon nanostructures decorated with transition metal species (including nanoparticles and atomically dispersed supported metal) are discussed. The porous nanostructures can provide large surface area as well as abundant pore channels, leading to sufficient exposure of active sites and efficient mass transfer. These nanostructures can be synthesized by several approaches, including the templated method, the self‐templated method, the impregnation process, and so on. Furthermore, the ORR performance and the exploration of active sites are also discussed for further enhancement of the ORR catalysts. Finally, the challenges and prospects are discussed, which would push forward the development of ORR catalysts in the near future.     

Silver Nanoparticle Arrays on a DVD-Derived Template: An easy&cheap SERS Substrate

Commercially available digital versatile discs (DVDs) contain a silver-coated spiral distribution of rectangular-shaped grooves (AgDVD): for the first time, they have been used to produce surface-enhanced Raman scattering (SERS) substrates by electrochemical deposition of silver nanoparticles (AgNPs@AgDVD). The overall procedure only requires cheap and widely available materials and can be easily accomplished. Scanning electron microscopy images of AgNPs@AgDVD revealed that small AgNPs (average diameter about 15 nm) are present within the valleys of AgDVD, whereas over the ridges, the AgNPs are bigger, more densely packed and with a dendrite-like morphology somewhere. The SERS properties of these substrates have been studied in terms of the enhancement factor (EF), point-to-point reproducibility and sample-to-sample repeatability. It turned out that high SERS EF and good reproducibility requirements are both fulfilled. As for repeatability, remarkably better results than typical literature values have been achieved. Such an easy&cheap preparation along with efficient SERS properties make DVD-derived SERS substrates very good candidates for the development of convenient and disposable sensing platforms.     

Corrugation Architecture Enabled Ultraflexible Wafer‐Scale High‐Efficiency Monocrystalline Silicon Solar Cell

Advanced classes of modern application require new generation of versatile solar cells showcasing extreme mechanical resilience, large‐scale, low cost, and excellent power conversion efficiency. Conventional crystalline silicon‐based solar cells offer one of the most highly efficient power sources, but a key challenge remains to attain mechanical resilience while preserving electrical performance. A complementary metal oxide semiconductor‐based integration strategy where corrugation architecture enables ultraflexible and low‐cost solar cell modules from bulk monocrystalline large‐scale (127 × 127 cm²) silicon solar wafers with a 17% power conversion efficiency. This periodic corrugated array benefits from an interchangeable solar cell segmentation scheme which preserves the active silicon thickness of 240 µm and achieves flexibility via interdigitated back contacts. These cells can reversibly withstand high mechanical stress and can be deformed to zigzag and bifacial modules. These corrugation silicon‐based solar cells offer ultraflexibility with high stability over 1000 bending cycles including convex and concave bending to broaden the application spectrum. Finally, the smallest bending radius of curvature lower than 140 µm of the back contacts is shown that carries the solar cells segments.