High Enhancement Factor Research Articles

PVP-capped silver nanoparticles for efficient SERS detection of adenine based on the stabilizing and enrichment roles of PVP.

Apolyvinylpyrrolidone-capped (PVP-capped) strategy is reportedto synthesize Ag NPs on silicon wafers via galvanic replacement reaction for SERS detection of adenine, where PVP acts as stabilizing agent in synthesis and efficient enrichment in detection. The morphologies of Ag NPs are optimized with uniform particle size by adjusting synthesis conditions, which hold excellent SERS performances like a high enhancement factor of 1.42 × 106, good uniform, reproducibility, and transferable nature. With the protection of the capped PVP, the Ag NPs keep excellent SERS properties even against harsh conditions of high temperature (100 ℃) and strong acid and base for 24h. Utilizing the structural feature of PVP with abundant carbonyl groups, the PVP-capped Ag NPs achieve efficient enrichment of adenine through hydrogen bonding and π-interactions, which is analyzed by density functional theory. Quantitative detection of adenine is performed with a wide linear range from 10-4 to 10-8M and a low limit of detection of 1nM. Detection of adenine in human urine samples is achieved with a recovery of 99.1-103.4% and an RSD of less than 5%.

Two-dimensional silver nanonetwork on Ag4Ti5O12 film as highly efficient SERS substrate

Surface Enhanced Raman Spectroscopy (SERS) is a powerful technique to study and detect single molecules adsorbed onto a surface. In this work, molar concentrations were varied over three consecutive orders of magnitude (10-3 M, 10-6 M, 10-9 M) of Methylene Blue (MB) to study SERS on different thicknesses of silver (6, 8, 10, 12 nm) coated on Ag4Ti5O12 deposited onto glass substrates as the base material. The Ag4Ti5O12 thin films were prepared by a unique ion-exchange method where Li4Ti5O12 thin films were initially deposited by the sol–gel method followed by the exchange of Li+ ion with Ag+ ion. The varied thicknesses of thermally deposited Ag-thin films were grown with unaltered Ag+ ions nucleation sites atop the Ag4Ti5O12 layer to create the two-dimensional (2D) nanonetwork. The structure and morphology of the as-prepared thin-film samples were characterized using X-ray diffraction, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) techniques. The SERS enhancement factor (EF), calculated using Raman spectroscopy, showed the systematic changes in the Raman signal enhancement as a function of Ag-thickness. The 10 nm thick as-deposited Ag sample showed the highest signal enhancement in Raman spectra than the other Ag thickness films. The successive signal enhancement was obtained due to forming the critical nuclei size of Ag on top of Ag4Ti5O12, which was further bolstered with film surface roughness and surface energy measurements. The as-prepared Ag-10 nm sample showed the lowest film roughness of ∼2.07 nm, in tune with the maximum enhancement factor (EF). We believe this work could open wide opportunities for developing efficient SERS substrates with sensing capabilities for ultra-low analyte concentration coupled with low cost and high enhancement factors.

A novel core-shell heterostructure of zinc oxide/metal-organic frameworks anchored silver nanoparticles for enhanced SERS and photocatalytic performance

Here, a novel well-ordered ZnO rod-flower/zeolitic imidazolate framework-M (ZIF-M, using 5-mercapto-1-methyltetrazole as ligand) core-shell heterostructure (Al/ZnO/ZIF-M, AZZ*) is induced by aluminum (Al) sheet. Subsequently, Ag nanoparticles (AgNPs) are tightly attached to the ZIF-M layer in AZZ* through the strong Ag-N and Ag-S bonds, and a portable bifunctional substrate of Al/ZnO/ZIF-M/Ag (AZZ*Ag) is constructed. The finite difference time domain (FDTD) analysis shows that the AZZ*Ag substrate generates the stronger electromagnetic field intensity than the AZAg. Also, there is a strong synergistic effect among Al, ZnO, ZIF-M and Ag which can effectively facilitate the electron transfer. Importantly, the AZZ*Ag substrate exhibits outstanding SERS response with high sensitivity and selectivity for crystal violet (CV) molecules. The low detection limit (LOD) of CV molecule is 2.81 × 10−11 mol·L−1 with high analysis enhancement factor (AEF) of 1.93 × 106. In addition, AZZ*Ag substrate shows good photocatalytic performance for CV molecules with high degradation efficiency of 97.35% within 105 min, which is 4.72 times that of AZAg. Importantly, the SERS and photocatalytic performance of AZZ*Ag are 4.4 times and 3.09 times those of the Al/ZnO/ZIF-8/Ag (AZZ#Ag, using 2-methylimidazole as ligand), respectively. Moreover, the AZZ*Ag substrate displays excellent stability, good reproducibility, recyclability and uniformity. Thus, the designed portable bifunctional composite exhibits great potential for SERS detection and photocatalytic degradation of other pollutants in environmental wastewater.

The Effect of Nanoparticle Composition on the Surface-Enhanced Raman Scattering Performance of Plasmonic DNA Origami Nanoantennas.

A versatile generation of plasmonic nanoparticle dimers for surface-enhanced Raman scattering (SERS) is presented by combining a DNA origami nanofork and spherical and nonspherical Au or Ag nanoparticles. Combining different nanoparticle species with a DNA origami nanofork to form DNA origami nanoantennas (DONAs), the plasmonic nanoparticle dimers can be optimized for a specific excitation wavelength in SERS. The preparation of such nanoparticle dimers is robust enough to enable the characterization of SERS intensities and SERS enhancement factors of dye-modified DONAs on a single dimer level by measuring in total several thousands of dimers from five different dimer designs, each functionalized with three different Raman reporter molecules and measured at four different excitation wavelengths. Based on these data, SERS enhancement factor (EF) distributions have been determined for each dimer design and excitation wavelengths. The structures and measurement conditions with the highest EFs are suitable for single-molecule SERS (SM-SERS), which is realized by placing single dye molecules into hot spots. We demonstrate that the probability of placing single molecules in a strongly enhancing hot spot for SM-SERS can be increased by using anisotropic nanoparticles with several sharp edges, such as nanoflowers. Combining a Ag nanoparticle with a Au particle in one dimer structure allows for a broadband excitation covering almost the whole visible range. The most versatile plasmonic dimer structure for SERS combines a spherical Ag nanoparticle with a Au nanoflower. Employing the discontinuous Galerkin time domain method, we numerically investigate the bare, symmetric dimers with respect to spectral and near-field properties, showing that, indeed, the nanoflowers induce multiple hot spots located at the edges which surpass the intensity of the spherical dimers, indicating the possibility for SM-SERS. The presented DONA structures and SERS data provide a robust basis for applying such designs as versatile SERS tags and as substrates for SM-SERS measurements.

A sonochemical approach for a silver particle layer SERS substrates preparation and subsequent application in qualitative analysis

We present an easy and efficient method for silver particle layer SERS substrate preparation that combines a modified Tollens’ approach with using ultrasound to obtain unique reaction conditions by generating high-energy hot-spots as the arising acoustic cavities implode. The silver layers were deposited on various substrates in a one-step reduction process of silver nitrate. Three different reductants (maltose, glucose, ascorbic acid) were used to obtain silver particle layers with different particle sizes, morphologies, and inter-particle distances. To further optimize the properties of the silver particles for SERS and to provide higher signal enhancement, all the prepared nanoparticle layers were activated in 4 M Cl− solution. The size of silver particles was in most samples under 100 nm and the particles formed clusters, but they were also present on the surface individually. In some of the activated substrates, bigger particles (0.5–1 μm) occur as well. The activated as well as non-activated substrates were tested as SERS substrates using 10−5 M adenine as a model analyte. Laser wavelengths of 455 nm, 532 nm, 633 nm, 780 nm, and 785 nm were used for the SERS measurements. High enhancement factors up to 3.5·105 and 2.8·105 were obtained for SERS measurements using lasers of 532 nm and 780 nm, respectively.

Facile synthesis of spherical covalent organic frameworks for enrichment and quantification of aryl organophosphate esters in mouse serum and tissues.

Here, an imine-linked-based spherical covalent organic framework (COF) was prepared at room temperature. The as-synthesized spherical COF served as an adsorbent in dispersive solid-phase extraction (dSPE), by its virtue of great surface area (1542.68 m2 /g), regular distribution of pore size (2.95nm), and excellent stability. Therefore, a simple and high-efficiency dispersive solid phase extraction method based on a spherical COF coupled with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established to determine aryl organophosphate esters in biological samples. This approach displayed favorable linearity in the range of 10.0-1000.0ng/L (r>0.9989), a high signal enhancement factor (58.8-181.8 folds) with low limits of detection (0.3-3.3ng/L). Moreover, it could effectively eliminate complex matrix interference to accurately extract seven aryl organophosphate esters from mouse serum and tissue samples with spiked recoveries of 82.0%-117.4%. The as-synthesized spherical COF has been successfully applied in sample preparation. The dSPE-HPLC-MS/MS method based on a spherical COF has potential application to study the pollutants' metabolism in vivo.

Plasma-Made Nanogold for DNA Sensing with SERS

Facilitated electrochemical properties of plasma are crucial for improving functional nanomaterials synthesis and design for novel sensor development. Controlled customization and functionality tailoring at multiscale is the targeted challenge for better detection devices performance. In the modern era of optoelectronics, among various probing approaches, plasmonic sensing accompanied by Raman, FTIR or Fluorescent spectroscopy is considered a tool for the efficient investigation of molecular properties. In particular, Raman scattering is often called SERS (surface-enhanced Raman scattering) due to plasmonic enhancers, which are used to improve the probing of analytes at a reduced scale. This feature is extremely useful for biologically relevant analytical tasks when samples alike DNA and similar need to be investigated fast and accurately. DNA/RNA-related investigations are highly important in modern nanomedicine due to the solid progress of bionanotechnology, DNA vaccines, and functional gene engineering. DNA is the most valued substance for microbiologists because it contains information about bio-species' nature.[1] Currently, the number of molecular-sensitive methods for DNA-level study is quite limited, among which PCR (polymer chain reaction) related methods dominate the field. However, it is challenging to investigate it with optical techniques like SERS. Despite being promising, SERS is still under technological and analytical improvement. Better performance comes with sophisticated plasmonic nanomaterials, which provide considerably improved photon scattering due to the strongly localized field confinement effect.[2] In the current report, a well-performing nanoplasmonic sensor was designed using a plasma-driven electrochemical reduction mechanism. Exploiting atmospheric pressure He-plasma jet setup operating kHz frequency, the reactive oxidative species donated electrons via liquid-gas electrochemistry towards the Ar-delivered Au(3+)-containing microdroplets. Through this method, microscaled aggregates composed of AuNPs were obtained from the nebulized ionic gold liquid precursor. Due to the strong coupling between nanoparticles, a high analytical enhancement factor of about 107 was achieved and the substrate allowed to obtain Raman fingerprints of bacterial DNA fragments (M. luteus and S. aureus, E. coli, J. lividum) at nanovolume sample quantities. In addition, main DNA molecular vibrational signatures associated with nucleobase motions were extracted from spectra collected and used to classify the bacterial strains reliably by employing statistical principal component analysis.

Graphene nanospacer layer modulated multilayer composite structures of precious metals and their SERS performance.

Graphene(G)-noble metal-ZnO hybrid systems were developed as highly sensitive and recyclable surface enhanced Raman scattering (SERS) platforms, in which ultrathin graphene of varying thickness was embedded between two metallic layers on top of a ZnO layer. Due to the multi-dimensional plasmonic coupling effect, the Au/G/Ag@ZnO multilayer structure possessed ultrahigh sensitivity with the detection limit of Rhodamine 6 G (R6G) as low as 1.0×10-13 mol/L and a high enhancement factor of 5.68×107. Both experimental and simulation results showed that graphene films could significantly regulate the interlayer plasmon resonance coupling strength, and single-layer graphene had the best interlayer regulation effect. Additionally, the SERS substrate structure prepared through physical methods exhibited high uniformity, the graphene component of the substrate possessed excellent molecular enrichment ability and silver oxidation inhibition characteristics, resulting in a substrate with high stability and exceptional reproducibility. The signal change was less than 15%. Simultaneously, due to the excellent photocatalytic performance of the low-cost and wide-band-gap semiconductor material ZnO, the SERS substrate exhibited exceptional reusability. Even after five cycles of adsorption-desorption, the SERS performance remained stable and maintained a reliable detection limit. The study introduced a novel approach to creating multilayer composite SERS substrates that exhibited exceptional performance, offering a new analytical tool with high sensitivity, stability, and reusability.

A core-molecule-shell Au@PATP@Ag nanorod for nicotine detection based on surface-enhanced Raman scattering technology

Nicotine is an addictive substance often found in tobacco and cigarette smoke and excessive exposure to it can cause various diseases. Herein, core-molecule-shell gold/4-aminothiophenol/silver nanorods (Au@PATP@Ag NRs) were prepared for quantitative detection of nicotine by using surface-enhanced Raman scattering (SERS) technology. The obtained Au@PATP@Ag NRs showed an outstanding SERS effect due to the plasticity of their morphology and the bimetallic synergistic effect between the excellent stability of Au and the highly enhanced effect of Ag. The Au@PATP@Ag NRs substrate exhibited an extremely high enhancement factor (EF) of 2.17 × 107. In addition, in-situ synthesized PATP was used as an internal standard to correct signal fluctuation and improve the reliability of quantitative nicotine detection. A wide linear dynamic range from 10−8 to 10−3 M was obtained and an ultra-low limit of detection (LOD) was about 3.12 × 10−9 M, which was superior to most of previously reported methods. This work has also been used for determining nicotine content in cigarettes and simulated environmental tobacco smoke by using a portable device. These results indicated that the developed SERS method had many potential applications in the quantitative determination of nicotine in real tobacco samples.

Fabrication of flexible multidimensional CC/MoS2@Ag@PDMS hybrids as stable and self-cleaning SERS substrate for sensitive and quantitative point-of-care testing

Flexible surface-enhanced Raman scattering (SERS) sensors are ideal for point-of-care testing (POCT) of hazardous materials. The key to practical applications lies in their quantitative detection capabilities and high stability for cycle use. In this study, we propose a simple method to develop a recoverable CC/MoS2@Ag@PDMS composite SERS substrate using chemical vapor deposition (CVD) technology. This flexible SERS substrate, utilizing 4-aminothiophenol (4-ATP) as the detection molecule, demonstrated a high enhancement factor (∼ 107) and a low detection limit (10−12 M). The corrected linearity problem achieved good linear correlation (R2 = 0.997) by using the intrinsic Raman signal from the polydimethylsiloxane (PDMS) substrate. The results of theoretical calculations illustrate this excellent SERS performance by a combination of electromagnetic and chemical enhancements. In addition, in the presence of MoS2, the substrate demonstrated excellent self-cleaning cycle detection and maintained high SERS activity through more than 100 mechanical deformations of bending and twisting. In situ detection was performed for tetramethylthiuram disulfide (TMTD), ampicillin (AMP), and ciprofloxacin (CI) with detection limits of 10−9 M. These promising detection results suggest that this highly stable and flexible substrate can be used for POCT and environmental safety by simply wiping objects to obtain contaminant samples.

Manifold enhancement in the near-field and SERS efficiency of all-sputter grown Ag-nanoparticles on Al-film based mirror structures

Gap mode plasmonic coupling of noble metal nanoparticles with metal films makes them ideal candidates for manifold improvement in the surface-enhanced Raman scattering (SERS) efficacy via strong near-field enhancement in their gap realized by deposition of sandwiched dielectric spacer layers. This report presents an all-sputtering grown SERS substrate based on gap mode plasmonic coupling of Ag-NPs with Al films separated with thin dielectric overlayers of AlOx or polytetrafluoroethylene (PTFE). A remarkably high Analytical enhancement factor (as high as 3.7 × 109) with manifold SERS enhancement (as high as 26 times) is obtained with a limit of detection up to 10−13 M concentration of CV dye. Growth of thin dielectric over layer remains conformal on randomly orientated hillocks-like Al nanocrystallites (NCs) on Si substrates. Reflection studies show the broadband absorption of gap plasmon mode coupled Ag nanoparticles (NPs) and Al films. An optical model constructed using generalized oscillator model with the help of Lorentz and Tauc-Lorentz oscillators which reveals the localized surface plasmon resonance (LSPR) of Ag-NPs is strongly enhanced after gap mode plasmonic coupling (GMPC) in Ag-NPs and Al film based nanoparticles-on-mirror (NPoM) system. Finite difference time domain (FDTD) simulations validate the experimental findings that NPoM structure results in GMPC between Ag-NPs and underlying Al films. This study paves a way towards NPoM-based manifold enhancement in SERS-based detection efficacy of ultralow concentration of complex molecules.

Flexible silver-nanoparticles/PMMA SERS substrate derived from nanotips-equipped chemically patterned ferroelectric crystals for detecting antibiotics on irregular surfaces

Development of flexible and transparent detection platforms using surface-enhanced Raman spectroscopy has emerged as an intense research field due to the demand for in-situ, real-time analysis. Herein, we present the fabrication of soft and ultra-thin substrates composed of silver nanoparticles that are photoreduced on nanotips-equipped ferroelectric templates and then transferred to the poly(methyl methacrylate) film for ultrasensitive detection of antibiotics, nitrofurantoin and nifuroxazide. Compared with the conventional ferroelectric templates, the utilization of nanotips-equipped ferroelectric template boosts the effective mass transfer of dense silver nanoparticles to the polymeric film, which can effectively enhance the Raman performance through the electromagnetic mechanism. The produced substrate shows excellent performance for the detection of antibiotics, including ultra-low limit of detection in the order of 10−12 M, high enhancement factor about 1010, excellent sensitivity, superior reproducibility and uniformity. Besides, the quantitative multiplex detection of nitrofurantoin and nifuroxazide is demonstrated to discriminate the five-order concentration difference. The practicality of the developed substrate is proved by the detection of nitrofurantoin and nifuroxazide on fish surfaces by utilizing the fiber-coupled Raman probe with the limit of detection of 2.08 × 10−10 M and 1.25 × 10−9 M The proposed detection strategy can be applied to perform the in-situ, real-time analysis for the identification of antibiotics in environmental samples.

Ag microlabyrinth/nanoparticles coated large-area thin PDMS films as flexible and transparent SERS substrates for in situ detection

Flexible and transparent surface-enhanced Raman scattering (SERS) substrates haveattractedmuchattention as a fast, sensitive and in situ detection platform for practical applications. However, the large-area fabrication of flexible and transparent SERS substrates with high performance is still challenging. Here, a flexible and transparent SERS substrate based on large-area thin PDMS film decorated with Ag microlabyrinth/nanoparticles hierarchical structures (denoted as ALNHS@PDMS) is fabricated by using the floating-on-water method and magnetron sputtering technology. By optimizing the sputtering time, the ALNHS with multiple hot spots are uniformly distributed on the PDMS surface. Based on characterizing the rhodamine 6G (R6G) with a portable Raman spectrometer, the optimal ALNHS@PDMS film exhibits a high enhancement factor (5.2 × 106), excellent uniformity and reproducibility, as well as superior mechanical stability. In addition, thanks to the good sticky feature and bi-directional activation property of the thin ALNHS@PDMS film, the prepared flexible and transparent SERS substrate can achieve in situ detection of malachite green residues (10-6 M) on apple and tomato skins. This large-area, thin, mechanically robust, flexible and transparent ALNHS@PDMS film, integrated with a portable Raman spectrometer, shows great potential for point-of-care testing (POCT)in practical applications.

Colorimetric and surface-enhanced Raman scattering method for vanillin detection based on two types of reduced silver nanoparticles

It’s the first time we found that vanillin and 3,3′,5,5′-tetramethylbenzidine (TMB) can reduce Tollens’ reagent to different types of Ag nanoparticles (Ag NPs) because of their different reducibility. Vanillin reduced the Tollens’ reagent to small size of Ag NPs (Ag45 NPs) which was colorless and has the maxmium absorption at 350 nm, while pink large Ag NPs (Ag100 NPs) with the maxmium absorption at 490 nm was reduced by TMB. Based on different types of AgNPs reduced by vanillin and TMB, dual-mode detection of vanillin by colorimetry and surface-enhanced Raman scattering (SERS) was designed. The solution changed from pink to colorless with the increasing concentration of vanillin (within 3 min). On the other hand, the reduced Ag45 NPs shows a high SERS enhancement factor, which can be applied for ultra-sensitive detection of vanillin in situ. The SERS had a low detection limit of 25.8 pM, which was 5-orders lower than the colorimetric method and most previously reported methods. Importantly, It avoids the additional procedures to prepare SERS-active substrates and can be used to discriminate vanillin from ethylvanillin, both of which are very difficult to be distinguished because of their much highly similar structure and property. Therefore, the visual, fast and high-sensitive dual-mode strategy has great potential in food safety assessment.

Asymmetric L-shaped resonant optical antennas with plasmon length tuning and high-electric field enhancement

L-shaped resonant optical antennas (ROAs) are low-symmetry plasmonic nanostructures with the unique ability to show two tunable resonances in the optical and near-infrared wavelength regions. The plasmon length of the so-called longitudinal dipolar fundamental plasmon mode of these asymmetric L-shaped ROAs can be used as plasmon resonance building blocks to design polarization-sensitive devices. This paper introduces and numerically analyzes a novel design of asymmetric L-shape ROAs. The reported design offers two resonance modes, i.e., bimodal longitudinal antenna resonance behavior with a high enhancement factor. These two resonances can be selectively excited by changing the linear polarization angle. It is found that the coupled L-shaped ROA with a very small 2 nm gap width exhibits field enhancements 40 and 147.3 on scale left|{E}_{TOT}right|/left|{E}_{IN}right| for the high energy and low energy resonance, respectively. The obtained results and the analysis open a new route for multiple plasmon resonance devices with ultra-high field enhancement that can be easily integrated with future nano-optical circuits with multiple operational frequencies.

Preparation and SERS performance of gold nanoparticles-decorated patterned silicon substrate

Noble metal nanoparticles (NPs) are frequently utilized in surface-enhanced Raman scattering (SERS) due to their localized surface plasmon resonance (LSPR) effect, whose preparation in high density and suitable size is a prerequisite for high enhancement factors and homogeneity of SERS substrates. Here, a method combining femtosecond (fs) laser direct writing silicon with solid-state dewetting of Au nanofilm was proposed. Patterned silicon with nanostructures modulates the solid-state dewetting of Au nanofilm deposited on its surface by structural curvature, resulting in the formation of patterned silicon decorated with Au-NPs (Au-NPs/PSi). The Au-NPs formed on the patterned silicon are denser and have a 72 nm average diameter better suited to SERS compared to the flat silicon. By the simulation of finite-difference time-domain (FDTD) method, we found the significantly enhanced local electric field in the nanogaps between Au-NPs and between Au-NPs and silicon. Furthermore, the substrate shows excellent SERS ability in detecting R6G molecules, with detection limit as low as 10−10 M and an enhancement factor (EF) of 2.68 × 107. The results indicate that Au-NPs/PSi substrate is a promising candidate for obtaining reliable and high-quality SERS, promoting the application of SERS in trace molecules detection in solution.

Tubular Diamond as an Efficient Electron Field Emitter

Herein, we present a straightforward and cost-effective procedure for producing conductive diamond tubes on the surface of porous carbon nanotube hollow fibers using successive 10-pulsed laser annealing shots and 6 h of hot filament chemical vapor deposition techniques. Room-temperature Raman and X-ray diffraction spectra reveal the signature T2g peaks near 1332.4 cm–1 and 111 planes of diamonds near 43.9°, respectively. A low turn-on field (ETO) ∼1.85 V/μm@1 μA/cm2 and a threshold field (ETH) ∼2.54 V/μm@10 μA/cm2 were observed for the tubular diamond structures. The field enhancement factor (β) was calculated at 3594 and highly stable field emission current stability was observed over a long period of 4 h. For the first time, a good insight into the field emission results of the diamond is established with the structural, electronic properties, and the work function (φ) ∼4.84 eV analysis conducted by the density functional theory simulation. Finite electronic states at the Fermi level are observed beyond a band gap, and it demonstrates the wide-band gap (4.4 eV) semiconducting nature of the diamond. The Bader charge analysis and maximum entropy method pattern revealed the negative electron affinity of the diamond, and it is responsible for the emission of electrons from the conduction band of the diamond. Besides, the accumulation of charge carriers, which contributes to the electric field emission, takes place due to the weak π bonds of carbon atoms. The low turn-on field, the high field enhancement factor, and the good field emission current stability of tubular diamond offer great prospects for future efficient and low-cost field emission devices.

Parahydrogen-induced polarization enables the single-scan NMR detection of a 236 kDa biopolymer at nanomolar concentrations

Nuclear magnetic resonance (NMR) experiments utilizing parahydrogen-induced polarization (PHIP) were performed to elucidate the PHIP activity of the synthetic 236 kDa biopolymer poly-γ-(4-propargyloxy)-benzyl-L-glutamate) (PPOBLG). The homopolypeptide was successfully hyperpolarized and the enhanced signals were detected in 11.7 T solution NMR as a function of the PPOBLG concentration. The hydrogenation with parahydrogen caused signal enhancements of 800 and more for the vinyl protons of the side chain at low substrate concentration. As a result of this high enhancement factor, even at 13 nM of PPOBLG, a single scan 1H-NMR detection of the hyperpolarized protons was possible, owing to the combination of hyperpolarization and density of PHIP active sites.

Unique high-performance metal-nanoparticle-free SERS substrate with rapid-fabricated hybrid 3D-Nano-Micro-Cavities anodic alumina for label-free detection

Conventional surface-enhanced Raman scattering (SERS) substrates were usually nanofabricated by coating Ag or Au metal nano particles (MNPs) to modify the surface. However, the complex and time-consuming nanofabrication prevents those good-performance substrates from the practical applications together with the instability of MNPs as a challenge. Here, a unique Roughened-Surface-with-hybrid-3D-Nano-Micro-Cavities (RS3DNMC) SERS substrate free of MNPs is proposed for high-performance enhancement using facile and rapid electrochemically micromachining aluminum foil to form randomly-distributed 3D over-etched cavities of 1 ∼ 2 μm in diameter embedded with the nanopores of anodized aluminum oxide (AAO). The metal-film-coated AAO with RS3DNMC structure creates great SERS enhancement because of two mechanisms from the significantly reduced reflectance for increasing the photonic-scattering-and-multi-reflection and the more peripheral-and-gap hotspots of 3D-nano-micro-cavities compared to the 2D flat surface. Our SERS substrate merits a high analytical enhancement factor (AEF) of 1.15x106 and a low limit of detection (LOD) of 1x10-10 M for methylene blue (MB) with a good uniformity of 9.64% relative standard deviation (RSD) in a large area of 2.25 cm2. The melamine widely remained in human body and environment was detected at LOD of 0.05 ppm that is much lower than WHO-recommended criteria (1 ppm).

Versatile flexible SERS substrate for in situ detection of contaminants in water and fruits based on Ag NPs decorated wrinkled PDMS film.

Flexible surface-enhanced Raman spectroscopy (SERS) substrate has attracted great attention due to its convenient sampling and on-site monitoring capability. However, it is still challenging to fabricate a versatile flexible SERS substrate, which can be used for in situ detection of analytes either in water or on irregular solid surfaces. Here, we report a flexible and transparent SERS substrate based on a wrinkled polydimethylsiloxane (PDMS) film obtained by transferring corrugated structures on the aluminium/polystyrene bilayer film, onto which silver nanoparticles (Ag NPs) are deposited by thermal evaporation. The as-fabricated SERS substrate exhibits a high enhancement factor (∼1.19×105), good signal uniformity (RSD of 6.27%), and excellent batch-to-batch reproducibility (RSD of 7.3%) for rhodamine 6 G. In addition, the Ag NPs@W-PDMS film can maintain high detection sensitivity even after mechanical deformations of bending or torsion for 100 cycles. More importantly, being flexible, transparent, and light, the Ag NPs@W-PDMS film can both float on the water surface and conformally contact with the curved surface for in situ detection. The malachite green in aqueous environment and on apple peel can be easily detected down to 10-6 M with a portable Raman spectrometer. Therefore, it is expected that such a versatile flexible SERS substrate has great potential in on-site, in situ contaminant monitoring for realistic applications.