Designing and fabricating of surface-enhanced Raman scattering substrate with high density hot spots by polyaniline template-assisted self-assembly

One-step fabrication of flexible polyamide@Ag-dodecanethiol membranes for highly sensitive SERS detection of thiram

The surface-enhanced Raman scattering (SERS) is an effective spectral technology based on Raman scattering, but in practice, the commonly used SERS substrates suffer from low sensitivity and poor stability. In order to overcome these limitations, the SERS substrates were prepared from hydrophobic modification of dodecanethiol (C12) coupled with a flexible substrate, which was then used for pesticides detection in water. A flexible PA@Ag-C12 substrate with surface functionalization has been obtained. This work aims to investigate the self-assembly of Ag NPs modified with C12 onto polyamide (PA) membranes. Initially, transmission electron microscopy and scanning electron microscopy were used to analyze the substrate's morphology. Then with the help of an energy-dispersive spectrometer, sulfur content of C12-modified Ag NPs was analyzed. In order to determine the hydrophobicity of the modified Ag NPs, the contact angle was used. The results indicate that the gap between Ag NPs on PA membrane can be effectively controlled in order to prevent Ag NPs from aggregating. Furthermore, the finite-difference time-domain analysis indicated that the PA@Ag-C12 substrate exhibited a stronger electromagnetic enhancement effect than the PA@Ag substrate. By reducing NPs gaps on the PA membrane, the number of 'hot spots' increased, and the SERS performance of the substrate was improved as a result. According to the results of this study, this method can greatly reduce the manufacturing costs and time costs of the SERS substrate while maintaining the original uniformity. The SERS performance of PA@Ag-C12 was found to be three orders of magnitude better than that of PA@Ag direct self-assembled substrate, and the detection limit for Rhodamine 6G (R6G) was approximately 8.47 × 10-14M. On the basis of the PA@Ag-C12 substrate, thiram is detectable at a detection limit of 5.88 × 10-11M with a high degree of sensitivity and repeatability.

Multimodal cellular redox nanosensors based on self-doped polyaniline nanocomposites

We have successfully fabricated a nanocomposite, which is composed of polyaniline (PAni) and pyrene butyric acid (Pyba) via a solvent shift method, which was self-doped at a neutral pH value. This PAni nanocomposite can act as a fine nanoagent expressing absorbance, fluorescence, and Raman properties according to the surrounding pH values.

Flower-like Ag coated with molecularly imprinted polymers as a surface-enhanced Raman scattering substrate for the sensitive and selective detection of glibenclamide

Flower-like Ag was formed by nanosheet self-assembly as a SERS-active substrate and was utilized for the preparation of flower-like Ag@molecularly imprinted polymers (MIPs) as a surface-enhanced Raman scattering (SERS) sensor. Based on the combination of the molecular imprinting technique and SERS technology, the flower-like Ag@MIPs with high sensitivity and excellent selectivity were used as SERS substrates for the detection of glibenclamide. The imprinted layer could effectively protect the flower-like Ag from oxidation and thereby may improve the stability of the SERS substrate. The intensities of the characteristic peaks obtained for the flower-like Ag@MIPs were higher than that of flower-like Ag. By applying the flower-like Ag@MIPs as an efficient and ultra-sensitive SERS platform, glibenclamide was quantitatively detected in trace concentrations as low as 1 ng mL-1. Furthermore, the SERS enhancement for the flower-like Ag@MIPs was due to the synergetic effect between electromagnetic enhancement and chemical enhancement. We believe that this reliable method can open up new opportunities for practical chemosensor or biosensor applications.

Sandwich-interface inspired strategy for controlled formation of nanoparticles

Nanoparticles are functional materials able to offer improved or new synergetic properties. By manipulating the interfacial properties, we demonstrate an innovative sandwich-interface method capable of forming various monodispersed nanostructures including metals, semiconductors, and inorganic and coordinated nanoparticles. By analysing of the reaction mechanism, we show that reaction time, the height of transition and presence of surfactant have the greatest influence on the formation of the products. These advances in the sandwich-interface synthesis significantly extend the scope of interface synthetic methods, facilitating a new level of structural-architectural control which may lead to future developments in the field of crystallography.

Dual-responsive biocompatible microgels as high loaded cargo: understanding of encapsulation/release driving forces by NMR NOESY

The suitability of biocompatible microgels as a new cosmetic carrier has been demonstrated through their ability of encapsulation/release of cosmetic active molecules.

SERS Active Nanobiosensor Functionalized by Self-Assembled 3D Nickel Nanonetworks for Glutathione Detection

We introduce a "non-noble metal" based SERS active nanobiosensor using a self-assembled 3D hybrid nickel nanonetwork. A tunable biomolecule detector fabricated by a bottom-up approach was functionalized using a multiphoton ionization energy mechanism to create a self-assembled 3D hybrid nickel nanonetwork. The nanonetwork was tested for SERS detection of crystal violet (CV) and glutathione (GSH) at two excitation wavelengths, 532 and 785 nm. The results reveal indiscernible peaks with a limit of detection (LOD) of 1 picomolar (pM) concentration. An enhancement factor (EF) of 9.3 × 10⁸ was achieved for the chemical molecule CV and 1.8 × 10⁹ for the biomolecule GSH, which are the highest reported values so far. The two results, one being the CV molecule proved that nickel nanonetwork is indeed SERS active and the second being the GSH biomolecule detection at both 532 and 785 nm, confirm that the nanonetwork is a biosensor which has potential for both in vivo and in vitro sensing. In addition, the selectivity and versatility of this biosensor is examined with biomolecules such as l-Cysteine, l-Methionine, and sensing GSH in cell culture medium which mimics the complex biological environment. The functionalized self-assembled 3D hybrid nickel nanonetwork exhibits electromagnetic and charge transfer based SERS activation mechanisms.

Synergistically enhanced upconversion luminescence in Li+-doped core–shell-structured ultrasmall nanoprobes for dual-mode deep tissue fluorescence/CT imaging

The development of upconversion luminescence that allows for multimodal imaging in terms of resolution and penetration depth using a single system is attracting increasing interest for use in clinical molecular imaging and diagnostics.

SERS activity with tenfold detection limit optimization on a type of nanoporous AAO-based complex multilayer substrate

Most of SERS applications are constricted by heterogeneous hotspots and aggregates of nanostructure, which result in low sensitivity and poor reproducibility of characteristic signals. This work intends to introduce SERS properties of a type of SERS-active substrate, Au-CuCl2-AAO, which is innovatively developed on a porous anodic alumina oxide (AAO) template. Spectral measuring results of Rhodamine 6G (R6G) on this substrate optimized by controlling morphology and gold thickness showed that enhancement factor (2.30 × 10(7)) and detection limit (10(-10) M) were both improved and represented better performance than its template AAO. Homogenous hot spots across the region of interest were achieved by scanning SERS intensity distribution for the band at 1505 cm(-1) in 5 × 5 μm(2) area. Furthermore, the promising SERS activity of the flower-patterned substrate was theoretically explained through simulation of the electromagnetic field distribution. In addition, this SERS substrate is proposed for applications within the field of chemical and biochemical analyses.

Fabrication and Formation Mechanism of Ag Nanoplate-Decorated Nanofiber Mats and Their Application in SERS

We report a new simple method to fabricate a highly active SERS substrate consisting of poly-m-phenylenediamine/polyacrylonitrile (PmPD/PAN) decorated with Ag nanoplates. The formation mechanism of Ag nanoplates is investigated. The synthetic process of the Ag nanoplate-decorated PmPD/PAN (Ag nanoplates@PmPD/PAN) nanofiber mats consists of the assembly of Ag nanoparticles on the surface of PmPD/PAN nanofibers as crystal nuclei followed by in situ growth of Ag nanoparticles exclusively into nanoplates. Both the reducibility of the polymer and the concentration of AgNO3 are found to play important roles in the formation and the density of Ag nanoplates. The optimized Ag nanoplates@PmPD/PAN nanofiber mats exhibit excellent activity and reproducibility in surface-enhanced Raman scattering (SERS) detection of 4-mercaptobenzoic acid (4-MBA) with a detection limit of 10(-10)  m, making the Ag nanoplates@PmPD/PAN nanofiber mats a promising substrate for SERS detection of chemical molecules. In addition, this work also provides a design and fabrication process for a 3D SERS substrate made of a reducible polymer with noble metals.

Anchoring gold nanoparticles inside polyaniline shells with magnetic cores for the enhancement of catalytic stability

Owing to the protection effect and stability of polyaniline, the yolk–shell nanostructured Fe₃O₄@Au–polyaniline illustrated enhanced catalytic stability.

Self-assembly of various silver nanocrystals on PmPD/PAN nanofibers as a high-performance 3D SERS substrate

The AgNCs (AgNPs, AgNTs and AgNDs) decorated-PmPD/PAN nanofiber mats were obtained as highly sensitive 3D SERS substrates.

A Ag-molecularly imprinted polymer composite for efficient surface-enhanced Raman scattering activities under a low-energy laser

In this work, we have fabricated flower-shaped Ag particles coated with a molecularly imprinted polymer (Ag@MIP) based on the molecular imprinting technique and SERS technology.

A dynamic surface enhanced Raman spectroscopy method for ultra-sensitive detection: from the wet state to the dry state

A dynamic surface-enhanced Raman spectroscopy method from the wet state to the dry state.

Nanoporous gold film: fabrication and role as a catalytic reactor

A thin NPG film with a thickness of 90 nm can be prepared on various substrates to form a catalytic reactor conveniently by using seed-mediated growth. Because of the nanoporous characterization, the film exhibits high catalytic activity both for oxidative and hydrogenation reactions.

Large-volume hot spots in gold spiky nanoparticle dimers for high-performance surface-enhanced spectroscopy

Hot spots with a large electric field enhancement usually come in small volumes, limiting their applications in surface-enhanced spectroscopy. Using a finite-difference time-domain method, we demonstrate that spiky nanoparticle dimers (SNPD) can provide hot spots with both large electric field enhancement and large volumes because of the pronounced lightning rod effect of spiky nanoparticles. We find that the strongest electric fields lie in the gap region when SNPD is in a tip-to-tip (T-T) configuration. The enhancement of electric fields (|E|(2)/|E0|(2)) in T-T SNPD with a 2 nm gap can be as large as 1.21 × 10(6). And the hot spot volume in T-T SNPD is almost 7 times and 5 times larger than those in the spike dimer and sphere dimer with the same gap size of 2 nm, respectively. The hot spot volume in SNPD can be further improved by manipulating the arrangements of spiky nanoparticles, where crossed T-T SNPD provides the largest hot spot volume, which is 1.5 times that of T-T SNPD. Our results provide a strategy to obtain hot spots with both intense electric fields and large volume by adding a bulky core at one end of the spindly building block in dimers.

Detection of aniline oligomers on polyaniline-gold interface using resonance Raman scattering

In situ deposited conducting polyaniline films prepared by the oxidation of aniline with ammonium peroxydisulfate in aqueous media of various acidities on gold and silicon supports were characterized by Raman spectroscopy. Enhanced Raman bands were found in the spectra of polyaniline films produced in the solutions of weak acids or in water on gold surface. These bands were weak for the films prepared in solutions of a strong acid on a gold support. The same bands are present in the Raman spectra of the reaction intermediates deposited during aniline oxidation in water or aqueous solutions of weak or strong acids on silicon removed from the reaction mixture at the beginning of the reaction. Such films are formed by aniline oligomers adsorbed on the surface. They were detected on the polyaniline-gold interface using resonance Raman scattering on the final films deposited on gold. The surface resonance Raman spectroscopy of the monolayer of oligomers found in the bulk polyaniline film makes this method advantageous in surface science, with many applications in electrochemistry, catalysis, and biophysical, polymer, or analytical chemistry.

Au/montmorillonite/polyaniline nanoflakes: facile fabrication by self-assembly and application as catalyst

Hydrogen bonding between citrate-stabilized Au NPs and the PANI backbone is proposed to play a pivotal role in driving the self-assembly between Au NPs and dedoped PANI, from which a highly catalytic Au NP/PANI/MMT nanocomposite was then synthesized.

Bio-inspired in situ growth of monolayer silver nanoparticles on graphene oxide paper as multifunctional substrate

In this study, we report a facile bio-inspired method for large-scale preparation of highly dispersed Ag nanoparticles (NPs) on the surface of flexible reduced graphene oxide (rGO) paper with using dopamine (DA) both as a reductant and a surface modifier. Through the self-polymerization of dopamine, free-standing GO paper can be simultaneously reduced and modified with following in situ growth of monolayer Ag NPs on such a substrate. The spherical Ag NPs with an average diameter of 80 nm have a narrow size distribution and tunable cover density. Such a flexible rGO/Ag hybrid paper presents enhanced antibacterial activity against E. coli and a high active and sensitive SERS response toward Rhodamine 6G (R6G) molecules. The detection signals can be obtained while the R6G concentration is as low as to 10(-8) M. This work provides a simple strategy for large-scale fabrication of monolayer Ag NPs on flexible rGO paper as a portable antibacterial substrate and a potential SERS substrate for molecular detection applications.

Highly uniform and optical visualization of SERS substrate for pesticide analysis based on Au nanoparticles grafted on dendritic α-Fe2O3

Here, Au nanoparticles (NPs) grafted on dendritic α-Fe2O3 (NPGDF) are designed as a highly uniform surface-enhanced Raman scattering (SERS) substrate with a feature of optical visualization by an optical microscope (OM) system and used for in situ detection of pesticide residues that are annually used in agriculture. With this strategy, the dendritic α-Fe2O3 has been synthesized by a hydrothermal method and significantly functionalized by an inductively coupled plasma (ICP) apparatus and then Au NPs were grafted on it densely and uniformly. In addition, the profile of NPGDF can be clearly observed using an OM platform of a Raman spectrometer, and the profile of SERS spectral mapping with NPGDF as substrate almost exactly coincides with the OM image, the electron microscope (EM) image and the elemental mapping of NPGDF, which indicates remarkable uniformity of the NPGDF as SERS substrate, thus ensuring the laser beam focuses on the efficient sites of the substrate under the OM platform. Moreover, NPGDF can be dispersed in the liquor and the NPGDF microparticles can be adsorbed on the target surface. Therefore, it can be used for in situ detection of pesticide residues on tea leaves, fruits etc., with high sensitivity and reproducibility.

In situ fabricated polymer-silver nanocomposite thin film as an inexpensive and efficient substrate for surface-enhanced Raman scattering

The utility of polymer-metal nanocomposite thin films with in situ generated silver nanoparticles as substrates for surface-enhanced Raman scattering (SERS) is demonstrated. Thin films of poly(vinyl alcohol) and poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) containing Ag nanoparticles generated in situ through thermal annealing and photoirradiation, respectively (Ag-PVA and Ag-PVVV), are investigated as potential SERS substrates using 4-aminothiophenol and rhodamine 6G as probe molecules. The fabrication protocols are extremely simple and the materials inexpensive. The Ag-PVA substrate is found to produce Raman spectral enhancement factors of ~10(6), whereas Ag-PVVV, a novel nanocomposite thin film developed in the present study, provides enhancement factors of ~10(7). A unique advantage of these nanocomposite films is demonstrated by fabricating them by the in situ process as a thin coating inside glass capillaries and using these disposable SERS substrates for the sensitive detection of the probe molecules. The thin film substrates prepared on glass plates and capillaries facilitate convenient sample preparation for recording the Raman spectra and provide strongly enhanced spectra with high reproducibility, allowing picomols of the analytes to be detected. These aspects combined with the ease of fabrication and low cost of these in situ fabricated nanocomposite thin films make them highly attractive SERS substrates.