Surface enhanced Raman scattering (SERS) fabrics for trace analysis

Flexible SERS active substrates were prepared by modification of silk fabrics with gold nanoparticles. Gold nanoparticles were in-situ synthesized after heating the silk fabrics immersed in gold ion solution. Localized surface plasmon resonance (LSPR) properties of the treated silk fabrics varied as the concentration of gold ions changed, in relation to the morphologies of gold nanoparticles on silk. In addition, X-ray diffraction (XRD) was used to observe the structure of the gold nanoparticle treated silk fabrics. The SERS enhancement effect of the silk fabrics treated with gold nanoparticles was evaluated by collecting Raman signals of different concentrations of p-aminothiophenol (PATP), 4-mercaptopyridine (4-MPy) and crystal violet (CV) solutions. The results demonstrate that the silk fabrics corresponding to 0.3 and 0.4 mM of gold ions possess high SERS activity compared to the other treated fabrics. It is suggested that both the gold content and morphologies of gold nanoparticles dominate the SERS effect of the treated silk fabrics.

Optical actuation of inorganic/organic interfaces: comparing peptide-azobenzene ligand reconfiguration on gold and silver nanoparticles

Photoresponsive molecules that incorporate peptides capable of material-specific recognition provide a basis for biomolecule-mediated control of the nucleation, growth, organization, and activation of hybrid inorganic/organic nanostructures. These hybrid molecules interact with the inorganic surface through multiple noncovalent interactions which allow reconfiguration in response to optical stimuli. Here, we quantify the binding of azobenzene-peptide conjugates that exhibit optically triggered cis-trans isomerization on Ag surfaces and compare to their behavior on Au. These results demonstrate differences in binding and switching behavior between the Au and Ag surfaces. These molecules can also produce and stabilize Au and Ag nanoparticles in aqueous media where the biointerface can be reproducibly and reversibly switched by optically triggered azobenzene isomerization. Comparisons of switching rates and reversibility on the nanoparticles reveal differences that depend upon whether the azobenzene is attached at the peptide N- or C-terminus, its isomerization state, and the nanoparticle composition. Our integrated experimental and computational investigation shows that the number of ligand anchor sites strongly influences the nanoparticle size. As predicted by our molecular simulations, weaker contact between the hybrid biomolecules and the Ag surface, with fewer anchor residues compared with Au, gives rise to differences in switching kinetics on Ag versus Au. Our findings provide a pathway toward achieving new remotely actuatable nanomaterials for multiple applications from a single system, which remains difficult to achieve using conventional approaches.

Optical actuation of inorganic/organic interfaces: comparing peptide-azobenzene ligand reconfiguration on gold and silver nanoparticles

Photoresponsive molecules that incorporate peptides capable of material-specific recognition provide a basis for biomolecule-mediated control of the nucleation, growth, organization, and activation of hybrid inorganic/organic nanostructures. These hybrid molecules interact with the inorganic surface through multiple noncovalent interactions which allow reconfiguration in response to optical stimuli. Here, we quantify the binding of azobenzene-peptide conjugates that exhibit optically triggered cis-trans isomerization on Ag surfaces and compare to their behavior on Au. These results demonstrate differences in binding and switching behavior between the Au and Ag surfaces. These molecules can also produce and stabilize Au and Ag nanoparticles in aqueous media where the biointerface can be reproducibly and reversibly switched by optically triggered azobenzene isomerization. Comparisons of switching rates and reversibility on the nanoparticles reveal differences that depend upon whether the azobenzene is attached at the peptide N- or C-terminus, its isomerization state, and the nanoparticle composition. Our integrated experimental and computational investigation shows that the number of ligand anchor sites strongly influences the nanoparticle size. As predicted by our molecular simulations, weaker contact between the hybrid biomolecules and the Ag surface, with fewer anchor residues compared with Au, gives rise to differences in switching kinetics on Ag versus Au. Our findings provide a pathway toward achieving new remotely actuatable nanomaterials for multiple applications from a single system, which remains difficult to achieve using conventional approaches.

Ionic liquid-assisted synthesis of polyaniline/gold nanocomposite and its biocatalytic application

In this report, a novel chemical synthesis of polyaniline/gold nanocomposite is explored using ionic liquid (IL) 1-Butyl-3-methylimidazolium hexafluorophosphate. The direct chemical synthesis of polyaniline/gold nanocomposite was initiated via the spontaneous oxidation of aniline by AuCl4 − in IL. A nearly uniform dispersion of polyaniline/Au particles with a diameter of 450 ± 80 nm was produced by this method, which indicates that this method is more suitable for controlling particle dimensions. It was also found that the electrical conductivity of the polyaniline/gold nanocomposite was more than 100 times higher than that of the pure polyaniline nanoparticles. The polyaniline/gold nanocomposite displays superior function in the biocatalytic activation of microperoxidase-11 because of the high surface area of the assembly and the enhanced charge transport properties of the composite material. We also report the possible application of polyaniline/gold nanocomposite as a H2O2 biosensor.

Photothermally induced apoptosis of cancer cells using gold nanorods for low energy cancer therapy

Gold nanorods functionalised with transferrin were used for photothermally induced necrosis and apoptosis of cancer cells. It was observed that the laser energy required to induce cell apoptosis is significantly lower than that for cell necrosis, indicating that photothermally induced apoptosis can be used for medically safe laser cancer treatment.

Two-dimensional correlation localized surface plasmon resonance spectroscopy for analysis of the interaction between metal nanoparticles and bovine serum albumin

Time-resolved extinction spectra assisted with two-dimensional correlation spectroscopy (2DCOS) analysis and principal component analysis (PCA) were employed to investigate the interaction between bovine serum albumin (BSA) and metal nanoparticles (NPs). A series of localized surface plasmon resonance (LSPR) spectra of metal NPs were measured just after a small amount of BSA was added into metal colloids. Through 2DCOS analysis, remarkable changes in the intensities of the LSPR were observed. The interaction process was totally divided into three periods according to the PCA. Transmission electron microscopy, dynamic light scattering, and ζ-potential measurements were also employed to characterize the interaction between BSA and metal NPs. The addition of BSA brings silver NPs to aggregate through the electrostatic interaction between them, but it has less effect on gold NPs. In a gold and silver mixed system, gold NPs can affect the interaction of silver NPs and BSA, leading it to weaken. The combination of 2DCOS analysis and LSPR spectroscopy is powerful for exploring the LSPR spectra of the metal NP involved systems. This combined technique holds great potential in LSPR sensing through analysis of slight, slim spectral changes of metal colloids

Functionalization of bamboo pulp fabrics with noble metal nanoparticles

Noble metal (gold and silver) nanoparticles (NPs) were synthesized in-situ on bamboo pulp fabrics. The gold NPs were reduced by bamboo pulp fabrics and bonded to fibers under heating, and an alkaline condition was needed to synthesize silver NPs in the presence of bamboo pulp fabrics. The synthesized gold and silver NPs endowed bamboo pulp fabrics with different colors because of their localized surface plasmon resonance (LSPR) property. The colors of the fabrics treated with metal NPs were extended through complex synthesis of gold and silver NPs in different proportions. The bamboo pulp fabrics treated with noble metal NPs showed good fastness to light and rubbing. In addition, the gold and silver NPs imparted bamboo pulp fabrics excellent UV protection property and remarkable antibacterial activity.

Comparative study of materials-binding peptide interactions with gold and silver surfaces and nanostructures : A thermodynamic basis for biological selectivity of inorganic materials

Controllable 3D assembly of multicomponent inorganic nanomaterials by precisely positioning two or more types of nanoparticles to modulate their interactions and achieve multifunctionality remains a major challenge. The diverse chemical and structural features of biomolecules can generate the compositionally specific organic/inorganic interactions needed to create such assemblies. Toward this aim, we studied the materials-specific binding of peptides selected based upon affinity for Ag (AgBP1 and AgBP2) and Au (AuBP1 and AuBP2) surfaces, combining experimental binding measurements, advanced molecular simulation, and nanomaterial synthesis. This reveals, for the first time, different modes of binding on the chemically similar Au and Ag surfaces. Molecular simulations showed flatter configurations on Au and a greater variety of 3D adsorbed conformations on Ag, reflecting primarily enthalpically driven binding on Au and entropically driven binding on Ag. This may arise from differences in the interfacial solvent structure. On Au, direct interaction of peptide residues with the metal surface is dominant, while on Ag, solvent-mediated interactions are more important. Experimentally, AgBP1 is found to be selective for Ag over Au, while the other sequences have strong and comparable affinities for both surfaces, despite differences in binding modes. Finally, we show for the first time the impact of these differences on peptide mediated synthesis of nanoparticles, leading to significant variation in particle morphology, size, and aggregation state. Because the degree of contact with the metal surface affects the peptide's ability to cap the nanoparticles and thereby control growth and aggregation, the peptides with the least direct contact (AgBP1 and AgBP2 on Ag) produced relatively polydispersed and aggregated nanoparticles. Overall, we show that thermodynamically different binding modes at metallic interfaces can enable selective binding on very similar inorganic surfaces and can provide control over nanoparticle nucleation and growth. This supports the promise of bionanocombinatoric approaches that rely upon materials recognition.

Functionalized mesoporous silica nanoparticles with redox-responsive short-chain gatekeepers for agrochemical delivery.

The controlled release of salicylic acid (SA), a key phytohormone, was mediated by using a novel decanethiol gatekeeper system grafted onto mesoporous silica nanoparticles (MSNs). The decanethiol was conjugated only to the external surfaces of the MSNs through glutathione (GSH)-cleavable disulfide linkages and the introduction of a process to assemble gatekeepers only on the outer surface so that the mesopore area can be maintained for high cargo loading. Raman and nitrogen sorption isotherm analyses confirmed the successful linkage of decanethiol to the surface of MSNs. The in vitro release of SA from decanethiol gated MSNs indicated that the release rate of SA in an environment with a certain amount of GSH was significantly higher than that without GSH. More importantly, in planta experiments showed the release of SA from decanethiol gated MSNs by GSH induced sustained expression of the plant defense gene PR-1 up to 7 days after introduction, while free SA caused an early peak in PR-1 expression which steadily decreased after 3 days. This study demonstrates the redox-responsive release of a phytohormone in vitro and also indicates the potential use of MSNs in planta as a controlled agrochemical delivery system.

Graphene nanodots-encaged porous gold electrode fabricated via ion beam sputtering deposition for electrochemical analysis of heavy metal ions

All rights reserved. A graphene nanodots-encaged porous gold electrode via ion beam sputtering deposition (IBSD) for electrochemical sensing is presented. The electrodes were fabricated using Au target, and a composite target of Al and graphene, which were simultaneously sputtered onto glass substrates by Ar ion beam, followed with hydrochloric acid corrosion. The as-prepared graphene nanodots-encaged porous gold electrodes were then used for the analysis of heavy metal ions, e.g. Cu2+ and Pb2+ by Osteryoung square wave voltammetry (OSWV). These porous electrodes exhibited enhanced detection range for the heavy metal ions due to the entrapped graphene nanodots in 3-D porous structure. In addition, it was also found that when the thickness of porous electrode reached 40 nm the detection sensitivity came into saturation. The linear detection range is 0.009-4 μM for Cu2+ and 0.006-2.5 μM for Pb2+. Good reusability and repeatability were also observed. The formation mechanism and 3-D structure of the porous electrode were also investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectra (XPS). This graphene entrapped 3-D porous structure may envision promising applications in sensing devices.

A novel graphene nanodots inlaid porous gold electrode for electrochemically controlled drug release

A uniform graphene nanodots inlaid porous gold electrode was prepared via ion beam sputtering deposition (IBSD) and mild corrosion chemistry. HRTEM, SEM, AFM and XPS analyses revealed the successful fabrication of graphene nanodots inlaid porous gold electrode. The as-prepared porous electrode was used as π-orbital-rich drug loading platform to fabricate an electrochemically controlled drug release system with high performance. π-orbital-rich drugs with amino mioety, like doxorubicin (DOX) and tetracycline (TC), were loaded into the graphene nanodots inlaid porous gold electrode via non-covalent π-π stacking interaction. The amino groups in DOX and TC can be easily protonated at acidic medium to become positively-charged NH3(+), which allow these drug molecules to be desorbed from the porous electrode surface via electrostatic repulsion when positive potential is applied at the electrode. The drug loading and release experiment indicated that this graphene nanodots inlaid porous gold electrode can be used to conveniently and efficiently control the drug release electrochemically. Not only did our work provide a benign method to electrochemically controlled drug release via electrostatic repulsion process, it also enlighten the promising practical applications of micro electrode as a drug carrier for precisely and efficiently controlled drug release via embedding in the body.

Self-assembled core-satellite gold nanoparticle networks for ultrasensitive detection of chiral molecules by recognition tunneling current

Chirality sensing is a very challenging task. Here, we report a method for ultrasensitive detection of chiral molecule l/d-carnitine based on changes in the recognition tunneling current across self-assembled core-satellite gold nanoparticle (GNP) networks. The recognition tunneling technique has been demonstrated to work at the single molecule level where the binding between the reader molecules and the analytes in a nanojunction. This process was observed to generate a unique and sensitive change in tunneling current, which can be used to identify the analytes of interest. The molecular recognition mechanism between amino acid l-cysteine and l/d-carnitine has been studied with the aid of SERS. The different binding strength between homo- or heterochiral pairs can be effectively probed by the copper ion replacement fracture. The device resistance was measured before and after the sequential exposures to l/d-carnitine and copper ions. The normalized resistance change was found to be extremely sensitive to the chirality of carnitine molecule. The results suggested that a GNP networks device optimized for recognition tunneling was successfully built and that such a device can be used for ultrasensitive detection of chiral molecules.

Self-assembly of ultrathin gold nanowires and single walled carbon nanotubes as a highly sensitive substrate for surface enhanced Raman spectroscopy

Here we report self-assembly of ultrathin gold nanowires and single-walled carbon nanotubes with an ultrahigh aspect ratio as a highly sensitive substrate for surface enhanced Raman spectroscopy. And we demonstrated that the hybrids were especially efficient in adsorption of aromatic molecules such as 4-mercaptobenzoic acid and the hybrids materials could be used as a novel platform for trace level detection in the verification of paper notes through the Raman enhancement technique.