Electrochemical surface plasmon resonance detection of enzymatic reaction in bilayer lipid

In this paper, electrochemical surface plasmon resonance (SPR) method was first used to detect enzymatic reaction in bilayer lipid membrane (BLM) based on immobilizing horseradish peroxidase (HRP) in the BLMs supported by the redox polyaniline (PAn) film. By SPR kinetic curve in situ monitoring the redox transformation of PAn film resulted from the reaction between HRP and PAn, the enzymatic reaction of HRP with H2O2, was successfully analyzed by electrochemical SPR spectroscopy.

Nanoparticle-amplified Surface Plasmon Resonance Study of Protein Conformational Change at Interface

This paper reports the study of protein conformational change by Au nanoparticles (AUNPs)-amplified surface plasmon resonance (SPR) spectroscopy. Taking cytochrome c (Cyt c) as an example, this paper gives a detailed description of the construction of metal-protein-metal sandwich nanostructure consisting of an Au film underlayer, a cytochrome c intermediate layer and an AuNPs upper layer. The incorporation of AuNPs into SPR biosensing results in increased SPR sensitivity to protein conformational change as demonstrated by acid denaturation of Cyt c. It suggests the conformational change of surface-confined Cyt c leads to the distance and electromagnetic coupling variations of Au film-AuNPs.

Characterization of saccharides and phenolic acids in the Chinese herb Tanshen by ESI-FT-ICR-MS and HPLC

This study sought to determine the main components (saccharides and phenolic acids) in crude extract of the Chinese herb Tanshen by electrospray ionization Fourier transform ion cyclotron resonant mass spectrometry (ESI-FT-ICR-MS) in negative-ion mode. Eleven compounds were identified as phenolic acids by exact mass measurement and further confirmed by sustained off-resonance irradiation (SORI) CID data. In addition, monosaccharicles and oligosaccharides (n = 2 similar to 5) and a serial of corresponding anionic adducts of saccharide were observed without adding any anions additionally to the extract solution, and the anionic components were unambiguously identified as H2O, HCl, HCOOH, HNO3, C3H6O2, H2SO4 and C5H7NO3 according to the exact mass measurement results.

Surface-enhanced Raman scattering of 4-aminothiophenol self-assembled monolayers in sandwich structure with nanoparticle shape dependence: Off-surface plasmon resonance condition

A universal metal-molecule-metal sandwich architecture by the self-assembly of Ag nanoparticles (NPs) and Au NPs of various shapes interconnected with 4-aminothiophenol (4-ATP) molecules was presented. These Ag NPs/4-ATP/Au NPs sandwich structures were characterized by surface enhanced Raman scattering (SERS) using an off-surface plasmon resonance condition. Enhancement factors (EF) on the order of 10(8) for 9b(b(2)) vibration mode were observed for the 4-ATP self-assembled monolayers (SAMs) in such sandwich structures. The factors are 2 orders of magnitude larger than that on the monolayer of Au NPs of various shapes under similar condition. More importantly, remarkable increase in the intensity of b(2) vibrational modes, which is characteristic of the charge transfer (CT) behavior between metal NPs and 4-ATP molecules, was observed in these sandwich structures under 1064 nm excitation. The obtained EF on these sandwich structure for 9b(b(2)) is larger than that for 7a vibration mode by a factor of similar to 10(2), demonstrating the importance of the contribution of the CT mechanism and the CT behavior of metal contacts, which play a significant role in metal-molecule-metal nanosystems.

Interaction between alpha-actinin and negatively charged lipids membrane investigated by surface plasmon resonance and electrochemical methods

alpha-Actinin has been shown to be capable of interacting with some special membrane phospholipids directly, which is important for its function. In this study, hybrid bilayer membranes composed of negatively charged lipids are constructed on the surface plasmon resonance gold substrate and on the gold electrode, respectively, and the interaction between alpha-actinin and negatively charged lipids membrane is investigated by surface plasmon resonance, cyclic voltammetry and electrochemical impedance spectroscopy methods. alpha-Actinin is proved to be able to interact with the negatively charged lipids membrane directly. It can also insert at least partly into the membrane or lead to some defect or lesion in the membrane, which increase the permeability of the membrane. This study would bring some insight on the interaction between the alpha-actinin and the cell membranes in vivo.

Surface plasmon resonance and electrochemistry for detection of small molecules using catalyzed deposition of metal ions on gold substrate

Small molecules are difficult to detect by conventional surface plasmon resonance (SPR) spectroscopy due to the fact that the changes in the refractive index resulted from the binding process of small biomolecules are quite small. Here, we report a simple and effective method to detect small biomolecule using SPR spectroscopy and electrochemistry by catalyzed deposition of metal ions on SPR gold film. As an example, the ascorbic acid-mediated deposition of Ag on gold film was monitored by in situ SPR spectrum. The deposition of Ag atom on gold film resulted in an obvious decrease of depth in SPR angular scan curves of reflectance intensity and minimum reflectivity angle. The depth change of the SPR reflectance intensity and minimum reflectivity angle curves mainly relied on the amount of Ag atom deposited on gold film that can be controlled by the concentration of ascorbic acid. By monitoring the deposition of Ag atom on gold film, ascorbic acid was detected in the concentration range of 2 x 10(-5) M to 1 x 10(-3) M. After each of detections, the SPR sensor surface was completely regenerated by a potential step that stripped off the Ag atom. Furthermore, the regeneration process of the sensor surface provides the feasibility for detecting the concentration of ascorbic acid by electrochemical method.

Surface plasmon resonance and electrochemistry characterization of layer-by-layer self-assembled DNA and Zr4+ thin films, and their interaction with cytochrome c

Through electrostatic layer-by-layer (LbL) assembly, negatively charged calf thymus double stranded DNA (CTds-DNA), and positively charged Zr4+ ions were alternately deposited on gold substrate modified with chemisorbed cysteamine. Thus-prepared three-dimensional DNA networks were characterized by surface plasmon resonance (SPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS). SPR spectroscopy indicates that the effective thickness of DNA monolayer in the (DNA/Zr4+), bilayer was 1.5 +/- 0.1 nm, which corresponds to the surface coverage of 79% of its full packed monolayer. At the same time, a linear increase of film thickness with increasing number of layers was also confirmed by SPR characterizations. The data of XPS and IR-RAS show that Zr4+ ions interact with both the phosphate groups and nitrogenous bases of DNA and load into the framework of DNA. Furthermore, the interactions between this composite film and heme protein cytochrome c (Cyt c) were investigated by SPR spectroscopy and electrochemistry.

Surface plasmon resonance and electrochemistry characterization of layer-by-layer self-assembled DNA and Zr4+ thin films, and their interaction with cytochrome c

Through electrostatic layer-by-layer (LbL) assembly, negatively charged calf thymus double stranded DNA (CTds-DNA), and positively charged Zr4+ ions were alternately deposited on gold substrate modified with chemisorbed cysteamine. Thus-prepared three-dimensional DNA networks were characterized by surface plasmon resonance (SPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS). SPR spectroscopy indicates that the effective thickness of DNA monolayer in the (DNA/Zr4+), bilayer was 1.5 +/- 0.1 nm, which corresponds to the surface coverage of 79% of its full packed monolayer. At the same time, a linear increase of film thickness with increasing number of layers was also confirmed by SPR characterizations. The data of XPS and IR-RAS show that Zr4+ ions interact with both the phosphate groups and nitrogenous bases of DNA and load into the framework of DNA. Furthermore, the interactions between this composite film and heme protein cytochrome c (Cyt c) were investigated by SPR spectroscopy and electrochemistry. Compared with the adsorption of Cyt c on DNA monolayer, this composite multilayer film can obviously enhance the amount of immobilized Cyt c confirmed by SPR reflectivity-incident angle (R-theta) curves.

Mn(II)-monosubstituted polyoxometalates as candidates for contrast agents in magnetic resonance imaging

Two mono-substituted manganese polyoxometalates, K6MnSiW11O39 (MnSiW11) and K8MnP2W17O61 (MnP2W17), have been evaluated by in vivo and in vitro experiments as the candidates of potential tissue-specific contrast agents for magnetic resonance imaging (MRI). T-1-relaxivities of 12.1 mM(-1) s(-1) for MnSiW11 and 4.7 mM(-1) s(-1) for MnP2W17 (400 MHz, 25 degrees C) were higher than or similar to that of the commercial MRI contrast agent (GdDTPA). Their relaxivities in BSA and hTf solutions were also reported. After administration of MnSiW11 and MnP2W17 to Wistar rats, MR imaging showed longer and remarkable enhancement in rat liver and favorable renal excretion capability. The signal intensity increased by 74.0 +/- 4.9% for the liver during the whole imaging period (90 min) and by 67.2 +/- 5.3% for kidney within 20-70 min after injection at 40 +/- 3 mu mol kg(-1) dose for MnSiW11. MnP2W17 induced 71.5 +/- 15.1%. enhancement for the liver in 10-45 min range and 73.1 +/- 3.2% enhancement for kidney within 5-40 min after injection at 39 +/- 3 mu mol kg(-1) dose. In vitro and in vivo study showed MnSiW11 and MnP2W17 being favorable candidates as the tissue-specific contrast agents for MRI.

Surface-enhanced resonance Raman spectroscopy and spectroscopy study of redox-induced conformational equilibrium of cytochrome c adsorbed on DNA-modified metal electrode

The redox-induced conformational equilibrium of cytochrome c (cyt c) adsorbed on DNA-modified metal electrode and the interaction mechanism of DNA with cyt c have been studied by electrochemical, spectroscopic and spectroelectrochemical techniques. The results indicate that the external electric field induces potential-dependent coordination equilibrium of the adsorbed cyt c between its oxidized state (with native six-coordinate low-spin and non-native five-coordinate high-spin heme configuration) and its reduced state (with native six-coordinate low-spin heme configuration) on DNA-modified metal electrode. The strong interactions between DNA and cyt c induce the self-aggregation of cyt c adsorbed on DNA. The orientational distribution of cyt c adsorbed on DNA-modified metal electrode is potential-dependent, which results in the deviation from an ideal Nernstian behavior of the adsorbed cyt c at high electrode potentials. The electric-field-induced increase in the activation barrier of proton-transfer steps attributed to the rearrangement of the hydrogen bond network and the self-aggregation of cyt c upon adsorption on DNA-modified electrode strongly decrease the interfacial electron transfer rate.

The interaction of recombinant Pseudomonas aeruginosa exotoxin A with DNA and mimic biomembrane investigated by surface plasmon resonance and electrochemical methods

Based on the multidomain structure of Pseudomonas aeruginosa exotoxin A, a fusion protein termed rPEA has been constructed, which is expected to serve as a gene carrier in vitro. The expression and purification of rPEA are described. The basal properties of rPEA as a gene carrier are evaluated by investigating its interaction with plasmid DNA and mimic biomembrane by surface plasmon resonance (SPR) and electrochemical methods. rPEA is proved to be able to bind with plasmid DNA with high affinity. It can also interact with lipid membrane and increase permeability of the membrane, so the probe molecules can easily reach the gold surface and exhibit the electrochemical response.

Probing UPD-induced surface atomic rearrangement of polycrystalline gold nanofilms with surface plasmon resonance spectroscopy and cyclic voltammetry

Silver underpotential deposition (UPD)-induced surface atomic rearrangement of polycrystalline gold nanofilms was probed with use of surface plasmon resonance spectroscopy (SPRs) as a novel probe tool in combination with cyclic voltammetry. Interestingly, upon repetitive electrochemical UPD and stripping of Ag, the surface structure of the resulting bare Au film is rearranged due to strong adatom-substrate interactions, which causes a large angle shift of SPR R-theta curves, in a good linear relationship with the number of UPDs, to a lower SPR angle. The n, K values of the surfacial Au monolayers before and after the repetitive Ag UPD and stripping for 27 times are found to be 0.133, 3.60 and 0.565, 9.39, respectively, corresponding to the huge shift of 1.61degrees to the left of the SPR minima. Cyclic voltammetry experiments in 0.10 M H2SO4 are carried out before and after the UPD treatment to examine the quality of the whole electrode surface and confirmed this change. To correlate the angle change in SPRs with the profile change in the cyclic voltammogram, the UPD treatment was also performed on a Au(111) textured thin film. It was therefore confirmed that the resonance position of the SPR spectrum is very sensitive to the surface crystallographic orientation of the bare Au substrates. Some surface atomic rearrangement can cause a pronounced SPR angle shift.

Direct electrochemistry and surface plasmon resonance characterization of alternate layer-by-layer self-assembled DNA-myoglobin thin films on chemically modified gold surfaces

Alternate layer-by-layer (L-by-L) polyion adsorption onto gold electrodes coated with chemisorbed cysteamine gave stable, electroactive multilayer films containing calf thymus double stranded DNA (CT ds-DNA) and myoglobin (Mb). Direct, quasi-reversible electron exchange between gold electrodes and proteins involved the Mb heme Fe2+/Fe3+ redox couple. The formation of L-by-L (DNA/Mb), films was characterized by both in situ surface plasmon resonance (SPR) monitoring and cyclic voltammetry (CV). The effective thickness of DNA and Mb monolayers in the (DNA/Mb)l bilayer were 1.0 +/- 0.1 and 2.5 +/- 0.1 mn, corresponding to the surface coverage of similar to65% and similar to89% of its full packed monolayer, respectively. A linear increase of film thickness with increasing number of layers was confirmed by SPR characterizations. At pH 5.5, the electroactive Mb in films are those closest to the electrode surface; additional protein layers did not communicate with the electrode. CV studies showed that electrical communication might occur through hopping conduction via the electrode/base pair/Mb channel, thanks to the DNA-Mb interaction. After the uptake of Zn2+, a special electrochemical behavior, where MbFe(2+) acts as a DNA-binding reduction catalyst in the Zn2+-DNA/Mb assembly, takes place.

Real-time immunoassay of ferritin using surface plasmon resonance biosensor

A surface plasmon resonance (SPR) biosensor was used for the first time to determine the concentration of ferritin in both HBS-EP buffer and serum. The monoclonal antibody was immobilized on the carboxymethyl dextran-modified gold surface by an amine coupling method. The interaction of antibody with antigen was monitored in real-time. The signal was enhanced by sandwich amplification strategy to improve the sensitivity and specificity of the immunoassay, especially in serum. The linear range of the assay in serum is over 30-200 ng ml with the detection limit of 28 ng ml(-1). The sensitivity, specificity, and reproducibility of the assay are satisfactory. The analyte and enhancement antibody-binding surface could be regenerated by pH 2.0 glycine-HCl buffer and the same antibody-immobilized surface could be used for more than 50 cycles of ferritin binding and regeneration.