Isolation and structure determination of a new bisabolane-type sesquiterpenoid with cytotoxicity from Penicillium oxalicum MZY-202312-521.

Endophytic fungi can produce attractive secondary metabolites with various biological activities that have contributed significantly to pharmacotherapy. In this study, three bisabolane-type sesquiterpenoids, including a new one, namely, inonotic acid C (1), together with previously reported compounds (S)-(+)-11-dehydrosydonic acid (2) and sydonic acid (3), were isolated from a marine algal-derived endophytic fungus Penicillium oxalicum MZY-202312-521. Their structures were determined by means of extensive spectroscopic analyses. The absolute configurations of inonotic acid C (1) were established by single-crystal X-ray diffraction method. In vitro cytotoxic experiments on human A549, MCF-7, HeLa, and HepG2 carcinoma cell lines were carried out. The new compound inonotic acid C (1) was found to possess strong inhibitory activity against the MCF-7 cell line, with an IC50 value of 7.7 µM.

PNA-DNA hybridization study using labeled streptavidin by voltammetry and surface plasmon fluorescence spectroscopy.

Using ferrocene-streptavidin conjugates as amplifiers, we recently have demonstrated the simultaneous detection of DNA hybridization to peptide nucleic acid (PNA)-modified gold surfaces at the femtomole level by electrochemical and surface plasmon resonance techniques (Liu, J.; Tian, S.; Tiefenauer, L.; Nielsen, P. E.; Knoll, W. Anal. Chem. 2005, 77, 2756-2761). In this paper, a detailed study of the binding behavior of PNA-DNA is presented by square wave voltammetry and surface plasmon field-enhanced fluorescence spectroscopy (SPFS). The different binding constants for fully matched and single-mismatched DNA were obtained. The effect of the buffer concentration on the PNA-DNA hybrids was investigated using labeled streptavidin by cyclic voltammetry (CV) and SPFS. At high ionic strength, both the CV and SPFS signals were restrained dramatically, which is most probably due to a conformational change of the short-strand PNA-DNA helices on the surface. We conclude that the combination of electrochemical techniques with SPFS is very useful for the study of short DNA structure transformation.

One-step route to the fabrication of highly porous polyaniline nanofiber films by using PS-b-PVP diblock copolymers as templates.

We report a new method to control both the nucleation and growth of highly porous polyaniline (PANI) nanofiber films using porous poly(styrene-block-2-vinylpyridine) diblock copolymer (PS-b-P2VP) films as templates. A micellar thin film composed of P2VP spheres within a PS matrix is prepared by spin coating a PS-b-P2VP micellar solution onto substrates. The P2VP domains are swollen in a selective solvent of acetic acid, which results in the formation of pores in the block copolymer film. PANI is then deposited onto the substrates modified with such a porous film using electrochemical methods. During the deposition, the nucleation and growth of PANI occur only at the pores of the block copolymer film. After the continued growth of PANI by the electrochemical deposition, a porous PANI nanofiber film is obtained.

Electrochemically tunable surface-plasmon-enhanced diffraction gratings and their (bio-)sensing applications.

Electrochemistry was combined with surface-plasmon-enhanced diffraction (ESPD) to investigate a redox-switchable polymer grating and its (bio-)sensing applications. Patterned arrays of polyaniline (PANI)/ poly(styrenesulfonate) (PSS) were fabricated by the combination of electropolymerization and micromolding in capillaries (MIMIC) and were used as an optical grating for surface-plasmon-enhanced diffraction experiments. The diffraction efficiency (DE) could be tuned by changes in the applied potential, and by changes in the pH of the surrounding solution (dielectric medium). The response of the DE to the pH depends strongly on the redox state of the PANI/PSS grating. If the polymer grating is mainly in its reduced state, the DE shows a linear dependence on the pH. The DE of the PANI/PSS grating can also be modulated by an electrocatalytic event: by keeping PANI/PSS in its oxidized form, the addition of beta-nicotinamide adenine dinucleotide (NADH) increases the DE with the increase of NADH concentration, which points to the possibility of the use of ESPD technologies for biosensing.

Properties of polyaniline/carbon nanotube multilayer films in neutral solution and their application for stable low-potential detection of reduced beta-nicotinamide adenine dinucleotide.

A conducting polymer, polyaniline (PANI), was successfully assembled with commercially available poly(aminobenzenesulfonic acid)-modified single-walled carbon nanotubes (PABS-SWNTs) via the simple layer-by-layer method. PABS-SWNTs inside the multilayer film can dope PANI effectively and shift its electroactivity to a neutral pH environment, pointing to their potential biological applications. The obtained PANI/PABS-SWNTs multilayer films are very stable and show a high electrocatalytic ability toward the oxidation of reduced beta-nicotinamide adenine dinucleotide (NADH) at a much lower potential (about +50 mV vs Ag/AgCl), which makes it an ideal substrate for NADH detection and offers great promise for developing dehydrogenase-based biosensors depending on NADH as a cofactor. For a six-bilayer sample, the detection limit can go down to 1 x 10(-6) M as detected by the simple cyclic voltammetry method, with a linear detection range for NADH at concentrations between 5 x 10(-6) and 1 x 10(-3) M. The substrate can be used repeatedly for consecutive detection cycles of NADH with a very stable signal.

In situ hybridization of PNA/DNA studied label-free by electrochemical impedance spectroscopy.

The in situ hybridization kinetics of label-free DNA on mixed monolayers of peptide nucleic acid (PNA) and 6-mercapto-1-hexanol (MCH) on Au electrodes was investigated by electrochemical impedance spectroscopy (EIS) and used to discriminate the fully complementary DNA from the single-base mismatched hybrids.

Simultaneously amplified electrochemical and surface plasmon optical detection of DNA hybridization based on ferrocene-streptavidin conjugates.

A sensitive method based on ferrocene-streptavidin (Fc-Stv) conjugates for the simultaneously amplified electrochemical and surface plasmon optical detection of DNA target hybridization to peptide nucleic acid-modified gold surfaces is reported. The attachment of Fc-Stv to the biotinylated complementary target DNA not only amplified the surface plasmon resonance signal but also enhanced the electrochemical signal due to the many Fc markers per Stv. The ferrocene redox peak current increased with the increase of the target DNA concentration. Consequently, the amount of hybridized target DNA can be estimated by cyclic voltammetry and chronocoulometry. The detection limit of this DNA sensor is 10 pM (2 fmol, with signal to noise > 3). This sensor was also shown to have high selectivity (at the single-base mismatch level) and good reproducibility.

Surface plasmon enhanced diffraction for label-free biosensing.

Surface plasmon enhanced evanescent field at a (noble) metal/dielectric interface can be employed to enhance the diffraction efficiency of surface grating structure composed of biomolecules. Based on a Kretschmann configuration, we realized a diffraction biosensor to monitor the dynamic interaction of biological molecules in a label-free way. It was demonstrated by the binding of an anti-biotin antibody to the biotin-functionalized region of a periodically patterned surface, which generated significant optical contrast to diffract the surface plasmon field. With the aid of the synchronic surface plasmon resonance signal, a quadratic dependence of diffraction signal on the amount of bound antibody was found, which coincides with the theoretical expectation. Time-dependent measurements were conducted to estimate the density of biotin thiols on the functional region.

Polyaniline doped with modified gold nanoparticles and its electrochemical properties in neutral aqueous solution.

Doping polyaniline with COO(-)-modified gold nanoparticles by forming stable layer-by-layer multilayer films can shift its electroactivity to neutral pH. The films can electrocatalyze the oxidation of NADH and offer potential applications in other fields, e.g., optoelectronics or biosensing.