Biogenic nanoporous silica-based sensor for enhanced electrochemical detection of cardiovascular biomarkers proteins.

The goal of our research is to demonstrate the feasibility of employing biogenic nanoporous silica as a key component in developing a biosensor platform for rapid label-free electrochemical detection of cardiovascular biomarkers from pure and commercial human serum samples with high sensitivity and selectivity. The biosensor platform consists of a silicon chip with an array of gold electrodes forming multiple sensor sites and works on the principle of electrochemical impedance spectroscopy. Each sensor site is overlaid with a biogenic nanoporous silica membrane that forms a high density of nanowells on top of each electrode. When specific protein biomarkers: C-reactive protein (CRP) and myeloperoxidase (MPO) from a test sample bind to antibodies conjugated to the surface of the gold surface at the base of each nanowell, a perturbation of electrical double layer occurs resulting in a change in the impedance. The performance of the biogenic silica membrane biosensor was tested in comparison with nanoporous alumina membrane-based biosensor and plain metallic thin film biosensor. Significant enhancement in the sensitivity and selectivity was achieved with the biogenic silica biosensor, in comparison to the other two, for detecting the two protein biomarkers from both pure and commercial human serum samples. The sensitivity of the biogenic silica biosensor is approximately 1 pg/ml and the linear dose response is observed over a large dynamic range from 1 pg/ml to 1 microg/ml. Based on its performance metrics, the biogenic silica biosensor has excellent potential for development as a point of care handheld electronic biosensor device for detection of protein biomarkers from clinical samples.

Self quenching of chlorosome chlorophylls in water and hexanol-saturated water.

The optical properties of a methyl ester homolog of bacteriochlorophylld (BChld M ) and bacteriochlorophyllc (BChlc) in H2O, hexanol-saturated H2O and methanol were studied by absorption, fluorescence emission, and circular dichroism (CD). In H2O, BChld M spontaneously forms an aggregate similar to that formed in hexane, with absorption maximum at 730 nm and fluorescence emission at 748 nm. For the pigment sample in hexanol-saturated H2O, while the absorption peaks at 661 nm, only slightly red-shifted compared to the monomer, the fluorescence emission is highly quenched. When diluted 2-3 fold with H2O, the absorption returns to around 720 nm, characteristic of an aggregate. The CD spectrum of the H2O aggregate exhibits a derivative-shaped feature with positive and negative peaks, while the amplitude is lower than that of chlorosomes. The Fourier transform infrared spectra of BChld M aggregates in H2O and hexane were measured. A 1644 cm(-1) band, indicative of a bonded 13(1)-keto group, is detected for both samples. A marker band for 5-coordinated Mg was observed at 1611 cm(-1) for the two samples as well. To study the kinetic behavior of the samples, both single-photon counting (SPC) fluorescence and transient absorption difference spectroscopic measurements were performed. For BChld M in hexanol-saturated H2O, a fast decay component with a lifetime of 10 to 14 ps was detected using the two different techniques. The fast decay could be explained by the concentration quenching phenomenon due to a high local pigment concentration. For the pigment sample in H2O, SPC gave a 16 ps component, whereas global analysis of transient absorption data generated two fast components: 3.5 and 26 ps. The difference may arise from the different excitation intensities. With a much higher excitation in the latter measurements, other quenching processes, e.g. annihilation, might be introduced, giving the 3.5 ps component. Finally, atomic force microscopy was used to examine the ultrastructure of BChld M in H2O and hexanol-saturated H2O. Pigment clusters with diameters ranging from 15 to 45 nm were observed in both samples.

Superconductivity at 45 k in rb/tl codoped c60 and c60/c70 mixtures.

The appearance of superconductivity at relatively high temperatures in alkali metal-doped C(60) fullerene provides the challenge to both understand the nature and origin of the superconductivity and to determine the upper limit of the superconducting transition temperature (T(c)). Towards the latter goal, it is shown that doping with potassium-thallium and rubidium-thallium alloys in the 400 to 430 degrees C temperature range increases the T(c) of C(60)/C(70) mixtures to 25.6 K and above 45 K, respectively. Similar increases in T(c) were also observed upon analogous doping of pure C(60). Partial substitution of potassium with thallium in interstitial sites between C(60) molecules is suggested by larger observed unit cell parameters than for the K(3)C(60) and K(4)C(60) phases. Contrary to previous results for C(60) doped with different alkali metals, such expansion does not alone account for the changes in critical temperature.