Shiva K. Rastogi

8-aminoquinoline functionalized silica nanoparticles: a fluorescent nanosensor for detection of divalent zinc in aqueous and in yeast cell suspension.

Zinc is one of the most important transition metal of physiological importance, existing primarily as a divalent cation. A number of sensors have been developed for Zn(II) detection. Here, we present a novel fluorescent nanosensor for Zn(II) detection using a derivative of 8-aminoquinoline (N-(quinolin-8-yl)-2-(3 (triethoxysilyl)propylamino)acetamide (QTEPA) grafted on silica nanoparticles (SiNPs). These functionalized SiNPs were used to demonstrate specific detection of Zn(II) in tris-HCl buffer (pH 7.22), in yeast cell (Saccharomyces cerevisiae) suspension, and in tap water. The silane QTEPA, SiNPs and final product were characterized using solution and solid state nuclear magnetic resonance, Fourier transform infrared, ultraviolet-visible absorption spectroscopy, transmission electron microscopy, elemental analysis, thermogravimetric techniques, and fluorescence spectroscopy. The nanosensor shows almost 2.8-fold fluorescence emission enhancement and about 55 nm red-shift upon excitation with 330 ± 5 nm wavelength in presence of 1 μM Zn(II) ions in tris-HCl (pH 7.22). The presence of other metal ions has no observable effect on the sensitivity and selectivity of nanosensor. This sensor selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 μM. The sensor shows good applicability in the determination of Zn(II) in tris-HCl buffer and yeast cell environment. Further, it shows enhancement in fluorescence intensity in tap water samples.

Ag colloids and Ag clusters over EDAPTMS-coated silica nanoparticles: synthesis, characterization, and antibacterial activity against Escherichia coli

UNLABELLED To produce better antibacterial water-insoluble nanocomposites of silver (Ag), silver-silicon dioxide (Ag-SiO(2)) hybrid and silver colloid (Ag-c) nanoparticles (NPs) were studied. Ag-c NPs were synthesized using reduction of AgNO(3), and Ag-SiO(2) composites were prepared on a core of silica NPs functionalized with ethylenediamino-propyltrimethoxysilane, where Ag clusters were fabricated on amino groups using seed-mediated growth and characterized by transmission electron microscopy and ultraviolet-visible absorption spectroscopy. Antibacterial effectiveness of the Ag-SiO(2) NPs was tested against general Escherichia coli (E. coli ATCC 25922) and E. coli O157:H7 by measuring the growth based on optical density and digital counting of live-dead cells using a fluorescent microscope, and a field emission scanning electron microscope. Minimum inhibitory concentration values were studied against four representative bacteria along with E. coli O157:H7. Results showed that Ag NPs of 6.6 ± 4.5 nm were attached to the surface of SiO(2) NPs (74 ± 13.5 nm), and the Ag-c NPs (3.5 ± 2 nm) showed excellent antibacterial properties. FROM THE CLINICAL EDITOR In this paper, the synthesis of Ag colloids and Ag clusters over EDAPTMS-coated silica nanoparticles is reported. Both NPs were examined for antibacterial effectiveness against representative bacteria including E. coli O157:H7 and found to have excellent antibacterial properties.

Fluorescence sensing of zinc(II) using ordered mesoporous silica material (MCM-41) functionalized with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide.

A novel fluorescent zinc sensor was designed and synthesized on ordered mesoporous silica material, MCM-41, with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide (QTEPA; 3) using a simple one-step molecular self-assembly of the silane. The solution and solid samples were characterized using solid-state nuclear magnetic resonance, transmission electron microscopy, diffuse-reflectance infrared Fourier transform, and thermogravimetric analysis techniques. The QTEPA-modified MCM-41 (4) shows 3-fold fluorescence emission enhancement and about a 55 nm red shift upon addition of 1 μM Zn(II) ions in a Tris-HCl (pH 7.22) aqueous buffer solution. The UV-vis absorption maximum is at 330 ± 5 nm, and the fluorescence emission maximum wavelength is at 468 nm, with an increase in quantum yield from 0.032 to 0.106 under the same conditions. The presence of other metal ions has no observable effect on the sensitivity and selectivity of 4. This system selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 μM. The MCM-41-based systems have the advantage that they can be employed in aqueous solutions without any aggregation.

Characterization of a vertically aligned silica nanospring-based sensor by alternating current impedance spectroscopy

In this study, the initial phase of development of a vertically aligned (silica) nanospring (VANS)-based sensor utilizing alternating current impedance spectroscopy is presented. The sensor is a capacitor consisting of two glass substrates coated with indium tin oxide, where the VANS are grown on one substrate, following a top-down approach, serving as the dielectric spacer layer. The sensitivity of the VANS sensors was evaluated using deionized water (of an effective 10?3 mM monovalent ion concentration) and saline-phosphate (SP) solutions of pH 7.3 with concentrations 0.1, 1, 10 and 100 mM. Similar tests were performed with sensors without VANS or blank sensors. The modeling of the VANS impedance spectra required an equivalent circuit consisting of eight elements compared to four elements for the blank sensor. VANS sensors exhibited greater sensitivity to changes in the SP concentration relative to the blank sensors. The enhanced sensitivity is attributed to the addition of an ionic diffusion barrier at the VANS?solution interface and to ionic diffusion within the VANS.

A novel homogeneous bioluminescence resonance energy transfer element for biomolecular detection with CCD camera or CMOS device

A novel optical signal element based on homogeneous bioluminescence resonance energy transfer (BRET) was developed for biomolecular detection. A fluorescent dye and alkaline phosphatase (AP) conjugate was used as a reporter and light-generation element for imaging detection platforms that use a CCD camera or CMOS chip-based devices. In the presence of a luminescence substrate, the energy from the first light emission of a bioluminescence enzymatic reaction was transferred to fluorescent dyes which were conjugated to an enzyme. This resulted in a second light emission with a shorter wavelength. The second light was localized at the position of target molecules without the diffusion problems present in current technology. To optimize energy transfer efficiency, the ratio of enzyme to fluorophore in the conjugates, the fluorescent dyes used in the conjugates and the luminescence substrates used for BRET were investigated. BRET was demonstrated by using both a CCD camera and a CMOS imaging device. Image spatial resolution was greatly improved compared with conventional chemiluminescence detection. This new signal element opens a door for the direct measurement of fluorescent signals on an imaging chip without an external light source and portable instrumentation normally required for the fluorescent detection of biomolecules.

Antibody@Silica Coated Iron Oxide Nanoparticles: Synthesis, Capture of E. coli and SERS Titration of Biomolecules with Antibacterial Silver Colloid

Silica coated iron oxide (SiO 2 /Fe 3 O 4 + γ- Fe 2 O 3 ) nanoparticles (SIO-NPs; 75±10 nm in diameter) were prepared by encapsulation of iron oxide NPs with silica using sol-gel method and characterized through spectroscopy methods. The SIO NPs were chemically activated by cyanogens bromide and then functionalized with Escherichia coli ( E. coli ) antibodies. These immuno-magnetic (IM NPs) were used to capture and concentrate E. coli from ~ 180 cfu/ mL suspension. The identification of bacteria was performed by plating on nutrient agar, fluorescent microscopy and scanning electron microscopy. Surface enhanced Raman spectroscopy (SERS) was used to identify different biomolecules of bacterial cell upon the interaction of colloidal silver nanoparticle (Ag NPs 6±4 nm) at different period of time. In our previous report we demonstrated the antibacterial property of colloidal Ag NPs. Therefore, current approach, using IM, and Ag NPs and SERS, provide detailed molecular identification of E. coli as Ag NPs interact over the time. This method would be applicable for food safety, environment protection, biological threat material, antibacterial and other routine E. coli identification projects.

Hybridization Study of PNA-DNA in the Solution and Surface-Solution Interface for Biosensor Application

Abstract Hybridization of 12-mers peptide nucleic acid (PNA) to complementary DNA was investigated in solution and on gold surfaces. The oligomers were designed to improve mismatch discrimination and minimize formation of secondary structures. Thermal denaturation experiments indicate high thermal stabilities for PNA-DNA hybrid with T m values close to calculated values. Hybridization of PNA-DNA at 45°C and room temperature showed no difference. Hybridization on gold surface was also investigated with complementary and noncomplementary DNAs. The results show that 12-mer PNA and DNA hybridization at room temperature retained high specificity within ∼5 ng.

Non‐enzymatic aqueous peroxyoxalate chemiluminescence immune detection using a CCD camera and a CMOS device

A new method for non-enzymatic aqueous peroxyoxalate chemiluminescence (POCL) biomolecular detection using imaging chip-based devices has been developed. A water-soluble amide of oxalic acid was synthesized and used in the investigation and characterization of POCL immunodetection in an aqueous environment. Six fluorescent dyes commonly used in biological detection were tested, and the intensity of light generated from the aqueous POCL reactions was characterized in the liquid phase. Direct detection sensitivity comparisons between a standard fluorescent method and this POCL method were performed in both liquid and solid phases. Results showed that detection sensitivity using the POCL method is comparable to that of the fluorescent method. POCL biomolecular detection on a nitrocellulose membrane was also investigated using a charge-coupled device (CCD) camera. Again, POCL detection sensitivity proved to be comparable to that using the fluorescent detection method. In an application of aqueous POCL biomolecular detection, Staphylococcus aureus enterotoxin B (SEB) and its antibody were used to demonstrate immuno- and affinity detection. For further applications, such as DNA and protein arrays, simultaneous detection of biomolecules labelled with different fluorescent labels was investigated, using a complementary metal oxide semiconductor (CMOS) colour imaging chip.