SERS-Based Detection of Calcein Blue Using Nanoparticle-Modified Silica Sol-Gels

Surface-enhanced Raman spectroscopy (SERS) has gained interest recently due to its compatibility with aqueous solutions and unique spectra for all molecules. These qualities make SERS an ideal technique for sensing applications; however, an appropriate substrate is needed for effective measurements. Silica sol-gels containing silver nanoparticles may be able to act as SERS substrates, given their porosity and high surface area, and may be able to act as sensors if modified with additional small molecules. In this study, the SERS activity of silica sol-gels containing silver nanoparticles and calcein blue (CB) was investigated to determine their suitability as metal ion sensors. Sol-gels were prepared via the base-catalyzed hydrolysis of tetramethyl orthosilicate (TMOS) in the presence of aqueous CB and silver nanoparticles. SERS measurements of synthesized sol-gels were obtained using a home built Raman spectrometer; obtained spectra indicate that sol-gels containing silver nanoparticles are viable substrates for the SERS of CB and thus may be viable as metal ion sensors

Examination of Silica Sol-Gels and Aerogels Containing Silver Nanoparticles and 4-Mercaptobenzoic Acid Using Surface-Enhanced Raman Spectroscopy

Sol-gels and aero-gels containing silver nanoparticles have been investigated for use as substrates in surface-enhanced Raman spectroscopy (SERS). 4-Mercaptobenzoic acid (4-MBA) was chosen as the target molecule in this study, as it has been well-characterized using SERS. The orientation of the 4-MBA at different coverages in gels, and at differing concentrations of silver colloid, has not been well studied. For both base and acid-catalyzed sol-gels, xerogels, and aerogels, the concentration of 4-MBA was varied with a constant silver colloid concentration in the silica gels and the effects were measured with SERS. The effect of varying silver colloid concentration against a constant 4-MBA concentration was also investigated. The results of each process were compared

Stabilization of DAPI in Base-Catalyzed Sol-Gels Using Surface Enhanced Raman Spectroscopy

Sol-gels can be used as substrates for sensory materials in solutions. A fluorescent dye that binds to DNA, 4’,6-diamidino-2-phenylindole (DAPI), could be used as a biosensor for a solution. Adsorption of DAPI onto silver nanoparticles causes rapid precipitation and loss of DAPI in solution. UV-vis and surface-enhanced Raman spectroscopy (SERS) were performed to observe a solution of silver nanoparticles and DAPI. Over time, spectra of the solution greatly diminished and could no longer be accurately observed. To facilitate the stabilization of DAPI in the solution, sol-gels were synthesized via base-catalyzed hydrolysis of tetramethyl orthosilicate while in the DAPI-silver solution. Sol-gels were successfully synthesized and DAPI precipitation was prevented as suggested by UV-vis and SERS

Ultrapure glass optical waveguide development in microgravity by the sol-gel process

Multicomponent, homogeneous, noncrystalline oxide gels can be prepared by the sol-gel process and these gels are promising starting materials for melting glasses in the space environment. The sol-gel process referred to here is based on the polymerization reaction of alkoxysilane with other metal alkoxy compounds or suitable metal salts. Many of the alkoxysilanes or other metal alkoxides are liquids and thus can be purified by distillation. The use of gels offers several advantages such as high purity and lower melting times and temperatures. The sol-gel process is studied for utilization in the preparation of multicomponent ultrapure glass batches for subsequent containerless melting of the batches in space to prepare glass blanks for optical waveguides

Examination of 4’,6-diamidino-2-phenylindole (DAPI) in Silica Gels through Fluorometry

Silica sol-gels synthesized through hydrolysis and condensation reactions via acid- and base-catalyzed procedures containing 4’,6-diamidino-2-phenylindole (DAPI) have been examined using fluorescence spectroscopy. DAPI is a fluorescent molecule that has traditionally been used in biosensors as a target molecule and a fluorescent stain known to bind strongly to the A-T rich regions of DNA. Sol-gels containing various concentrations of DAPI were dried conventionally to form xerogels or supercritically to form aerogels and then analyzed using fluorescence spectroscopy to determine the most optimal concentration of DAPI

Optimization of 4-Mercaptobenzoic Acid in SiO2-Ag Colloid Aerogel Using Surface-Enhanced Raman Spectroscopy

Aerogels have been studied as potential insulating and conducting materials, but little research has been conducted characterizing organic molecules in aerogel matrices using surface-enhanced Raman spectroscopy (SERS). In this study, SiO2-Ag colloid aerogels were used as enhanced surfaces for SERS. SERS spectra of 4-mercaptobenzoic acid (4-MCBA) adsorbed to acid- and base-catalyzed SiO2-Ag colloid aerogels were obtained. It was observed that acid-catalyzed silver sol gels with 4-MCBA mixed within the matrix provided SERS spectra with sharper and more enhanced peaks than the base-catalyzed silver sol gels

Methylene blue doped sol-gels preparation and application as fiber-optic fluorescence sensors

The goal of this thesis project was to create a Methylene Blue (MB) doped sol-gel fiber-optic fluorescence sensor. Ideally this sensor would be capable of detecting changes in sulfite concentration in solution continuously and reversibly. In aqueous solution, MB, a redox indicator, is converted from a bright blue color to the colorless leuco-MB species upon exposure to sulfite or other reducing agents. This reaction is reversible in the presence of an oxidizing agent Therefore, if MB can be immobilized properly, it would make a suitable reversible indicator for the sulfite anion in solution. The method of MB immobilization employed in this project was the sol-gel method. Organic solutes can be physically entrapped in sol-gels without being altered chemically. In this project, sol-gels were prepared by the hydrolysis and condensation of either tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS). MB doped sol-gels were prepared using both TMOS and TEOS as precursors. Leaching of MB from these sol-gels does not appear to occur in neutral aqueous solution. The MB doped sol-gels prepared are responsive to the sulfite ion in solution; however, they are significantly less responsive to oxidizing agents. Blue MB is not readily regenerated from leuco-MB within the sol-gels. Moreover, the MB converts to the colorless leuco-MB form within the sol-gels over time even in the presence of oxidizing agents. Hence, this system requires further fundamental study before it can be used in the preparation of a reusable sol-gel fiber-optic fluorescence sulfite sensor. This system, however, is currently suitable for use as a disposable sulfite sensor

Metal Ion Detection Using Silica Sol-gels Containing Silver Nanoparticles and Calcein Blue (CB)

Surface-enhanced Raman spectroscopy (SERS) is a spectroscopic technique which relies on the inelastic scattering of photons from a target molecule. SERS is both sensitive and specific; the technique produces a unique spectrum for all molecules while offering up to single molecule detection with proper conditions. However, acquisition of SERS spectra requires the presence of a suitable substrate, such as noble metal nanoparticles or roughened metal electrodes. Silica sol-gels are porous, amorphous silica matrices formed by the hydrolysis of a silicon containing precursor molecule. As a result of their unique structure, these compounds have a variety of unique properties, such as high surface area and low thermal conductivity. They can be easily modified, and metal-colloid-modified silica sol-gels represent a relatively unknown class of compounds which can function as substrates for SERS measurements. In this study, the fluorescent dye calcein blue (CB) was chosen as a target molecule due to its ability to interact with various metal ions. As a result, it has found use as an indicator in EDTA titrations and has potential applications in metal ion sensing devices. Thus, detection of calcein blue within modified sol-gels could lead to the development of new techniques for the detection of metal ions. Such techniques could have applications in fields such as water quality analysis or other environmental assays