Functionalized nanoporous silica for the removal of heavy metals from biological systems: adsorption and application.

Surface-functionalized nanoporous silica, often referred to as self-assembled monolayers on mesoporous supports (SAMMS), has previously demonstrated the ability to serve as very effective heavy metal sorbents in a range of aquatic and environmental systems, suggesting that they may be advantageously utilized for biomedical applications such as chelation therapy. Herein we evaluate surface chemistries for heavy metal capture from biological fluids, various facets of the materials' biocompatibility, and the suitability of these materials as potential therapeutics. Of the materials tested, thiol-functionalized SAMMS proved most capable of removing selected heavy metals from biological solutions (i.e., blood, urine, etc.) Consequentially, thiol-functionalized SAMMS was further analyzed to assess the material's performance under a number of different biologically relevant conditions (i.e., variable pH and ionic strength) to gauge any potentially negative effects resulting from interaction with the sorbent, such as cellular toxicity or the removal of essential minerals. Additionally, cellular uptake studies demonstrated no cell membrane permeation by the silica-based materials generally highlighting their ability to remain cellularly inert and thus nontoxic. The results show that organic ligand functionalized nanoporous silica could be a valuable material for a range of detoxification therapies and potentially other biomedical applications.

Detection of Cd, Pb, and Cu in non-pretreated natural waters and urine with thiol functionalized mesoporous silica and Nafion composite electrodes.

Electrochemical sensors have great potential for environmental monitoring of toxic metal ions in waters due to their portability, field-deployability and excellent detection limits. However, electrochemical sensors employing mercury-free approaches typically suffer from binding competition for metal ions and fouling by organic substances and surfactants in natural waters, making sample pretreatments such as wet ashing necessary. In this work, we have developed mercury-free sensors by coating a composite of thiol self-assembled monolayers on mesoporous supports (SH-SAMMS) and Nafion on glassy-carbon electrodes. With the combined benefit of SH-SAMMS as an outstanding metal preconcentrator and Nafion as an antifouling binder, the sensors could detect 0.5 pp b of Pb and 2.5 pp b of Cd in river water, Hanford groundwater, and seawater with a minimal amount of preconcentration time (few minutes) and without any sample pretreatment. The sensor could also detect 2.5 pp b of Cd, Pb, and Cu simultaneously. The electrodes have long service times and excellent single and inter-electrode reproducibility (5% R.S.D. after 8 consecutive measurements). Unlike SAMMS-carbon paste electrodes, the SAMMS-Nafion electrodes were not fouled in samples containing albumin and successfully detected Cd in human urine. Other potentially confounding factors affecting metal detection at SAMMS-Nafion electrodes were studied, including pH effect, transport resistance of metal ions, and detection interference. With the ability to reliably detect low metal concentration ranges without sample pretreatment and fouling, SAMMS-Nafion composite sensors have the potential to become the next-generation metal analyzers for environmental and bio-monitoring of toxic metals.

A bifunctional poly(ethylene glycol) silane immobilized on metallic oxide-based nanoparticles for conjugation with cell targeting agents.

A trifluoroethylester-terminal poly(ethylene glycol) (PEG) silane was synthesized and self-assembled on iron oxide nanoparticles. The nanoparticle system thus prepared has the flexibility to conjugate with cell targeting agents via either carboxylic or amine terminal groups for a number of biomedical applications, including magnetic resonance imaging (MRI) and controlled drug delivery. The trifluoroethylester silane was synthesized by modifying a PEG diacid to form the corresponding bistrifluoroethylester (TFEE), followed by a reaction with 3-aminopropyltriethoxysilane (APS). The APS coupled with PEG chains confers the stability of PEG self-assembled monolayers (SAMs) and increases the PEG packing density on nanoparticles by establishing hydrogen bonding between the carbonyl and amine groups present within the monolayer structure. The success of the synthesis of the PEG TEFE silane was confirmed with (1)H NMR and Fourier transform infrared spectroscopy (FTIR). The conjugating flexibility of the PEG TEFE was demonstrated with folic acid that had carboxylic acid groups and amine terminal groups, respectively, and was confirmed by FTIR. TEM analysis showed the well-dispersed nanoparticles before and after they were coated with PEG and folic acid.

Effects of template and precursor chemistry on structure and properties of mesoporous TiO2 thin films.

Mesoporous TiO2 thin films were synthesized by sol-gel processing using an aqueous-based, inexpensive, and environmentally friendly precursor and cationic surfactants as templates under mild reaction conditions. The films were prepared by spin-coating on glass substrates followed by calcination to remove the surfactant. N2 sorption, X-ray diffraction, and transmission electron microscopy were used to characterize the porosity, pore size, and pore structure before and after calcination. Films were found to have wormlike pore structures after calcination and surface areas on the order of 200 m2/g. These results show that the mesostructure and porosity of the thin films can be controlled by the surfactant template chemistry such as surfactant/Ti ratio, pH, and rate of solvent evaporation.