No abstract

Enzyme adsorption to Au nanoparticles is important for bioanalytical, catalytic, and biotechnological applications. In this manuscript, adsorption of horseradish peroxidase (HRP) and fluorescein labeled HRP (F-HRP) to colloidal Au nanoparticles is compared. Flocculation analysis indicates some differences in adsorption behavior for the labeled and unlabeled enzymes, particularly at pH 8.0, and to a lesser extent also, at pH 4.0. Zeta potential measurements were quite similar for HRP and F-HRP and leveled off at lower enzyme:Au ratios than observed by flocculation, particularly for pH 6.0 and 8.0. Direct quantification of bound F-HRP was performed by dissolution of Au nanoparticles before fluorescence measurements. We observed F-HRP binding at greater than monolayer coverage on the particles and did not reach saturation even at high solution F-HRP:Au ratios. Indirect quantification of bound unlabeled HRP based on supernatant analysis followed similar trends. More than 50% of the specific enzyme activity was retained for conjugates with a low HRP coverage. With increasing enzyme coverage, the specific activity decreased significantly; however, the total activity per particle remained nearly constant. These findings suggest HRP multilayer formation on the Au nanoparticles, with the outermost layer of HRP contributing to the major part of the conjugate enzyme activity.

Encoded anisotropic nano- and microparticles represent an exciting new class of detection and identification strategies for bioanalysis. These particles are synthesized in a number of different ways and can be encoded by shape, composition, topographical features, or optical properties. In this review, we explore synthetic methods for the formation of anisotropic encoded particles and evaluate these systems as multiplexed biosensing platforms. Suspension arrays using anisotropic particles have been used to detect a range of biological species including proteins, nucleic acids, spores, cells, and small molecules. Because in many cases a large number of codes should be obtainable, the potential exists for high levels of multiplexing (thousands or more). The bulk of work in this area to date has focused on initial proof of principle synthesis and identification; however, multiplexed bioassays have been demonstrated for a number of different anisotropic carrier particles and are beginning to be adopted in commercial assays.

The catalytic activity and resistance to poisoning of Pd catalysts supported on swellable organically-modified silica (SOMS) were investigated for hydrodechlorination (HDC) of trichloroethylene (TCE). The promising catalytic activity of 1% Pd/SOMS sample was attributed to the high affinity of SOMS for organics and its high hydrophobicity. While latter characteristic repels water, the adsorptive capacity for organics allows TCE dissolved in aqueous media to concentrate inside the pores, in the vicinity of the active sites, thus helping the kinetics. In the liquid phase, using a continuous flow reactor, higher TCE conversion was obtained over the 1% Pd/SOMS compared to the commercial 1% Pd/Al2O3 catalyst. When the pores of 1% Pd/SOMS sample were fully opened by pre-treating it with ethanol prior to the reaction, HDC activity was seen to significantly increase. In the gas phase, the extent of adsorption was less, reducing the concentration of reactants near the active sites. As a result, 1% Pd/SOMS was less active than 1% Pd/Al2O3 for HDC of TCE. To determine their resistance to poisoning, 1% Pd/SOMS and 1% Pd/Al2O3 catalysts were poisoned ex-situ with Li2S. The ex-situ poisoned Pd/SOMS sample maintained its catalytic activity for HDC of TCE. However, a significant loss in catalytic activity of the Pd/Al2O3 catalyst was observed after poisoning. Protection from aqueous phase sulfide poisoning was attributed to the hydrophobicity of the Pd/SOMS, which would exclude anionic species from the embedded Pd particles. The XPS, STEM and ICP-OES results indicated that when Pd/Al2O3 and Pd/SOMS were treated with 1 M HCl, most of the Pd metal was leached from the Pd/Al2O3 catalyst in contrast to Pd/SOMS, which had negligible leaching. Overall, due to hydrophobicity and high affinity for organics, SOMS has potential as a catalyst scaffold for different reactions in groundwater remediation applications.

A sample preparation method that combines a modified target plate with a nanoscale reversed-phase column (nanocolumn) was developed for detection of neuropeptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A gold-coated MALDI plate was modified with an octadecanethiol (ODT) self-assembled monolayer to create a hydrophobic surface that could concentrate peptide samples into a approximately 200-500-microm diameter spot. The spot sizes generated were comparable to those obtained for a substrate patterned with 200-microm hydrophilic spots on a hydrophobic substrate. The sample spots on the ODT-coated plate were 100-fold smaller than those formed on an unmodified gold plate with a 1-microl sample and generated 10 to 50 times higher mass sensitivity for peptide standards by MALDI-TOF MS. When the sample was deposited on an ODT-modified plate from a nanocolumn, the detection limit for peptides was as low as 20 pM for 5-microl samples corresponding to 80 amol deposited. This technique was used to analyze extracts of microwave-fixed tissue from rat brain striatum. Ninety-eight putative peptides were detected including several that had masses matching neuropeptides expected in this brain region such as substance P, rimorphin, and neurotensin. Twenty-three peptides had masses that matched peaks detected by capillary liquid chromatography with electrospray ionization MS.