Patterned immobilization of antibodies in mechanically induced cracks

A new approach of chemically immobilizing antibody within a pattern based on thin-film cracking is presented. An adjustable pattern width is achieved with resolutions varied from nano- to microscale by using loading stress on thin-film coated elastomer substrate in both one and two dimensions. By introduction of solution or chemical vapor deposition approaches, antibodies were covalently immobilized in the channels. To demonstrate the bioactivity, specificity, and response rate of antibody patterned structure, scanning electron microscopy was used to enumerating bacteria. The chemically coupled antibody is found to retain its specificity when incubated with different bacteria solutions. Trichloro(1H,1H,2H,2H-perfluoroctyl)silane coating on nonsensing regions exhibits a distinguished bacteria-resistant function that is beneficial for providing a low intrinsic background signal in detection. This technique shows a great potential for applications in the fields of sensing and tissue engineering.     

Giant excitonic Zeeman splittings in colloidal Co2+ -doped ZnSe quantum dots

Colloidal Co(2+):ZnSe diluted magnetic semiconductor quantum dots (DMS-QDs) were prepared by the hot injection method and studied spectroscopically. Ligand-field electronic absorption and magnetic circular dichroism (MCD) spectra confirm homogeneous substitutional speciation of Co(2+) in the ZnSe QDs. Absorption spectra collected at various times throughout the syntheses reveal that dopants are absent from the central cores of the QDs but are incorporated at a constant concentration during nanocrystal growth. The undoped cores are associated with dopant exclusion from the ZnSe critical nuclei. Analysis of low-temperature electronic absorption and MCD spectra revealed excitonic Zeeman splitting energies (DeltaE(Zeeman)) of these Co(2+):ZnSe QDs that were substantially smaller than anticipated from bulk Co(2+):ZnSe data. This reduction in DeltaE(Zeeman) is explained quantitatively by the absence of dopants from the QD cores, where dopant-exciton overlap would be greatest. Since dopant exclusion from nucleation appears to be a general phenomenon for DMS-QDs grown by direct chemical methods, we propose that DeltaE(Zeeman) will always be smaller in colloidal DMS-QDs grown by such methods than in the corresponding bulk materials.     

In vitro haemocompatibility and stability of two types of heparin-immobilized silicon surfaces

Heparin was covalently immobilized onto a silicon surface by two different methods, carbodiimide-based immobilization and photo-immobilization. In the former method, a (3-aminopropyl) trimethoxysilane (APTMS) self-assembled monolayer (SAM) or multilayer was first coated onto the silicon surface as the bridging layer, and heparin was then attached to the surface in the presence of water-soluble carbodiimide. In the latter method, an octadecyltrichlorosilane (OTS) SAM was coated on the silicon surface as the bridging layer, and heparin was modified by attaching photosensitive aryl azide groups. Upon UV illumination, the modified heparin was then covalently immobilized onto the surface. The hydrophilicity of the silicon surface changed after each coating step, and heparin aggregates on APTMS SAM and OTS SAM were observed by atomic force microscopy (AFM). In vitro haemocompatibility assays demonstrated that the deposition of APTMS SAM, APTMS multilayer and OTS SAM enhanced the silicon's haemocompatibility, which was further enhanced by the heparin immobilization. There is no evident distinction regarding the haemocompatibility between the heparin-immobilized surfaces by both methods. However, heparin on silicon with APTMS SAM and multilayer as the bridging layers is very unstable when tested in vitro with a saline solution at 37 °C, due to the instability of APTMS SAM and multilayer on silicon. Meanwhile, photo-immobilized heparin on silicon with OTS SAM as the bridging layer showed superb stability.     

In vitro stability study of organosilane self-assemble monolayers and multilayers

The stability of self-assembled monolayers (SAMs) and multilayers formed on silicon surface by amino-terminated silanes and SAMs formed by alkyl and glycidyl terminated silanes were investigated in vitro with saline solution at 37 degrees C for up to 10 days. FTIR and XPS results indicated that amino-terminated SAMs and multilayers are very unstable if the alkyl chain is short ((CH2)3), while stable if the alkyl chain is long ((CH2)11). On the other hand, alkyl-terminated SAMs are very stable regardless of the alkyl chain length, and glycidyl terminated SAM retained approximately 77% of the organosilane molecules after 10 days. Hydrogen bonding between the organosilane monomer and silicon surface and among the organosilane monomers is believed to contribute to the instability of the SAM and multilayer formed by amino-terminated silane with a short alkyl chain ((CH2)3). Therefore, the widely used (3-aminopropyl) trimethoxysilane (APTMS) SAM and multilayer may not be suitable for implantable biomedical applications.     

Functionalization of AlN surface and effect of spacer density on Escherichia coli pili-antibody molecular recognition

The immobilization of antibodies to sensor surfaces is critical in biochemical sensor development. In this study, Jeffamine spacers were employed to tether Escherichia coli K99 pilus antibody to AlN/sapphire surfaces which may allow the antibody to freely reorient and potentially improving the antigen capture efficiency. Spacer density was one of the key parameters to be optimized in studying its effect on the immobilization of antibody. The spacer density was controlled by functionalizing AlN/sapphire surfaces with a mixed (3-glycidyloxypropyl)trimethoxysilane (GPTMS) and trichloro(1H,1H,2H,2H-perfluoroctyl)silane (FAS) self-assembled monolayer (SAM) through a step-wise method. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface coverage of GPTMS and surface chemical composition. Compared to spacer fully covered samples, the capture efficiency was improved by 28% with optimal Jeffamine ED 600 spacer density, which depends on the spacer properties such as the number of monomer units and its size.     

Immobilization of polysaccharides on a fluorinated silicon surface

A self-assembled monolayer (SAM) of fluoroalkyl silane (FAS) was deposited on a silicon surface by chemical vapor deposition (CVD) at room temperature under 1.01x10(5)Pa nitrogen. Using this new approach, the quality and reproducibility of the SAM are better than those prepared either in solution or by vapor phase deposition, and the deposition process is simpler. In this modified CVD process, the silane monomers, instead of the oligomeric species, are the primary reactants. Full coverage of the silicon surface by FAS molecules was achieved within 5 min. Heparin and hyaluronan, two naturally occurring biocompatible polysaccharides, were successfully covalently attached on the FAS SAM/Si surface by photo-immobilization. Atomic force microscopy (AFM) revealed the morphologic changes after the immobilization of heparin and hyaluronan, and X-ray photoelectron spectroscopy (XPS) confirmed the change in chemical compositions. Such combination of coatings is expected to enhance the stability and biocompatibility of the base material.     

Studies on simplified ergoline derivatives. A general six-step synthesis of phenyl-substituted 4-methyl-3,4,4a,5,6,10b-hexahydrobenzo[f]quinolin-1-(2H)-one analogs

This communication outlines the development of a novel, general synthetic route to substituted α-tetralones 5 , their subsequent conversion to the α,β-unsaturated ketones 11 , and an improved, one-step transformation of 11 to the tricyclic title compounds 1. Thus, substituted derivatives of 1 can be prepared in six steps from simple benzaldehydes, or, in three steps from more readily available α-tetralones.     

Effect of surface proteins on Staphylococcus epidermidis adhesion and colonization on silicone

Shunt infections are one of the most serious complications in shunt implant surgery. Previous studies have suggested that cerebrospinal fluid (CSF) proteins could affect bacterial adhesion and subsequent shunt infection. A systematic study using immobilized protein on the surface of silane-modified silicone was conducted to determine how these modifications influenced Staphylococcus epidermidis adhesion and colonization. A comparison was also made with silicone having physically adsorbed protein. A colony-counting adhesion assay and scanning electron microscopy (SEM) were used to provide quantitative analysis of bacterial adhesion and semi-quantitative analysis of bacterial colonization, respectively. In order to determine the appropriate silanization process for effective protein immobilization, the effect of bovine serum albumin (BSA) immobilized on n-3-(trimethoxysilyl)propyl-ethylenediamine (AEAPS)/silicone, aminopropyltriethoxysilane (APTMS)/silicone, 3-(glycidyloxypropyl)trimethoxysilane (GPTMS)/silicone, and octadecyltrichlorosilane (OTS)/silicone on bacterial adhesion was investigated. Upon identifying that OTS is the most effective silane, different types of proteins, including: BSA, human serum albumin (HSA), gamma-globulin, and fibrinogen were immobilized on OTS/silicone by a photo-immobilization method. Immobilized protein on modified silicone surfaces was found to be stable in saline for 30 days, while physically adsorbed protein showed instability within hours as determined by contact angle measurements and X-ray photoelectron spectroscopy (XPS). For HSA/OTS/silicone, BSA/OTS/silicone, gamma-globulin/OTS/silicone, fibrinogen/OTS/silicon, and physically absorbed BSA on silicone, the contact angles were 78.5 degrees, 80.7 degrees, 78.9 degrees, 81.3 degrees, and 96.5 degrees; and the amount of nitrogen content was found to be 4.6%, 5.0%, 5.6%, 7.2%, and 3.2%, respectively. All protein immobilized on OTS/silicone surfaces significantly reduced bacterial adhesion by around 75% compared to untreated silicone, while physically adsorbed BSA on silicone reduced by only 29.4%, as determined by colony-counting adhesion assay. However, there was no significant difference on bacterial adhesion among the different types of proteins immobilized on OTS/silicone. Minimizing bacterial adhesion and colonization can be attributed to the increased concentration of -NH2 group, and stability and more hydrophilic nature of the protein/OTS/silicone surfaces.     

Association of Molybdenum Ionic Species with Alumina Surface

The adsorption isotherms at 25, 45, and 65 degrees C of molybdenum solutions of concentration ranges between 10(-3) and 3x10(-2) M(Mo) (pH 4-5) on different alumina samples are investigated. The analysis is conducted using a modified Frumkin isotherm which takes a more realistic account of the lateral interaction between adsorbed species and considers that the adsorption takes place on the most basic OH groups on the surface of alumina. The results are discussed in view of the difference in solutions speciation, and the changes in the pH of the remaining supernatant solutions. The solution temperature, PZC of the used aluminas, the configuration of the basic OH groups on their surface, and the pore structure have been shown to intervene effectively. Copyright 2000 Academic Press.     

Spectroscopy of photovoltaic and photoconductive nanocrystalline Co2+-doped ZnO electrodes

Photocurrent and photoconductivity measurements have been used in combination with absorption and magnetic circular dichroism (MCD) spectroscopic measurements to elucidate the mechanism of photoinduced carrier generation in nanocrystalline Co(2+):ZnO electrodes. These experiments allowed direct observation of two broad Co(2+) charge transfer (CT) bands extending throughout the visible energy range. The lower energy CT transition is assigned as a Co(2+) --> conduction band excitation (ML(CB)CT). Sensitization of this ML(CB)CT level by (4)A(2) --> (4)T(1)(P) ligand-field excitation is concluded to be responsible for the distinctive structured photocurrent action spectrum of these electrodes at ca. 14 000 cm(-1). The higher energy CT transition is assigned as a valence band --> Co(2+) excitation (L(VB)MCT) and is found to have an internal quantum efficiency for charge separation that is approximately four times larger than that of the ML(CB)CT excitation. The different internal quantum efficiencies for the two CT excitations are related to differences in excited-state wave functions arising from configuration interaction with the 1S excitonic levels of ZnO. Whereas the ML(CB)CT excited state is best described as a localized Co(3+) + e(-)(CB) configuration, the L(VB)MCT excited state (Co(+) + h(+)(VB)) has a 4-fold greater admixture of delocalized excitonic (Co(2+) + h(+)(VB) + e(-)(CB)) character in its wave function, a conclusion supported by quantitative analysis of the CT absorption intensities. Practical factors controlling the overall photovoltaic efficiencies of the photoelectrochemical cells, including electrode conductivity and porosity, were also examined.