Biomedical subjects

James R Engstrom

Publications and source records attributed to James R Engstrom.

4 recordsLinked to original sources

PubMed2006

Ab initio calculations of the reaction mechanisms for metal-nitride deposition from organo-metallic precursors onto functionalized self-assembled monolayers.

An atomistic mechanism has been derived for the initial stages of the adsorption reaction for metal-nitride atomic layer deposition (ALD) from alkylamido organometallic precursors of Ti and Zr on alkyltrichorosilane-based self-assembled monolayers (SAMs). The effect of altering the terminal functional group on the SAM (including -OH, -NH2, -SH, and -NH(CH3)) has been investigated using the density functional theory and the MP2 perturbation theory. Reactions on amine-terminated SAMs proceed through the formation of a dative-bond complex with an activation barrier of 16-20 kcal/mol. In contrast, thiol-terminated SAMs form weak hydrogen-bonded intermediates with activation barriers between 7 and 10 kcal/mol. The deposition of Ti organometallic precursors on hydroxyl-terminated SAMs proceeds through the formation of stronger hydrogen-bonded complexes with barriers of 7 kcal/mol. Zr-based precursors form dative-bonded adducts with near barrierless transitions. This variety allows us to select a kinetically favorable substrate for a chosen precursor. The predicted order of reactivity of differently terminated SAMs and the temperature dependence of the initial reaction probability have been confirmed for Ti-based precursors by recent experimental results. We predict that the replacement of methyl groups by trifluoromethyl groups on the SAM backbone decreases the activation barrier for amine-terminated SAMs by 5 kcal/mol. This opens a route to alter the native reactivities of a given SAM termination, in this case making amine termination energetically viable. The surface distribution of SAM molecules has a strong effect on the adsorption kinetics of Ti-based precursors. Unimolecular side decomposition reactions were found to be kinetically competitive with adsorption at 400 K.

Journal Article↗

PubMed2005

Covalent attachment of a transition metal coordination complex to functionalized oligo(phenylene-ethynylene) self-assembled monolayers.

We have investigated the reaction of tetrakis(dimethylamido)titanium, Ti[N(CH(3))(2)](4), with N-isopropyl-N-[4-(thien-3-ylethynyl) phenyl] amine and N-isopropyl-N-(4-{[4-(thien-3-ylethynyl) phenyl]ethynyl}phenyl) amine self-assembled monolayers (SAMs), on polycrystalline Au substrates. The structure of the SAMs themselves has also been investigated. Both molecules form SAMs on polycrystalline Au bound by the thiophene group. The longer-molecular-backbone molecule forms a denser SAM, with molecules characterized by a smaller tilt angle. X-ray photoelectron spectroscopy (XPS) and angle-resolved XPS have been employed to examine the kinetics of adsorption, the spatial extent of reaction, and the stoichiometry of reaction. For both the SAMs, adsorption is described well by first-order Langmuirian kinetics, and adsorption is self-limiting from T(s) = -50 to 30 degrees C. The use of angle-resolved XPS clearly demonstrates that the Ti[N(CH(3))(2)](4) reacts exclusively with the isopropylamine end group via ligand exchange, and there is no penetration of the SAM, followed by reaction at the SAM-Au interface. Moreover, the SAM molecules remain bound to the Au surface via their thiopene functionalites. From XPS, we have found that, in both cases, approximately one Ti[N(CH(3))(2)](4) is adsorbed per two SAM molecules.

Crystallization↗

PubMed2005

A surface modification strategy on silicon nitride for developing biosensors.

A surface modification strategy for the use of giant magnetoresistive materials in the detection of protein-protein interactions is developed. This modification strategy is based on silanization of semiconductive materials. A native silicon nitride surface was treated with concentrated hydrofluoric acid to improve surface homogeneity. Nano-strip was used to oxidize silicon nitride to form a hydrophilic layer. Aminopropyltriethoxysilane was subsequently used to functionalize the treated surfaces to form amine groups, which were further activated with glutaraldehyde to introduce a layer of aldehyde groups. The effectiveness of this modification strategy was validated by chemiluminescence immunoassays of purified 6x His-HrpW of Pseudomonas syringae pv. tomato DC3000 and human transferrin. Signals with intensities related to concentrations of these two immobilized model proteins were observed. The modified surface was also validated by a more complex system: intercellular proteins secreted by DC3000. HrpW in these protein mixtures was successfully recognized by anti-HrpW antibodies when mixed proteins were immobilized onto activated surfaces. This surface modification strategy provides a platform onto which proteins can be directly immobilized for biosensor and protein array applications.

Biosensing Techniques↗

PubMed2005

The reaction of tetrakis(dimethylamido)titanium with self-assembled alkyltrichlorosilane monolayers possessing -OH, -NH2, and -CH3 terminal groups.

The reactions of tetrakis(dimethylamido)titanium, Ti[N(CH(3))(2)](4), with alkyltrichlorosilane self-assembled monolayers (SAMs) terminated by -OH, -NH(2), and -CH(3) groups have been investigated with X-ray photoelectron spectroscopy (XPS). For comparison, a chemically oxidized Si surface, which serves as the starting point for formation of the SAMs, has also been investigated. In this work, we examined the kinetics of adsorption, the spatial extent, and stoichiometry of the reaction. Chemically oxidized Si has been found to be the most reactive surface examined here, followed by the -OH, -NH(2), and -CH(3) terminated SAMs, in that order. On all surfaces, the reaction of Ti[N(CH(3))(2)](4) was relatively facile, as evidenced by a rather weak dependence of the initial reaction probability on substrate temperature (T(s) = -50 to 110 degrees C), and adsorption could be described by first-order Langmuirian kinetics. The use of angle-resolved XPS demonstrated clearly that the anomalous reactivity of the -CH(3) terminated SAM could be attributed to reaction of Ti[N(CH(3))(2)](4) at the SAM/SiO(2) interface. Reaction on the -NH(2) terminated SAM proved to be the "cleanest", where essentially all of the reactivity could be associated with the terminal amine group. In this case, we found that approximately one Ti[N(CH(3))(2)](4) adsorbed per two SAM molecules. On all surfaces, there was significant loss of the N(CH(3))(2) ligand, particularly at high substrate temperatures, T(s) = 110 degrees C. These results show for the first time that it is possible to attach a transition metal coordination complex from the vapor phase to a surface with an appropriately functionalized self-assembled monolayer.

Journal Article↗