Exercising spatiotemporal control of cell attachment with optically transparent microelectrodes

This paper describes a novel approach of controlling cell-surface interactions through an electrochemical "switching" of biointerfacial properties of optically transparent microelectrodes. The indium tin oxide (ITO) microelectrodes, fabricated on glass substrates, were modified with poly(ethylene glycol) (PEG) silane to make glass and ITO regions resistant to protein and cell adhesion. Cyclic voltammetry, with potassium ferricyanide serving as a redox reporter molecule, was used to monitor electron transfer across the electrolyte-ITO interface. PEG silane modification of ITO correlated with diminished electron transfer, judged by the disappearance of ferricyanide redox activity. Importantly, application of reductive potential (-1.4 V vs Ag/AgCl reference) corresponded with reappearance of typical ferricyanide redox peaks, thus pointing to desorption of an insulating PEG silane layer. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterization of the silanized ITO surfaces after electrical stimulation indicated complete removal of the silane layer. Significantly, electrical stimulation allowed to "switch" chosen electrodes from nonfouling to protein-adhesive while leaving other ITO and glass regions protected by a nonfouling PEG silane layer. The spatial and temporal control of biointerfacial properties afforded by our approach was utilized to micropattern proteins and cells and to construct micropatterned co-cultures. In the future, control of the biointerfacial properties afforded by this novel approach may allow the organization of multiple cell types into precise geometric configurations in order to create better in vitro mimics of cellular complexity of the native tissues.     

Matrix Effects on the Fragmentation of Vitamin B12 in Plasma Desorption Mass Spectrometry

A continuing effort in mass spectrometry is to optimize desorption/ionization processes in order to enhance analyte ion yields and reduce fragmentation. The effect of small carbohydrate and amino acid matrices on the yield of secondary ions from vitamin B₁₂ (cyanocobalamin) was examined using plasma desorption mass spectrometry. The extent of the corrin decomposition is dependent upon the matrix-to-analyte ratio. The enhanced yields of the high-mass fragment ion [M–CN + H]⁺ and the ions corresponding to protonated molecules, however, are dependent upon both the matrix-to-analyte ratio and the nature of the matrix. © 1997 John Wiley & Sons, Ltd.     

Structural characterization of organic molecules by negative ions in laser microprobe mass spectrometry. Part 2—Salts

Laser microprobe mass spectrometry (LMMS) has been applied systematically to a variety of organic polyfunctional molecules, covering a wide range of structures and polarities. The microprobe generally offers a combination of desorption under relatively mild conditions with abundant fragmentation. We attempted an empirical approach by tentative hypotheses about desorption and ionization in LMMS to consistently rationalize the detected fragments. The complementary nature of structural data, carried by positive and negative ions, is characteristic for LMMS results of non-ionic compounds. The analysis of salts represents, traditionally, an ultimate test case for soft methods in organic mass spectrometry. Hence, by a selected series of compounds, we have tried to assess to which extent the presence of preformed ions becomes an asset for LMMS analysis and affects the amount, the accessibility or the distribution of organic information between positive and negative fragments.     

Nuclear analytical facilities at Texas A&M University

Nuclear Analytical Chemistry at Texas A&M University is based in large part on the facilities of the Center for Chemical Characterization and Analysis and the Nuclear Science Center. This paper describes the capabilities of these two centers for instrumental and fast neutron activation analysis, neutron depth profiling, prompt gamma activation analysis, neutron radiography and the unique features of the large volume irradiation cell and reactor pulsing operation.