PH-Microscopy

E Klusmann, JW Schultze. pH-Microscopy—theoretical and experimental investigations. Electrochim Acta 42 3123-3134, 1997. 

With an SECM positioned above a surface with deposited nanoparticles of dioxygen reduction electrocatalysts in a solution saturated with dioxygen, significant decreases of tip current are observed. Variations in the nature of catalyst spots, including inhomogeneities, could be localised. Further modes include the potentio-metric mode with an ion selective UME that is used to probe the local composition of the solution. This method is basically equivalent to the scanning ion-sensitive electrode technique SIET (see p. 270, particularly pH microscopy). 

Boldt, F. M., J. Heinze, M. Diez, J. Petersen, and M. Borsch, Real-time pH microscopy down to the molecular level by combined scanning electrochemical microscopy/single-molecule fluorescence spectroscopy, AwaZ. Chem., Vol. 76, 2004 pp. 3473-3481. 

Interestingly for pH microscopy often micropipette tips have been used [53], in spite of the existences of several different more stable, less fragile pH microelectrodes. Recently development of solid contact micropipettes of improved properties... 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

The effect is more than just a matter of pH. As shown in Fig. XV-14, phospholipid monolayers can be expanded at low pH values by the presence of phosphotungstate ions [123], which disrupt the stmctival order in the lipid film [124]. Uranyl ions, by contrast, contract the low-pH expanded phase presumably because of a type of counterion condensation [123]. These effects caution against using these ions as stains in electron microscopy. Clearly the nature of the counterion is very important. It is dramatically so with fatty acids that form an insoluble salt with the ion here quite low concentrations (10 M) of divalent ions lead to the formation of the metal salt unless the pH is quite low. Such films are much more condensed than the fatty-acid monolayers themselves [125-127]. 

B. J. Fergus, "The Distribution of Lignin in Wood as Determined by Ultraviolet Microscopy," Ph.D. thesis, McGill University, Montreal, Canada,... 

Ph. Ebert, B. Engels, P. Richard, K. Schroeder, S. Bluegel, C. Domke, M. Heinrich, K. Urban. Contribution of surface resonances to scanning tunneling microscopy images (110) surfaces of III-V semiconductors. Phys Rev Lett 77 2997, 1996. 

Scanning electrochemical microscopy can also be applied to study localized biological activity, as desired, for example, for in-situ characterization of biosensors (59,60). In this mode, the tip is used to probe the biological generation or consumption of electroactive species, for example, the product of an enzymatic surface reaction. The utility of potentiometric (pH-selective) tips has also been... 

Rugar, D., Cryogenic Acoustic Microscopy, Ph.D. thesis, Stanford University, 1981. 

Since our backbone 2 aPNA incorporates six Lys residues in its peptide sequence and is cationic at a physiological pH, we were optimistic that this aPNA would be taken up into cells without the need for any external carrier system. To answer the simple question of whether b2 aPNAs are intemahzed, a standard fluorescence microscopy experiment was performed to see if whole cells that were incubated with a fluorescent-labeled aPNA would internahze labeled material [70]. Chinese Hamster Ovary (CHO) cells in culture were incubated with BODIPY-la-beled TCCCT(b2) at 37 °C for various periods of time. Following incubation, the cells were rinsed in phosphate-buffered sahne (PBS), fixed with 4% formaldehyde at ambient temperature for 20 min, then washed with PBS and stored in a refrigerator until examined by fluorescence microscopy. 

FIG. 7 Brewster-angle microscopy Image of POAS monolayer at air/water interface at pH 1 and various pressures. 

In the same year, Fulda and Tieke [75] reported on Langmuir films of monodisperse, 0.5-pm spherical polymer particles with hydrophobic polystyrene cores and hydrophilic shells containing polyacrylic acid or polyacrylamide. Measurement of ir-A curves and scanning electron microscopy (SEM) were used to determine the structure of the monolayers. In subsequent work, Fulda et al. [76] studied a variety of particles with different hydrophilic shells for their ability to form Langmuir films. Fulda and Tieke [77] investigated the influence of subphase conditions (pH, ionic strength) on monolayer formation of cationic and anionic particles as well as the structure of films made from bidisperse mixtures of anionic latex particles. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

Reynolds E. S. (1963). The use of lead citrate at high pH as an electron opaque stain in electron microscopy. Journal of Cell Biology 17 208-212. 

Yoshidome, M. (2006) Study of molecular aggregates on solid surface using scanning tunneling microscopy and Raman spectroscopy, Ph.D. thesis, Tohoku University. 

In order to evaluate the release and self-assembly of the diphenylalanine end groups, dendron 22 was incubated in PBS, pH 7.4, without PGA at a concentration of 1.5 mM. Transmission electron microscopy (TEM) analysis revealed that attachment of the diphenylalanine to the dendritic platform prevented self-assembly, and therefore, no organized structures were observed (Fig. 5.17a). Then, dendron... 

Cotte, M., P. Dumas, G. Richard, R. Breniaux, and Ph. Walter (2005), New insight on ancient cosmetic preparation by synchrotron-based infrared microscopy, Anal. Chim. Acta 553, 105-110. 

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