Colloidal detection

Porion, P., Al-Mukhtar, M., Meyer, S., Faugere, A.M., van der Maarel, J.R.C. and Delville, A. (2001) Nematic Ordering of Suspensions of Charged Anisotropic Colloids Detected by 23Na Nuclear Magnetic Resonance. The Journal of Physical Chemistry B... 

Kneipp K, Kneipp H, Deinum G, Itzkan I, Dasari R R and Feld M S 1998 Single-molecule detection of a cyanine dye in silver colloidal solution using near-infrared surface-enhanced Raman scattering App/. Spectrosc. 52 175-8... 

SERS has also been applied as a sensitive, molecule-specific detection method in chromatography, e.g. thin layer, liquid, and gas chromatography. SERS-active colloids were deposited on the thin layer plates or mixed continuously with the liquid mobile phases. After adsorption of the analytes, characteristic spectra of the fractions were obtained and enabled unambiguous identification of very small amounts of substance. 

The term particle and particle size are so highly ambiguous as to require precise definition. As used in this article particles will.be limited by size to those distinct entities which have physically detectable boundaries in any direction within the limits of 0.05 and 10 microns (1 micron, p -0.001mm). This size range covers those particles which can be directly measured without magnification down to those which exhibit colloidal behavior... 

Where-high purity MU is provided for higher pressure WT boiler plant FW, some form of continuous analyzers for measuring treated water pH and conductivity are almost always installed, as are sodium (Na) ion-selective electrodes for detection of sodium leakage. Automatic online silica analyzers also may be installed, but they measure only reactive (ionizable) silica (Si02), not colloidal or total silica, so caution is required where unforeseen silica leakage may present a problem. 

The surface force apparatus (SFA) is a device that detects the variations of normal and tangential forces resulting from the molecule interactions, as a function of normal distance between two curved surfaces in relative motion. SFA has been successfully used over the past years for investigating various surface phenomena, such as adhesion, rheology of confined liquid and polymers, colloid stability, and boundary friction. The first SFA was invented in 1969 by Tabor and Winterton [23] and was further developed in 1972 by Israela-chivili and Tabor [24]. The device was employed for direct measurement of the van der Waals forces in the air or vacuum between molecularly smooth mica surfaces in the distance range of 1.5-130 nm. The results confirmed the prediction of the Lifshitz theory on van der Waals interactions down to the separations as small as 1.5 nm. 

This protocol was extended to other inorganic colloids (e.g., ZnS, PbS), and it was pointed out that such extension paves the way to an electrochemical coding technology for the simultaneous detection of multiple DNA targets based on nanocrystal tags with diverse redox potentials [148]. 

A precursor of the studies on electron transfer reactions between short-lived radicals and colloidal particles was the development of a fast pulse radiolysis method to measure. the polarograms of radicals in the 10 s range . After considerable information had been acquired about the electron transfer reactions of a few dozen radicals at the mercury electrode, this compact electrode was replaced by metal colloids somewhat later, by semiconductor colloids These studies led to the detection of the electron-storing properties of certain colloids and of reactions of the stored electrons. 

Flash photolysis with microwave detection of charge carriers could become an additional technique in the future. The method has not yet been applied to colloids but has been used with small suspended particles. Immediately after the laser flash a conductivity signal was observed which decayed in the 0.1 to 1 microsecond range. The signal was longer-lived for a suspension of TiOj in para-dioxane than in Decalin. Such an effect of the surrounding medium on the decay kinetics of the conductivity indicates that surface states are involved... 

With respect to using methyl viologen as electron relay, it might be of interest to note tlmt MV " can be oxidized by positive holes produced in illuminated colloidal semiconductors such as Ti02 Two oxidation products of MV are 1, 2 -di-hydro-l,r-dimethyl-2 -oxo-4,4 -bipyridylium chloride and 3,4-dihydro-l,r-dime-thyl-3-oxo-4,4 -bipyridylium chloride, which can readily be detected by their strong fluorescences at 516 nm and 528 nm, respectively. These products are also produced in the direct photolysis of MV " solutions and in the reaction of MV "" with OH radicals in homogeneous solution... 

Separation of colloids by GPC is an important technical advance that may help in the characterization of novel materials. One such separation was the shape separation of gold particles of nanometer size by GPC on a Nucleogel GFC 1000-8 column using sodium dodecyl sulfate and Brij-35 [polyoxyethylene (23) dodecanol] to modulate the adsorption properties of the colloidal gold.42 Rodlike and spherical particles were separated using UV-VIS detection. 

Tran [391,392] has reported ng detection of dyes on filter paper by SERS. Silver colloidal hydrosols stabilised by filter supports enhance the Raman scattering of adsorbed dyes. Typical detection limits are 500 pg (crystal violet), 7 ng (l,l,9-trimethyl-2,2 -cyanine perchlorate), 15 ng (3,3 -diethylthiacarbocyanine chloride) and 240 ng (methyl red) using a 3 mW He-Ne laser. 

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