Spectrophotometric estimation of functional groups on microslides for preparation of biochips

Purification of Coomassie Brilliant Blue G-250 by multiple dual mode countercurrent chromatography

Commercial samples of Coomassie Brilliant Blue G-250 (CBB) were not pure enough to give reliable results when used as indicator of amine content in biological material. The polar and apolar impurities produce unacceptable biases in the results. Counter current chromatography (CCC) was used to purify significant amounts of CBB. The liquid system heptane/1-butanol/water 2:3:4 (v/v) was appropriate to separate crude CBB in three groups of components: polar, partitioning in the aqueous lower phase, intermediate, partitioning well between the aqueous and organic phases, and apolar, preferring greatly the organic phase. The dual-mode way of using a CCC chromatograph was found appropriate for the separation injecting the crude CBB in the middle of a two coil CCC instrument. A multi dual-mode purification was performed allowing to eliminate the polar impurities in the aqueous phase at the column tail and the apolar ones in the organic phase at the column head, trapping the purified dye inside the CCC column. 200mg of purified CBB were obtained from 1g of crude CBB in 3h using as little as 150 mL of butanol and 70 mL of heptane with 200 mL of water. The purified CBB gave total satisfaction in testing amine content in polyclonal antibody containing monolith pipettes.

2-O-[2-(4,4'-dimethoxytrityloxyethyl)]-hydroxy acetaldehyde: a universal reagent for spectrophotometric estimation of polymer-supported functional groups

A new universal reagent, 2-O-[2-(4,4'-dimethoxytrityloxyethyl)]-hydroxy acetaldehyde (DEA), has been synthesized and used for the estimation of surface-bound aminoalkyl, aminooxyalkyl, hydrazinyl, and semicarbazide functions. The reaction completes in just 10 min in the case of aminoalkylated supports and 30 min in hydrazinyl supports, whereas it takes approximately 60 min in both aminooxyalkylated and semicarbazide-modified polymer supports. DEA-treated supports, including glass slides and PP films on exposure to acid, liberates 4,4'-dimethoxytrityl cation, which was measured spectrophotometrically to estimate these functionalities. The method estimates accessible functional groups, useful for calculating the quantity of the ligands to be immobilized.

Choice of polymer matrix, its functionalization and estimation of functional group density for preparation of biochips

Oligonucleotide microarray has become an important and powerful tool for various genomic analyses, where, unlike conventional methods, one can identify simultaneously a large number of targets in a given sample. Postsynthesis immobilization, the most widely used method, involves the noncovalent and covalent fixing of suitably modified oligonucleotides on the solid supports. Among the various functional groups aminoalkyl, hydroxyalkyl, mercaptoalkyl, aldehyde, epoxy, and carboxyl the most frequently used functional groups on the polymeric surfaces. Because glass and polypropylene, the most widely used materials, are nonporous in nature, the functional groups density on the surface remains very low. In order to know the exact concentration of a ligand to be immobilized, it is essential to estimate the accessible functional groups on these surfaces. For this purpose, sensitive methods are required to estimate exact density of available functional groups on the surfaces. Apart from physical methods, a number of sensitive chemical methods, by making use of high extinction coefficient of 4,4'-dimethoxytrityl cation (epsilon(498) = 70,000 L mol-1 cm-1), have been reported to estimate accessible functional groups on the glass based polymer supports. In this chapter, use of these reagents for spectrophotometric determination of functional group density on glass microslides and polypropylene film has been discussed.