We report here the chemical modification of poly(methyl methacrylate) (PMMA) surfaces by their reaction with the monoanion of alpha,omega-diaminoalkanes (aminolysis reaction) to yield amine-terminated PMMA surfaces. It is found that the amine functionalities are tethered to the PMMA backbone through an alkane bridge to amide bonds formed during the aminolysis of the surface ester functionalities. The distribution of the amine termini is quite uniform as judged by fluorescence micrographs. It is found that the electroosmotic flow in aminated PMMA microchannels is reversed when compared to that in unmodified channels. In addition, it is demonstrated that enzymes can be immobilized onto the amine-terminated PMMA surfaces and are effective in the restriction digestion of dsDNAs. Finally, the availability of the surface amine groups is further demonstrated by their reaction with n-octadecane-1-isocyanate to form PMMA surfaces terminated with well-ordered and highly crystalline octadecane chains.
Figure 5. Electropherograms of ΦX 174 DNA restriction fragments obtained using (a) 4.0, (b) 1.0, and (c) 0.2 µM dye in the running buffer. See Figure 3 for experimental details.
The noncovalent binding and spectroscopic properties of several near-infrared tricarbocyanine dyes with respect to sonicated calf-thymus DNA are reported. The dyes investigated were diethylthiatricarbocyanine iodide (DTTCI), diethyloxatricarbocyanine iodide (DOTCI), and 1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide (HITCI), which are cationic and possess absorption maxima at 772, 695, and 750 nm, respectively, in DMSO. In buffered aqueous solutions, these dyes demonstrated extensive ground-state aggregation in aqueous solvents when compared to DMSO. In the presence of double-stranded DNA (dsDNA), the fluorescence emission spectra revealed enhancement ratios of bound-to-free dye ranging from 4.5 for DOTCI to 128 for DTTCI. Spectrophotometric titrations and Scatchard analyses of the dye-dsDNA complexes yielded nonlinear plots, suggestive of possible multiple binding sites on the DNA. Viscometric titrations of the complexes showed increased solution viscosities for DTTCI, consistent with an unraveling and lengthening of the dsDNA upon complexation. Fluorescence lifetime data of the dye-dsDNA complexes showed longer lifetimes exhibited by these dyes in the presence of the dsDNA compared with those in solutions with no DNA.
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