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.

In order to rationally design probes appropriate for sensitive near-infrared (NIR) applications, fluorescence studies of two representative tricarbocyanine NIR dyes, IR-125 and IR-132, were undertaken to evaluate solventdependent and independent nonradiative relaxation pathways. The fluorescence quantum yields, lifetimes, and the radiative and nonradiative rates in aqueous solvents, organic alcohols, and binary mixtures of water/methanol were measured using steady-state and picosecond laser techniques. In addition, organized media and solvent viscosity effects on the NIR dyes' photophysical properties were investigated, The quantum yields were less than 15% with subnanosecond lifetimes in all solvent systems investigated with severely reduced quantum yields and lifetimes in aqueous solvents when compared to those in the neat organic alcohols. Inspection of the absorption spectra indicated extensive ground-state aggregation for IR-132 in aqueous solvents, while IR-125 showed little evidence of aggregation. The fluorescence lifetimes for both dyes demonstrated negligible dependence on solution viscosity, indicating that photoisomerization is not a major nonradiative path for these tricarbocyanine dyes. Linear free energy plots of the nonradiative rates (knr) and the solvent's E~( 3 0 ) value (parameter indicative of solvent polarity and hydrogen bond donating ability) showed a linear relationship in the neat alcohols and HlO/methanol binary mixtures, with larger solvent E~ ( 3 0 ) values yielding larger nonradiative rates. Inverse linear relationships with poor correlations were found between the solvent's nucleophilicity and the nonradiative rates. The addition of certain surfactants, such as sodium dodecyl sulfate (anionic), and tert-octylphenoxy polyethoxyethanol (nonionic) above their critical micelle concentrations improved the photophysical properties of these dyes when compared to the pure aqueous solvents. Internal conversion resulting from the small electronic energy difference between the ground and first excited singlet, a nonrigid molecular structure giving rise to many vibrational degrees of freedom and distortion of the molecule from planarity, was surmised to be the major nonradiative manifold of the singlet excited state. A solvent-dependent nonradiative rate was also discovered, with the efficiency of this process determined by the hydrogen bond donating strength and/or polarity of the solvent. The photophysical results warrant consideration of the following constraints in the design of new fluorochromes requiring high fluorescence efficiencies appropriate for the NIR: inclusion of charged functionalities on the dye to prevent aggregation; exclusion of heavy atoms within the dye structure; structural reinforcement within the polymethine chain to reduce the rate of internal conversion; and inclusion of organized media in the aqueous environment when appropriate to shield the dye from the strong hydrogen bond donating strength and/or polarity of the interstitial solution.

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The successful implementation of ultrasensitive fluorescence spectroscopy of biological and chemical species depends upon certain photophysical parameters associated with the fluorescent dye used in the investigation. These parameters include the fluorescence quantum efficiency, photodestruction quantum efficiency, absorption cross section and fluorescence lifetime. These photophysical constants were measured for several fluorescent dyes that are used for the tagging of biological species. Three different solvents, ethanol, water and a cationic surfactant used above its critical micelle concentration, were studied. The effective photon yield (ratio of the fluorescence quantum yield to the photodestruction quantum efficiency) for the dyes is nearly 100 times greater in ethanol than it is in water because of the superior photostabilities of these dyes in ethanol solvents. The implications of these parameters for the design of an ukrasensitive fluorescence experiment are discussed.

We present a critical review of microfluidic technologies and material effects on the analyses of circulating tumour cells (CTCs) selected from the peripheral blood of cancer patients. CTCs are a minimally invasive source of clinical information that can be used to prognose patient outcome, monitor minimal residual disease, assess tumour resistance to therapeutic agents, and potentially screen individuals for the early diagnosis of cancer. The performance of CTC isolation technologies depends on microfluidic architectures, the underyling principles of isolation, and the choice of materials. In this review, we present a critical review of the fundamental principles used in these technologies and discuss their performance. We also give context to how CTC isolation technologies enable downstream analysis of selected CTCs in terms of detecting genetic mutations and gene expression that could be used to gain information that may affect patient outcome.