This report describes a UV laser photoablation method for the production of miniaturized liquid-handling systems on polymer substrate chips. The fabrication of fluid channel and reservoir networks is accomplished by firing 200 mJ pulses from an UV excimer laser at substrates moving in predefined computer-controlled patterns. This method was used for producing channels in polystyrene, polycarbonate, cellulose acetate, and poly(ethylene terephthalate). Efficient sealing of the resulting photoablated polymer channels was accomplished using a low-cost film lamination technique. After fabrication, the ablated structures were observed to be well defined, i.e., possessing high aspect ratios, as seen by light, scanning electron, and atomic force microscopy. Relative to the original polymer samples, photoablated surfaces showed an increase in their hydrophilicity and rugosity as a group, yet differences were noted between the polymers studied. These surface characteristics demonstrate the capability of generating electroosmotic flow in the cathodic direction, which is characterized here as a function of applied electric field, pH, and ionic strength of common electrophoretic buffer systems. These results show a correlation between the ablative changes in surface conditions and the resulting electroosmotic flow. The effect of protein coatings on ablated surfaces is also demonstrated to significantly dampen the electroosmotic flow for all polymers. All of these results are discussed in terms of developing liquid-handling capability, which is an essential part of many μ-TAS and chemical diagnostic systems.

The increased availability of saturated lipids has been correlated with development of insulin resistance, although the basis for this impairment is not defined. This work examined the interaction of saturated and unsaturated fatty acids (FA) with insulin stimulation of glucose uptake and its relation to the FA incorporation into different lipid pools in cultured human muscle. It is shown that basal or insulin-stimulated 2-deoxyglucose uptake was unaltered in cells preincubated with oleate, whereas basal glucose uptake was increased and insulin response was impaired in palmitate- and stearate-loaded cells. Analysis of the incorporation of FA into different lipid pools showed that palmitate, stearate, and oleate were similarly incorporated into phospholipids (PL) and did not modify the FA profile. In contrast, differences were observed in the total incorporation of FA into triacylglycerides (TAG): unsaturated FA were readily diverted toward TAG, whereas saturated FA could accumulate as diacylglycerol (DAG). Treatment with palmitate increased the activity of membrane-associated protein kinase C, whereas oleate had no effect. Mixture of palmitate with oleate diverted the saturated FA toward TAG and abolished its effect on glucose uptake. In conclusion, our data indicate that saturated FA-promoted changes in basal glucose uptake and insulin response were not correlated to a modification of the FA profile in PL or TAG accumulation. In contrast, these changes were related to saturated FA being accumulated as DAG and activating protein kinase C. Therefore, our results suggest that accumulation of DAG may be a molecular link between an increased availability of saturated FA and the induction of insulin resistance.

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A method, using UV laser photoablation, is presented for the fabrication and the integration of an electrochemical detector in a microchannel device, where carbon microband electrodes are placed either in the bottom or in the side walls of the rectangular microchannel. The different electrochemical cell geometries are tested with a model compound (ferrocenecarboxylic acid) in 40- and 100-μm-wide capillaries fabricated in planar polymer substrates. The experimental results are compared to numerical simulations for stagnant stream conditions. Depending on the scan rate and on the microchannel depth, the system behaves as a microband electrode until a linear diffusion field develops within the channel. The limit of detection for a one electron redox species within the 120-pL detection volume is ∼1 fmol with both cyclic voltammetry and chronoamperometric detection.

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