A novel approach to integrating a buffer ion-permeable membrane in a poly(glycidyl methacrylate-co-methyl methacrylate) micro electric field gradient focusing (muEFGF) device is described. A weir structure on which the membrane was positioned was fabricated between the separation channel and field gradient-generating channel. Before formation of the membrane, the surface of the polymeric microdevice was treated for covalent bonding of the membrane. Following surface modification, a prepolymer solution containing poly(ethylene glycol) acrylate/methacrylate and Tris-HCl buffer was loaded into the microdevice. Low-pressure nitrogen gas was then purged through the separation and field gradient-generating channels to remove the prepolymer solution from these channels. Residual prepolymer solution was retained on the weir structure due to surface tension. Finally, the premembrane was cured in place on the weir using UV radiation. Using a muEFGF device, green fluorescent protein (GFP) was concentrated 4000-fold. Separation of GFP and R-phycoerythrin, and selective elution of GFP from a protein mixture containing GFP, FITC-labeled casein, and FITC-labeled hemoglobin were also demonstrated. It was found that the membrane conductivity and presence of carboxylic acid impurities in the membrane strongly affected the behavior of the muEFGF device.

A 260 nm deep UV LED-based absorption detector with low detection limits was developed and integrated with a small nanoflow pumping system. The detector is small in size (5.2 × 3.0 cm) and weighs only 85 g (without electronics). This detector was specifically designed and optimized for on-column detection to minimize extra-column band broadening. No optical reference was included due to the low drift in the signal. Two ball lenses, one of which was integrated with the LED, were used to increase light throughput through the capillary column. Stray light was minimized by the use of a band-pass filter and an adjustable slit. Signals down to the parts per billion level (nanomolar) were easily detected with a short-term noise level of 4.4 μAU, confirming a low limit of detection and low noise. The detection limit for adenosine-5'-monophosphate was 230 times lower than any previously reported values. Good linearities (3 orders of magnitude) were obtained using sodium anthraquinone-2-sulfonate, adenosine-5'-monophosphate, dl-tryptophan, and phenol. The LC system was demonstrated by performing isocratic separation of phenolic compounds using a monolithic capillary column (16.5 cm × 150 μm i.d.) synthesized from poly(ethylene glycol) diacrylate.

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[reaction: see text] The development of an ion-selective chemosensor for Cd(2+) allows generation of a "real-time" sensor. Immobilization of the chemosensor on quartz was achieved in a simple monolayer and in a thin film using a polymer intermediary. As intended, the thin film contains much more chemosensor than the monolayer and provides measurable responses to aqueous Cd(2+) concentrations below 1 microM. Alkali and alkaline earth ions do not interfere with Cd(2+) sensing; Zn(2+) and Cu(2+) are potential interferents.