Microfabricated fluidic systems have emerged as a powerful approach for chemical analysis. Relatively unexplored is the use of microfabrication to create sampling probes. We have developed a sampling probe microfabricated in Si by bulk micromachining and lithography. The probe is 70 μm wide by 85 μm thick by 11 mm long and incorporates two buried channels that are 20 μm diameter. The tip of the probe has two 20 μm holes where fluid is ejected or collected for sampling. Utility of the probe was demonstrated by sampling from the brain of live rats. For sampling, artificial cerebral spinal fluid was infused in through one channel at 50 nL/min while sample was withdrawn at the same flow rate from the other channel. Analysis of resulting fractions collected every 20 min from the striatum of rats by liquid chromatography with mass spectrometry demonstrated reliable detection of 17 neurotransmitters and metabolites. The small probe dimensions suggest it is less perturbing to tissue and can be used to sample smaller brain nuclei than larger sampling devices, such as microdialysis probes. This sampling probe may have other applications such as sampling from cells in culture. The use of microfabrication may also enable incorporation of electrodes for electrochemical or electrophysiological recording and other channels that enable more complex sample preparation on the device.

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Novel solid-state sensors for biomedically important polyions (i.e., heparin and protamine) that exhibit significantly enhanced initial EMF stability are prepared by incorporation of lipophilic silver-calixarene complexes along with the required ion-exchangers within polymeric films. A dithioether of tertiary butyl calix[4]arene together with its silver complex are added to the polyion sensing membranes which are deposited on a silver-epoxy conductor of a solid-state transducer. The silver-complex serves as a reversible electron transfer agent between the organic polymer film and the underlying solid-state conductor, resulting in highly reproducible starting EMF values and improved initial signal stability. This approach is further employed to devise a heparin sensing cartridge for blood measurements based on a novel differential measurement mode. One sensor responds to heparin, while the second identical solid-state sensor serves as a pseudo reference electrode with all heparin present in the sample within this half-cell complexed by the addition of excess protamine. The cartridges are evaluated by monitoring heparin response in spiked dog blood using poly(vinyl chloride) (PVC) blends and fluorinated silicone rubber (Dow Corning RTV 730) films containing appropriate levels of ionexchanger and Ag +-calixarene/free calixarene additives.