Living PC12 cells, a model cell type for studying neuronal function, were imaged using the negative feedback mode of a scanning electrochemical microscope (SECM). Six biocompatible redox mediators were successfully identified from a large pool of candidates and were then used for imaging PC12 cells before and after exposure to nerve growth factor (NGF). When exposed to NGF, cells differentiate into a neuron phenotype by growing narrow neurites (1-2 microm wide) that can extend > 100 microm from the cell proper. We demonstrate that carbon fiber electrodes with reduced tip diameters can be used for imaging both the cell proper and these neurites. Regions of decreased current, possibly resulting from raised features not identifiable by light microscopy, are clearly evident in the SECM images. Changes in the morphology of undifferentiated PC12 cells could be detected in real time with the SECM. After exposure to hypotonic and hypertonic solutions, reversible changes in cell height of <2 microm were measured.

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In two con gurations, a solid-state acousto-optic (AO ) de ector or modulator is mounted in a 0.5 m m onochrom ator for background correction with inductively coupled plasma atomic em ission spectrometry (ICP-A ES). A fused silica acousto-optic modulator (AO M) is used in the ultraviolet (UV) spectral region applications while a glass AO de ector (AOD ) is used for the visible (VIS) region. The system provides rapid sequential observation of adjacent on-and off-line wavelengths for background correctio n. Seventeen elem ents are examined using pneumatic nebulization (PN) and electrothermal vaporization (ETV) sample introduction. Calibration plots were obtained with each sample introduction technique. Potable water and vitamin tablets were analyzed. Flame atomic absorption (FAA) was used to verify the accuracy of the AO background correctio n system .Index Headings: Acousto-optic de ector; Acousto-optic modulator; Background correction; Inductively coupled plasma; Electrothermal vaporization; Flame atomic absorption. INT RODUCTIO NInductively coupled plasm a atomic emission spectrometry (ICP-AES) is a robust and versatile source for tracemetals analysis. This technique is used for the analysis of a wide variety of samples. A sampling of recent publications illustrate ICP-AES being used for the determination of m etals in drinking water, 1 food, 2-4 soils, 5,6 biological materials, 7,8 and many other samples. Inherent plasm a icker dictates that best results are obtained when it is possible to correct for ''baseline'' or ''background'' instabilities. Various background correction methods have been examined. Charge-coupled and injection devices (CCD and CID) are becoming the dominant detectors for ICP-AES. W hile excellent for background correction, these detectors have moderately high costs, require system complexity, and produce large data les that require considerable manipulation time. W hen fewer elements are determined with high throughput, ICP spectrometers with photom ultiplier tube (PMT) detectors are still widely in use. PM Ts offer high ef ciency in a single unit detector and are less expensive than CCDs and CIDs.For background correction using PM Ts, techniques often involve the m ovement of devices such as refractor plates, choppers, and gratings. Since these m ethods involve m oving objects, there are inertia-based limitations that limit their effectiveness and speed. Acousto-optic devices offer a solid-state alternative for background correction. Acousto-optic de ectors and m odulators have been used for m any years in applications such as laser beam steering. The detailed theory of AODs and AOMs has been presented elsewhere.9 -12 In short, radiation enters and travels through a transparent AO material. A piezo-electric transducer, driven at a frequency in the tens to hundreds of megahertz range, is used to launch compression waves in the AO m edium. The wave travels at a near-acoustic velocity in a direction nearly perpendicular to the path of the radiation traversing the AO medium. As the radiation...