SECM IMAGING

Since the SECM response is a function of the rate of the heterogeneous reaction at the substrate, it can be used to image the local chemical and electrochemical reactivity of surface features. A technique called reaction-rate imaging, which is unique to SECM, is particularly useful in imaging the areas on a surface where reactions occur. Membranes (5-7), leaves (8-10), polymers (11,12), surface films (13-17), and artificially patterned biological systems (7,18-20) have been imaged with SECM. 

In a previous work, SECM was used to obtain topographic information about biological samples immersed in an electrolyte solution either by using the feedback mode or by detecting a substrate-generated electroactive species 

As stated above, SECM can be used to image the reactivity of surface features. A feedback detection scheme was used to observe the localized reaction of glucose oxidase and mitochondria-bound NADH-cytochrome c reductase (7). The spatial resolution of the imaging is high for enzymatic 

The enzyme-linked immunosorbent assay (ELISA) method (23) has recently been used for the preparation of ultrasmall biological structures for 

6 (A) 02 evolution from three stomata of an illuminated green leaf region 

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FIGURE 2-18 SECM image of a gold minigrid surface. (Reproduced with permission from reference 57.)... 

Explain clearly how SECM images the microdistribution of the electrochemical activity of composite electrode materials. 

Figure 19. SECM—AFM images of a polycarbonate membrane containing 100-nm-radius pores. (Top) AFM topography image (Bottom) SECM image of Ru(NH3)6 transport in membrane pores. (Reprinted with permission from ref 227. Copyright 2001 American Chemical Society.)...

SECM imaging of local enzyme activities in GC mode... 

Figure 7 SECM image (A) and optical image (B) acquired over the same 1-mm region of hairless mouse skin visualize the real-time iontophoretic deposition of FeCCN)" at a current density of 40 p.A/cm. The bright spot in A corresponds to high Fe(CN)" flux above a pore. The dark spot in B corresptonds to the site of Prussian blue deposition at the pore opening. (Reproduced with permission from Ref. 65.)...

Additional vibration isolation may not be required for SECM. For SECM imaging with probes of 10 pun and larger, isolation is not critical. For smaller tips, some attempt should be made to determine if vibration isolation is needed. One simple check is to observe an increase in noise as the probe approaches the surface in a feedback experiment. Another check is to determine the frequency distribution of vibrations. Use a lock-in amplifier to examine frequencies from 10 mHz to 10 kHz with the probe positioned as close as possible to an electrode surface in a positive feedback configuration. Alternatively, perform a Fourier transform of the probe noise signal. Any peaks in the signal versus frequency plot are candidates for vibrational resonances. Discriminating vibrational and electrical noise is pos-... 

Nearly all of the published SECM images are made in the constant-height mode, where the probe is scanned at a constant reference plane above the... 

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