Bio-sensing using recessed gold-filled capillary amperometric electrodes

Abstract

A novel recessed electrode is reported for amperometric detection of hydrogen peroxide and via glucose oxidase for the detection of glucose. The electrode utilised electrodeposited platinum over a gold wire surface, which proved to be an effective peroxide-detecting surface. Compared with a traditional exposed electrode surface, the recessed tip facilitated an extended linear range for glucose from 4 to over 14 mM. Bio-fouling, as assessed by exposure to bovine serum albumin, was also significantly reduced. Though response time at the recess was increased, it was within an acceptable range for physiological monitoring. Moreover, the recess enabled precise measurement of the hydrogen peroxide diffusion coefficient; this was based on a bipartite expression for the transient amperometric current at the recessed structure following a step change in ambient hydrogen peroxide concentration. An important aspect of the diffusion measurement was the curve fitting routine used to map on to the theoretical response curve.

Stabilised Biosensing Using Needle‐Based Recess Electrodes

“…An increase in the recess depth leads to a slower response, as evident from the time traces (Figure 3), which vary from 3 min in the 35 µm recess (Figure 3a) to 10 min in the case of the 546 µm recess (Figure 3d). This trend has been observed previously 20. The inlaid disc probes exhibited the fastest (<3 min) response times, which is due to the absence of an extended diffusion path between the sample medium and the cathode.…”

“…Thus, the percentage reduction of the response after 17 h went down to 6 % for the recess with 880 µm depth. Our previous report 20 showed reduced biofouling at a bare electrode; the current data shows that the benefit of a recess is evident even at a membrane protected electrode and, moreover, the recess length has an incremental effect on the protection afforded…”

“…This effect was particularly significant in the case of the anionic species, ascorbate and urate, fully ionised under the buffer conditions used, where almost no added change in the response was observed (Figure 5c,d). This molecular resolution, based simply on a macroscopic barrier, was not anticipated; selectivitiy had not been assessed in our previous study of recess electrodes 20. One possible explanation for this phenomenon is that as the silica glass surface of the electrode imposes a charge effect modifying transport/partitioning in the recess.…”

“…More fundamental studies using planar recess microarrays have been carried out, including as use as microphysiometers 19, but these again are geometrically inappropriate for implantation, and their use as low fouling devices for biofluid analysis remains to be tested. We have established a needle type robust electrode platform for possible in vivo use 20. This utilised mechanically stable hollow silica fibres (photonic optical crystals) housing a working electrode.…”

“…Structurally, it protected the vulnerable sensing tip from direct mechanical damage and abrasion. However, a particularly significant benefit for use in biological samples was the apparent reduction in bio‐fouling due to protein 20, likely to be especially critical for future in vivo use.…”