Abstract
In this paper the effect of solvent induced chemical surface enhancements upon graphitic screen-printed electrodes (SPEs) is explored. Previous literature has indicated that treating the working electrode of a SPE with the solvent N,N-dimethylformamide (DMF) offers improvements within the electroanalytical response, resulting in a 57-fold increment in the electrode surface area compared to their unmodified counterparts. The protocol involves two steps: (i) the SPE is placed into DMF for a selected time, and (ii) it is cured in an oven at a selected time and temperature. Beneficial electroanalytical outputs are reported to be due to the increased surface area attributed to the binder within the bulk surface of the SPEs dissolving out during the immersion step (step i). We revisit this exciting concept and explore these solvent induced chemical surface enhancements using edge- and basal-plane like SPEs and a new bespoke SPE, utilising the solvent DMF and explore, in detail, the parameters utilised in steps (i) and (ii). The electrochemical performance following steps (i) and (ii) is evaluated using the outer-sphere redox probe hexaammineruthenium(iii) chloride/0.1 M KCl, where it is found that the largest improvement is obtained using DMF with an immersion time of 10 minutes and a curing time of 30 minutes at 100 °C. Solvent induced chemical surface enhancement upon the electrochemical performance of SPEs is also benchmarked in terms of their electroanalytical sensing of NADH (dihydronicotinamide adenine dinucleotide reduced form) and capsaicin both of which are compared to their unmodified SPE counterparts. In both cases, it is apparent that a marginal improvement in the electroanalytical sensitivity (i.e. gradient of calibration plots) of 1.08-fold and 1.38-fold are found respectively. Returning to the original exciting concept, interestingly it was found that when a poor experimental technique was employed, only then significant increases within the working electrode area are evident. In this case, the insulating layer that defines the working electrode surface, which was not protected from the solvent (step (i)) creates cracks within the insulating layer exposing the underlying carbon connections and thus increasing the electrode area by an unknown quantity. We infer that the origin of the response reported within the literature, where an extreme increase in the electrochemical surface area (57-fold) was reported, is unlikely to be solely due to the binder dissolving but rather poor experimental control over step (i).
Highlights
The utilisation of carbon materials for applications within electroanalytical sensors have become a major factor over recent decades, as researchers strive to find cheap and effective electrochemical systems that possess the capabilities for the simplistic retrieval of analytical data
The application of porous electrodes have expanded towards the sensing of heavy metal ions, for example Niu et al.[19] have applied a highly porous carbon paste electrode for the detection of Cd(II), Pb(II) and Ni(II) within real water samples, which due to the large analytical current/signal provided by the porosity/increase in surface area allows for extreme improvements in the electroanalytical sensitivity
In this paper we explore solvent induced surface modifications, via steps (i) and (ii), in detail and benchmark these to their unmodified counterparts utilising the redox probe hexaammineruthenium(III) chloride
Summary
The utilisation of carbon materials for applications within electroanalytical sensors have become a major factor over recent decades, as researchers strive to find cheap and effective electrochemical systems that possess the capabilities for the simplistic retrieval of analytical data. The application of porous electrodes have expanded towards the sensing of heavy metal ions, for example Niu et al.[19] have applied a highly porous carbon paste electrode for the detection of Cd(II), Pb(II) and Ni(II) within real water samples, which due to the large analytical current/signal provided by the porosity/increase in surface area allows for extreme improvements in the electroanalytical sensitivity It has become apparent within recent literature that a different approach for improving electroanalytical capabilities of screen-printed electrodes (SPEs) has been undertaken, exploiting the nature of the ink used in the manufacture process, utilising the solvent N,N-dimethylformamide (DMF).[20] It has been reported that exposure of SPEs to DMF results in an extreme increase of the electrochemically active surface area, increasing the electroanalytical sensitivity towards target analytes. The results arising from this work show that the electrochemical improvement from utilising steps (i) and (ii) are not as beneficial as previously reported; reasons for this are given.[20]
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