Abstract
AbstractElectrochemical methods offer great promise in meeting the demand for user‐friendly on‐site devices for monitoring important parameters. The food industry often runs own lab procedures, for example, for mycotoxin analysis, but it is a major goal to simplify analysis, linking analytical methods with smart technologies. Enzyme‐linked immunosorbent assays, with photometric detection of 3,3’,5,5’‐tetramethylbenzidine (TMB), form a good basis for sensitive detection. To provide a straightforward approach for the miniaturization of the detection step, we have studied the pitfalls of the electrochemical TMB detection. By cyclic voltammetry it was found that the TMB electrochemistry is strongly dependent on the pH and the electrode material. A stable electrode response to TMB could be achieved at pH 1 on gold electrodes. We created a smartphone‐based, electrochemical, immunomagnetic assay for the detection of ochratoxin A in real samples, providing a solid basis for sensing of further analytes.
Highlights
For food and feed safety, the monitoring of numerous contaminants such as mycotoxins plays a vital role since these fungal secondary metabolites can pose a severe health risk to humans and animals
It could be demonstrated that the pH value and electrode material significantly control the electrochemistry of TMB
It was found that screen-printed gold electrodes and a highly acidic pH value are well-suited to perform the electrochemical detection of TMB, due to the reversible character of the redox reaction under these conditions
Summary
For food and feed safety, the monitoring of numerous contaminants such as mycotoxins plays a vital role since these fungal secondary metabolites can pose a severe health risk to humans and animals. Most ELISA systems are based on antibodies, proteins or haptens conjugated to horseradish peroxidase (HRP) and by far the most used HRP substrate for optical detection is 3,3’,5,5’tetramethylbenzidine (TMB) in combination with H2O2 This is attributed to the fact that TMB is a non-mutagenic chromogen which, due to the high turnover rates by HRP, provides high sensitivity in HRP-based assays.[16] Josephy et al described that the enzymatic oxidation of TMB by HRP in the presence of H2O2 initially generates a blue-colored charge-transfer complex existing in a rapid equilibrium with a radical cation which can further get oxidized to the yellow diimine.[17] The formation of the yellow diimine can be accelerated by the addition of acids, such as H2SO4,[18] and appears to be stable over time.[17] It was shown that TMB is electroactive and can be detected by voltammetric techniques in HRP-based immunoassays or sensors.[19] In principle there are two possible electroactive species which can be quantified by reduction at an electrode after the enzymatic oxidation. We applied our detection system to the analysis of OTA-spiked beer, the read-out performed with a smartphone connected via Bluetooth to a miniaturized potentiostat, providing a basis for onsite sensing of mycotoxins without conventional laboratory equipment
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