Colorimetric biosensors for the detection of analytes with the naked eye are required in environmental monitoring, point-of-care diagnostics, and analyses in resources constrained settings, where detection instruments may not be available. However, instrument-based detection methods are usually more adequate for detecting small variations in the signal compared to naked-eye detection schemes, and consequently the limit of detection of the latter is usually higher than the former. Here, we demonstrate that the limit of detection of colorimetric enzyme-linked immunoassays can be decreased several orders of magnitude when using naked-eye detection instead of a spectrophotometer for detecting the signal. The key step to lower the limit of detection is adding a small volume of chromogenic substrate during the signal generation step. This generates highly colored solutions that can be easily visualized with the naked eye and recorded with the camera of a mobile phone. The proposed method does not require expensive equipment or complex protocols to enhance the signal, and therefore it is a universal approach to lower the limit of detection of colorimetric enzyme-linked immunoassays.
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This work was supported by a Tom West Analytical Fellowship and an Analytical Chemistry Summer Studentship from the Analytical Chemistry Trust Fund, and by a research grant from Tenovus Scotland.
The authors state no potential conflicts of interest.
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O’Connor, E.F., Paterson, S. & de la Rica, R. Naked-eye detection as a universal approach to lower the limit of detection of enzyme-linked immunoassays. Anal Bioanal Chem 408, 3389–3393 (2016). https://doi.org/10.1007/s00216-016-9453-8
- Naked-eye detection