Abstract
Diagnosis of disease outside of sophisticated laboratories urgently requires low-cost, user-friendly devices. Disposable, instrument-free testing devices are used for home and physician office testing, but are limited in applicability to a small class of highly abundant analytes. Direct, unambiguous visual read-out is an ideal way to deliver a result on a disposable device; however, existing strategies that deliver appropriate sensitivity produce only subtle colour changes. Here we report a new approach, which we term electrocatalytic fluid displacement, where a molecular binding event is transduced into an electrochemical current, which drives the electrodeposition of a metal catalyst. The catalyst promotes bubble formation that displaces a fluid to reveal a high contrast change. We couple the read-out system to a nanostructured microelectrode and demonstrate direct visual detection of 100 fM DNA in 10 min. This represents the lowest limit of detection of nucleic acids reported using high contrast visual read-out.
Highlights
Diagnosis of disease outside of sophisticated laboratories urgently requires low-cost, user-friendly devices
We here develop an approach to amplify the changes to optical density triggered by the levels of electrochemical current generated at a nucleic acid sensor
We demonstrate sensitive colorimetric detection of ssDNA by coupling the read-out to a nanostructured microelectrode (NME) and a novel electrocatalytic assay
Summary
Diagnosis of disease outside of sophisticated laboratories urgently requires low-cost, user-friendly devices. We report a new approach, which we term electrocatalytic fluid displacement, where a molecular binding event is transduced into an electrochemical current, which drives the electrodeposition of a metal catalyst. A variety of direct, colorimetric read-out strategies have been reported: these include approaches based on nanoparticles[12,13], plasmonic nanomaterials14, 2D materials[15] and enzymatic reactions[7] These approaches require interpretation of subtle colour changes. New strategies to transduce extremely small electrochemical currents into perceived, high-contrast visual changes would allow the visual detection of low abundance analytes using electrochemical biosensors. After optimizing the device parameters and geometry, we determine the minimum current necessary for successful colorimetric read-out To showcase this approach, we demonstrate sensitive colorimetric detection of ssDNA by coupling the read-out to a nanostructured microelectrode (NME) and a novel electrocatalytic assay
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