A portable and quantitative biosensor for cadmium detection using glucometer as the point-of-use device

As an ubiquitous heavy metal pollutant, cadmium ion (Cd2+) is detrimental to food and human health even at low concentrations. Conventional methods require costly instruments and cannot meet the requirements of on-site analysis. Here we report the use of a personal glucose meter (PGM) as the point-of-use (POU) device for portable and quantitative detection of Cd2+. The specific recognition between the aptamer and Cd2+ trigger the recycling signal amplification process by exonuclease III (Exo III). After successive hybridization and cleavage reactions, numerous single-stranded DNA were liberated on the surface of the magnetic bead. An invertase-conjugated DNA that is complementary to the single-stranded DNA is introduced into the sensing system. After magnetic separation, the invertase conjugates hydrolyze sucrose into glucose, thus establishing direct conversion of Cd2+ concentration to glucose amount, which can be directly quantified by a PGM. Thanks to the synergistic signal amplification of Exo III and invertase, the POU device greatly improves the sensitivity for Cd2+ analysis, with a detection limit of 5 p.M. With the advantages of portability, cost-effectiveness, wide availability, and ease of use, the PGM-based detector has the potential to be used by the public as a routine tool for reliable and quantitative detection of Cd2+.