Abstract
An electrochemical assay based on underpotential deposition (UPD) of metal has been utilised for the detection of Cd 2+ using surface immobilized single-stranded DNA (ss-DNA). Since Cd 2+ is able to undergo UPD on gold surface, this allows the opportunity to detect the amount of Cd 2+ accumulated by immobilized ss-DNA directly via voltammetry. This is evidenced by the appearance of Cd 2+/Cd 0 electrochemistry at E 0′ of 92 mV (rather than E 0′ of −795 mV in bulk solution) at the ss-DNA modified gold electrode only after an exposure to Cd 2+ solution. An association constant of 8.33 × 10 5 M −1 was determined from a Cd 2+ calibration curve assuming a Langmuir-binding model for Cd 2+ with surface-immobilized DNA. The high association constant is reflected in a low detectable concentration of 10 pM. The sensing layer can also be regenerated to metal-free status and can be reused up to 18 times without significant signal degradation.
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