Field-ready Voltammetric Detection of Aqueous Cadmium (II) Ions on Aptamer-modified Inkjet-printed Gold Electrode

In this work, a simple and cost-effective integrated electrode system consisting of aptamer- modified inkjet-printed (IJP) gold working electrode and unmodified IJP gold as counter electrode (both printed on polyethylene naphthalate substrate) has been developed for low-cost detection of cadmium (II) ion in water. The technique uses a Cd2+ (Cd-4) aptamer, a single- stranded DNA with 31 nucleotides trapped on the working electrode using the self-assembly monolayer (SAM) technique. The electrochemical detection of Cd2+ is based on the change in redox peaks of [Fe(CN)6]3-/4- as a redox probe in cyclic voltammetry. The change in peak current is caused by a difference in electron transfer rate before and after binding the aptamer with the target ion (Cd2+). The electrochemical properties were further characterized using electrochemical impedance spectroscopy under optimal conditions, revealing changes in the charge transfer resistance upon binding the Cd2+ ion with the aptamer on gold. Detection by CV, the anodic peak currents (Ipa) varied linearly with Cd2+ concentration from 0.1–10 ng/ mL. Saturation of the working electrode's active surface area was achieved with 10 ng/mL. The regression coefficient was 0.9977, whereas for the Cd2+ aptasensor, the limit of detection (LOD) was 0.5 ng/mL. The developed electrochemical aptasensor showed good sensitivity with a value of 1.94 μA/ng/mL and was partially selective in the presence of interfering divalent ions (Cu2+, Hg2+, Ni2+, and Zn2+). The RSD within the linear detection range (0.1–10 ppb) is 0.28%. The IJP aptasensor has simple and cost-effective compositions, consuming only 0.5 mg of Au loading of ink during the inkjet-printing process. Minimal chemical waste is also produced because the sample volume requirement for the analysis is only 50 μL. The IJP aptasensor has promising potential for rapid and on-site detection of Cd2+ in water samples using a portable CV system.