Potentiometric enzymatic aptasensing of paralytic shellfish toxins using graphene-wrapped magnetic nanospheres and an all-solid-state cadmium-selective microelectrode

A highly sensitive potentiometric enzymatic aptasensing system for the detection of paralytic shellfish toxins (PSTs) is developed by integrating graphene-wrapped magnetic nanospheres (Fe₃O₄@SiO₂@rGO) with an all-solid-state ion-selective microelectrode. The multilayered core-shell structure of Fe₃O₄@SiO₂@rGO enhances the efficient adsorption of aptamer molecules tagged with cadmium sulfide (CdS) nanoparticles. These CdS-aptamer conjugates, when bound with PST molecules, can be desorbed from the Fe₃O₄@SiO₂@rGO surface into the sample solution and subsequently digested by deoxyribonuclease I (DNase I). This digestion process releases the PST molecules for recirculation, significantly reducing the retention of CdS on the surface of Fe₃O₄@SiO₂@rGO. After magnetic separation and acid dissolution, the released Cd²⁺ from the magnetic nanospheres are measured using an all-solid-state Cd²⁺-selective microelectrode, enabling sensitive potentiometric detection of PSTs. Using gonyautoxin 1/4 (GTX 1/4) as a model, the sensing system exhibits a linear concentration range from 5 to 150 pM and a low detection limit of 1.7 pM for GTX 1/4, and has been successfully applied in the analysis of seawater samples.