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A novel ultrasensitive electrochemical aptasensor was proposed for quantitative detection of Cd2+. To this end, flower-like polyethyleneimine-functionalized molybdenum disulfide-supported gold nanoparticles (PEI-MoS 2 NFs@Au NPs) were used as substrates for the modification of bare gold electrodes (AuE). PEI-MoS 2 NFs@Au NPs not only possessed excellent biocompatibility and large specific surface area to enhance the cDNA loading capacity, but also possessed good conductivity to accelerate the electron transfer rate. Furthermore, the preparation of dendritic platinum-palladium nanoparticles (PtPd NPs) can effectively load Cd2+-aptamer. Thionine and aptamers were loaded onto PtPd NPs to construct Thi-PtPd NPs-aptamer signal probes. The signal probes were captured by the cDNA immobilized on the electrode via base-pairing rule, and the signal of Thi was detected by differential pulse voltammetry (DPV). In the presence of Cd2+, aptamer-cDNA unwinded, and the combination of aptamer and Cd2+ caused the signal probes to fall off the electrode and the electrical signal decreases. Under optimal conditions, the proposed aptasensor exhibited a linear relationship between the logarithm of Cd2+ concentration and the current response over a wide range of 1 × 10−3 nM to 1 × 102 nM, with a detection limit of 2.34 × 10−4 nM. At the same time, the aptasensor was used to detect Cd2+ in tap water with satisfactory results. In addition, it has good reproducibility, selectivity and stability, and has broad application prospects in heavy metal analysis. [Display omitted] • The electrochemical signal could be amplified largely by the synthesized PEI-MoS 2 @Au NPs. • PtPd NPs were severed as nanocarrier for aptamer and Thi. • Ultrasensitive detection of Cd2+ by reliable electrochemical aptasensor. • The competitive recognition was utilized for the Cd2+ detection. [ABSTRACT FROM AUTHOR]