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Graphical abstract Highlights • Ultrasensitive electrochemical aptasensor was developed for detecting Pb2+. • Au@p-rGO was applied as support for immobilizing the aptamer. • Au NPs@GO as signal probe exhibited high electrocatalytic activity towards H 2 O 2. • The aptasensor displayed low detection limit of 1.67 pmol/L for Pb2+. Abstract A sensitive electrochemical aptasensor was designed based on gold modified graphene nanocomposite with different morphologies for the detection of lead ion (Pb2+). Specifically, a sulfydryl-labeled substrate strand (Apt1) and a sulfydryl-labeled catalytic strand (Apt2) were devised in fabricating the electrochemical aptasensor. Gold modified porous reduced graphene oxide (Au@p-rGO) was synthesized and applied as support for immobilizing the Apt1. And gold modified graphene oxide (Au NPs@GO) was employed as signal probe and connected with Apt2 to realize the immobilization of it on the electrode by means of the principle of complementary base pairing. The current signal can be obtained by recording the electrocatalytic conditions toward H 2 O 2. The Pb2+-dependent DNAzyme could play a role when Pb2+ existed. With the increase of the concentration of Pb2+, the current response revealed a diminishing signal, thus realizing the sensitive detection of Pb2+. Under the optimal conditions, the fabricated electrochemical aptasensor exhibited a linear response toward Pb2+ ranging from 5 pmol/L to 1 μmol/L, together with a low limit of detection of 1.67 pmol/L. Moreover, the prepared aptasensor displayed outstanding selectivity, acceptable stability and superior reproducibility for detecting Pb2+. This proposed tactics may provide reference and potential applications for detecting some other heavy metal ions. [ABSTRACT FROM AUTHOR]

• Ultrasensitive electrochemical aptasensor was fabricated for detecting Pb2+. • AuPd@Fe-MOFs labeled DNA was firstly applied to produce the electrical signal. • Au@MoS 2 /rGO was utilized as sensing platform to construct the aptasensor. • The aptasensor displayed low detection limit of 0.07 pmol/L for Pb2+ detection. In this work, an electrochemical aptasensor was proposed by using gold-modified molybdenum disulfide/reduced graphene oxide (Au@MoS 2 /rGO) nanocomposite and gold-palladium (AuPd)-modified MIL-88 (Fe) metal-organic frameworks (AuPd@Fe-MOFs) for sensitive detection of lead ions (Pb2+). The 8–17 DNAzyme consisting of a substrate strand (Apt1) and a catalytic strand (Apt2) was used to construct the aptasensor. Au@MoS 2 /rGO nanocomposite was applied as the sensing platform to immobilize the mercapto-group-labeled Apt1. Meanwhile, AuPd@Fe-MOFs was employed to label Apt2, which showed excellent catalytic ability toward H 2 O 2. In the presence of Pb2+, the Apt1 of the DNAzyme was catalytically cut off, decreasing the amount of AuPd@Fe-MOFs. The current response was correlated to the Pb2+concentration, thereby achieving Pb2+ detection. Under the optimal experimental conditions, the fabricated aptasensor showed a highly linear response for Pb2+ in the range from 5.0 pmol/L to 2.0 μmol/L, with a detection limit of 0.07 pmol/L. Additionally, the proposed electrochemical aptasensor exhibited excellent selectivity, stability and reproducibility. Moreover, the proposed aptasensor demonstrated good performance in real water sample analysis, making it promising for use in Pb2+ detection in environmental monitoring. [ABSTRACT FROM AUTHOR]