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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]

An original electrochemiluminescent (ECL) luminophore porphyrin nanosphere–graphene oxide composite (TCPP NS-GO) was prepared. The TCPP NS-GO could produce greatly enhanced ECL in buffer with potassium peroxydisulfate (K 2 S 2 O 8 ) as the co-reactant. The enhancement ECL mechanism of TCPP NS-GO/K 2 S 2 O 8 system was investigated in detail. Moreover, The TCPP NS-GO composite had an abundant surface functional group to expand its application, which exhibited high sensitivity and selectivity to Fe 3+ . The wide linear relationship between ECL intensity and Fe 3+ concentration from 0.002 to 5.128 μmol L −1 (R 2 = 0.998) was found with the detection limit as low as 1 nmol L −1 . The ECL quenching mechanism of Fe 3+ was proved by UV-vis absorption spectroscopy, Fluorescence emission spectroscopy (FL) and Fourier transform infrared spectroscopy (FT-IR) analysis technology. [ABSTRACT FROM AUTHOR]

• Manganese-eumelanin coordination nanocomposites quenched ECL behavior of luminol. • Luminol was anchored on PtCo and CuFe 2 O 4 nanoparticles decorated with rGO. • Quenching mechanism maybe inhibit electrooxidation of H 2 O 2 and ECL energy transfer. • The sandwich quenching ECL immunosensor was used to detect procalcitonin. Herein, a facile one-pot intrapolymerization strategy to synthesize manganese-eumelanin coordination nanocomposites (Mn-Eu) was introduced to quench the electrochemiluminescence (ECL) behavior of luminol/H 2 O 2 system. Bimetallic PtCo and CuFe 2 O 4 nanoparticles decorated with reduced graphene oxide was prepared to combine with luminol via electrostatic attractions (Lu-PtCo-CuFe 2 O 4 -rGO) which possessed excellent ECL signals. PtCo-CuFe 2 O 4 -rGO not only exhibited well electrocatalytic activity toward the electrooxidation reactions of luminol and H 2 O 2 , but also facilitated the electroreduction of H 2 O 2 producing more reactive oxygen species (ROSs) which can further enhance the ECL intensity of luminol. To sensitively detect procalcitonin, Mn-Eu labeled-secondary antibodies were employed to specific recognize antigen which incubated with primary antibodies/Lu-PtCo-CuFe 2 O 4 -rGO. The quenching mechanism may be via the synergistic effect between Mn-Eu inhibiting the electrooxidation of H 2 O 2 and ECL resonance energy transfer (ECL-RET) from ECL donor luminol to ECL acceptor Mn-Eu. Under optimal experiments, the ECL immunosensor for detecting procalcitonin with a wider linear range from 0.005 pg/mL to 100 pg/mL and a detection limit of 0.0021 pg/mL (S/N = 3) was obtained. The suggested strategy possessed great potential in bioanalysis and will broaden the application of Mn-Eu. [ABSTRACT FROM AUTHOR]

An electrochemical biosensor was fabricated for reliable and highly sensitive microRNA-21 assay by catalytic hairpin assembly and Pd nanoparticles-DNA layered nanoreticulation, providing a new way in the biochemical assay for detecting microRNA-21 in early disease diagnosis. • The sensitive biosensor was constructed for the detection of miR-21 based on CHA and Pd NPs-DNA LNR. • This biosensor shows low limit of detection and wide dynamic correlation of miR-21, providing a powerful platform for detecting miR-21. • The proposed method was enzyme-free, PCR-free, and convenient without the requirement of any additional separation steps. Herein, a Pd nanoparticles-DNA layered nanoreticulation (Pd NPs-DNA LNR) sensor was assembled to a graphene oxide (GO)-modified electrode by catalytic hairpin assembly (CHA) and a self-assembly process. In this process, GO was modified on the electrode surface to provide -COOH sites for DNA bonding. Moreover, with the CHA circular amplification strategy, many single DNA1 were exposed to be able to be bound with Pd-DNA2 for the formation of the Pd NPs-DNA LNR, which enabled the ultrasensitive detection of microRNA-21 (miR-21) with a low limit of detection 63.1 aM. This strategy combines the amplification technology of CHA and Pd NPs-DNA LNR with Pd NPs. Such a layered nanoreticulation material can support abundant Pd NPs to avoid aggregation and obtain enhanced electrochemical signals. Significantly, this method can be successfully applied in tumor cell lysates and provides a neoteric channel for early disease diagnosis. [ABSTRACT FROM AUTHOR]