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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]

Biocompatible nitrogen-doped hydrazide-conjugated carbon dots (NHCDs) as an anodic luminophores with low excitation potential were equipped with an efficient multiple signal-amplification strategy for electrochemiluminescence (ECL) trace bioanalysis. To promote the ECL emission of NHCDs-H 2 O 2 system, gold nanoparticles (Au NPs) functionalized tin oxide nanocrystals (Au@SnO 2 NCs) were adopted to anchor large amount of NHCDs, the formed NHCDs-Au@SnO 2 NCs could conjugate with detection antibody as the signal label. Moreover, 3,4,9,10-perylenetetracarboxylic acid (PTCA) molecules were immobilized on the flower-like microsphere (PTCA@ZnCo 2 O 4 /ZnO) nanocomposites to fabricate as an electro-active sensing substrate to incubate the capture antibody, which could efficiently accelerate the generation of reactive oxygen species (OH · /O 2 ·- ) through electrocatalytic excitation and co-reaction acceleration. Integrating with the sandwich-type sensing model, an ECL immunosensor was established to detect biomarkers of squamous cell carcinomas named cytokeratin 19 fragments (cyfra21–1). Combining with the synergistic signal-amplification induced by the Au@SnO 2 NCs, PTCA, and ZnCo 2 O 4 /ZnO nanocomposites, the developed immunosensor performed detection range from 0.09 pg/mL to 100 ng/mL with a detection limit of 34.38 fg/mL. The results showcased the great potential of this sensing strategy for real sample analysis of biomarker with reliable stability, selectivity and repeatability. • Flower-like PTCA-modified ZnCo 2 O 4 /ZnO was synthesized by hydrothermal method. • PTCA-modified ZnCo 2 O 4 /ZnO was demonstrated that can efficiently achieve electrocatalytic excitation and catalyze the ROSs production to amplify the ECL signal. • Au@SnO 2 NCs was utilized to construct highly efficient catalytic nanocarriers. • Signal multiple-amplification strategy was built to improve sensitivity. • The established immunosensor exhibited low detection limit of 34.38 fg·mL-1 for CYFRA21-1. [ABSTRACT FROM AUTHOR]

• CoOOH was used as the ECL quencher probe for the first time. • A new ECL-RET donor-receptor was proposed and fabricated for ultrasensitive detection of PCT. • Dual-quenching system was built to improve sensitivity. • NH 2 -MIL-101 conjugated with g-C 3 N 4 to increase its biocompatibility and emission performance. • The established immunosensor exhibited low detection limit of 3.4 fg mL−1 for PCT. Herein, an ultrasensitive electrochemiluminescence (ECL) biosensing platform for early diagnosis of procalcitonin (PCT) was developed based on enhancing the stability of ECL signal and dual-quenching strategies. In this proposal, in order to improve the deficient of luminescence signal stability of semiconductor luminescent materials, the chromophore graphitic carbon nitride (g-C 3 N 4) was loaded onto the MOF material (amine-functionalized MIL-101: NH 2 -MIL-101). Due to the excellent catalytic performance of NH 2 -MIL-101, more ECL reaction intermediate SO 4 - are restored from the co-reactant S 2 O 8 2-, thus the ECL signal of g-C 3 N 4 becomes stronger and more stable. With the aim of achieving detection of trace markers and improving sensor sensitivity, the dual-quenching strategy is carried out, which was achieved as follows: (i) the strong energy transfer between the donor of g-C 3 N 4 @NH 2 -MIL-101 and the acceptor of cobalt oxyhydroxide nanoflakes@gold nanoparticle (CoOOH@Au NPs) rational diminishes the ECL signal of g-C 3 N 4 ; (ii) the perfect spectral overlap with the luminescent matrix achieves efficiency quenching through resonance energy transfer (RET). Benefiting from the ultrastability of luminophore and the reasonable dual quenching effect, the fabricated ECL biosensor presented dominant stability, selectivity and reproducibility accompanied by detection ranges from 0.014 pg/mL to 40 ng/mL and extremely low detection limit of 3.4 fg/mL. Consequently, it is worth believing that this method can provide a potential analytical strategy for trace immunoassay in clinical analysis. [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]

• A novel PEC signal amplification assay was presented for sensitivity PCT detection. • Zn x Bi 2 S 3+x were used as the sensitizer through the SILAR method modified on to NiTiO 3 rod surface. • The proposed immunosensor owns a large linear range of 0.0005–50 ng mL−1 with a 0.18 pg mL-1 detection limit. • The signal amplification strategy provide applicable to other targets PEC immunosensors. An original signal amplification photoelectrochemical (PEC) immunosensor for procalcitonin detection was fabricated based on Zn x Bi 2 S 3+x sensitized NiTiO 3 nanorods. Using ethylene glycol as medium, the NiTiO 3 nanorods were successfully manufactured after calcination in air atmosphere, the rod-like structure have rough surface that produced benefit to capture lots of functional Zn x Bi 2 S 3+x , the sensitizer sensitized NiTiO 3 on ITO substrate by means of a sequential ionic layer adsorption reaction, and the obtained Zn x Bi 2 S 3+x /NiTiO 3 composites showed an excellent absorption of visible light owing to the matched band gap. By the way, Zn x Bi 2 S 3+x /NiTiO 3 composites as mimic enzyme of glucose oxidase, high sensitivity was achieved due to the generated H 2 O 2 as holes scavenger when glucose added, that promote the photo electrons transfer quickly, further increased the PEC signal. The as prepared sensor showed a large linear range of 0.0001–50 ng·mL−1 with 0.04 pg·mL−1 detection limit. Simultaneously, the signal amplification strategy of this sensor provides applicable to other PEC immunosensors for detection of other targets. [ABSTRACT FROM AUTHOR]

• We systematically synthesis a series of well-defined nanocomposites, like dumbbell-style AuPd and dendrite-like AuPt. • The Au 3 Pd 4 and Au 3 Pt 3 possess excellent catalysis, which can improve the current response of Au 3 Pd 4 /GCE and Au 3 Pt 3 /GCE. • This is the first time that a list of dumbbell-style AuPd modified GCEs to detect nitrite and dendrite-like AuPt modified GCEs to detect TBHQ. • Au 3 Pd 4 /GCE and Au 3 Pt 3 /GCE sensors can respectively detect nitrite and TBHQ with wide linear range and low detection limit. The paper reported the controlled synthesis of dumbbell-style AuPd and dendrite-like AuPt by a simple seed-mediated growth method, respectively. The composition and performances of the resulting nanomaterials were measured using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), UV–vis absorption spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. Moreover, the dumbbell-style AuPd modified glassy carbon electrode (GCE) showed excellent electrocatalytic ability towards nitrite with a fairly wide concentration range from 2 μM to 4200 μM and a 0.67 μM detection limit. The dendrite-like AuPt modified GCE showed excellent electrocatalytic ability towards tert-butyl hydroquinone (TBHQ) with a linear range from 0.35 μM to 625 μM and a relatively low detection limit of 0.075 μM. The electrochemical testing results exhibited the two kinds of sensors, Au 3 Pd 4 /GCE and Au 3 Pt 3 /GCE, possessed accepted selectivity, long-term stability and good reproducibility. Thus, the proposed two sensors could be applied in the determination of food samples. It is expected that the unique AuPd and AuPt are promising materials, which have great potential application in many fields of clinical diagnosis, new energy technologies, catalysis and sensors. [ABSTRACT FROM AUTHOR]