In this work, a novel electrochemical DNA sensor based on exonuclease III (Exo III)-assisted autocatalytic DNA biosensing platform for ultrasensitive detection of antibiotics has been reported. When the arched probe was challenged with target, the released primer caused by the specific recognition of the aptamer and target antibiotics hybridized with the 3′-protruding terminus in the HP1. Then, Exo III could catalyze the stepwise removal of mononucleotides from this flat terminus, resulting in the release of the primer and trigger. As a secondary target, trigger could replace Helper from the 5′-MB labeled HP2, and HP2 formed a “close” probe structure, confining MB close to the electrode surface for efficient electron transfer. To our best knowledge, such work is the first report about Exo III-assisted autocatalytic DNA biosensing platform combing with signal-on sensing strategy, which has been utilized for quantitative determination of antibiotics. It would be further used as a general strategy associated with more analytical techniques toward the detection of a wide spectrum of analytes. Thus, it holds great potential for the development of ultrasensitive biosensing platform for the applications in bioanalysis, disease diagnostics, and clinical biomedicine.

•A label-free electrochemical biosensor for detecting E. coli has been developed.•RCA coupled DNAzyme amplification has been integrated into electrochemical assay.•DNAzyme is used as catalytic tag, making our approach technically label-free.In this work, a simple, label-free, low cost electrochemical biosensor for highly sensitive and selective detection of Escherichia coli has been developed on the basis of rolling circle amplification (RCA) coupled peroxidase-mimicking DNAzyme amplification. A aptamer-primer probe (APP) containing anti-E. coli aptamer and a primer sequence complementary to a circular probe, which includes two G-quadruplex units, is used for recognizing target and triggering RCA-based polymerase elongation. Due to RCA coupled DNAzyme amplification strategy, the presence of target E. coli leads to the formation of numerous G-quadruplex oligomers on electrode, which folds into G-quadruplex/hemin complexs with the help of K+ and hemin, thus generating extremely strong catalytic activity toward H2O2 and giving a remarkably strong electrochemical response. As far as we know, this work is the first time that RCA coupled peroxidase-mimicking DNAzyme amplification technique have been integrated into electrochemical assay for detecting pathogenic bacteria. Under optimal conditions, the proposed biosensor exhibits ultrahigh sensitivity toward E. coli with detection limits of 8 cfu mL−1 and a detection range of 5 orders of magnitude. Besides, our biosensor also shows high selectivity toward target E. coli and has the advantages in its rapidness, low cost, simplified operations without the need of electrochemical labeling steps and additional labile reagents. Hence, the RCA coupled peroxidase-mimicking DNAzyme amplification-based electrochemical method might create a useful and practical platform for detecting E. coli and related food safety analysis and clinical diagnosis.

•A novel trigger-assisted exponential enzymatic amplification (T-EXPEA) method has been reported.•The feature of our strategy lies in the T-EXPEA combining with 3-WJ structure.•The design of restriction enzyme cutting sites using the same restriction enzyme (Nt.BbvCI) has many advantages.•The same sequence of the triggers generated from both the 3-WJ part and T-EXPEA part.Aberrant expression of micro RNA (miRNA) is associated with development of cancers and diseases, so miRNA has become a tissue-based biomarker for cancer prognosis and diagnosis. Herein, a novel trigger-assisted exponential enzymatic amplification (T-EXPEA) method for ultrasensitive miRNA detection based on three-way junction (3-WJ) structure driven has been reported, which can be used in potential applications in cancer prognosis and diagnoses. In this assay, target miRNA can unfold hairpin probe and start the reaction, and thus specifically form stable 3-WJ structure with helper. Then it can produce triggers under the synergetic polymerase and restriction endonucleases amplification. The produced triggers could be used to unfold molecular beacon (MB) and initiate T-EXPEA process. In the EXPEA part, the exponential triggers were generated to initiate new T-EXPEA and high enhancement fluorescence amplification efficiency was obtained. The feature of our strategy lies in the T-EXPEA combining with 3-WJ structure has been utilized for fluorescence miRNA detection. It is worth noting that the sequence of the triggers in T-EXPEA part is the same to that of triggers generated from the 3-WJ part. In addition, the design of restriction enzyme cutting sites using the same restriction enzyme (Nt.BbvCI) in hairpin probe and MB respectively, improved reaction efficiency cost-efficiently. This method can quantitatively detect sequence-specific miRNA in a dynamic range from 10 aM to 10 pM with a detection limit as low as 7.8 aM.

A novel electrochemical aptasensor for ultrasensitive detection of antibiotics by combining polymerase-assisted target recycling amplification with strand displacement amplification with the help of polymerase and nicking endonuclease has been reported. This work is the first time that target–aptamer binding triggered quadratic recycling amplification has been utilized for electrochemical detection of antibiotics.

•The PtPd PNRs were porous and alloy-structured and showed much higher affinity to H2O2.•Colorimetric method for the flux of H2O2 release from living cell was developed using PtPd PNRs as a peroxidase mimetic.•The PtPd PNRs have good stability, and fine biocompatibility which can greatly overcome the intrinsic shortcomings.One-dimensional PtPd porous nanorods (PtPd PNRs) were successfully synthesized through a bromide-induced galvanic replacement reaction between Pd nanowires and K2PtCl6. The PtPd PNRs were porous and alloy-structured with Pt/Pd atomic ratio up to 1:1 which were demonstrated by spectroscopic methods. We had also proved that the nanorods could function as peroxidase mimetic for the detection of H2O2, with the detection limit of 8.6 nM and the linear range from 20 nM to 50 mM. The result demonstrated that PtPd PNRs exhibited much higher affinity to H2O2 over other peroxidase mimetics due to synergistically integrating highly catalytic activity of two metals. On the basis of the peroxidase-like activity, the PtPd PNRs were used as a signal transducer to develop a novel and simple colorimetric method for the study of the flux of H2O2 released from living cell. By using 3,3,5,5-tetramethylbenzidine as substrate, the H2O2 concentration could be distinguished by naked-eye observation without any instrumentation or complicated design. The method developed a new platform for a reliable collection of information on cellular reactive oxygen species release. And the nanomaterial could be used as a power tool for a wide range of potential applications in biotechnology and medicine.

In this work, we explored an amplification strategy which was based on graphene oxide–polyaniline (GO–PANI) and horseradish peroxidase (HRP) to construct the competitive aptasensor for ultrasensitive detection of oxytetracycline (OTC). In the protocol, the GO–PANI film was immobilized on the surface of the electrodes. Then, gold nanoparticles (AuNPs) were electrodeposited on the electrode surface using a constant potential stripping technique. The selected aptamer which had high affinity and specificity for OTC was used as a capture probe and labeled with HRP. The linear response to OTC concentration of the developed aptasensor was in the range of 4.0 × 10−6 mg L−1 to 1.0 mg L−1. The detection limit (LOD) of 2.3 × 10−6 mg L−1 was obtained (S/N = 3). In addition to good repeatability and stability, the proposed aptamer sensor also showed the advantages of low background current and high sensitivity to examine OTC in real samples.

In this work, we report a novel sandwich-type electrochemical aptasensor for sensitive and selective detection of antibiotic kanamycin. This aptasensor was constructed by assembling graphene–polyaniline (GR–PANI) and polyamidoamine dendrimer–Au nanoparticle (PAMAM–Au) nanocomposites on the surfaces of a glass carbon electrode, which as electrode materials exhibited excellent charge-transport property and loading capacity of biomolecules. Followed by the sandwich-type specific identification, kanamycin detection was realized by outputting a redox current from electro-reduction reaction of H2O2 catalyzed by HRP. It was demonstrated that the developed strategy had a wide linear response range from 5 × 10−6 to 4 × 10−2 μg mL−1 and a low detection limit of 4.6 × 10−6 μg mL−1. Additionally, this aptasensor had the advantages in its low cost, high sensitivity, and superb specificity. Thus, it might provide a useful tool for kanamycin determination and related food safety analysis and clinical diagnosis.

In this study, we developed a novel molecularly-imprinted electrochemical sensor based on a glassy carbon electrode (GCE) decorated by graphene–Prussian blue (GR–PB) composites for the selective and sensitive determination of butylated hydroxyanisole (BHA). The molecularly-imprinted polymers (MIPs) were synthesized by BHA and pyrrole as the template molecule and functional monomer, respectively. Also, the MIPs were assembled on the surface of the GR–PB/GCE by electropolymerization. The sensor was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and chronoamperometry. It was confirmed that the synergistic effects of GR and PB could improve the electrochemical response and the sensitivity of the sensor. The linear range of the sensor was from 9 × 10−8 mol L−1 to 7 × 10−5 mol L−1, with a limit of detection (LOD) of 7.63 × 10−8 mol L−1 (S/N = 3). The proposed sensor displayed high selectivity, excellent stability and good reproducibility for the determination of BHA. It was successfully applied to the determination of BHA in real samples.

A novel estradiol immunosensor based on graphene–polyaniline (GR–PANI) composites and carboxylated graphene oxide (GO) was developed. GR–PANI composites were used to enhance the electroactivity and stability of the electrode. The current response of the immunosensor was remarkably improved due to the synergistic effects of GR and PANI. Horseradish peroxidase–graphene oxide–antibody (HRP–GO–Ab) conjugates which were constructed by using the carboxylated GO as the carrier of the antibody and horseradish peroxidase as the label improved the catalytic activity for hydrogen reduction of the electrode. A competitive immunoassay was facilitated between 17β-estradiol and the HRP–GO–Ab conjugates. Based on this competitive immunoassay, the immunosensor showed a wide linear response to estradiol in the range 0.04–7.00 ng/mL and a limit of detection of 0.02 ng/mL (S/N = 3). The developed immunosensor was successfully applied to the detection of estradiol in real samples.

A novel imprinted electrochemical sensor for neomycin recognition was developed based on chitosan-silver nanoparticles (CS-SNP)/graphene-multiwalled carbon nanotubes (GR-MWCNTs) composites decorated gold electrode. Molecularly imprinted polymers (MIPs) were synthesized by electropolymerization using neomycin as the template, and pyrrole as the monomer. The mechanism of the fabrication process and a number of factors affecting the activity of the imprinted sensor have been discussed and optimized. The characterization of imprinted sensor has been carried out by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The performance of the proposed imprinted sensor has been investigated using cyclic voltammetry (CV) and amperometry. Under the optimized conditions, the linear range of the sensor was from 9×10−9 mol/L to 7×10−6 mol/L, with the limit of detection (LOD) of 7.63×10−9 mol/L (S/N=3). The film exhibited high binding affinity and selectivity towards the template neomycin, as well as good reproducibility and stability. Furthermore, the proposed sensor was applied to determine the neomycin in milk and honey samples based on its good reproducibility and stability, and the acceptable recovery implied its feasibility for practical application.Highlights► A selective electrochemical molecularly imprinted sensor for the detection of neomycin was developed. ► CS-SNP and GR-MWCNTs nanocomposites were used to improve the sensitivity of the sensor. ► MIPs were synthesized by electropolymerization using neomycin as the template, and pyrrole as the monomer. ► The sensor showed high selectivity, excellent stability and good reproducibility for the determination of neomycin. ► The developed sensor was successfully used for neomycin determination in real spiked samples.

An imprinted electrochemical sensor based on polypyrrole-sulfonated graphene (PPy-SG)/hyaluronic acid-multiwalled carbon nanotubes (HA-MWCNTs) for sensitive detection of tryptamine was presented. Molecularly imprinted polymers (MIPs) were synthesized by electropolymerization using tryptamine as the template, and para-aminobenzoic acid (pABA) as the monomer. The surface feature of the modified electrode was characterized by cyclic voltammetry (CV). The proposed sensor was tested by chronoamperometry. Several important parameters controlling the performance of the molecularly imprinted sensor were investigated and optimized. The results showed that the PPy-SG composites films showed improved conductivity and electrochemical performances. HA-MWCNTs bionanocomposites could enhance the current response evidently. The good selectivity of the sensor allowed three discriminations of tryptamine from interferents, which include tyramine, dopamine and tryptophan. Under the optimal conditions, a linear ranging from 9.0 × 10−8 mol L−1 to 7.0 × 10−5 mol L−1 for the detection of tryptamine was observed with the detection limit of 7.4 × 10−8 mol L−1 (S/N = 3). This imprinted electrochemical sensor was successfully employed to detect tryptamine in real samples.Highlights► A molecularly imprinted electrochemical sensor was developed for tryptamine studied. ► PPy-SG and HA-MWCNTs nanocomposite were used in the experiment. ► Different experimental parameters were studied. ► Determination of tryptamine in practical samples showed good recovery.

A novel label-free electrochemical aptasensor based on graphene–polyaniline (GR–PANI) nanocomposites film for dopamine (DA) determination was reported. The resulting GR–PANI layer exhibited good current response for DA determination. The good electron transfer activity might be attributed to the effect of GR and PANI. The highly conductive and biocompatible nanostructure of GR–PANI nanocomposites was characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). To quantify the amount of DA, the peaks of square-wave voltammetry (SWV) were monitored using the redox couple of an [Fe(CN)6]4−/3− probe. The electrochemical aptasensor showed a linear response to DA in the range 0.007–90 nmol/L and a limit of detection of 0.00198 nmol/L (S/N=3). The electrochemical aptasensor was successfully tested on human serum samples.Highlights► A novel label-free electrochemical aptasensor was developed for DA studied. ► GR–PANI nanocomposite was used in the experiment. ► Different experimental parameters were studied. ► Determination of DA in human serum sample showed good recovery.

A molecularly imprinted electrochemical sensor was fabricated based on gold electrode decorated by chitosan–platinum nanoparticles (CS–PtNPs) and graphene–gold nanoparticles (GR–AuNPs) nanocomposites for convenient and sensitive determination of erythromycin. The synergistic effects of CS–PtNPs and GR–AuNPs nanocomposites improved the electrochemical response and the sensitivity of the sensor. The molecularly imprinted polymers (MIPs) were prepared by HAuCl4, 2-mercaptonicotinic acid (MNA) and erythromycin. Erythromycin and MNA were used as template molecule and functional monomer, respectively. They were first assembled on the surface of GR–AuNPs/CS–PtNPs/gold electrode by the formation of Au–S bonds and hydrogen-bonding interactions. Then the MIPs were formed by electropolymerization of HAuCl4, MNA and erythromycin. The sensor was characterized by cyclic voltammetry (CV), scanning electron microscope (SEM), UV–visible (UV–vis) absorption speactra and amperometry. The linear range of the sensor was from 7.0×10−8 mol/L–9.0×10−5 mol/L, with the limit of detection (LOD) of 2.3×10−8 mol/L (S/N=3). The sensor showed high selectivity, excellent stability and good reproducibility for the determination of erythromycin, and it was successfully applied to the detection of erythromycin in real spiked samples.Highlights► A selective electrochemical molecularly imprinted sensor for the detection of erythromycin was developed. ► CS–PtNPs and GR–AuNPs nanocomposites were used to improve the sensitivity of the sensor. ► AuNPs was introduced in the preparation processes of MIPs films to improve the current response of MIPs. ► We combined self-assembly technology and electropolymerization method together in the preparation processes of MIPs. ► The sensor showed high selectivity, excellent stability and good reproducibility for the determination of erythromycin.

An ultrasensitive electrochemical immunosensor based on mesoporous silica–gold nanoparticles–multiwall carbon nanotubes (MSN–GNPs–MWCNTs) nanocomposites and horseradish peroxidase–antibody–Prussian blue–multiwall carbon nanotubes (HRP–Ab–GNPs–PB–MWCNTs) bioconjugates was developed for the detection of diethylstilbestrol (DES). MSN–GNPs–MWCNTs nanocomposites as immobilization matrix were used to enhance the electroactivity and stability of the electrode. HRP–Ab–GNPs–PB–MWCNTs bioconjugates as label were used to improve catalytic activity for hydrogen reduction of the electrode. Meanwhile, HRP–Ab–GNPs–PB–MWCNTs were used as the second signal amplification strategy for the detection of DES in the sandwich immunoreaction. Under the optimized conditions, a calibration plot for DES was obtained with a linear range between 3.3 × 10−7 mg/mL and 4.5 × 10−3 mg/mL (r = 0.996). The detection limit was 1.2 × 10−7 mg/mL (S/N = 3). The proposed electrochemical immunosensor has excellent selectivity, good reproducibility and long-term stability. The total time taken for the assay was 7 min. The electrochemical immunosensor was examined in real samples for the analysis of DES. A good recovery in the range of 92–107% was obtained in milk and pork samples.

An ultrasensitive electrochemical immunosensor based on chitosan-iron oxide-poly(amino-amine) dendrimers-gold nanoparticles (CS-Fe3O4-PAMAM-GNPs) nanocomposites and horseradish peroxidase-multiwall carbon nanotubes-antibody (HRP-MWCNTs-Ab) bioconjugates was developed for the detection of salbutamol (SAL). CS-Fe3O4-PAMAM-GNPs nanocomposites as immobilization matrix were used to enhance the electroactivity and stability of the electrode. HRP-MWCNTs-Ab bioconjugates as label were used to improve catalytic activity for hydrogen reduction of the electrode. Under the optimized conditions, a calibration plot for SAL was obtained with a linear range between 0.11 ng/mL and 1061 ng/mL (r = 0.9984). The detection limit was 0.06 ng/mL. The immunosensor was examined in real samples for the analysis of SAL.

A novel bisphenol A (BPA) sensor based on amperometric detection has been developed by using molecularly imprinted polymers (MIPs) and gold nanoparticles. The sensitive layer was prepared by electropolymerization of 2-aminothiophenol on a gold nanoparticles-modified glassy carbon electrode in the presence of BPA as a template. Cyclic voltammetry was used to monitor the process of electropolymerization. The properties of the layer were studied in the presence of Fe(CN)63−/Fe(CN)64− redox couples. The template and the non-binding molecules were removed by washing with H2SO4 (0.65 mol L−1) solution. The linear response range of the sensor was between 8.0 × 10−6–6.0 × 10−2 mol L−1, with a detection limit of 1.38 × 10−7 mol L−1 (S/N = 3). The proposed MIPs sensor exhibited good selectivity for BPA. The stability and repeatability of the MIPs senor were found to be satisfactory. The results from real sample analysis confirmed the applicability of the MIPs sensor to quantitative analysis.

4-Nonylphenol (4-NP) was reported to affect the health of wildlife and humans through altering endocrine function. A novel electrochemical sensor for sensitive and fast determination of 4-NP was developed. Titanium oxide (TiO2) nanoparticles and gold nanoparticles (AuNPs) were introduced for the enhancement of electron conduction and sensitivity. 4-NP-imprinted functionalized AuNPs composites with specific binding sites for 4-NP was modified on electrode. The resulting electrodes were characterized by cyclic voltammetry (CV). Rebinding experiments were carried out to determine the specific binding capacity and selective recognition. The linear range was over the range from 4.80 × 10−4 to 9.50 × 10−7 mol L−1, with the detection limit of 3.20 × 10−7 mol L−1 (S/N = 3). The sensor was successfully employed to detect 4-NP in real samples.

An ultrasensitive electrochemical immunosensor based on mesoporous silica–gold nanoparticles–multiwall carbon nanotubes (MSN–GNPs–MWCNTs) nanocomposites and horseradish peroxidase–antibody–Prussian blue–multiwall carbon nanotubes (HRP–Ab–GNPs–PB–MWCNTs) bioconjugates was developed for the detection of diethylstilbestrol (DES). MSN–GNPs–MWCNTs nanocomposites as immobilization matrix were used to enhance the electroactivity and stability of the electrode. HRP–Ab–GNPs–PB–MWCNTs bioconjugates as label were used to improve catalytic activity for hydrogen reduction of the electrode. Meanwhile, HRP–Ab–GNPs–PB–MWCNTs were used as the second signal amplification strategy for the detection of DES in the sandwich immunoreaction. Under the optimized conditions, a calibration plot for DES was obtained with a linear range between 3.3 × 10−7 mg/mL and 4.5 × 10−3 mg/mL (r = 0.996). The detection limit was 1.2 × 10−7 mg/mL (S/N = 3). The proposed electrochemical immunosensor has excellent selectivity, good reproducibility and long-term stability. The total time taken for the assay was 7 min. The electrochemical immunosensor was examined in real samples for the analysis of DES. A good recovery in the range of 92–107% was obtained in milk and pork samples.

A novel electrochemical aptasensor for ultrasensitive detection of antibiotics by combining polymerase-assisted target recycling amplification with strand displacement amplification with the help of polymerase and nicking endonuclease has been reported. This work is the first time that target–aptamer binding triggered quadratic recycling amplification has been utilized for electrochemical detection of antibiotics.