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Various mycotoxins are widely present in crop products, which cause serious harm to human and animals. In this study, combining the specific recognition of aptamer with catalytic hairpin assembly (CHA) strategy, the pregnancy test strip is used to detect multiple mycotoxins. The signal amplification can be further achieved through following enzymatic reaction to increase sensitivity. In the experiment, there is no need to assemble test strip as well as prepare and purify antibody/hapten. It only requires to couple human chorionic gonadotropin (hCG) with DNA probe to realize the target determination via CHA process and enzymatic signal amplification on the test strip. Under optimal conditions, using the CHA based pregnancy test strip detection platform, the visual limits of detection for aflatoxin B1, ochratoxin and zearalenone can be obtained within 15 min, which are 20, 50 and 20 pg/mL, respectively. The detection results of the spiked samples show that the platform possesses satisfied accuracy, reproducibility and practicability. The method has facile scheme, low cost and good design versatility, and reveals potential application prospects in high sensitivity, low cost, and convenient detection of mycotoxins.

PS2M aptamer was selected as sensing element to construct Pb2+ strip biosensor, and for the first time, AuNP-DNA polymer was used as sensitivity enhancement probe (SEP) to improve sensitivity. Pb2+ separated the double-strand formed by PS2M and its complementary sequence at Anti-PS2M and induced PS2M to form G-quadruplex structure, then single-strand Anti-PS2M was released. When migrated along the strip, sequence at one end of Anti-PS2M hybridized with AuNP-DNA probe G immobilized on conjugate pad, when the composite migrated to test zone (TZ), other end of Anti-PS2M hybridized with biotin-DNA probe T on TZ to form sandwich structure. Subsequent SEP hybridized with the remaining oligonucleotides of AuNP-DNA probe G on TZ thus enhanced the signal. After optimization, the false positive result could be eliminated and the best signal value could be obtained. The results showed that the limit of detection of Pb2+ strip biosensor was 2.5 nM by adding the sensitivity enhancement probe, which was 40 times better than that strip without enhancement. The test strip showed good results in the direct detection of soil and lake samples, presenting good practical value. In addition, the cost of this strip biosensor was low, with good market prospect.

Pregnancy test strip is currently one of the most mature and widely used biomedical test products. In this study, based on its simplicity and rapidity, the detecting target-human chorionic gonadotropin (hCG) is coupled with different hybridization probes, while the aptamer is linked with the initiator used for hybridization chain reaction (HCR), which can construct a signal amplification platform based on HCR. The method converts the detection of other biochemical molecules into the detection of hCG signal, and combines the magnetic separation technology to realize the detection of various targets with pregnancy test strip. The rapid quantitative detection can be achieved with smartphone App and portable detection device. Under the optimal experiment conditions, the method can realize rapid and sensitive detection of adenosine triphosphate, thrombin, carcinoembryonic antigen and DNA fragment in human serum, and the visual detection limits can reach 100 pM, 0.2 pM, 5 ng/mL and 5 pM, respectively. The design has low cost, simple operation, and good sensitivity and selectivity for target detection. Based on this design, the detection of multiple analytes can be implemented with different aptamer sequences, thereby broadening the application of commercial pregnancy test strip in the biomedical testing field.

In this paper, we proposed an amplified assay using DNase I for sensitively sensing prostate specific antigen (PSA) based on CdSe/ZnS quantum dot labelled PSA aptamer/graphene oxide (QD-aptamer/GO). In this sensing system, GO could strongly bind QD conjugated aptamer and quench the fluorescence of QD, furthermore, GO could protect DNA from nuclease cleavage. When binding target PSA, aptamer probe released from the surface of GO nanosheet, then the free aptamer could be cleaved by nuclease, thus the QD and PSA were liberated, after that, the released PSA would bind another aptamer on GO nanosheet and start a new cycle, which resulted in amplification of restoring signal. The probe possessed steady fluorescence signal and high specificity due to the anti photobleaching of QD and the high affinity of aptamer to PSA. Under the optimum experimental conditions, fluorescence intensity increased linearly with the PSA concentration between 0.1 fg mL −1 and 3 fg mL −1 with the limit of quantification of 0.05 fg mL −1 , which was three orders of magnitude lower than that without DNase I. Finally, the method was applied to quantification of PSA in human serum samples.

This study has developed a new membrane based visualization method for the detection of ultratrace lead and cadmium ions. The basic steps were mainly as follows. Dithizone (Dz) was adsorbed on cellulose acetate membrane (CAM) and formed Dz-Pb 2+ /Cd 2+ complexes in the presence of lead and cadmium ions. Then the complexes were converted into Dz-PbS/CdS composites after further processing with sulfide ions. While the new formed Dz-PbS/CdS composites could act as a catalyst in the subsequent silver stain reaction. With the silver nanoparticles depositing on CAM, the color of the membrane turned gray to black, which could be observed by naked eye. Semi-quantitative analysis of Pb 2+ /Cd 2+ was performed according to the ΔAverage gray value of CAM grayscale images. Results showed that under the optimal conditions, ΔAverage gray value had a good linear relation with the logarithm of the Pb 2+ /Cd 2+ concentration in the range from 1 nM to 100 nM, and the naked eye detection limit could reach 1 nM (∼0.0002 mg L −1 ). Besides, other common metal ions had no significant interference with the detection, indicating that the method had a good selectivity. Satisfactory results were obtained for the detection of Pb 2+ /Cd 2+ in real samples (lake water and soil samples).

a b s t r a c t A field-compatible technique involving the use of an electrochemical microbundle for real-time and simultaneous in vivo measurement of hydrogen peroxide, nitric oxide, and pH in plants was devel- oped. The sensing electrodes of the microbundle included one Pt microelectrode for H2O2 detection, one platinized Pt electrode for NO detection, and one iridium oxide electrodeposited Au electrode for pH detection. The microbundle showed a dynamic range up to 0.3 mM, with a low detection limit of 1.24 M (S/N = 3) and high sensitivity of 9.27 A/M for H2O2; and a dynamic range up to 0.26 mM, with a low detection limit of 1.38 M (S/N = 3) and high sensitivity of 27.1 A/M for NO. Anodically grown irid- ium oxide films showed a near-Nernstian response with a slope of 51 ± 1.4 mV/pH and linear responses within the pH range of 2-10. The H2O2/NO/pH electrochemical microbundle was successfully employed for quantitative in vivo monitoring of H2O2, NO, and pH in oilseed rape for 45 h in the presence or absence of drought stress. This H2O2/NO/pH electrochemical microbundle can be a powerful tool for the in vivo simultaneous investigation of changes in H2O2, NO, and pH and hence can be used in phenotype screening. © 2015 Elsevier B.V. All rights reserved.

Hepatitis B virus (HBV) can cause liver cancer, thus the detection of HBV-DNA is of great significance for liver cancer prevention. Since the concentration of HBV-DNA is often low, it is important to establish a highly sensitive detection method. In this study, microplate amplification and hybridization chain reaction (HCR) were used to improve the sensitive detection of HBV-DNA on dual strip biosensors. For the microplate-based amplification strategy on RS strip, the dual-DNA-AuNP probe could be immobilized on SA-Biotin-Anti-HBV-DNA-1 covered microplate through HBV-DNA. By adding dithiothreitol (DTT), a large amount of HS-RS-DNA on the dual-DNA-AuNP probe was dissociated. The indirect detection of HS-RS-DNA on RS strip could achieve the signal amplification of HBV-DNA. For the HCR-based strategy on HCR strip, HBV-DNA triggered the cascade reaction of H1-AuNP probe and H2-Biotin, a large amount of HCR product (AuNP-H1-H2-Biotin-AuNP-H1…) was produced. Thus, a lot of AuNP was fixed on the test zone of HCR strip to improve the HBV-DNA detection sensitivity. The detection limits by HCR strategy on HCR strip and microplate strategy on RS strip could reach to 5 pM and 0.1 nM, respectively, which were 200 and 10-fold higher than that of unamplified strategy, respectively. The recovery of HBV-DNA ranged from 97.2 to 102 % in the spiked human serum, presented a good accuracy for HBV-DNA detection in actual samples.

Liver cancer is one of the most common cancers in the world. The gene CYP1A1 is closely related to the occurrence of cancer, and the tumor marker alpha-fetoprotein (AFP) is also one of the important indicators for liver cancer screening. Therefore, detection of these two substances is of great significance. In this paper, a test strip biosensor capable of simultaneously detecting cancer susceptibility gene CYP1A1 and AFP has been established. There were two detection lines in the strip biosensor, one was used for qualitative detection of susceptible gene by base complementary pairing, and the other was used for semi-quantitative detection of AFP by antigen-antibody reaction. Finally, signal amplification was achieved by horseradish peroxidase catalyzing substrate 3-amino-9-ethylcarbazole. Results showed that under the optimized conditions, the strip biosensor had a good linear relationship (R2 = 0.987) when AFP concentration was in the range of 20–250 ng/mL, and the other hundred times of proteins had no obvious interference to the detection, indicating that the method presented good selectivity. The detection of susceptibility gene CYP1A1 and AFP in real blood samples by the strip was in accordance the standard method, which showed that the method had good accuracy and could be used for qualitative judgment of SNP locus base type of susceptibility gene and semi-quantitative detection of tumor marker in real sample, so it had a good application potential.

A new method is proposed for determination of carcino-embryonic antigen (CEA) based on quantum dot (QD)-modified aptamer probe by capillary electrophoresis-chemiluminescence (CE-CL) detection system. An oligonucleotide sequence A contains two parts, one is CEA aptamer and the other is bridging segment. Horseradish peroxidase (HRP) conjugates with sequence A (HRP-DNAA) and then mixes with QD labeling complementary bridging segment (QD-DNAB), forming HRP-DNAA-B-QD probe. When CEA exists, the specific combination of the aptamer in sequence A and CEA can form CEA/HRP-DNAA-B-QD complex. After separation of CEA/HRP-DNAA-B-QD complex and HRP-DNAA-B-QD probe by capillary electrophoresis (CE), the chemiluminescence (CL) catalyzed by CEA/HRP-DNAA-B-QD complex can be detected without any interference, and the content of CEA can be estimated by the CL intensity. It has been proved that the separation efficiency of HRP-DNAA-B-QD and CEA/HRP-DNAA-B-QD complex is improved greatly after QD modification, then the interference issue resulted from free HRP-DNAA-B-QD probe is solved well; and the specific combination of HRP-DNAA-B-QD and CEA leads to a closer distance of HRP and QD, then chemiluminescent resonance energy transfer (CRET) occurs, which confirms the validity of the strategy. Results show that the CL intensity has a linear relationship with the concentration of CEA in the range from 0.0654 to 6.54 ng/mL, and the limit of detection is approximately 8 pg/mL (S/N = 3). This proposed method with high specificity has been applied for the accurate analysis of content of CEA in patient's serum.

It is important to design new ways with high specificity and sensitivity to detect lead (II). Here, ‘8–17’ DNAzyme was used as a Pb 2+ -dependent probe with high sensibility and selectivity based on chemiluminescence (CL). When Pb 2+ was present, the substrate strand was cleaved and the active hemin/G-quadruplex DNAzyme structure was formed in the presence of another sequence which contained two parts, one could be complementary with part of the substrate strand and the other was a G rich subunit. The active hemin/G-quadruplex DNAzyme structure could catalyze luminol oxidation and quantitative analysis of Pb 2+ was carried out according to the CL of luminol. Results showed that CL intensity of luminol at 452 nm had a linear relation with the concentration of Pb 2+ in the range from 5 nM to 1 μM, and the limit of detection was 0.79 nM ( S / N = 3). This method was also used to detect the contents of Pb 2+ in lake water and tobacco and the results (62.4 ± 4.0 nM and 15.2 ± 2.2 nM, respectively) were extremely closed to those of inductively coupled plasma-mass spectrometry (ICP-MS) (57.0 ± 1.4 nM and 14.5 ± 0.91 nM, respectively).

Graphene (GR) can strongly interact with aptamers due to hydrophobic and π–π stacking interactions between nucleotide bases and GR, but hardly interact with aptamer–target complexes or rigid double-stranded DNA. The unique GR/aptamers interaction has been fascinatingly developed in fluorescent assay, colorimetric biosensing and mass spectrometric analysis. However, exploration of the unique GR/aptamers interaction in electrochemical biosensing is still at an early stage. In this regard, we reported herein a novel, sensitive and relatively cushy approach to construct electrochemical aptasensors by immobilizing GR/aptamers complex on the surface of poly(o-phenylenediamine) (PoPD) modified glassy carbon electrodes (GCE). Adenosine triphosphate (ATP) was chosen as a model analyte and a well-studied 27-mer single-stranded DNA aptamer was tailor-made to have methylene-blue (Mb) at both ends for use as an electrochemical probe. The Mb-dual-labeled aptamers/GR/PoPD/GCE exhibited a strong electrochemical signal due to the high electrons transfer and large surface area of GR and using double Mb labeled at two ends of aptamers. The presence of ATP triggers the structure switching of aptamer to form aptamer–ATP complex, causing the destruction of the interaction between aptamer and GR and thus the release of Mb-dual-labeled aptamer from the GR, resulting in a low electrochemical signal. Under optimal conditions, we have successfully detected ATP down to a detection limit of 0.3 nM with a wide detection range of 10 nM–2 mM. And from the experiment of cancer cellular ATP assay, it is proved that the method may have great prospects in the field of biological analysis.

In this study, one-step electrochemical polymerized method for the fabrication of poly( o -aminophenol)/multi-walled carbon nanotubes (PoAP/MWCNTs) composite film was developed for the quantitative determination of levofloxacin. Scanning electron microscopy and electrochemical methods were used to characterize the PoAP/MWCNTs nanocomposite film. The sensor fabricated from the nanocomposite film showed good stability and enhanced electrocatalytic ability for the detection of levofloxacin. The large current response of levofloxacin on PoAP/MWCNTs composite film-modified electrode could be ascribed to the synergistic effect of the electrocatalytic property of PoAP and MWCNTs. The oxidative peak current increased linearly with the concentration of levofloxacin in the range of 3.0–200 μM by differential pulse voltammetry, and the detection limit was 1.0 μM (S/N = 3). The proposed modified electrode also can be successfully applied to the determination of levofloxacin hydrochloride in pharmaceutical formulations.

Nitric oxide (NO) is a key signaling molecule in different physiological processes of plants. It is therefore very important to establish a simple, fast, sensitive and accurate detection method for NO detection. In this study, a novel amperometric biosensor based on immobilization of hemoglobin (Hb), chitosan (CS), graphene (GR) and the surfactant hexadecyltrimethylammonium bromide (CTAB) on a glassy carbon electrode was constructed to quantitatively measure NO. Atomic force microscopy, scanning electron microscopy and electrochemical methods were used to characterize the Hb–CS/GR–CTAB nanocomposite film. The biosensor fabricated from the nanocomposite film showed direct electrochemistry with a fast electron-transfer rate (60.3 s −1 ) and high electrocatalytic activity towards the reduction of NO. Under optimal conditions, the resulting biosensor exhibited a high sensitivity of 615 μA mM −1 , a low detection limit of 6.75 × 10 −9 M (S/N = 3) and a small apparent Michaelis–Menten constant of 0.315 μM. These results were superior to those for biosensors based on the graphite, GR/ionic liquid and carbon nanotubes. The biosensor was also used successfully for detection of additional NO in oilseed rape leaf homogenate samples. Furthermore, the biosensor had excellent long-term storage stability, as well as reproducibility and selectivity, and should have a potential application in monitoring NO in plant samples.

In this paper, poly- o -phenylenediamine and Pt microparticle modified Pt electrode (POPD/Pt-MP/Pt) as microbiosensor has been developed to monitor in vivo oxidative burst induced by ultraviolet A (UV-A) and ultraviolet C (UV-C) radiation stress in oilseed rape ( Brassica napus L.). Twice oxidative bursts were detected, appearing at 2 and 25 h, respectively. According to the peak area of amperometry, the amount of H 2 O 2 induced by UV stress was estimated to be 6.2 × 10 −10 and 3.1 × 10 −10 mol for such two oxidative bursts in detected leafstalk, respectively. This novel microbiosensor provides an effective tool for studying the defense reaction of the plant in the situation of UV stress and probing the antioxidative mechanism of the antioxidative enzyme.

Horseradish peroxidase (HRP) and lipophilic quantum dots (QDs) were incorporated onto the surface of glassy carbon (GC) electrodes in various ways. It was found that HRP transfers electron directly onto the GC electrode only when the electrode was modified with QDs through vapor deposition. The response currents were linearly correlated with scan rate, indicating that the reaction is a surface controlled process. The average coverage of HRP on the electrode surface can be calculated as 2.29 × 10−11 mol cm−2, and the heterogeneous electron transfer rate constant k was 5.80 ± 0.70 s−1. Absorption spectra and Fourier-transform infrared spectra showed that the conformation of HRP immobilized on the electrode has no obvious change. Further studies indicated that immobilized HRP retains excellent catalytic activity to H2O2. The apparent Michaelis–Menten constant was calculated as 0.152 mM. It was also found that the modified electrode could be used as a sensor for H2O2, and the linear range of detection was 5.0 × 10−6 to 1.0 × 10−4 M, with a detection limit of 2.84 × 10−7 M. The sensor exhibited reproducibility, stability.

The electrocatalytic oxidation of cysteine at carbon nanotube (CNT) was studied. It was found that the electrochemical behaviors of cysteine were greatly improved at CNTs, indicating that the anodic oxidation could be catalyzed at CNTs. The kinetics parameters of this process were calculated, the heterogeneous electron transfer rate constant k was 0.0042 cm s−1, (1−α)nα was 0.30. The carbon nanotube powder microelectrodes (CNTPMEs) were also found with higher sensitivity for cysteine detection than other common electrodes, and 2 μM sample could be determined easily, indicating that it could be used as cysteine sensors.

HRP was found with a direct electrochemistry at carbon nanotube microelectrode. The adsorbing HRP could transfer electron directly at CNT compared with common carbon electrode material. It was calculated that the transfer coefficient α was 0.57, and heterogeneous electron transfer rate constant was 2.48±0.03 s −1 . It was found that the adsorbing HRP still keeps its catalytic activity to H 2 O 2 .