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Microcystin LR (MC-LR) is a hazardous cyanotoxin produced by cyanobacteria during freshwater eutrophication, which can cause liver cancer. Here, a photoelectrochemical (PEC) aptasensor based on methylene blue (MB)–loaded Ni-MOF composite (Ni-MOF/MB) with spatial confinement was constructed for the sensitive detection of MC-LR. Ni-MOF with two-dimensional sheet structure was prepared via a liquid–liquid interface synthesis method with environmental-friendly solvent and milder reaction conditions. Benefiting from the uniform pore size, Ni-MOF acted as reaction platform to anchor the photosensitive molecule MB. The electron donor, ascorbic acid (AA), was produced by alkaline phosphatase (ALP) loaded on DNA strand catalyzing ascorbic acid phosphate. The generated AA was absorbed by Ni-MOF/MB, thereby effectively improving the utilization of AA and avoiding the external environment interferences to enlarge the photocurrent of MB. For analysis, ALP-labeled aptamer can specifically recognize MC-LR by forming a complex to strip from aptasensor, thus leading to a decreased photocurrent. The developed PEC aptasensor offered a linear range of 10 fM–100 pM with a detection limit of 6 fM. It was successfully employed for detecting MC-LR in farm water and fish meat, and the results were validated by ultrahigh-performance liquid chromatography-mass spectrometry. This method presents a new idea of MOF-limited domain for PEC aptasensing. [ABSTRACT FROM AUTHOR]

Here, we develop an all-in-one strategy for efficient assembly of an electrochemical aptasensor. A multifunctional structure based on a tetrahedral DNA nanostructure (TDN) was synthesized via a one-step annealing process, providing DNA fixation, target recognition, signal amplification and space regulation. Based on the integration of this multifunctional structure, the sensing interface was assembled in one step. A ratiometric aptasensor was constructed by anchoring methylene blue (MB) to the TDN and ferrocene (Fc) on the cDNA. Using the ratio of the currents obtained from Fc and MB as a measure, the developed aptasensor shows excellent analytical performance for fumonisin B1 detection. This strategy is universal and could simplify the fabrication of aptasensors. [ABSTRACT FROM AUTHOR]

In this study, a novel one-step hydrothermal method was developed and composite material of CoFe 2 O 4 /graphene-like carbons (LGC) was successfully prepared from pomelo peels (PP), Fe(NO 3 ) 3 ·9H 2 O and Co(NO 3 ) 2 ·6H 2 O. The characterizing results demonstrate that during the hydrothermal process, (Fe 3+ + Co 2+ ) ions adsorbed on the active surface of PP and PP catalyze/prompt the conversions of PP to LGC and (Fe 3+ + Co 2+ ) to CoFe 2 O 4 , respectively, to produce the composite CoFe 2 O 4 /LGC. And CoFe 2 O 4 /LGC is nanosized and made of multilayer nanosheets. Its improved adsorptive property for methylene blue (MB) in water is ascribed to the conversion of PP to LGC and exfoliation of PP sheets to nanosheets. Additionally, the composite can be easily and rapidly separated under an external magnetic field and repeatedly used. MB adsorption on CoFe 2 O 4 /LGC follows pseudo-second-order kinetics model and Langmuir isotherm models. The synthesis is of simpleness, speediness, low cost, and green non-pollution. CoFe 2 O 4 /LGC is an ideal adsorbent candidate. [ABSTRACT FROM AUTHOR]

Fumonisin B1 (FB1) is common contaminant in agricultural and food products, and sensors with high sensitivity and broad dynamic range are extremely required for FB1 determination. Herein, we reported the tetrahedral DNA nanostructure (TDN)-enabled electrochemical aptasensor for FB1 detection at sub-fg mL−1 level with a dynamic range of 7-folds magnitude. TDN with side length of 5.67 nm was designed to fabricate the substrate for FB1 aptamer anchoring, aiming to achieve the controllable and stable assembly of sensing interface by tuning the assembly density of TDN; TDN at the electrode acts as the anchor for aptamer, absorption of methylene blue as signal generator. Assistant aptamer was added into the sample solution to deplete FB1, reducing the amount of free FB1, thereby extending dynamic range of sensing system. Simultaneously, the negatively-charged TDN can efficiently depress absorption of free aptamer in sample solution. In this way, the utilization of TDN helps to enable the sensor with higher sensitivity and extended dynamic range for FB1. Consequently, the developed sensor allowed a linear dynamic range of 0.500 fg mL−1~1.00 ng mL−1, while the limit of detection was offered to be 0.306 fg mL−1, which was the lowest among the available methods. The applicability of aptasensor was validated by rice sample analysis, which exhibited the comparable reliability of liquid-chromatography tandem mass spectrometry/mass spectrometry. Our work has provided an efficient sensing platform for FB1, and the strategy can be also extended to fabricate sensors for other mycotoxins. • TDN was applied to controllable assembly of sensing interface, which endowed aptasensor with the lowest LOD among all reported sensors for FB1. • Negatively-charged TDN was subtly applied to generate electrostatic repulsion on assistant aptamer, addressing the impact of interfering substances. • TDN was smartly adsorbed methylene blue to generate large and stable redox current. [ABSTRACT FROM AUTHOR]

The development of accurate and reliable sensor for on-site detection of microcystin-LR (MC-LR), one of hazardous environmental pollutants, is highly required. Herein, a laser induced graphene (LIG)-based electrochemical aptasensor for sensitive on-site detection of MC-LR was reported. LIG electrode, the substrate of aptasensor, was prepared via thermal transfer with ethylene-vinyl acetate copolymer, and LIG acted as quasi-reference electrode to replace conventional Ag/AgCl electrode for better operability and robustness. LIG electrode provided large surface area to assemble tetrahedral DNA to absorb methylene blue (MB) for the signal amplification. For detection, the specific recognition of MC-LR with aptamer led to the stripping of tetrahedral DNA complex and further the decreased redox current of MB (I MB). Consequently, the fabricated aptasensor offered high analytical performance for MC-LR detection with a linear range of 1 × 10-2-1 × 105 pM and a detection limit of 3 × 10-3 pM, which was successfully used for water sample analysis with comparable reliability and accuracy of standard method. Furthermore, a portable detection platform by coupling of LIG-based electrochemical aptasensor with electrochemical workstation was constructed for on-site detection of MC-LR. This work offers a novel method for the on-site monitoring of MC-LR, which promotes the investigation of LIG-based electrochemical biosensing in the field of environmental analysis. [ABSTRACT FROM AUTHOR]

Signal amplification is one of the most effective ways to develop the high-performance electrochemical sensors. However, it can be more complicated for ratiometric detections. Herein, a ratiometric electrochemical aptasensor for aflatoxin B1 (AFB1) was proposed by taking advantage of a dual-amplification strategy by coupling of DNA walker (DW) with hybridization chain reaction (HCR). The special binding of AFB1 with ferrocene (Fc)-labelled aptamer triggers DW on hairpin DNA (hDNA) tracks to produce abundant double-stranded DNA (dsDNA). HCR-based strand amplification occurs on these dsDNA to absorb more methylene blue (MB). Then current ratio of MB (I MB) and Fc (I Fc) is designed as a yardstick to detect AFB1. Our experiments reveal that the interaction between Fc and MB (i.e., steric hindrance, electron mediator) varies. In addition to steric hindrance, the presence of MB also acts as electron mediator, thereby facilitating the electron transfer between Fc and electrode. Such combined effect consequently depresses the efficiency of dual-amplification strategy to improve the detection. The developed ratiometric electrochemical aptasensor allows the accurate detection of AFB1 in the 0.003–3 pg mL−1 range. Our work has shed light on the amplification strategy for ratiometric sensing, and provided a new route in integrating different amplification strategies. • A dual-amplification strategy was proposed by the coupling of DNA walker and hybridization chain reaction. • The developed aptasensor exhibits superior analytical performance for the detection of aflatoxin B1. • The interaction of probes depresses the efficiency of amplification strategy on the improvement of ratiometric sensing. [ABSTRACT FROM AUTHOR]

Efficient signal amplification using light irradiation in electrochemistry-based sensing attracts growing interest; however, the modulation of electrochemical and photoelectrochemical behaviors of bifunctional probes remains challenging for the better analytical performance. Here, we found that the bifunctional probe methylene blue (MB) under irradiation followed two routes, i.e., photoelectrochemistry (PEC)-driven and electrochemistry (EC)-driven route, while plasmon-modulated competition between PEC-driven and EC-driven routes efficiently enhanced the analytical performance of aptasensor. Ferrocene-labeled aptamer (Fc-apt) was applied to tune the interaction between MB labeled complementary DNA (MB-cDNA) and plasmonic gold nanoparticles (AuNPs). Under visible light illumination, the aptasensor output a weak current of MB (I MB) for the depressed EC-driven redox. The binding of Fc-apt with target led to its stripping from electrode and released MB-cDNA to approach AuNPs, and an increase in I MB was observed due to the synergy of the depressed PEC-driven redox while the restored EC-driven redox. In this way, the amplified response for target could be obtained by depressing background signal while enlarging response signal of I MB under visible light. Consequently, the developed model ratiometric aptasensor offered a higher sensitivity for the determination of aflatoxin B1. Our observation should be favorable to shed light on photo-induced electrochemical mechanism, and the proposed amplification strategy is valuable for the construction of efficient sensors. [ABSTRACT FROM AUTHOR]