Self-designed portable dual-mode fluorescence device with custom python-based analysis software for rapid detection via dual-color FRET aptasensor with IoT capabilities.

An innovative aptasensor incorporating MoS2-modified bicolor quantum dots and a portable spectrometer, designed for the simultaneous detection of ochratoxin A (OTA) and aflatoxin B1 (AFB1) in corn was developed. Carbon dots and CdZnTe quantum dots were as nano-donors to label OTA and AFB1 aptamers, respectively. These labeled aptamers were subsequently attached to MoS2 receptors, enabling fluorescence resonance energy transfer (FRET). With targets, the labeled aptamers detached from the nano-donors, thereby disrupting the FRET process and resulting in fluorescence recovery. Furthermore, a portable dual-mode fluorescence detection system, complemented with customized python-based analysis software, was developed to facilitate rapid and convenient detection using this dual-color FRET aptasensor. The developed host program is connected to the spectrometer and transmits data to the cloud, enabling the device to have Internet of Things (IoT) characteristics. Connected to the cloud, this IoT-enabled device offers convenient and reliable fungal toxin detection for food safety.

Simultaneous detection of multiple mycotoxins using MXene-based electrochemical aptasensor array and a self-developed multi-channel portable device.

In response to the pressing need for highly efficient simultaneous detection of multiple mycotoxins, which are often found co-occurring in food raw materials and feed, an MXene-based electrochemical aptasensor array (MBEAA) was developed. This aptasensor array utilizes high-specificity aptamers as recognition elements, enabling the capture of electrical signal changes in the presence of target mycotoxins. Based on this platform, a multi-channel portable electrochemical device, enabling rapid, cost-effective, and simultaneous detection of aflatoxin B1 (AFB1), ochratoxin A (OTA), and zealenone (ZEN) was further developed. The developed system boasts a wide detection range of 1.0 × 10-1 to 10.0 ng mL-1, with remarkable performance characterized by ultra-low detection limits of 41.2 pg mL-1, 27.6 pg mL-1, and 33.0 pg mL-1 for AFB1, OTA, and ZEN, respectively. Successfully applied in corn samples, this method offers a portable, easy-to-operate, and cost-effective solution for simultaneous multi-mycotoxin detection. Moreover, the application of the self-developed detection system could be expanded for simultaneous detection of many different targets when their specific aptamers or antibodies were available.

Programmable DNA Templates for Silver Nanoclusters Synthesis To Develop On-Demand FRET Aptasensor.

DNA-templated silver nanoclusters (AgNCs-DNA) can be synthesized via a one-pot method bypassing the tedious process of biomolecular labeling. Appending an aptamer to DNA templates results in dual-functionalized DNA strands that can be utilized for synthesizing aptamer-modified AgNCs, thereby enabling the development of label-free fluorescence aptasensors. However, a major challenge lies in the necessity to redesign the dual-functionalized DNA strand for each specific target, thus increasing the complexity and hindering widespread application of these aptasensors. To overcome this challenge, we designed six DNA strands (DNA1-DNA6) that incorporate the templates for AgNCs synthesis and A4-linker for further aptamer coupling. Among all the synthesized AgNCs-DNA samples, it was found that both AgNCs-DNA1 and AgNCs-DNA2 stood out for their excellent long-term stability. After capturing the T4-linker that connected with aptamer1 specific for aflatoxin B1 (AFB1), however, we found that only AgNCs-DNA1/aptamer1 maintained excellent long-term stability. This finding highlighted the potential of AgNCs-DNA1 as a versatile label-free fluorescence probe for the development of on-demand fluorescence aptasensors. To emphasize its benefits in aptasensing applications, we utilized AgNCs-DNA1/aptamer1 as the fluorescence probe and MoS2 nanosheets as the quencher to develop a FRET aptasensor for AFB1 detection. This aptasensor demonstrated remarkable sensitivity, enabling the detection of AFB1 within a wide concentration range of 0.03-120 ng/mL, with a limit of detection as low as 3.6 pg/mL (S/N = 3). The versatility of the aptasensor has been validated through the recognition of diverse targets, employing aptamer2 specific for ochratoxin A and aptamer3 specific for zearalenone, thereby showcasing its extensive applicability for on-demand detection. The universal applicability of this aptasensor holds great promise for future applications in diverse fields including food safety, environmental monitoring, and clinical diagnosis.

Fabrication of a disposable aptasensing chip for simultaneous label-free detection of four common coexisting mycotoxins.

BACKGROUND: Coexisting multiple mycotoxins in food poses severe health risks on humans due to the augmented toxicity. Current multiplex detection methods for mycotoxins have evolved from instrumental analyses to rapid methods based on the specific recognition of antibody/aptamer using different signal transducers. However, nearly all of the reported aptasensors for multiple mycotoxins detection require external labels and can only simultaneous detection of two mycotoxins due to the limitation of distinguishable labels. The tedious labeling process definitely increases the operation complexity and the detection cost. Therefore, rapid method for simultaneous label-free detection of multiple mycotoxins in cereals is urgently needed. RESULTS: A disposable aptasensing chip was designed for simultaneous label-free detection of fumonisin B1 (FB1), aflatoxin B1 (AFB1), zearalenone (ZEN), and ochratoxin A (OTA) in one sample. Specifically, ITO conductive glass was divided into a rectangle (35 × 25 mm) and then etched by laser to set aside the required four ITO working electrodes (6 mm in diameter) with respective conductive channels. Gold nanoparticles were electrodeposited on the working electrodes to provide abundant anchoring sites for thiolated aptamers immobilization. On this basis, a disposable aptasensing chip for simultaneous label-free detection of four common coexisting mycotoxins has been developed, which used electrochemical impedance spectroscopy as transducer to measure direct biorecognition of the aptamer and corresponding target. This aptasensing chip provided wide linear ranges of 5-1000, 10-250, 10-1250, 10-1500 ng/mL for FB1, AFB1, ZEN, OTA, respectively, with the respective detection limit of 2.47, 3.19, 5.38, 4.87 ng/mL (S/N = 3). SIGNIFICANCE AND NOVELTY: This aptasensing chip shows fantastic characteristics of great simplicity and portability, easy operation, and multiple mycotoxins recognition. They are easy to produce on a large scale at low cost and the design concept can be easily expanded to screen a large panel of coexisting targets. This work provides a new avenue for multi-target detection and represents a substantial advance toward food quality and safety monitoring or other fields.

Growth of AgI semiconductors on tailored 3D porous Ti3C2 MXene/graphene oxide aerogel to develop sensitive and selective "signal-on" photoelectrochemical sensor for H2S determination.

Long term exposure to hydrogen sulfide (H2S) even in low concentration poses a serious threat to human health and the ecosystem, pointing to the significance for its effective supervision. In this study, we report a sensitive and selective "signal-on" photoelectrochemical (PEC) sensor for the determination of toxic H2S in aqueous solution by in situ growth of AgI semiconductors on tailored three-dimensional (3D) porous Ti3C2 MXene/graphene oxide aerogel (MGA). Our research demonstrated that the resultant MGA with the starting feeding mass ratio of MXene and graphene oxide (GO) of 1:8 (MGA1:8) possessed the most excellent PEC performance after the growth of AgI semiconductors than their monomers (Ti3C2 MXene and GO) and the MGAs with other starting feeding mass ratio. Such designed PEC sensor based on MGA1:8/AgI heterojunction showed dramatically strengthened PEC responses with increasing concentrations of S2-. Correspondingly, a wide linear range of 5 nM-200 µM, a low limit of detection of 1.54 nM (S/N = 3), and exclusively unique selectivity have been achieved. Our research illustrates that the PEC sensor designed with tailored MGA constitutes is an effective pathway to enhance the overall sensing performance, which will envision to boost more efforts for advanced 3D porous aerogel using in PEC sensors.

Numerical Investigations on Seismic Behavior of Segmental Assembly of Concrete Filled Steel Tube Piers with External Replaceable Energy-Dissipating Links.

In order to reduce the damage sustained by the substructure of bridges during an earthquake, reduce economic loss, avoid casualties, and ensure the quick repair of bridges after an earthquake, this paper, inspired by the good seismic performance of the rhombic opening in the shear wall structure, proposes a precast segmental concrete-filled steel tubular (PSCFST) pier with external replaceable energy-dissipating links (EREDL).Through finite element simulation analysis, it can be found that the energy dissipation capacity of a PSCFST pier with external EREDL is increased by 104% compared with that of a PSCFST pier without EREDL, and the lateral bearing capacity is increased by 76.9%. Through parameter analysis, it can be found that the change of initial prestress has little effect on the energy dissipation capacity of PSCFST piers, and the seismic performance of PSCFST piers can be improved by properly increasing the ultimate tensile strength of the energy dissipator materials. Compared with the energy dissipators made of Q235 steel, the energy dissipation capacity of PSCFST piers made of Q435 steel energy dissipators is increased by about 85.4%; At the same time, the thicker the energy dissipator, the stronger the energy dissipation capacity of the PSCFST pier, and the lateral bearing capacity is further improved.

Numerical Investigation of the Performance of Segmental CFST Piers with External Energy Dissipators under Lateral Cyclic Loadings.

In order to improve the construction efficiency of piers and reduce the local damage of piers, concrete-filled steel tubes (CFST) are used to precast pier segments. Aiming at the problems of the poor integrity and insufficient energy dissipation capacity of dry joint segmental assembled piers, segmental assembled concrete-filled steel tubular piers with external replaceable energy dissipators are being developed. Based on the low cyclic test of a segmental assembled CFST pier, the finite element numerical simulation model of a CFST pier is established based on ABAQUS software, and the validity of the numerical model is verified by the experimental results. The effects of the section ratio, axial compression ratio, and initial prestress on the seismic performance of piers are studied through a pseudostatic analysis. The results show that an increase in the section ratio can improve the lateral bearing capacity and energy dissipation capacity of the pier. When the section ratio is increased to 4%, the energy dissipation capacity of a CFST pier is increased by 77.8% and the lateral bearing capacity is increased by 33.9% compared with a section ratio of 2%, but the residual displacement of the pier top also increases. With an increase in the axial compression ratio, the energy dissipation capacity of the pier is significantly improved; when the axial compression ratio is increased to 0.30, the energy dissipation capacity of CFST piers is increased by 27.5% compared with a section ratio of 0.05, the residual displacement of the pier top is reduced, and the self-resetting effect of the pier is improved. A change in the initial prestress has no effect on the energy dissipation capacity of piers. Finally, based on an analysis of mechanical theory, a formula of bending capacity suitable for this type of pier is proposed, and the error is within 10%.

3D-printed spider-web structures for highly efficient water collection.

Fog and moisture in nature are important freshwater resources, and the collection of these fog water is of great significance to arid regions. Inspired by the unique geometric structure of the spindle knot on spider silk, artificial fibers with periodic structures have been fabricated for water collection, which can effectively alleviate the problem of water shortage in arid areas. Traditional manufacturing methods are difficult to replicate the true shape of the spindle knot, and related research has encountered a bottleneck in improving water collection efficiency. 3D printing technology, which is different from traditional subtractive manufacturing, can directly replicate spider silk with periodic knots, making it possible to study water collection by artificial spider webs of various designs. Here, 3D printing technology is used to fabricate artificial spider webs with different geometric structures for efficient transportation and collection of water. In addition, the artificial spider web is treated with hydrophilic surfaces. In the humid environment for 2 h, the spider web with convex-concave multi-size spindle knots and multi-curvature connections has a maximum water collection capacity of 6.2g, and the mass of water collection is 35% higher than the existing best water collection artificial fibers. This work provides a sustainable and environmentally friendly route for the effective collection of humid air, and has certain reference value for the development of environmentally friendly water collection equipment.

Programmable dual-electric-field immunosensor using MXene-Au-based competitive signal probe for natural parathion-methyl detection.

Immunosensor is a promising tool for natural parathion-methyl (PTM) detection, and its analytical advantages can be magnified by introducing flexibly-fabricating technique. Herein, we present a dual-electric-field PTM immunosensor on highly-compatible screen-printed electrode (SPE). MXene-Au, the product of in-situ gold nanoparticle growth on MXene, provides considerable binding sites for PTM antigen (ATG) and methylene blue (MB). During sensing, the MXene-Au-MB-ATG probe competitively binds antibody against PTM, composing a ratiometric immune-system. With DC-biased sine excitations from complementary waveforms, on-chip electric field couple improves immunoreactions among PTM, probe, and antibody. Electric field distribution is programmed by trimming bypass resistors to pursue optimal performance. Probe synthesis is solidly proven with morphological examinations, and competition mechanism between the probe and target PTM is clarified in electrochemical analyses. Remarkably, this method brings less consumption of immune time than electric-field-free or solo-electric-field setup (50 s vs. 900 or 70 s), and simultaneously provides more powerful ratiometric signal than the rivals. Log-linear relationship, between PTM level and sensor readout, is established in 0.02-38 ng/mL, and limit of detection is found as 0.01 ng/mL. This method is applied in laboratorial and natural PTM analyses, and the readouts are consistent with high performance liquid chromatography and recovery test.

Fabrication and evaluation of chitosan modified filter paper for chlorpyrifos detection in wheat by surface-enhanced Raman spectroscopy.

BACKGROUND: Chlorpyrifos is a commonly used organophosphorus pesticide in agriculture. However, its neurotoxicity poses a huge threat to human health. In the present study, a chitosan-modified filter paper-based surface enhanced Raman scattering active substrate (Ch/AgNPs/paper) was fabricated and used to detect trace amounts of chlorpyrifos in 120 treated wheat samples. RESULTS: Results showed that the Ch/AgNPs/paper substrate could be used to enhance the chlorpyrifos spectral fingerprint only up to a concentration of 0.000558 mg L-1 . Following Raman spectra acquisition, three pre-processing methods, including Savitzky-Golay (Savitsky-Golay filter with a second order polynomial) smoothing with first derivative and second derivative and normalization, were used to reduce baseline variation and increase resolutions of spectral peak features of the original spectra dataset. Then, prediction models based on partial least squares were established for detecting chlorpyrifos pesticide residue in wheat. The partial least squares model with normalization yielded optimal result, with a correlation coefficient of 0.9764, root mean square error of prediction of 1.22 mg L-1 in the prediction, and relative analysis deviation of 4.12. Five unknown samples were prepared to verify the accuracy of the prediction model. The predicted recoveries were calculated to be between 97.25% and 119.38% with an absolute t value of 0.598. The value of a t-test shows that the prediction model is accurate and reliable. CONCLUSION: The present study demonstrates that the proposed method can achieve rapid detection of chlorpyrifos in wheat. © 2022 Society of Chemical Industry.

An upgraded 2D nanosheet-based FRET biosensor: insights into avoiding background and eliminating effects of background fluctuations.

We demonstrated a new class of 2D nanosheet-based FRET biosensor utilizing vertically oriented MoS2 nanosheets on a magnetic nanocarrier. Compared with the non-separated biosensor under identical conditions, this upgraded one can avoid the background signal of the system and eliminate the effects of background fluctuations, which produces more excellent detection methods.

Quasistatic Analysis of Precast Segmental Concrete-Filled Steel-Tube Bridge Pier with External Arched Energy Dissipation Device.

In order to further promote the application of segment-assembled bridge piers in medium- and high-intensity areas, and to reduce the post-earthquake damage and repair cost of bridge piers, in this paper, a precast segmental concrete-filled steel-tube bridge pier (PSCFSTBP) with an external arched energy dissipation device (AEDD) is proposed. Firstly, the effectiveness of the finite-element analysis software ABAQUS 6.14-4 is proved by the test results of the PSCFSTBP and the corresponding finite-element model analysis results. Secondly, ABAQUS 6.14-4 was used to establish four-segment PSCFSTBP models with four different structural forms (non-energy dissipation device, external arch steel plate, external vertical steel plate, and external AEDD), and the seismic performance of each model was compared and analyzed under reciprocating displacement loading. The results show that compared with the PSCFSTBP with an external AEDD, the lateral bearing capacity of the PSCFSTBP with an external vertical steel plate is increased by about 11.9%, and the initial stiffness is increased by about 2.5%. Compared with the PSCFSTBP with an external arch steel plate, the lateral bearing capacity, initial stiffness, and energy dissipation capacity are increased by 28.8%, 4.6%, and 13 times, respectively. Compared with the PSCFSTBP without an energy dissipation device, its lateral bearing capacity, initial stiffness, and energy dissipation capacity are increased by 39.4%, 10.4%, and 18 times, respectively. The residual displacement of the PSCFSTBP with an external AEDD is kept within 1 mm in the whole displacement loading stage, the offset rate is less than 1%, and the pier damage is controllable, which can realize rapid repair after an earthquake. Finally, the multi-level energy consumption and local replacement of the AEDD are also explored.

Controlling the ligands of CdZnTe quantum dots to design a super simple ratiometric fluorescence nanosensor for silver ion detection.

A super simple ratiometric fluorescence nanosensor has been fabricated by controlling the ligands of CdZnTe quantum dots (QDs), allowing the sensitive and visual detection of silver ions (Ag+). The green-emitting L-cysteine-protected CdZnTe QDs (Lcys-CdZnTe QDs) had a specific response to Ag+ and were used as the reporting probe, while the red-emitting N-acetyl-L-cysteine-protected CdZnTe QDs (NAC-CdZnTe QDs) showed no obvious response to all tested metal ions and were selected as the reference probe. Simply mixing them without any encapsulated synthesis ultimately produced a time-saving, low-cost detection method, allowing the sensitive and visual detection of Ag+ in samples. The proposed nanosensor exhibited a linear range of 0.5-4.0 µM along with a detection limit of 0.17 µM, and has been successfully applied in real tap water and lake water samples. This nanosensor also showed obvious color changes in the detection process and has potential in visual semi-quantitative detection. Our approach may provide a general and feasible strategy for designing ratiometric fluorescence nanosensors, which will attract a wide range of interest in sensing-related fields.

An evaluation of biochemical, structural and volatile changes of dry-cured pork using a combined ion mobility spectrometry, hyperspectral and confocal imaging approach.

BACKGROUND: Food processing induces various modifications that affect the structure, physical and chemical properties of food products and hence the acceptance of the product by the consumer. In this work, the evolution of volatile components, 2-thiobarbituric acid reactive substances (TBARS), moisture content (MC) and microstructural changes of pork was investigated by hyperspectral (HSI) and confocal imaging (CLSM) techniques in synergy with gas chromatography-ion mobility spectrometry (GC-IMS). Models based on partial least squares regression (PLSR) were developed using the full HSI spectrum variables as well as optimum variables selected through a competitive adaptive reweighted sampling algorithm. RESULTS: Prediction results for MC and TBARS using multiplicative scatter correction pre-processed spectra models demonstrated greater efficiency and predictability with determination coefficient of prediction of 0.928, 0.930 and root mean square error of prediction of 0.114, 1.002, respectively. Major structural changes were also observed during CLSM imaging, which were greatly pronounced in pork samples oven cooked for 15 and 20 h. These structural changes could be related to the denaturation of the major meat components, which could explain the loss of moisture and the formation of TBARS visualized from the HSI chemical distribution maps. GC-IMS identified 35 volatile components, including hexanal and pentanal, which are also known to have a higher lipid oxidation specificity. CONCLUSION: The synergistic application of HSI, CLSM and GC-IMS enhanced data mining and interpretation and provided a convenient way for analyzing the chemical, structural and volatile changes occurring in meat during processing. © 2021 Society of Chemical Industry.

A FRET aptasensor for sensitive detection of aflatoxin B1 based on a novel donor-acceptor pair between ZnS quantum dots and Ag nanocubes.

Aflatoxin B1 (AFB1) is one of the most carcinogenic chemicals. A novel fluorescence resonance energy transfer (FRET) sensor based on aptamer recognition technology is proposed for the sensitive detection of AFB1 in moldy peanuts using Ag nanocubes as energy acceptors and ZnS quantum dots (QDs) as energy donors. Compared to the traditional FRET system based on an Au quencher, Ag nanocubes can not only quench the fluorescence of aptamer modified ZnS QDs, but are also inexpensive. In addition, compared with heavy metal QDs, ZnS QDs are environmentally friendly, have excellent photochemical properties, and are ideal energy donors. Without Ag nanocubes, the aptamer modified ZnS QDs emits blue fluorescence under an ultraviolet lamp. Because the emission spectrum of ZnS and the absorption spectrum of Ag nanocubes meet the requirements of FRET, the fluorescence quenching of ZnS QDs is realized. Nevertheless, with AFB1, the specific binding of aptamer and complementary chain makes the ZnS QDs break away from the Ag nanocubes, which leads to the fluorescence recovery of the ZnS QDs. Under the optimized detection conditions, the linear range of AFB1 was 5 pg mL-1 to 300 ng mL-1, and there was no obvious reaction with other similar mycotoxins. According to S/N = 3, the detection limit of AFB1 was 2.67 pg mL-1. The detection of AFB1 in peanut samples shows that the new FRET system can successfully be applied in the future to agricultural products.

Applications of surface functionalized Fe3O4 NPs-based detection methods in food safety.

Food safety has always been an issue of great concern to people. The development of rapid, sensitive and specific detection technology of food pollutants is one of the hot issues in food science field. The rapid development of functionalized Fe3O4 nanoparticles (NPs) provides unprecedented opportunities and technical support for the innovation of food safety detection. The surface functionalized Fe3O4 NPs, which combine superparamagnetic with nanoscale feature, have become an excellent tool for food quality and safety detection. This review highlights the mechanism, principles, and applications of surface functionalized Fe3O4 NPs-based detection technique in the agrifood industry. Then the relevant characteristics, functional roles and general mechanisms of nanomaterial-based detection of various endogenous components and exogenous pollutants in foods are discussed in detail. Ultimately, this review is expected to promote the optimization of functionalized Fe3O4 NPs and provide direction for the diversity of signal recognition and the sustainability of detection methods.

Application of volatile and spectral profiling together with multimode data fusion strategy for the discrimination of preserved eggs.

The maturity level of eggs during pickling is conventionally assessed by choosing few eggs from each curing batch to crack open. Yet, this method is destructive, creates waste and has consequences for financial losses. In this work, the feasibility of integrating electronic nose (EN) with reflectance hyperspectral (RH) and transmittance hyperspectral (TH) data for accurate classification of preserved eggs (PEs) at different maturation periods was investigated. Classifier models based solely on RH and TH with EN achieved a training accuracy (93.33%, 97.78%) and prediction accuracy (88.89%; 93.33%) respectively. The fusion of the three datasets, (EN + RH + TH) as a single classifier model yielded an overall training accuracy of 98.89% and prediction accuracy of 95.56%. Also, 52 volatile compounds were obtained from the PE headspace, of which 32 belonged to seven functional groups. This study demonstrates the ability to integrate EN with RH and TH data to effectively identify PEs during processing.

Gold nanoparticles mediated designing of versatile aptasensor for colorimetric/electrochemical dual-channel detection of aflatoxin B1.

This work is aimed to develop of a new class of versatile aptasensor to specifically detect aflatoxin B1 (AFB1) using dual-channel detection method. To achieve this objective, gold nanoparticles (AuNPs) having peroxidase-like activity and capability of promoting silver deposition were used as the versatile label for both colorimetric and electrochemical techniques. First of all, aptamer (apt) modified Fe3O4@Au magnetic beads (MBs-apt) and cDNA modified AuNPs (cDNA-AuNPs) were prepared to use as capture probes and signal probes, respectively. Taking advantage of hybridization reaction between apt and cDNA, these two probes were coupled with each other to generate MBs-apt/cDNA-AuNPs bioconjugations. The high affinity between apt and AFB1 made cDNA-AuNPs detached from MBs-apt, and the released signal probes were separated and collected using an external magnetic field and used for both colorimetric and electrochemical detection channels. The dual-channel signals were directly proportional to logarithm of AFB1 concentration within the ranges of 5-200 ng mL-1 and 0.05-100 ng mL-1. The detection limit can reach as low as 35 pg mL-1 and 0.43 pg mL-1 for colorimetric and electrochemical channel, respectively. Moreover, the proposed aptasensor has been successfully applied to determine AFB1 in corn samples with satisfactory results. This dual-channel detection method can not only improve the detection precision and diversity significantly, but also can reduce the false-negative and-positive rates in food quality monitoring. We believe we have provided a general strategy with the convincing dual-readout mode which possess great promising in all of the aptamer related fields.

Dynamic characteristics of dough during the fermentation process of Chinese steamed bread.

The fermentation process is crucial to the production of Chinese steamed bread (CSB). In order to select suitable indicators as the basis for further research of establishing intelligent monitoring method for dough fermentation state, this study investigated the dynamic characteristics of dough during fermentation. Indicators included water mobility and distribution, starch-pasting properties, content of free amino acid (FAA), volatile organic compounds (VOCs) and electronic nose (E-nose) response value. Starch-pasting properties of dough and relaxation time (T21, T22) did not change significantly during the fermentation process (p < 0.05). The VOCs and FAAs of the dough had significant differences (p < 0.05) in different fermentation times, but no rule was established. The E-nose response value to headspace was most suitable to monitor the fermentation of dough. Principal component analysis (PCA) was performed on E-nose data from 75 samples and the results indicated that samples of different fermentation states were accurately classified.

A multiplexed FRET aptasensor for the simultaneous detection of mycotoxins with magnetically controlled graphene oxide/Fe3O4 as a single energy acceptor.

Aflatoxin B1 (AFB1) and fumonisin B1 (FB1) are the most common mycotoxins and often coexist in agricultural products, and are known to form a toxic superposition and even have carcinogenic effects on humans. We propose a multiplexed fluorescence resonance energy transfer (FRET) aptasensor for the simultaneous detection of mycotoxins with magnetically controlled graphene oxide (GO)/Fe3O4 as the single energy acceptor. CdTe quantum dots emitting green (GQDs) and red (RQDs) fluorescence were modified by aptamers that are specific for AFB1 and FB1 and used as dual energy donors. Compared with conventional FRET systems based on a GO quencher, GO/Fe3O4, as a single energy acceptor, not only simultaneously quenches the different fluorescence emission peaks of the aptamer-modified GQDs and RQDs but also can be effectively removed by magnetic separation to eliminate background interference. In the absence of the GO/Fe3O4 nanocomposites, the aptamer-modified GQDs and RQDs emit strong fluorescence under ultraviolet radiation. The fluorescence of the GQDs and RQDs is quenched when the GO/Fe3O4 nanocomposites are added to the system owing to the π-π stacking interactions between the GO/Fe3O4 nanocomposites and the GQD- and RQD-labeled aptamers. However, in the presence of AFB1 and FB1, the binding of aptamers to their specific targets will fold their single stranded structures and hinder the contact between the base group in the aptamers and GO/Fe3O4, which will cause the fluorescence recovery of GQDs and RQDs. With the help of a one-step magnetic separation, the supernatants can be collected for fluorescence analysis. After the optimization of detection conditions, the developed method had a wide linear range of 10 pg mL-1-100 ng mL-1 for AFB1 and 50 pg mL-1-300 ng mL-1 for FB1 and showed no cross-reactivity with other closely related mycotoxins. The limit of detection for AFB1 and FB1 were calculated to be 6.7 and 16.2 pg mL-1 based on S/N = 3, respectively. The detection of mycotoxins was successfully realized in peanut samples, indicating the successful application of this new FRET system for various future targets.