Dual-mode aptasensor based on P-CeO2NR@Mxene and exonuclease I-assisted target recycling for malachite green detection.

Malachite green (MG) has been illicitly employed in aquaculture as a parasiticide, however, its teratogenic and carcinogenic effects pose a significant human health threat. Herein, a dual-mode colorimetric and electrochemical aptasensor was fabricated for MG detection, capitalizing on the robust catalytic and peroxidase-like activity of P-CeO2NR@Mxene and good capture efficiency of a tetrahedral DNA nanostructure (TDN) designed with multiple aptamers (m-TDN). P-CeO2NR@Mxene-modified complementary DNA (cDNA) served as both colorimetric and electrochemical probe. m-TDN was attached to AuE to capture MG and P-CeO2NR@Mxene/cDNA. The superior aptamer and MG binding to cDNA regulated signals and enabled precise MG quantification. The further introduced Exo I enabled aptamer hydrolysis, releasing MG for further binding rounds, allowing target recycling amplification. Under the optimal conditions, the aptasensor reached an impressively low detection limit 95.4 pM in colorimetric mode and 83.6 fM in electrochemical mode. We believe this dual-mode approach holds promise for veterinary drug residue detection.

Detection of acrylamide in food based on MIL-glucose oxidase cascade colorimetric aptasensor.

BACKGROUND: Maillard reaction involves the polymerization, condensation, and other reactions between compounds containing free amino groups and reducing sugars or carbonyl compounds during heat processing. This process endows unique flavors and colors to food, while it can also produce numerous hazards. Acrylamide (AAm) is one of Maillard's hazards with neurotoxicity and carcinogenicity, these effects can trigger mutations and alternations in gene expression in human cells and accelerate organ aging. An accurate and reliable acrylamide detection method with high sensitivity and specificity for future regulatory activities is urgently needed. RESULTS: Herein, we constructed a colorimetric aptasensor with the hybridization of MIL-glucose oxidase (MGzyme)-cDNA and magnetic nanoparticle-aptamer (MNP-Apt) to specifically detect AAm. The incorporation of MB-Apt and AAm released MGzyme-cDNA in the supernatant, took the supernatant out, with the addition of glucose and TMB, MGzyme would oxidize glucose, the resulting •OH facilitated the oxidation of colorless TMB to blue ox-TMB. The absorbance value at 652 nm, which indicates the characteristic absorption peak of ox-TMB, exhibited a proportion to the concentration of AAm. MGzyme avoided the addition of harmful intermediate H2O2 and created an acid microenvironment for the catalytic reaction. MNP-Apt possessed the advantages of high specificity and simplified separation. Under optimal conditions, this method displayed a linear range of 0.01-100 µM with the limit of detection of 1.53 nM. With the spiked analysis data cross-verified by ELISA kit, this aptasensor was proven to specifically detect AAm at low concentrations. SIGNIFICANCE: This colorimetric aptasensor was the integration of aptamer and the enzyme-cascade system, which could broaden the applicable range of enzyme-cascade system, break the limits of specific detection of substrates, eliminate the need for harmful intermediates, improve the reaction efficiency, implement the specific detection, whilst enabling the accurate detection of AAm. Given these remarkable performances, this method has shown significant potential in the field of food safety inspection.

Split aptamer remodeling-initiated target-self-service 3D-DNA walker for ultrasensitive detection of 17ß-estradiol.

DNA walker machines, as one of the dynamic DNA nanodevices, have attracted extensive interest in the field of analysis due to their inherent superiority. Herein, we reported a split aptamer remodeling-initiated target-self-service 3D-DNA walker for ultrasensitive, specific, and high-signal-background ratio determination of 17ß-estradiol (E2) in food samples. Two split probes (STWS-a and STWS-b) were rationally designed that can undergo structural reassembled to serve as walking strands (STWS) under the induction of the target. Meanwhile, an intact E6-DNAzyme region was formed and activated at the tail of STWS. The activated E6-DNAzyme then continuously drives the 3D-DNA walker for signal amplification and specific detection of E2. Under optimal conditions, the proposed DNA walker-based biosensor exhibited excellent linearity in the range of 1 pM to 50 nM with a low limit of detection (LOD) of 0.28 pM, and good precision (2.7%) for 11 replicate determinations of 1 nM of E2. Furthermore, the developed DNA walker-based biosensor achieved excellent sensitive analysis of E2 in the complex food matrix with recoveries of 95.6-106.5%. This newly proposed split aptamer-based strategy has the advantages of ultrasensitive, high signal-to-background ratio, and high stability. Noteworthy, the successful operation of the DNA walker initiated by the split aptamer expands the principles of DNA walker design and provides a universal signal amplification platform for trace analysis.

Protective Effects of Ferulic Acid on Deoxynivalenol-Induced Toxicity in IPEC-J2 Cells.

Deoxynivalenol (DON), a mycotoxin that contaminates crops such as wheat and corn, can cause severe acute or chronic injury when ingested by animals or humans. This study investigated the protective effect of ferulic acid (FA), a polyphenolic substance, on alleviating the toxicity induced by DON (40 µM) in IPEC-J2 cells. The experiments results showed that FA not only alleviated the decrease in cell viability caused by DON (p < 0.05), but increased the level of superoxide dismutase (SOD) (p < 0.01), glutathione peroxidase (GSH-Px), (catalase) CAT and glutathione (GSH) (p < 0.05) through the nuclear factor erythroid 2-related factor 2 (Nrf2)-epoxy chloropropane Kelch sample related protein-1 (keap1) pathway, and then decreased the levels of intracellular oxidative stress. Additionally, FA could alleviate DON-induced inflammation through mitogen-activated protein kinases (MAPKs) and nuclear factor kappa-B (NF-κB) pathways, down-regulated the secretion of interleukin-6 (IL-6) (p < 0.0001), interleukin-8 (IL-8) (p < 0.05), interleukin-1ß (IL-1ß), interferon-γ (IFN-γ) and further attenuated the DON-induced intracellular apoptosis (10.7% to 6.84%) by regulating the expression of Bcl2-associated X protein (Bax) (p < 0.0001), B-cell lymphoma-2 (Bcl-2) (p < 0.0001), and caspase-3 (p < 0.0001). All these results indicate that FA exhibits a significantly protective effect against DON-induced toxicity.

Double-enzymes-mediated fluorescent assay for sensitive determination of organophosphorus pesticides based on the quenching of upconversion nanoparticles by Fe3.

Herein, a new double-enzymes-modulated fluorescent assay based on the quenching of upconversion nanoparticles (UCNPs) by Fe3+ was constructed for sensitive determination of OPs. OPs can inhibit the activity of acetylcholinesterase to reduce the production of choline and further lead to the lack of H2O2 in the presence of choline oxidase. Therefore, Fe2+ cannot be converted into Fe3+, resulting in "turn-on" fluorescence of UCNPs. Under optimal conditions, an excellent linear correlation between the inhibition efficiency and the logarithm of the chlorpyrifos concentration was achieved with a detection limit (LOD) of 6.7 ng/mL in the range of 20-2000 ng/mL. The recovery for chlorpyrifos in apples and cucumbers was 89.5-97.1%. The results were consistent with those obtained by GC-MS. Overall, the integration of UCNPs into the double-enzymes-mediated Fe3+/Fe2+ conversion endows this method with desirable rapidity, sensitivity, selectivity, stability, operational simplicity, and strong anti-interference capability, holding great potential in the application of food safety.

Application of PEG-CdSe@ZnS quantum dots for ROS imaging and evaluation of deoxynivalenol-mediated oxidative stress in living cells.

Deoxynivalenol (DON), a trichothecene mycotoxin, has attracted global attention due to its prevalence and substantial effects on animal and human health. DON induces the upregulation of intracellular reactive oxygen species (ROS) by disrupting the normal mitochondrial functionality, which causes oxidative stress, cell apoptosis, and even severe disorders. The aim of present work is to develop a simple, convenient, and in situ method for monitoring ROS and evaluating DON-mediated oxidative stress. Herein, polyethylene glycol-modified CdSe@ZnS quantum dots (QDs) were employed as simple and convenient nanoprobe for ROS imaging and oxidative stress evaluating induced by DON in living cells. The results demonstrated 5 ppm QDs nanoprobe can be easily loaded into cells via endocytosis without readily observable oxidative effects. Once in presence of DON, the augmented ROS directly oxidize the QDs nanoprobe, which leads to the destruction of the QDs structure and quenched fluorescence. According to the weakened fluorescence intensity (FI), the oxidative damage mediated by DON can be rapidly monitored and found that the oxidative stress was the most severe when the DON concentration exceeded 10 ppm. The developed QDs nanoprobe is also suitable for assessing other mycotoxins and chemicals. We hope it will be beneficial for the early screening of toxic and harmful substances in in vitro toxicology.

A colorimetric aptamer-based method for detection of cadmium using the enhanced peroxidase-like activity of Au-MoS2 nanocomposites.

In this work, a colorimetric aptamer-based method for detection of cadmium using gold nanoparticles modified MoS2 nanocomposites as enzyme mimic is established. In short, biotinylated Cd2+ aptamers are immobilized by biotin-avidin binding on the bottoms of the microplate, the complementary strands of Cd2+ aptamers are connected to the Au-MoS2 nanocomposites which have the function of enhanced peroxidase-like activity. The csDNA-Au-MoS2 signal probe and target Cd2+ compete for binding Cd2+ aptamer, the color change can be observed by addition of chromogenic substrate, thereby realizing visual detection of Cd2+. The absorbance of the solution at 450 nm has a clear linear relationship with the Cd2+ concentration. The linear range is 1-500 ng/mL, and the limit of detection is 0.7 ng/mL. The assay was used to test white wine samples, the results are consistent with those of atomic absorption spectrometry; which prove that this method can be used for detection of Cd2+ in real samples.

Assessing the toxicity in vitro of degradation products from deoxynivalenol photocatalytic degradation by using upconversion nanoparticles@TiO2 composite.

Deoxynivalenol (DON) is one of the most globally prevalent mycotoxins mainly produced by Fusarium species. It can cause pollution to water environmental quality due to its water solubility. Therefore, it is necessary to develop a green and efficient detoxification technology for DON. More importantly, the toxicity of the degradation products should be assessed. Photocatalytic degradation technology has attracted increasing attention in the field of pollutants treatment, especially for wastewater treatment. Herein, the as-prepared NaYF4:Yb,Tm@TiO2 composite (UCNP@TiO2) was employed as a novel photocatalyst for the NIR-enhanced photocatalytic degradation of DON. Three intermediate products were identified by using the ESI/MS analysis and secondary mass spectrogram, with the m/z values of 329.399, 311.243 and 280.913, respectively. Furthermore, the in vitro safety of the product mixtures with various degradation time (30 min, 60 min, 90 min and 120 min) were evaluated through the influences on cell viability, cell morphology, cell cycle, intracellular reactive oxygen species (ROS) level, cell apoptosis and antioxidant capacity of HepG2 cells. There were no significant differences in these investigated indicators between the control (free of DON) and 120 min products treatment. Overall, the results indicated that the toxicity of degradation products after 120 min irradiation was much lower and even nontoxic than that of DON.

Surface-enhanced Raman spectroscopic single step detection of Vibrio parahaemolyticus using gold coated polydimethylsiloxane as the active substrate and aptamer modified gold nanoparticles.

A method is described for single-step detection of V. parahaemolyticus in seafood via aptamer-based SERS. A gold-coated polydimethylsiloxane (PDMS) film was used for the enhancement of Raman scattering. The Raman reporter 4-mercaptobenzoic acid was linked to aptamer modified gold nanoparticles (AuNPs) served as a signalling probe. The negatively charged signalling probe was assembled onto the cysteamine-modified Au-PDMS film through electrostatic adsorption. On addition of V. parahaemolyticus, it will be bound by the aptamer as a biorecognition element, and this leads to the dissociation of the signalling probe from the Au-PDMS film. Hence, the Raman signal (at 1592 cm-1) decreases. The assay has a wide linear response that covers the 1.2 × 102 to 1.2 × 106 cfu·mL-1 V. parahaemolyticus concentration range. The detection limit is 12 cfu·mL-1. The method was successfully applied to the determination of V. parahaemolyticus in oyster and salmon samples. Graphical abstract Schematic presentation of a surface-enhanced Raman spectroscopic method for single step detection of Vibrio parahaemolyticus using gold coated polydimethylsiloxane as the active substrate and aptamer modified gold nanoparticles. This solid substrate simplified the analysis procedures and enhanced the sensitivity.

GO-amplified fluorescence polarization assay for high-sensitivity detection of aflatoxin B1 with low dosage aptamer probe.

Aflatoxin B1 (AFB1) is the most toxic mycotoxin of the aflatoxins (AFs) and shows carcinogenic, teratogenic and mutagenic effects in humans and animals. AFB1 is widely seen in cereal products such as rice and wheat. This research proposed a low-cost, high-sensitivity fluorescence polarization (FP) assay for detection of AFB1 using aptamer biosensors based on graphene oxide (GO). The aptamers labelled with fluorescein amidite (FAM) were adsorbed on the surface of GO through π-π stacking and electrostatic interaction, thus forming aptamer/GO macromolecular complexes. Under these conditions, the local rotation of fluorophores was limited and the system had a high FP value. When there was AFB1 in the system, aptamers were dissociated from the GO surface and combined with AFB1 owing to their specificity to form aptamer/AFB1 complexes. As a result, large changes were observed in the molecular weights of aptamers before, and after, the combination, therefore leading to the apparent changes in FP value. The results showed that when only 10 nM of aptamer was used, the changes in FP and the AFB1 concentration had a favourable linear relationship within 0.05 to 5 nM of AFB1, and the lowest detection limit (LOD) was 0.05 nM. In addition, the recoveries of rice sample extract ranged from 89.2% to 112%. The method is simple, highly sensitive, cost-efficient and shows potential application prospects.

Homogenous detection of fumonisin B(1) with a molecular beacon based on fluorescence resonance energy transfer between NaYF4: Yb, Ho upconversion nanoparticles and gold nanoparticles.

In this work, we presented a new aptasensor for fumonisin B1 (FB1) based on fluorescence resonance energy transfer (FRET) between NaYF4: Yb, Ho upconversion fluorescent nanoparticles (UCNPs) and gold nanoparticles (AuNPs). The quenchers (AuNPs) were attached to the 5' end of the molecular beacon (MB), and the donors (UCNPs) were attached to the 3' end of the MB. In the absence of target DNA (DNA complementary to FB1 aptamers), the energy donors and acceptors were placed in close proximity, leading to quenching of the fluorescence of the UCNPs. Due to the combination of FB1 and FB1-specific aptamers, this caused some complementary DNA dissociating from the magnetic nanoparticles (MNPs). In the presence of the complementary DNA, the MBs underwent spontaneous conformational change and caused the UCNPs and AuNPs to detach from each other, resulting in restoration of the upconversion fluorescence. Therefore, the fluorescence of UCNPs was restored in a FB1 concentration-dependent manner, which was the basis of the FB1 quantification. The aptasensors showed a linear relationship from 0.01 to 100 ng mL(-1) for FB1 with a detection limit of 0.01 ng mL(-1) in an aqueous buffer. As a practical application, the aptasensor was used to monitor FB1 levels in naturally contaminated maize samples. The results were consistent with that of a classic ELISA method, indicating that the UCNPs-FRET aptasensor, which benefited from the near infrared excitation of NaYF4: Yb, Ho UCNPs, was effective for directly sensing FB1 in foodstuff samples without optical interference. This work also created the opportunity to develop aptasensors for other targets using this FRET system.

Sensitive detection of carcinoembryonic antigen with magnetic nano-bead and upconversion nanoparticles-based immunoassay.

A novel magnetic nanobead-based immunoassay was developed for the quantification of carcinoembryonic antigen (CEA) in human serum in this study. Amine-functionalized Fe(3)O(4) magnetic nanoparticles (MNPs) were conjugated with capture anti-CEA antibodies and amine-functionalized NaY(0.78)F(4):Yb(0.20), Ho(0.02) upconversion nanoparticles (UCNPs) were synthesized and conjugated with detection anti-CEA antibodies, respectively. Based on a sandwich-type immunoassay format, the detection limit for CEA under optimal conditions was as low as 2.5 pg/mL, and the linear range of CEA detection was from 2.5×10(-12) to 1×10(-8) g/mL (I=406.19 logX+428.81) with a correlation coefficient equal to 0.9987. The established method was successfully applied to measure CEA in human serum samples and more sensitive than a commercially available chemiluminescence method. The precision expressed as the relative standard deviation of CEA detection was equal to 5.19% (1 ng/mL) or 4.36% (5 pg/mL), indicating that the developed method exhibited good reproducibility. The results demonstrate that the method offers potential advantages of sensitivity and good reproducibility for the determination of CEA, and is applicable to the determination of CEA in serum samples.

Magnetic nanobead-based immunoassay for the simultaneous detection of aflatoxin B1 and ochratoxin A using upconversion nanoparticles as multicolor labels.

A novel and sensitive immunoassay for the simultaneous detection of aflatoxin B(1) (AFB(1)) and ochratoxin A (OTA) in food samples was developed by using artificial antigen-modified magnetic nanoparticles (MNPs) as immunosensing probes and antibody functionalized upconversion nanoparticles (UCNPs) as signal probes. NaY(0.78)F(4):Yb(0.2), Tm(0.02) and NaY(0.28)F(4):Yb(0.7),Er(0.02) UCNPs were prepared and functionalized, respectively, with immobilized monoclonal anti-AFB(1) antibodies and anti-OTA antibodies as signal probes. Based on a competitive immunoassay format, the detection limit for both AFB(1) and OTA under optimal conditions was as low as 0.01 ng mL(-1), and the effective detection range was from 0.01 to 10 ng mL(-1). The proposed method was successfully applied to measure AFB(1) and OTA in naturally contaminated maize samples and compared to a commercially available ELISA method. The high sensitivity and selectivity of this method is due to the magnetic separation and concentration effect of the MNPs, the high sensitivity of the UCNPs, and the different emission lines of Yb/Tm and Yb/Er doped NaYF(4) UCNPs excited by 980 nm laser. Multicolor UCNPs have the potential to be used in other applications for detecting toxins in the field of food safety and other fields.