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A novel visual detection mode is proposed to improve the detection sensitivity for the determination of ochratoxin A (OTA). The mode is based on aptamer recognition and the signal amplification of rolling circle amplification (RCA) products self-assembled DNA hydrogel. Moreover, gold nanoparticles (AuNPs) were directly assembled inside the DNA hydrogel by adjusting the padlock probe sequences to achieve a stronger binding force between the DNA hydrogel and AuNPs; this avoids the need for modification of AuNPs with DNA sequences. In the presence of OTA, DNA hydrogel is formed. With higher concentrations of OTA, a larger amount of DNA hydrogel is formed. When AuNPs are added to the DNA hydrogel, AuNPs can be enclosed inside the DNA hydrogel. With more DNA hydrogel, there is less AuNPs in the supernatant. Thus, the absorbance of the supernatant is anti-correlated with the concentration of OTA. After optimization of the experimental conditions, the change in the absorbance of the supernatant was linearly correlated with the concentration of OTA, in the range 0.05 to 10 ng/mL; the limit of detection was 0.005 ng/mL. The good specificity of the developed biosensor was confirmed in the presence of other mycotoxins that are coexistent with or analogues of OTA. By comparing the developed method with the ELISA method, the accuracy and stability of this new method were also verified, with good performance obtained in real samples. [ABSTRACT FROM AUTHOR]

Saxitoxin (STX) is a major marine toxin from shellfish, and it is responsible for paralytic shellfish poisoning (PSP). In this study, a highly sensitive and rapid aptamer assay was developed for STX detection by combining fluorescence resonance energy transfer (FRET) and nuclease-assisted target recycling signal amplification. The aptamer STX-41 conjugated with graphene quantum dots (GQDs) was adsorbed on magnetic reduced graphene oxide (MRGO) to establish a fluorescence quenching system. Then, the binding between STX and aptamer induced the desorption of GQD-aptamer from MRGO and the restoring of fluorescence for the fluorescent determination of STX. The digestion of the target bound aptamer by DNase I could release the target for recycling thus achieving signal amplification. Under the optimized conditions, the aptamer assay showed a wide detection range (0.1–100 ng·mL−1), low detection limit (LOD of 0.035 ng·mL−1), high specificity, good recovery (86.75–94.08% in STX-spiked clam samples) and repeatability (RSD of 4.27–7.34%). Combined with fluorescent detection technology, signal amplification technology, and magnetic separation technology, the proposed method can be used to detect STX in seafood products successfully. [ABSTRACT FROM AUTHOR]

Purpose: Nano silicon particles (nSiO2) is one of the most widely used industrial engineered nanomaterials (ENMs). The extensive applications of nSiO2 may pose potential risks to aquatic ecosystems and human health. Humic acid (HA) is a major component of soil and water that exists widely in the natural environment and adsorbs to the surface of nanoparticles, which affects the fate and transport of ENMs in soil. Therefore, it triggers the necessity to study the chemical reaction of HA controlling the sedimentation and transport of nSiO2. Materials and methods: The sedimentation kinetics and transport breakthrough curves of nSiO2 with/without HA in water-saturated porous media were studied in two electrolyte (NaCl and CaCl2) solutions. The likely mechanisms were explored with both multiple technologies and numerical modeling including TEM-EDX, particle size distribution, zeta potentials, and the two-site kinetic attachment model (TSKAM). Results and discussion: Our experimental results showed that the existence of HA generally increased the suspensivity and the transportability of nSiO2 in NaCl and CaCl2 solutions in packed sand columns at acidic pH. This result was attributed to the HA adsorption leading to the more negatively charged surface and the smaller size of nSiO2 aggregates. However, the formation of coordination complexes associated with larger cluster among nSiO2 between HA and Ca2+ contributed to the increased sedimentation of nSiO2 at alkaline pH. Subsequently, the presence of HA inhibited the transport of nSiO2 in CaCl2 solution at pH 9.0. Comparably, in NaCl at pH 9.0, HA showed the negligible effect on the nSiO2 deposition in sand. Both the attachment and detachment parameters, which were obtained from fitting the breakthrough curves of ENMs using the TSKAM, could be used to well describe the transport behavior of nSiO2 with HA under various conditions. In particular, the irreversible attachment parameters at site 2 on sand were positively related to the retention of nSiO2 with HA. Conclusions: The fate and transport of nSiO2 can be distinctly affected by HA depending on the ion composition, ion strength, and pH in soil. This study will provide insights for assessing the mobility of nSiO2 with HA in subsurface soil and aquatic environments. [ABSTRACT FROM AUTHOR]

The authors describe a new kind of selection method (referred to as orientation selection) for improved screening for broad-spectrum lipopolysaccharides (LPSs) using unlabeled ssDNA aptamers. The method is based on the capture-SELEX technique using magnetic nanoparticles. LPS from Salmonella enterica serotype typhimurium was chosen as an exemplary target. Once the ssDNA library is preconcentrated to a certain degree, two Gram-negative bacteria were used as orientation molecules in the subsequent selection process. Using this strategy, one optimal aptamer ('EA7') was captured that has a high affinity (Kd = 102 ± 17 nM) for LPS and it was also confirmed that it can recognize three other bacterial LPSs. It is presumed that EA7 binds to the lipid A region of LPS. When using carboxyfluorescein labeled EA7, the observed fluorescence intensity and concentrations of four types of LPSs in drinking water are linearly correlated. The lower detection limit of the LPS is 3 ng·mL. Compared to multi-target mixed selection and conventional SELEX methods, the new orientation selection strategy produces results that are less uncertain. [ABSTRACT FROM AUTHOR]

Okadaic acid (OA) is a low molecular weight marine toxin from shellfish which causes diarrheic shellfish poisoning (DSP). Due to its frequent occurrence, OA has become a serious threat to human health and seafood industry. The authors describe a competitive fluorophore-linked aptamer assay for OA that is based on rolling circle amplification (RCA). It consists of the following steps: (a) The wells of a microplate are modified by fixing the OA aptamer on their surface; (b) The aptamer is hybridized with an aptamer-complementary sequence-primer complex; (c) the RCA reaction is performed; (d) the FAM labelled signal probe is added. OA competes with the detection probe for the immobilized aptamer. After the competitive reaction has occurred, the supernatants containing released detection probes are removed and then read with a microplate reader. This method, unlike in competitive assays where the signals negatively correlate with OA concentrations, has a positive correlation between fluorescence intensity and OA concentration. The optimized assay has a lower detection limit (1 pg·mL) and a wider linear range (from 1 pg·mL to 100 ng·mL) owning to signal amplification via RCA. It also is highly specific, repeatable, has good recovery and can be used to detect OA in seafood. [ABSTRACT FROM AUTHOR]

Bombyx mori L. ( B. mori) were exposed to cadmium chloride (CdCl) incorporated in an artificial diet (0, 6.25, 12.5, 25, and 50 mg kg) throughout the larval stage. Changes in malondialdehyde (MDA) and reduced glutathione (GSH) contents and activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), as well as their corresponding messenger RNA (mRNA) levels in the testes of the fifth instar larvae were evaluated. Additionally, spermatozoon deformation in the testes was examined. Upon Cd treatment, the MDA content in the testes was significantly increased in a concentration-dependent manner. Cd-exposed larvae had increased levels of glutathione. Pearson's correlation analysis revealed that SOD and CAT activities were positively correlated ( R = 0.605, P = 0.017). The changing trends in the mRNA levels of these enzymes were not always consistent with those of enzymatic activities. Alterations in GSH-Px activities and mRNA levels were positively correlated ( R = 0.771, P < 0.01). Morphological analysis revealed that Cd deformed and affected the maturation of spermatozoa. Our results collectively support a relationship between Cd and alterations in the levels of antioxidant enzymes in B. mori testes. [ABSTRACT FROM AUTHOR]

A broad-spectrum ssDNA aptamer containing 80 nucleotides (LA80) and capable of binding to four different sources of lipopolysaccharides (LPSs) was truncated. Two strategies are used to produce truncated aptamers of different length. The results show that LA27, a 27-nt aptamer, retained broad-spectrum capability and has a higher affinity (Kd = 46.2 ± 9.5 nM). A graphene oxide based fluorescence polarization assay (excitation/emission wavelengths: 485/520 nm) was worked out using FAM-labeled LA27. It can detect LPSs from Salmonella entericaserotype typhimurium, Pseudomonas aeruginosa 10 and Escherichia coli 055:B5 with enhanced performance (4.8 to 29-fold improvements) compared to LA80. The assay can be performed within 30 min, and the detection limits are 38.7, 88.0 and 154 ng·mL−1, respectively.Schematic presentation of the assay: A shorter aptamer, with higher affinity than its original aptamer, was obtained by truncated strategies. This core aptamer lead to release easily and enhance the sensivity of the GO-based fluorescence polarization assay. [ABSTRACT FROM AUTHOR]