A photoelectrochemical aptasensor for omethoate determination based on a photocatalysis of CeO2@MnO2 heterojunction for glucose oxidation.

In the present work, we developed a photoelectrochemical aptasensor to determine omethoate (OMT) based on the dual signal amplification of CeO2@MnO2 photocatalysis for glucose oxidation and exonuclease I-assisted cyclic catalytic hydrolysis. CeO2@MnO2 heterojunction material prepared by hydrothermal method was linked with captured DNA (cDNA) and then assembled on the ITO conductive glass to form ITO/CeO2@MnO2-cDNA, which exhibited significant photocurrent response and good photocatalytic performance for glucose oxidation under visible light irradiation, providing the feasibility for sensitive determining OMT. After binding with the aptamer of OMT (apt), the formation of rigid double stranded cDNA/apt kept CeO2@MnO2 away from ITO surface, which ensured a low photocurrent background for the constructed ITO/CeO2@MnO2-cDNA/apt aptasensor. In the presence of target OMT, the restoration of the cDNA hairpin structure and the exonuclease I-assisted cyclic catalytic hydrolysis led to the generation and amplification of measurement photocurrent signals, and allowed the aptasensor to have an ideal quantitative range of 0.01-10.0 nM and low detection limit of 0.0027 nM. Moreover, the aptasensor has been applied for selective determination of OMT in real samples with good precision of the relative standard deviation less than 6.2 % and good accuracy of the recoveries from 93 % to 108 %. What's more, the aptasensor can be used for other target determination only by replacing the captured DNA and corresponding aptamer.

A colorimetric aptasensor for CA125 determination based on dual catalytic performance of CeO2 nanozyme confined in macroporous silica foam.

A portable colorimetric aptasensor was constructed based on the dual catalytic performance of CeO2 nanozyme to determine carbohydrate antigen 125 (CA125). Firstly, CeO2 nanozyme was synthesized by calcination and ultrasonically dispersed in a macroporous silica foam (MSF) to form CeO2@MSF. Then the aptamer of CA125 (apt) and complementary DNA (c-DNA) were successively assembled on the CeO2@MSF to construct a CeO2@MSF/apt/c-DNA colorimetric aptasensor, which exhibited excellent oxidase-mimic performance and phosphatase-mimic activity simultaneously. In the presence of CA125, the apt specifically binds to target CA125, and the single-strand c-DNA leaves the CeO2@MSF/apt surface, which is catalytically hydrolyzed by exonuclease I. The produced phosphate ions inhibit the phosphatase-mimic activity of CeO2 nanozyme. Thus, the absorbance at 652 nm of 3,3',5,5'-tetramethylbenzidine solution containing ascorbic acid-2-phosphate increases with the concentration of CA125. The response is linearly related to the logarithm of CA125 concentration from 1.0 to 10.0 U/mL under optimal experimental conditions. Based on this, the constructed colorimetric aptasensor has a high sensitivity, good selectivity, and high accuracy for CA125 determination in real human serum sample.

Efficient removal of aqueous hexavalent chromium by activated carbon derived from Bermuda grass.

In this study, a novel raw material, Bermuda grass had been devised for the synthesis of activated carbon (BGAC) and enhanced the pore volume by potassium hydroxide. The effects of different factors on activated carbon products by orthogonal experiment was optimized. The synthesized BGAC was characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and then, Cr(VI) removal batch experiments were conducted to investigate the Cr(VI) removal performance. Kinetic model and Weber-Morris diffusion model were fitted to the Cr(VI) removal process indicated that the chemisorption was the predominant removal mechanism and intraparticle diffusion was the sole rate-controlling mechanism. Langmuir isotherms could fit the experimental date well, which revealed that the adsorption of Cr(VI) ions was monolayer adsorption and the maximum adsorption capacity could be reached at 403.23 mg g-1. The results also promulgated that BGAC had an excellent potential on Cr(VI) removal. The removal processes were considered to comprise adsorption, reduction, precipitation and other ways through the study of the removal mechanism.