No abstract

Antibiotic residues in the environment and in foods pose a serious threat to ecosystems and human health. Developing sensitive and on-site detection methods is therefore in high demand. In this work, a portable paper-based colorimetric sensor with a smartphone platform with an ultrahigh sensitivity has been designed for on-site and quantitative analysis of antibiotic residues based on aptamer-regulated nanozyme activity. The developed excellent peroxidase-like nanozymes, carbon-protected NiCo bimetal oxides with a unique hollow nanocage structure (NiCo@C HCs), could effectively catalyze the oxidation of chromogenic substrates by H2O2. Once bound to a specific aptamer, the enzyme-mimicking activity of NiCo@C HCs is obviously inhibited as a result of the masking of active sites but could be restored via the target-aptamer recognition. Herein, the aptamer-modified NiCo@C HCs are embedded on paper pieces to construct paper-based biochips for visual detection. Meanwhile, a smartphone platform is integrated for the signal readout. Using enrofloxacin (ENR) as an analyte model, the proposed paper-based analysis platform shows a reliable and sensitive detection of ENR with an ultralow detection limit of 0.029 ng/mL. The platform also works well in various real samples. This analysis method is facile in design, showing a great application potential for on-site and mass screening of antibiotic residues in the environment and in foods.

In conventional oxidation technologies for treatment of contaminated waters, secondary pollution of the aqueous environment often occurs because of the additional oxidants generated during the process. To avoid this problem, Fe/NG catalyst composites without additives were developed in this study for decontamination of methylene blue (MB) from waters. The Fe/NG catalyst, composed of carbon nitride and iron chloride (FeCl3∙6H2O), was prepared by high temperature pyrolysis. It is an exceptionally efficient, recoverable, and sustainable catalyst for degradation of organic matter. The morphological characteristics, chemical structure, and surface properties of the catalyst composites were investigated. The catalyst exhibited high MB removal efficiency (100%) within 30 min under ambient temperature and dark conditions. The experiments indicated that an MB degradation effect was also applicable under most acid–base conditions (pH = 2–10). The characterization results using electron spin resonance and analysis of intermediate products demonstrated that free radicals such as∙OH and∙O2− were produced from the Fe/NG composites in the heterogeneous system, which resulted in the high MB degradation efficiency. Moreover, the catalysis reaction generated reducing substances, triggering iron carbon micro-electrolysis to spontaneously develop a microcurrent, which assisted the degradation of MB. This study demonstrates the feasibility of Fe/NG catalysts that spontaneously generate active species for degrading pollutants in an aqueous environment at normal temperature, providing an attractive approach for treating organic-contaminated waters.

Excessive use of antibiotics causes their residues in the environment and food, seriously threatening ecosystem and human health. Designing a portable and sensitive sensor for on-site analysis of antibiotics is therefore in high demand. In this study, we have developed a smartphone-capable hydrogel colorimetric platform for ultrasensitive detection of kanamycin (KAN) based on aptamer-regulated nanozyme activity. The synthesized Fe/CeO2 hexagonal bipyramidal microcrystals (Fe/CeO2 HBs) exhibited excellent peroxidase-like activity, but it could be obviously inhibited by the aptamer, and the inhibition effect was further enhanced with the specific recognition between target and aptamer, making it possible to design a facile colorimetric method for KAN analysis. Moreover, the aptamer-functionalized Fe/CeO2 HBs (Fe/CeO2 HBs@Apt) were introduced into the hydrogel to fabricate a portable analytical tube, whose colorimetric signal was read out by a smartphone platform, realizing the on-site analysis of KAN. The linear response range was 0.05–48.45 ng mL–1 with an ultralow detection limit of 0.035 ng mL–1 and the recovery rate ranging from 99.57 to 103.76% for spiked real samples, demonstrating its superior accuracy and reliability. This work provides new insights into designing the solid-phase hydrogel-based colorimetric method for on-site analysis of antibiotic residues.