Ratio fluorescence test strip visualized by amino-functionalized metal-organic framework for rapid sensing of glyphosate.

As glyphosate is a broad-spectrum herbicide extensively used in agriculture worldwide, rapid glyphosate detection is essential for food safety and human health. Herein, a ratio fluorescence test strip was prepared and coupled with an amino-functionalized bismuth-based metal-organic framework (NH2-Bi-MOF) that bonded with copper ion for rapid visualization and determination of glyphosate. NH2-Bi-MOF had excellent fluorescence performance, and the copper ion, a Lewis acid, was selected as the quencher. The strong chelation of glyphosate with copper ion and its quick interaction with NH2-Bi-MOF would turn on the fluorescence signal, thus enabling the quantitative sensing of glyphosate, with a linear range of 0.10-200 µmol L-1, and recoveries between 94.8% and 113.5%. The system was then expanded to a ratio fluorescence test strip, in which the fluorescent ring sticker was set as a binding-in self-calibration to reduce errors from the angle and light dependency. The method realized the visual semi-quantitation referring to a standard card, as well as the ratio quantitation using the gray value output with LOD of 0.82 µmol L-1. And the as-developed test strip was accessible, portable, and reliable, thus offering a platform for the rapid on-site detection of glyphosate and other residual pesticides.

Paper-based analytical device coupled with Bi-MOF: Electric field amplification and fluorescence sensing of glyphosate.

Glyphosate, a potent herbicide wildly used in the world, involves potential hazards to human health by accumulating in the food chain. Due to its absence of chromophores and fluorophores, the rapid visual detection of glyphosate has always been difficult. Herein, a paper-based geometric field amplification device visualized by the amino-functionalized bismuth-based metal-organic framework (NH2-Bi-MOF) was constructed for sensitive fluorescence determination of glyphosate. Fluorescence of the synthesized NH2-Bi-MOF was immediately enhanced by interaction with glyphosate. The field amplification of glyphosate was implemented by coordinating the electric field and the electroosmotic flow, which was orchestrated by the geometric configuration of paper channel and the concentration of polyvinyl pyrrolidone, respectively. Under the optimal conditions, the developed method exhibited a linear range of 0.80-200 µmol L-1 with about 12500-fold signal enhancement achieved by just 100 s electric field amplification. It was applied to soil and water with recoveries between 95.7% and 105.6%, holding great prospects in on-site analysis of hazardous anions for environment safety.

Bismuth-based metal-organic framework peroxidase-mimic nanozyme: Preparation and mechanism for colorimetric-converted ultra-trace electrochemical sensing of chromium ion.

A colorimetric-electrochemical dual-mode analytical method based on bismuth metal-organic framework nanozyme was developed for label-free and trace/ultra-trace Cr6+ detection. 3D ball-flower shaped bismuth oxide formate (BiOCOOH) was used as the precursor and template to facilely construct the metal-organic framework nanozyme BiO-BDC-NH2, which possesses intrinsic peroxidase-mimic activity to effectively catalyze the colorless 3,3',5,5'-tetramethylbenzidine into blue oxidation products in the presence of hydrogen peroxide. Based on Cr6+ to promote the peroxide-mimic activity of BiO-BDC-NH2 nanozyme, a colorimetric method for Cr6+ detection was developed with the detection limit of 0.44 ng mL-1. Cr6+ can be electrochemically reduced to Cr3+ that would specifically inhibit the peroxidase-mimic activity of BiO-BDC-NH2 nanozyme. Thus, the colorimetric system for Cr6+ detection was converted into a low-toxic and signal-off electrochemical sensor. The electrochemical model showed upgraded sensitivity and a lower detection limit of 9.00 pg mL-1. The dual-model method was developed for selective appropriate sensing instruments in different detection scenarios, which can provide built-in correction for environmental effects, as well as the development and utilization of dual-signal sensing platforms for trace to ultra-trace Cr6+ rapid assay.

A ratio fluorescence sensor based on rhodamine B embedded metal-organic framework for glyphosate detection in agri-food products.

Glyphosate, a broad-spectrum and high-efficiency herbicide, could accumulate in the human body through the consumption of agri-food products. Herein, a ratio fluorescence sensor based on rhodamine B-embedded amino-functionalized iron-based metal-organic framework (MOF, NH2-MIL-88(Fe)@RhB) bonded with Cu2+ was developed for rapid detection of glyphosate. The synthesized NH2-MIL-88(Fe) was a biconical prism and had a cavity for the embedding of RhB as a reference compound. In the presence of Cu2+, Lewis interactions with NH2-MIL-88(Fe)@RhB cause the fluorescence signal to be turned off. When glyphosate was added, the signal was turned on due to chelation with Cu2+ and hydrogen bonding interactions with NH2-MIL-88(Fe)@RhB. Under optimal conditions, the developed sensor exhibited a linear range of 0.60-45 µmol L-1 with a response time of less than 1 min. The sensor was applied in the analysis of agri-food products (tea, soybean, wheat, cucumber), with recoveries between 97.93% and 109.06%, indicating its promising application in agri-food safety.