Engineered glyphosate oxidase coupled to spore-based chemiluminescence system for glyphosate detection

Semi-quantitative and visual detection of Cu2+ and glyphosate in real samples and living cells using fluorescent and colorimetric dual-signals peptide-based probe

The excessive emission of copper ions (Cu2+) and the abuse of glyphosate (Glyp) have caused serious harm to the ecological environment and human health, so it is important to develop a fast and convenient method for the analysis of Cu2+ and glyphosate to ensure environmental and food safety. Herein, a dual-signals peptide-based probe (FASRH) with fluorescent and colorimetric was prepared using 5-carboxyl fluorescein modified tetrapeptide (Ala-Ser-Arg-His-NH2). FASRH was successfully used to recognize Cu2+ as a fluorescence "on-off" probe, forming the FASRH-Cu2+ complex with non-fluorescence. As a new promising cascade probe, FASRH-Cu2+ complex probe has high selectivity (only Glyp), good sensitivity (50.2 nM), good anti-interference ability and wide pH range (7.0-11.0) for the detection of glyphosate by ligand replacement method. In addition, the recognizable color changed markedly under 365 nm UV light and natural light. Notably, FASRH not only achieved accurate monitoring of Cu2+ and glyphosate in two real water samples, but also successfully applied to detect Cu2+ and glyphosate in live Hacat cells based on low cytotoxicity. Moreover, it is worth noting that FASRH-impregnated test strips exhibited significant fluorescence and colorimetric color changes for Cu2+ and glyphosate via naked eye. Furthermore, smartphone-assisted FASRH was used for the portable detection of Cu2+ and glyphosate based on the advantages of simplicity, low cost and fast response.

A dual-signals fluorometric and colorimetric peptide-based probe for Cu(II) and glyphosate detection and its application for bioimaging and water testing

A novel dual-signal fluorometric and colorimetric probe FMDH (5-FAM-Met-Asp-His-NH2), incorporating a tripeptide (Met-Asp-His-NH2) linked to 5-carboxyfluorescein (5-FAM), was firstly synthesised. FMDH demonstrated exceptional selectivity and sensitivity, rapid response, wide pH response range and robust anti-interference capabilities for monitoring Cu2+. This was achieved through a distinctive naked-eye colorimetric and fluorescent quenching behaviour. A good linearity within the range of 0-3 μM (R2 = 0.9914) was attained, and the limit of detection (LOD) for Cu2+ was 47.4 nM. Furthermore, the FMDH-Cu2+ ensemble responded to glyphosate with notable selectivity and sensitivity. A good linear correlation (R2 = 0.9926) was observed at the lower concentration range (2.4-7.8 μM) and achieving a detection limit as low as 29.9 nM. The response time of FMDH with Cu2+ and glyphosate were less than 20 s, and the pH range of 7-11 that was suitable for practical application under physiological pH conditions. MTT assays confirmed that FMDH offers good permeability and low toxicity, facilitating successful application in imaging analysis of Cu2+ and glyphosate in living cells and zebrafish. In addition, FMDH was employed in the detection of these analytes in real water samples. Cost-effective, highly sensitive and easily prepared FMDH-impregnated test strips were developed for the efficient visual detection of Cu2+ and glyphosate under 365 nm UV light. Increasing concentrations of Cu2+ and glyphosate resulted in notable colour changes under 365 nm UV light, enabling visual semi-quantitative analysis via a smartphone colour-analysis App.

User-friendly one-step disposable signal-on bioassay for glyphosate detection in water samples

The onsite detection of glyphosate requires an easy-to-handle, low-cost and disposable assay for untrained users as requested by the ASSURED guidelines. A new strategy based on the expression of fusion proteins is proposed here. A glyphosate oxidase derived from Bacillus subtilis and the 6E10 variant of the dye peroxidase from Pseudomonas putida, both fused with the carbohydrate binding module (CBM) 3a from Clostridium thermocellum, were designed and expressed, leading to GlyphOx-CBM and 6E10-CBM. Cell lysates were used to immobilise both enzymes on cotton buds' heads without any purification. The cotton buds exhibit glyphosate oxidase activity when dipped into a glyphosate-contaminated water sample containing the 6E10-CBM chromogenic substrates. The chromophore could be quantified both in the solution and on the cotton buds' heads. Photography followed by image analysis allows to detect glyphosate with a linear range of 0.25-2.5 mM and a limit of detection (LoD) of 0.12 mM. When the chromogenic substrates are replaced by luminol, the chemiluminescence reaction allows the detection of glyphosate with a linear range of 2-500 μM and a LoD of 0.45 μM. No interference was observed using glyphosate analogues (glycine, sarcosine, aminomethylphosphonic acid) or other herbicides used in a mixture. Only cysteine was found to inhibit 6E10-CBM. Two river waters spiked with glyphosate lead to recoveries of 64-131%. This work describes a very easy-to-handle and inexpensive signal-on bioassay for glyphosate detection in real surface water samples.

Cu2+ assisted carnation-like fluorescent metal-organic framework for triple-mode detection of glyphosate in food samples

Herein, by employing a novel synthesized ligand H₂L, a flower-like luminescent metal-organic framework IRMOF-3-L was constructed for developing a triple-mode sensor for glyphosate (Glyp) detection. The ligand H₂L was designed to contain three functional parts, which endowed the resulted IRMOF-3-L with peroxidase-like activity and unique fluorescence property, as well as specific combining capacity for Cu²⁺ to quench its fluorescence. The quenched fluorescence of IRMOF-3-L/Cu²⁺ could be recovered by Glyp to realize fluorescence detection of Glyp. Besides, the peroxidase activity of IRMOF-3-L/Cu²⁺ could also be inhibited by Glyp, and result in the decrease of catalysate oxTMB, concurrently reducing the changes of colorimetric and SERS signal. Therefore, the fluorescent/colorimetric/SERS triple-mode based detection of Glyp was favorably realized, and the detection limits were calculated as low as 0.738, 2.26 and 0.186 nM, respectively. Furthermore, a portable test strips-smartphone sensing platform was constructed for point of care testing of Glyp in food samples.

Directed evolution of glyphosate oxidase and a chemiluminescence system for glyphosate detection: A comprehensive practical laboratory experiment on biotechnology

This article describes a comprehensive practical laboratory method for developing an enzyme to more easily measure glyphosate levels in solution. Through this article, undergraduate students of biology majors can conduct research experiments in critical fields by utilizing various techniques, such as chemiluminescence (CL) biosensors with engineered enzymes and are guided in molecular biology laboratories. A glyphosate oxidase mutant library was constructed by DNA shuffling, and a glyphosate oxidase variant with increased glyphosate degradation activity was selected by using a high-throughput screening assay. Following protein overexpression in Escherichia coli (DE3) and purification by affinity chromatography, the glyphosate oxidase variant protein combined with luminol-H₂ O₂ reaction was constructed as a new CL biosensor for detecting glyphosate in soils.

Laccase-luminol chemiluminescence system: an investigation of substrate inhibition

Chemiluminescence (CL) reactions are widely used for the detection and quantification of many types of analytes. Laccase has previously been proposed in CL reactions; however, its light emission behaviour has not been characterized. This study was conducted to characterize the laccase-luminol system, determine its kinetic parameters, and analyze the effects of protein and OH- concentration on the CL signal. Laccase from Coriolopsis gallica was combined with different concentrations of luminol (125 nM to 4 mM), and the enzyme kinetics were evaluated using diverse kinetic models. The laccase-luminol system was able to produce CL without an intermediate molecule, but it exhibited substrate-inhibition behaviour. A two-site random model was used and suggested that when the first luminol molecule was bound to the active site, laccase affinity for the second luminol molecule was increased. This inhibition effect could be avoided using a low luminol concentration. At 5 μM luminol concentration, 1 mg/ml (0.13 U) laccase is needed to achieve nearly 90% of the maximum CL signal, suggesting that the available luminol could not bind to all active sites. Furthermore, the concentration of NaOH negatively affected the CL signal. The laccase-luminol system represents an alternative to existing CL systems, with potential uses in molecular detection and quantification.

Functional characterization of glycine oxidase from Bacillus licheniformis in Escherichia coli and transgenic plants

OBJECTIVES

To find glycine oxidase genes that can be applied to the breeding of glyphosate resistant crops.

RESULTS

The glycine oxidase (GO, EC 1.4.3.19) gene (GenBank No: KC831746) from Bacillus licheniformis (B. licheniformis) was chemically synthesized and transformed into glyphosate-sensitive Escherichia coli (E. coli). The GO gene was transformed into Arabidopsis and rice through Agrobacterium-mediated transformation. The test results confirmed that transgenic plants containing GO genes are more resistant to glyphosate than wild-type plants. On solid Murashige and Skoog (MS) (Murashige and Skoog1962 ) medium containing 200 µM glyphosate, transgenic Arabidopsis thaliana grew normally, while wild-type plants were stunted and root growth was restricted. In a solution containing 500 µM glyphosate, wild-type rice showed severe yellowing, while transgenic rice grew normally. In addition, when sprayed with 10 mM glyphosate solution, wild-type rice withered and died, while transgenic rice grew well. The function of GO gene in glyphosate resistance and the application value of GO gene in the cultivation of glyphosate-resistant crops is proved.

CONCLUSIONS

The glycine oxidase gene from B. licheniformis enhances the resistance of E. coli, Arabidopsis and rice to glyphosate.

Label-Free Fluorescent Turn-On Glyphosate Sensing Based on DNA-Templated Silver Nanoclusters

In this work, a label-free fluorescent detection method for glyphosate, based on DNA-templated silver nanoclusters (DNA-Ag NCs) and a Cu²⁺-ion-modulated strategy, was developed. In the presence of Cu²⁺, the fluorescence of the DNA-Ag NCs was quenched. Glyphosate can restore the fluorescence of DNA-Ag NCs. By analyzing the storage stability of the obtained DNA-Ag NCs using different DNA templates, specific DNA-Ag NCs were selected for the construction of the glyphosate sensor. The ultrasensitive detection of glyphosate was achieved by optimizing the buffer pH and Cu²⁺ concentration. The sensing of glyphosate demonstrated a linear response in the range of 1.0-50 ng/mL. The limit of detection (LOD) was 0.2 ng/mL. The proposed method was successfully applied in the detection of glyphosate in a real sample, indicating its high application potential for glyphosate detection.

An “on-off-on” fluorescence probe for glyphosate detection based on Cu2+ modulated g-C3N4 nanosheets

The analysis of glyphosate is essential to agricultural production, environment protection and public health. Herein, we proposed a fast and convenient “on-off-on” fluorescence platform for sensitive detection of glyphosate via Cu²⁺ modulated g-C₃N₄ nanosheets. The fluorescence of the system was quenched by Cu²⁺. With the presence of glyphosate, the fluorescence could be restored due to the formation of Cu²⁺- glyphosate complex. The proposed method was cost-effective with label-free and enzyme-free. Moreover, it exhibits high sensitivity with a low detection limit of 0.01 μg/ml. Furthermore, the proposed method has been successfully monitored glyphosate in real samples.

A reaction-based system for the colorimetric detection of glyphosate in real samples

Glyphosate is widely used herbicides and causes several diseases in humans. Therefore, the detection of glyphosate is curial and urgent. Studies on the detection of glyphosate in literature are often based on inhibition of the enzyme acetylcholinesterase. In this study, we developed two simple colorimetric sensors, BP-Cl and CP-Cl, by linking 3-chloro-4-methylpyridine with 4-(dimethylamino)cinnamaldehyde or 4-(dimethylamino)benzaldehyde in a one-step reaction. The colorimetric and optical sensing properties of these compounds were investigated by the naked-eye and UV-Vis spectrophotometer in ACN/HEPES buffer (5 mM pH 8.0, 1:1 v/v). The sensors displayed high sensitivity and selectivity for glyphosate by color changes, which ranged from colorless to yellow for BP-Cl and yellow to orange for CP-Cl. The detection limits of BP-Cl and CP-Cl by the naked-eye detection were found as 15 µM and 10 µM. On the other hand, the detection limits of BP-Cl and CP-Cl via UV-Vis measurements were calculated as 0.847 µM and 1.23 µM, respectively. Moreover, the sensors were able to monitor glyphosate in water samples using the naked-eye, UV-Vis spectroscopy, and filter paper strips.

A spore-based portable kit for on-site detection of fluoride ions

The excess residues of fluoride ions cause serious human health problems, making their detection highly valuable. In this work, a whole-cell-based biosensor was presented for the detection of fluoride ions, which can inhibit the color reaction of 3,3',5,5',-tetramethylbenzidine (TMB) catalyzed by the CotA-laccase of spore surface. This reaction for the detection of fluoride ions could be read out through UV-vis spectrophotometer, smartphone, or standard colorimetric card within 10 min. Under optimum conditions, a linear range of 1-600 μmol L^-1 with a detection limit of 0.12 μmol L^-1 (3σ/k) was achieved for fluoride ions detection by using UV-vis spectrophotometer. The biosensor coupling with smartphone had a good linear response to fluoride ions concentration in the range of 5-600 μmol L^-1 with LOD of 0.90 μmol L^-1 (3σ/k). The standard colorimetric card can be directly used for recognizing the fluoride ions level via naked-eyes. A portable kit based on a colorimetric card and smartphone was developed and has been successfully applied for fluoride ions monitoring in surface waters and groundwater. This developed method has several advantages such as rapid, outstanding selectivity and anti-interference, low-cost, ease of operation and storage, and eco-friendliness, meeting the demands of point-of-care testing of fluoride ions and disease prevention.

Logarithmic Data Processing Can Be Used Justifiably in the Plotting of a Calibration Curve

The article is a response to a recent opinion piece that log concentration values should not be applied in analytical chemistry. An essential aim in the development of analytical chemistry methods is to obtain more sensitive and accurate detection values. For the application of chemical analysis methods, the obtained experiment data need to fit with the mathematical functions in the first place. As influenced by different detection principles and analytical methods, data can be displayed in a coordinate system with two linear axes for linear function fitting, or the data can first be taken through a logarithmic transformation and then for function fitting. Using raw data or data after logarithmic transformation primarily depends on analytical principles, without special rules of data formats. For example, ultraviolet-visible spectrophotometric data are more suitable for direct linear fitting. However, enzyme-catalyzed reaction or electrochemical data in logarithmic form are more appropriate for function fitting. This transformation of data form will not affect the soundness of fit statistics; rather, it simplifies the complexity of function analysis and calculation, which are the essence of analytical chemistry. In this brief article, we provide justification and legitimacy of the application of logarithmic processing in various fields of quantitative analytical chemistry.