Curcumin-Cu(II) Ensemble-Based Fluorescence "Turn-On" Mode Sensing the Plant Defensive Hormone Salicylic Acid In Situ and In Vivo

A novel sustainable biomass-based fluorescent probe for sensitive detection of salicylic acid in rice

Herein, a ratiometric fluorescent probe was developed for sensitive detection of salicylic acid (SA) in rice using silk-derived carbon quantum dots @ Curcumin @ iron-based metal organic framework (SCQDs@Cur@Fe-MOFs). Fe-MOFs with porous structure not only provided holes for SCQDs to evade self-aggregation of SCQDs, but Fe2+ ions from MOFs was ingeniously employed to capture active sites of Cur, solving the problem of lacking sufficient specificity of Cur to SA while converting weak response signal to amplified "turn on" mode. Upon exposed to SA, the probe interacted with SA to form Cur-Fe2+-SA ternary complex, which inhibited the internal filtration effect between Cur and SCQDs, and triggered a cascade of response signaling. With this strategy, the proposed probe achieved sensitive determination of salicylic acid in rice with detection limit as low as 0.14 μmol/L. This study provides unique insight into constructing economical and eco-friendly fluorescent sensor for SA detection with superior performance.

Highly Selective and Rapid "Turn-On" Fluorogenic Chemosensor for Detection of Salicylic Acid in Plants and Food Samples

Salicylic acid (SA) is one of the chemical molecules, involved in plant growth and immunity, thereby contributing to the control of pests and pathogens, and even applied in fruit and vegetable preservation. However, only a few tools have ever been designed or executed to understand the physiological processes induced by SA or its function in plant immunity and residue detection in food. Hence, three Rh6G-based fluorogenic chemosensors were synthesized to detect phytohormone SA based on the "OFF-ON" mechanism. The probes showed high selectivity, ultrafast response time (<60 s), and nanomolar detection limit for SA. Moreover, the probe possessed outstanding profiling that can be successfully used for SA imaging of callus and plants. Furthermore, the fluorescence pattern indicated that SA could occur in the distal transport in plants. These remarkable results contribute to improving our understanding of the multiple physiological and pathological processes involved in SA for plant disease diagnosis and for the development of immune activators. In addition, SA detection in some agricultural products used probes to extend the practical application because its use is prohibited in some countries and is harmful to SA-sensitized persons. Interestingly, the as-obtained test paper displayed that SA could be imaged by ultraviolet (UV) and was directly visible to the naked eye. Given the above outcomes, these probes could be used to monitor SA in vitro and in vivo, including, but not limited to, plant biology, food residue detection, and sewage detection.

A novel ratiometric fluorescent probe for sensitive detection of jasmonic acid in crops

Herein, a novel ratiometric fluorescent probe was proposed for sensitive detection of jasmonic acid (JA) based on NCQDs@Co-MOFs@MIPs. The prepared NCQDs, with uniquely dual-emissive performance, are insensitive to JA due to electrostatic repulsion. Interestingly, the introduction of Co-MOFs not only avoided the self-aggregation of NCQDs, but changed the surface charge of NCQDs and triggered the response of NCQDs to JA. More importantly, the imprinted recognition sites from MIPs provided "key-lock" structures to specifically capture JA molecules, greatly improving the selectivity of the probe to JA. Under the synergistic actions of Co-MOFs and MIPs, JA can interact with NCQDs through photo-induced electron transfer (PET), resulting in the changes on emission intensity of the probe at E_m = 367 nm and 442 nm. Based on the observations, the quantification of JA was realized in the range of 1-800 ng/mL with the limit of detection (LOD) of 0.35 ng/mL. In addition, the probe was used for detecting JA in rice with satisfactory analysis results, indicating the probe holds great potential for monitoring JA levels in crops. Overall, this strategy provides new insights into the construction of practical probes for sensitive detection of plant hormones in crops.

Solid Phase Microextraction-Multicapillary Column-Ion Mobility Spectrometry (SPME-MCC-IMS) for Detection of Methyl Salicylate in Tomato Leaves

Methyl salicylate (MeSA) is a plant-signaling molecule that plays an essential role in the regulation of plant responses to biotic and abiotic pathogens. In this work, solid phase microextraction (SPME) and a multicapillary column (MCC) are coupled to ion mobility spectrometry (IMS) to detect MeSA in tomato leaves. The SPME-MCC-IMS method provides two-dimensional (2D) separation by both MCC and IMS, based on the retention and drift times. The effect of the IMS polarity on the separation efficiency of MCCs was also investigated. In the positive polarity, ionization of MeSA resulted in [MeSA + H]⁺ formation while, in the negative, deprotonated ions, [MeSA - H]^-, and the O₂^- adduct ion, [MeSA + O₂]^-, were formed. In the real sample analysis, the negative polarity operation resulted in the suppression of many matrix molecules and thus in the reduction of interferences. Four different SPME fibers were used for head space analysis, and four MCC columns were investigated. In the negative polarity, complete separation was achieved for all of the MCCs columns. The limits of detection (LODs) of 0.1 μg mL^-1 and linear range of 0.25-12 μg mL^-1 were obtained for the measurement of MeSA in a standard solution (H₂O/CH₃OH, 50:50) by the SPME-IMS method with a 5 min extraction time using an SPME with a PDMS fiber, in the negative mode of IMS. The MeSA contents of fresh tomato leaves were determined as 1.5-9.8 μg g^-1, 24-96 h after inoculation by tomato mosaic ringspot virus (ToRSV).

Poly(allylamine)-copper(II) coordination complex grafted on core@shell upconversion nanoparticles for ultrafast and sensitive determination of the phytohormone salicylic acid in plant extracts

Salicylic acid (SA) is a phenolic phytohormone with critical roles in plant growth regulation and resistance to biotic and abiotic stress. Since low SA concentrations can modulate many plant biochemical responses, innovative analytical tools are required to deeply understand its activity and to control its exogenous application in modern agricultural systems. Herein, a NIR-activated composite based on NaYF₄:Yb,Er@NaYF₄ core@shell upconversion nanoparticles decorated with the poly(allylamine)-Cu(II) complex [UCNPs-PAAm-Cu(II)] was developed to sensitively determine the SA molecule in plant-derived samples. Accordingly, the PAAm-Cu(II) complex grafted on the UCNPs induces a strategic charge transfer band which triggers a quenching process through a resonance energy transfer (RET) mechanism. Such process is gradually deactivated upon the addition of SA and the consequent formation of the SA-Cu(II) complex, allowing a luminescence recovery in the 1-800 nM linear range. This mechanism is promoted by the strong stability of the SA-Cu(II) complex (log β_2-SA/Cu = 19.01) which is over twelve orders of magnitude stronger than the PAAm-Cu²⁺ counterpart. Furthermore, the equilibrium and kinetic studies on the involved mononuclear Cu²⁺ complexes formation permitted instantaneous analytical responses and excellent selectivity against other representative phytohormones and metallic cations. The reliability of this method was demonstrated by determining the SA content of some edible fruits and vegetables comprising apple, lemon, kiwi, tomato, and cucumber, whose concentrations ranged from 0.30 to 2.99 μg g^-1, with percent recoveries between 94.6 to 102.3%. Thereby, the reported nanocomplex can help to understand the SA activity in plants with significant applications in crop yield improvement and food quality assessment.

Recent Advances in Plant Nanoscience

Plants have complex internal signaling pathways to quickly adjust to environmental changes and harvest energy from the environment. Facing the growing population, there is an urgent need for plant transformation and precise monitoring of plant growth to improve crop yields. Nanotechnology, an interdisciplinary research field, has recently been boosting plant yields and meeting global energy needs. In this context, a new field, "plant nanoscience," which describes the interaction between plants and nanotechnology, emerges as the times require. Nanosensors, nanofertilizers, nanopesticides, and nano-plant genetic engineering are of great help in increasing crop yields. Nanogenerators are helping to develop the potential of plants in the field of energy harvesting. Furthermore, the uptake and internalization of nanomaterials in plants and the possible effects are also worthy of attention. In this review, a forward-looking perspective on the plant nanoscience is presented and feasible solutions for future food shortages and energy crises are provided.

Ratiometric Fluorescent Probe Based on Diazotization-Coupling Reaction for Determination of Clenbuterol

In view of the potential harm caused by illegal feeding of clenbuterol (CLB) in the livestock industry, herein, a novel ratiometric fluorescent probe based on graphene quantum dots (GQDs)@[Ru(bpy)₃]²⁺ was elaborately constructed for CLB detection. In this probe, GQDs acted as response signals, and their fluorescence was remarkably quenched by CLB through the diazotization-coupling reaction. As for [Ru(bpy)₃]²⁺ as a reference signal, its fluorescence was hardly affected. The intensity ratio of two fluorophores showed good linearity with CLB concentration in the range of 0.05-40 μM, accompanied by visualization of fluorescence variation from yellow to red. The detection limit was as low as 0.029 μM. Particularly, the probe was successfully used to detect CLB in pork and beef samples with satisfactory recoveries. To our knowledge, this is the first report on a ratiometric fluorescent probe for the detection of CLB, which possesses broad application prospects in food safety risk monitoring.