A facile fluorescent "turn-off" method for sensing paraquat based on pyranine-paraquat interaction

Highly selective and flexible silver nanoparticles-based paper sensor for on-site colorimetric detection of paraquat pesticide

Paper-based sensors or paper-based analytical devices (PADs) have recently emerged as the cost-efficient, and portable, on-site detection tools for various biological and environmental analytes. However, paper-based sensors often suffer from poor selectivity. Here, a single-step paper-based flexible sensor platform has been developed for the on-site detection of paraquat (PQ) pesticide in real samples, utilizing chitosan and citrate-capped silver nanoparticles integrated with a flexible paper. The nanocomposite paper film was thoroughly characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The composite paper platform demonstrated a color change with a reaction time within a few minutes (6-7 min) in the presence of PQ pesticide. The trace level PQ pesticide has been detected with a limit of detection (LOD) of 10 μM and a linear range (LR) of 10-100 μM. The sensor shows 3× more selective signal towards PQ pesticide compared to other similar pesticides. The relative standard deviation (RSD) was found to be 5% for repeatability, 4% for reproducibility, 2% for interference, and 3.5% for real sample analysis, indicating high precision sensing and within the WHO limit of RSD (20%). The present work will open up new avenues for the advancements in flexible paper sensors; cost-effective, portable, on-site sensors, and sustainable device development.

Fluorescence Spectroscopic Studies to Evaluate Binding Interaction between Hoechst 33258 and Bilirubin

A detailed spectroscopic study (fluorescence, absorption, and lifetime) was conducted to gain insight into the nature of the binding interaction between fluorophore Hoechst33258 (H258) and jaundice marker Bilirubin (Br). The fluorescence emission of the H258 (Ex/Em = 340-502nm) showed a conc. dependent quenching in the presence of Br (1.25 μ M to 10 μ M). The Stern-Volmer constant demonstrated an upward curve depicting the occurrence of both static and dynamic quenching with an acquired value of KSV = 3.1x 103 M- 1 and biomolecular quenching rate constant Kq = 8.6 x 1011 M- 1 S- 1 . The static quenching was evaluated using the sphere of action model and a sphere radius of 0.3nm indicated the presence of a static component in the quenching. The FRET analysis with overlap integral (J) = 1.4x1014 M- 1 cm- 1 nm4 and Foster Radius(R0 ) = 26.82 Å with 59% efficiency suggested occurrence of dynamic quenching. Further studies with the time-resolved fluorescence also indicated the presence of dynamic quenching. The lifetime values of H258 reduced from 3.9ns to 0.5ns. Molecular docking studies further support both static and dynamic components in quenching. A non-covalent interaction of H258 with Br in the presence of HSA is predominantly characterized by H-bonding with residues Lys, Asn, Glu, Gln, and Br. The H258 and Br interaction was within the distance of 3.04 Å, which is in coherence with the sphere of action model (0.3nm) and Van-der-Waals along with hydrophobic interactions, which suggested both static and dynamic quenching. Thus, H258 can serve as an efficient fluorophore to monitor binding interactions and can be further exploited as a suitable probe for investigating conformational changes and detection of Br in subsequent studies.

Selective detection of paraquat by a cucurbit[7]uril-based fluorescent probe

A simple fluorescent "on-off" system that can be utilized for the selective identification and determination of paraquat (PQ) is presented herein. 1H NMR spectroscopic data indicated that in aqueous solution the alkaloid palmatine can be partially encapsulated within the cucurbit[7]uril (Q[7]) cavity, whereby a stable 1 : 1 host-guest inclusion complex is formed. Other characterization techniques including mass spectrometry, UV-Vis and fluorescence spectroscopy also provided further evidence, and the host-guest inclusion complex was found to exhibit reasonable fluorescence intensity. It is noteworthy that the addition of PQ resulted in quenching the fluorescence of the host-guest inclusion complex, whereas the presence of 12 other pesticides did not significantly affect the fluorescence intensity. Given the linear relationship between the intensity of the fluorescence and the PQ concentration, the PQ concentration in aqueous solution was easily detected. Thus, a new method for identifying and determining the fluorescence quenching of PQ has been developed in this work.

Novel AIEE pillar[5]arene-fluorene fluorescent copolymer for selective recognition of paraquat by forming polypseudorotaxane

A novel conjugated polymer (Co-P[5]Flu) was synthesized by copolymerizing a difunctionalized pillar[5]arene and a fluorene derivative monomer. Co-P[5]Flu displayed an aggregation-induced emission enhancement (AIEE) effect because of the restricted intramolecular rotations of the pillar[5]arene unit. Co-P[5]Flu exhibited high selectivity and sensitivity towards the pesticide paraquat (PQ) with excellent anti-interference properties. It presented fluorescence quenching response (1-I/I0=96.6%) only towards paraquat and not towards other competitive guests. The fluorescence titration experiments revealed that the detection limit (LOD) for paraquat was as low as 1.69×10-8 M, and the Stern-Volmer constant (KSV) was determined to be 2.11×104 M-1. The recognition mechanism was studied using both 1H NMR titration and theoretical calculations. The Co-P[5]Flu showed fluorescence quenching for PQ due to the synergistic effect of polypseudorotaxane formation and photoinduced electron transfer (PET). Additionally, the polymer chemosensor demonstrated potential for the detection of paraquat in practical samples.

Supramolecular Fluorescence Sensor Array Based on Cucurbit[8]uril Complexes Used for the Detection of Multiplex Quaternary Ammonium Pesticides

The simultaneous detection of multiple quaternary ammonium pesticides (QAPs) in water is a challenge due to their high solubility in water and similar structures. In this paper, we have developed a quadruple-channel supramolecular fluorescence sensor array for the simultaneous analysis of five QAPs, including paraquat (PQ), diquat (DQ), difenzoquat (DFQ), mepiquat (MQ), and chlormequat (CQ). Not only were QAP samples of different concentrations (10, 50, and 300 μM) in water distinguished with 100% accuracy but also single QAP and binary QAP mixed samples (DFQ-DQ) were sensitively quantified. Our experimental interference study confirmed that the developed array has good anti-interference ability. The array can quickly identify five QAPs in river and tap water samples. In addition, it also qualitatively detected QAP residues in Chinese cabbage and wheat seedlings extract. This array has rich output signals, low cost, easy preparation, and simple technology, demonstrating great potential in environmental analysis.

Copper nanoparticle-decorated nitrogen-doped carbon nanosheets for electrochemical determination of paraquat

A new strategy to prepare copper (Cu) nanoparticles anchored in nitrogen-doped carbon nanosheets (Cu@CN) has been designed and the nanomaterial applied to the determination of paraquat (PQ). The nanocomposite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and several other techniques. We found that the Cu nanoparticles are uniformly distributed on the carbon materials, providing abundant active sites for electrochemical detection. The electrochemical behavior of the Cu@CN-based PQ sensor was investigated by square-wave voltammetry (SWV). Cu@CN exhibited excellent electrochemical activity and PQ detection performance. The Cu@CN-modified glassy carbon electrode (Cu@CN/GCE) exhibited excellent stability, favorable sensitivity, and high selectivity under optimized conditions (enrichment voltage -0.1 V and enrichment time 400 s) of the SWV test. The detection range reached 0.50 nM to 12.00 μM, and the limit of detection was 0.43 nM with high sensitivity of 18 μA·μM^-1·cm^-2. The detection limit is 9 times better than that of the high-performance liquid chromatography method. The Cu@CN electrochemical sensor demonstrated excellent sensitivity and selectivity also in environmental water and fruit samples enabling its use in practical, rapid trace-level detection of PQ in environmental samples.

Fluorescence Detecting of Paraquat and Diquat Using Host-Guest Chemistry with a Fluorophore-Pendant Calix[6]arene

Paraquat (PQ) and diquat (DQ), some of the most widely used herbicides in the world, both present a high mortality index after intentional exposure. In this paper, a fluorescence sensing method for PQ and DQ, based on host-guest molecular recognition, is proposed. Calix[6]arene derivatives containing anthracene or naphthalene as pendant fluorophore at their lower rim recognize DQ and PQ in hydroalcoholic solution with a broad linear response range at the μg L^-1 level concentration. The linear response ranges were found from 1.0 to 18 μg L^-1 with the detection limit of 31 ng L^-1 for paraquat, and from 1.0 to 44 μg L^-1 with the detection limit of 0.16 μg L^-1 for diquat. The recognition process is detected by following the decrease in the fluorescence emission consequent to complexation. The proposed quenching method has been applied to the determination of paraquat in drinking water samples.

Fluorescent and Colorimetric Ionic Probe Based on Fluorescein for the Rapid and On-Site Detection of Paraquat in Vegetables and the Environment

Detection of pesticide paraquat (PQ) is of considerable significance to ensure food safety, and its rapid and on-site detection is still a challenge. Aimed at the ion characteristics of PQ, an "enrichment and detection" strategy was proposed to improve the sensitivity through electrostatic attractions, and the ion characteristic of probes was adopted to increase the portability through avoiding aggregation-caused quenching effects in the paper strips. Herein, a novel anion-functionalized ionic liquid (IL) probe with a large conjugated plane and rich π-electrons ([Fluo][P₆₆₆₁₄]₂) was designed as a fluorescent and colorimetric dual-channel probe to sensitively and rapidly detect trace amounts of PQ in vegetables and the environment. The proposed probe exhibited good linearity with a detection limit of 64.0 nM in the PQ concentration range of 0.3-7.0 μM (fluorometry) and 0.1 μM in that of 0.1-8.0 μM (colorimetry), respectively. In addition, it displayed a rapid fluorescence quenching response from green to dark (<5 s) and excellent anti-interference (among 23 other pesticides) due to dual effects of electrostatic attraction and π-π stacking. Most importantly, the lipophilic IL probe could be applied in real vegetables and environmental samples with a satisfying recovery rate of 98-103% and assembled into a handy paper strip that achieved the visual semiquantitative detection of PQ. This ionic probe provides a feasible approach for rapidly and conveniently detecting PQ for ensuring agricultural and food safety and opens a new avenue to detect ion-responsive analytes in real complex samples by an "enrichment and detection" strategy.

Non-biological fluorescent chemosensors for pesticides detection

The ongoing poisoning of agricultural products has pushed the security problem to become an important issue. Among them, exceeding the standard rate of pesticide residues is the main factor influencing the quality and security of agricultural products. Moreover, the abuse of pesticides has introduced a large amount of residues in soil and drinking water, which will enter the food chain to the human body, leading to neurological disorders and cancer. Therefore, great efforts have been devoted to developing fluorescent sensors for detecting pesticide in a facile, quickly, sensitive, selective, accurate manner, which exhibit greater advantages than some traditional methods. In this review, we mainly focus on summarizing the non-biological fluorescent probes for organic pesticides detection with the detection limit of micromole to nanomole, including organic functional small molecules, calixarenes and pillararenes, metal organic framework systems, and nanomaterials. Meanwhile, we described the different sensing mechanisms for pesticides detection of these mentioned fluorescent sensors, the detection limit of each pesticide, the application in detecting actual samples, as well as their respective advantages and development prospects associated with present non-biological fluorescent sensors.

Electrochemical paraquat sensor based on lead oxide nanoparticles

1,1-Dimethyl-4,4-bipyridinium dichloride known as paraquat is a popular well-known herbicide that is widely used in agriculture around the world. However, paraquat is a highly toxic chemical causing damage to vital organs including the respiratory system, liver, heart, and kidneys and death. Therefore, detection of paraquat is still necessary to protect life and the environment. In this work, an electrochemical sensor based on lead oxide nanoparticles (PbO-NPs) modified on a screen-printed silver working electrode (SPE) has been fabricated for paraquat detection at room temperature. The PbO-NPs have been synthesized by using a sparking method via two Pb metal wires. The electrochemical paraquat sensors have been prepared by a simple drop-casting of PbO-NPs solution on the surface of the SPE. The PbO-NPs/SPE sensor exhibits a linear response in the range from 1 mM to 5 mM with good reproducibility and high sensitivity (204.85 μA mM⁻¹ cm⁻²) for paraquat detection at room temperature. The PbO-NPs/SPE sensor shows high selectivity to paraquat over other popular herbicides such as glyphosate, glufosinate-ammonium and butachlor-propanil. The application of the PbO-NPs/SPE sensor is also demonstrated via the monitoring of paraquat contamination in juice and milk.

The PbO nanoparticles-based electrochemical sensor can be integrated into a smartphone for on-site field testing of paraquat with high sensitivity and selectivity.

An indicator displacement assay-based optical chemosensor for heparin with a dual-readout and a reversible molecular logic gate operation based on the pyranine/methyl viologen

We have reported an optical indicator displacement assay (IDA) for heparin with a UV-vis absorbance and fluorescence dual-readout based on pyranine/methyl viologen (MV²⁺). Upon introducing heparin, pyranine/MV²⁺ shows a clearly observable increase in UV-vis absorbance and a turn-on of the fluorescence signal. We have demonstrated that the ionic nature of buffers significantly affects the pyranine displacement and the zwitterionic HEPES was most suitable for heparin sensing. After careful screening of experimental conditions, the pyranine/MV²⁺-based optical chemosensor exhibits a fast, sensitive, and selective response toward heparin. It shows dynamic linear concentration of heparin in the ranges of 0.1-40 U·mL^-1 and 0.01-20 U·mL^-1 for the absorptive and fluorescent measurements, respectively, which both cover the clinically relevant levels of heparin. As with the animal experiments, the optical chemosensor has been demonstrated to be selective and effective for heparin level qualification in rat plasma. The chemosensor is readily accessible, cost-effective, and reliable, which holds a great promise for potential application on clinical and biological studies. Furthermore, this IDA system can serve as an IMPLICATION logic gate with a reversible and switchable logical manner.

A Fluorescent Detection for Paraquat Based on β-CDs-Enhanced Fluorescent Gold Nanoclusters

In this report, a fluorescent sensing method for paraquat based on gold nanoclusters (AuNCs) is proposed. It was found that paraquat could quench both glutathione-capped AuNCs (GSH-AuNCs) and β-cyclodextrin-modified GSH-AuNCs (GSH/β-CDs-AuNCs). The modification of β-CDs on the surface of GSH-AuNCs obviously enhanced the fluorescence intensity of GSH-AuNCs and improved the sensitivity of paraquat sensing more than 4-fold. This sensibilization was ascribed to the obvious fluorescence intensity enhancement of GSH-AuNCs by β-CDs and the “host–guest” interaction between paraquat and β-CDs. The fluorescence quenching was mainly due to the photoinduced energy transfer (PET) between GSH/β-CDs-AuNCs and paraquat. With the optimized β-CDs modification of the GSH-AuNC surfaces and under buffer conditions, the fluorescent detection for paraquat demonstrated a linear response in the range of 5.0–350 ng/mL with a detection limit of 1.2 ng/mL. The fluorescent method also showed high selectivity toward common pesticides. The interference from metal ions could be easily masked by ethylene diamine tetraacetic acid (EDTA). This method was applied to the measurement of paraquat-spiked water samples and good recoveries (93.6–103.8%) were obtained. The above results indicate that host molecule modification of fluorescent metal NC surfaces has high potential in the development of robust fluorescent sensors.

An UPLC-MS/MS Method for Simultaneous Quantification of the Components of Shenyanyihao Oral Solution in Rat Plasma

Objectives

To study the quantification of the components in rat plasma after oral administration of Shenyanyihao oral solution.

Methods

Shenyanyihao oral solution has been traditionally used for the treatments of chronic nephritis in clinics. Stachydrine, Danshensu, chlorogenic acid, protocatechuic acid, plantamajoside, aesculetin, isoquercitrin, ferulic acid, baicalin, and baicalein are regarded as the main compounds in Shenyanyihao oral solution. A sensitive, efficient, and precise UPLC-MS/MS method was established and validated for the quantification of the components in rat plasma after oral administration of Shenyanyihao oral solution.

Results

The main pharmacokinetic parameters of the components were acquired based on the analysis of the plasma sample by a noncompartmental method using the WinNonlin7.0 pharmacokinetic program. Danshensu, protocatechuic acid, isoquercitrin, and ferulic acid from Shenyanyihao oral solution were quickly absorbed, and their peak concentration occurred at less than 0.5 h. The pharmacokinetic parameter of the average t_1/2 from Danshensu was 3.91 h in rats, and it was the most rapid distribution and elimination among the components. In addition, the C_max of stachydrine and baicalin were revealed as the higher plasma concentrations in rats.

Conclusions

This pharmacokinetic study seems to be useful for a further clinical study of Shenyanyihao oral solution in the treatments of chronic nephritis.

Highly Sensitive Fluorescent Probe for Detection of Paraquat Based on Nanocrystals

Paraquat is one of the most toxic materials widely applied in agriculture in most countries. In the present study, a simple, innovative and inexpensive nano biosensor which is based on a thioglycolic acid (TGA) - CdTe@CdS core-shell nanocrystals (NCs) to detect paraquat, is suggested. The NCs based biosensor shows a linear working range of 10-100 nM, and limited detection of 3.5 nM. The proposed sensor that has been well used for the detection and determination of paraquat in natural water samples is collected from corn field and a canal located near to the corn field yielding recoveries as high as 98%. According to our findings, the developed biosensor shows reproducibility and high sensitivity to determine paraquat in natural water samples in which the amount of paraquat has low levels. The suggested method is efficiently applied to paraquat determination in the samples of natural water that are collected from a tap water and a canal located near to the cornfield.

An anionic-ligand installed pyrene-based MOF for the fluorescence detection of paraquat

By anionic ligand installation, a pyrene-based MOF could distinguish paraquat from other electron-deficient agrochemicals and gave sensitive fluorescence response to it.

Naked-eye sensing of phytic acid at sub-nanomolar levels in 100% water medium by a charge transfer complex derived from off-the-shelf ingredients

Naked-eye sensing of phytic acid, one of the most abundant antinutrients, was achieved in 100% water medium using a charge transfer complex, composed of pyranine and methyl viologen. Since both the ingredients are commercially available, the design of such sensory systems needs zero synthetic effort, which essentially makes it economically viable. Only the physical mixture of both of these compounds showed a color-changing response from brown to yellow in the presence of phytic acid with a turn-on fluorescence response (LOD: 0.56 nM). The electrostatic interaction leads to charge pairing between phytic acid and methyl viologen, which releases free pyranine in solution. Considering its high sensitivity, low-cost test strips were developed for the on-site detection of phytic acid, even in remote locations. Additionally, estimation of phytic acid was achieved in grain samples with a sufficiently high accuracy, as evident from a sufficiently low relative standard deviation (<5%).

Fluorescence enhancement novel green analytical method for paraquat herbicide quantification based on immobilization on clay

Fluorescence emission enhancement by adsorption as a promising tool for the development of future green sensors.