Simultaneous detection and identification of thiometon, phosalone, and prothioconazole pesticides using a nanoplasmonic sensor array

Different sized gold nanoparticles for array-based sensing of pesticides and its application for strawberry pollution monitoring

The use of pesticides plays an essential role in improving crop quality and yield, however, it causes air, water, and soil pollution and the residue of these pesticides in agricultural products threatens the ecosystem and human life. Therefore, it is highly desirable to develop rapid, simple, and cost-effective methods for regular monitoring of pesticide residues in agricultural products especially strawberry that is consumed fresh and unpeeled. In this study, gold nanoparticles (AuNPs) of varying sizes have been exploited as sensing units to design a non-enzymatic colorimetric sensor array for the detection and discrimination of various pesticides including; bifenazate (BF), paraquat (PQ), diazinon (DZ), thiometon (TM), and carbendazim (CD) and chlorpyrifos (CP). Because of their strong size- and environmentally-dependent properties, AuNPs with different sizes produced distinguished plasmonic patterns in the presence of pesticides at a vast range of concentrations (25-800 ng mL-1). Plasmonic patterns of sensor units have been analyzed by various data visualization (bar plots and heat maps) and pattern recognition methods (linear discriminant analysis (LDA)). The multivariate calibrations showed linear responses ranging from 50 to 800 ng mL-1 for carbendazim, chlorpyrifos, paraquat, and bifenazate and 25-800 ng mL-1 for diazinon and thiometon. The limit of detection (LOD) was calculated to be 17.7, 22.8, 22.4, 9.7, 7.4, and 23.8 ng mL-1 for carbendazim, chlorpyrifos, paraquat, diazinon, thiometon, and bifenazate respectively. Finally, the applicability of the designed sensor was evaluated in real samples comprising tap water, well water, soil, and fruit, leave, drainage water, and culture substrate of strawberry.

Multiplex Detection of Biogenic Amines for Meat Freshness Monitoring Using Nanoplasmonic Colorimetric Sensor Array

Biogenic amines (BAs) were presented as significant markers for the evaluation of the spoilage of meat and meat products. In this work, a colorimetric sensor array was developed for the discrimination and detection of spermine (SP), spermidine (SD), histamine (HS), and tryptamine (TP) as important BAs in food assessment. For this aim, two important spherical plasmonic nanoparticles, namely gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), were utilized as the sensing elements of the probes. The cross-reactive interaction of the target biogenic amines and the plasmonic nanoparticles caused the aggregation-induced UV-Vis spectra changes, which were accompanied by visual color variation in the solution. The collected responses were analyzed by principal component analysis-linear discrimination analysis (PCA-LDA) to classify the four BAs. This colorimetric sensor array can also discriminate between the individual BAs and their mixture accurately. Partial least squares regression (PLS-R) was also utilized for quantitative analysis of the BAs. The wide linear concentration ranges of 0.1-10.0 µM for the four BAs and desirable figures of merits (FOMs) showed the potential of the developed sensor for quantitative detection of the BAs. Finally, the practical ability of the developed probe was studied by the determination of the BAs in the meat samples, which successfully proved the potential of the colorimetric sensor array in a food sample.

Chrono-colorimetric sensor array for detection and discrimination of halide ions using an all-in-one plasmonic sensor element

Most nanoparticle based colorimetric sensor array utilize several sensor elements and static response for discrimination of target analytes. This approach can be complicated and costly to synthesize or functionalize different nanoparticles for providing wide color variation. Herein, triangular silver nanoparticles (TSNPs) were used to develop a colorimetric sensor array by time-dimension responses. The principle of this sensor array is based on the diverse etching process of TSNPs in the presence of three halide ions, including bromide (Br^-), iodide (I^-) and chloride (Cl^-). Various etchings of TSNPs induced color changes at different reaction time intervals, which produced a colorimetric pattern for each ion. Therefore, using time dependent etching responses of TSNPs as a single sensing component can produce a wide color variation which can be distinguished by naked eyes. The colorimetric responses of TSNPs upon the addition of different concentrations of halide ions have been analyzed by PLS regression (PLS-R) and PLS discriminant analysis (PLS-DA). The analytical figures of merit confirmed that the developed chrono-colorimetric TSNPs -based sensor array is successful in both the discrimination and quantitative detection of halide ions. At the final step, the three halide ions were accurately determined in a real water sample, which verified the potential of the developed sensor in a real sample.

A facile way to construct sensor array library via supramolecular chemistry for discriminating complex systems

Differential sensing, which discriminates analytes via pattern recognition by sensor arrays, plays an important role in our understanding of many chemical and biological systems. However, it remains challenging to develop new methods to build a sensor unit library without incurring a high workload of synthesis. Herein, we propose a supramolecular approach to construct a sensor unit library by taking full advantage of recognition and assembly. Ten sensor arrays are developed by replacing the building block combinations, adjusting the ratio between system components, and changing the environment. Using proteins as model analytes, we examine the discriminative abilities of these supramolecular sensor arrays. Then the practical applicability for discriminating complex analytes is further demonstrated using honey as an example. This sensor array construction strategy is simple, tunable, and capable of developing many sensor units with as few syntheses as possible.

Analyte-restrained silver coating of gold nanostructures: an efficient strategy to advance multicolorimetric probes

Visual detection based on gold nanorods (AuNRs) has gained tremendous attention in sensing applications owing to the potential for simple, inexpensive, instrument-free, and on-site detection. The proper selection of the mechanism involved in the interaction between the analyte and the nanostructure plays a significant role in designing a selective and multicolorimetric probe for visual purposes. A winning mechanism to develop multicolorimetric probes is the silver metalization of AuNRs. Herein, an unprecedented idea is presented to expand the variety of multicolorimetric sensors relying on the mechanism of silver deposition. We introduce the anti-silver deposition mechanism in which the analyte directly or indirectly restrains the silver coating of AuNRs. To ascertain the anti-silver deposition mechanism, we have exploited the proposed idea for the direct detection of nitrate. The presence of nitrate (as restrainer agent), which was firstly treated with ascorbic acid (as reducing agent), induced a decrease in the spectral blueshift of AuNRs along with diverse sharp color transitions from reddish-orange (blank) to maroon, wine, berry/purple, dark blue, teal, green, seafoam, and mint. The difference in the spectrum area of the probe in the absent (S_o) and presence (S) of nitrate were linearly proportional to nitrate concentration in the range of 0.5-5.5 mmol l^-1and the limit of detection was calculated to be 465μmol l^-1. Furthermore, the practicability of the multicolor probe was assessed by the determination of nitrate in complex environmental samples.

Thiol-mediated etching of gold nanorods as a neoteric strategy for room-temperature and multicolor detection of nitrite and nitrate

The excessive presence of nitrite and nitrate in environmental matrixes has raised concerns among the scientific communities due to their negative impacts on human health and living organisms. Considering the necessity of regular monitoring and rapid evaluation of nitrite and nitrate, it is of great interest to develop methods capable of on-site detection of these compounds. This study presents a non-aggregation colorimetric method based on etching gold nanorods (AuNRs) for visual detection of nitrite and nitrate. Instead of temperature, we propose using thiourea as a sulfur-containing compound to accelerate the rate of AuNR etching. Thiourea forms stable cationic species with Au⁺ ions and consequently speeds up the etching process by reducing the redox potential of Au⁺/Au. In the presence of thiourea, the AuNRs are etched by nitrite resulting in wide obvious color changes from brown to light brown, green, blue, purple, pink, and colorless. In addition to nitrite, the developed method is capable of nitrate determination by reducing nitrate to nitrite through acid-washed zinc powder and is the first report of colorful detection of nitrate. Under optimized conditions, a good linear relationship was found between nitrite/nitrate concentration and the colorimetric response in the range of 8.0 to 100 μmol L^-1 and 0.5 to 3.0 mmol L^-1 with a limit of detection (LOD) as low as 1.3 μmol L^-1 and 173.3 μmol L^-1 for nitrite and nitrate, respectively. Furthermore, the practical application of our developed probe was confirmed by accurate determination of nitrite and nitrate in various complex media including water samples, soil extracts, and food products such as salami and sausage.