Hinge-like paper-based dual-channel enzyme-free ratiometric fluorescent microfluidic platform for simultaneous visual detection of carbaryl and glyphosate

An ion synergism fluorescence probe via Cu2+ triggered competition interaction to detect glyphosate

The widespread use of glyphosate (Gly) poses significant risks to environmental and human health, underscoring the urgent need for its sensitive and rapid detection. In this work, we innovated by developing a novel material, ionic liquids, which formed the ionic probe "[P66614]2[2,3-DHN]-Cu2+ (PDHN-Cu2+)" through coordination with Cu2+. This probe capitalized on the distinctive fluorescence quenching properties of ionic liquids in the presence of Cu2+, driven by synergistic interactions between anions and cations. Glyphosate disrupted the PDHN-Cu2+ coordination structure due to its stronger affinity for Cu2+, triggering a "turn-on" fluorescence response. Impressively, PDHN-Cu2+ enabled the sensitive detection of glyphosate within just one minute, achieving a detection limit as low as 71.4 nM and excellent recovery rates of 97-103% in diverse samples. This groundbreaking approach, utilizing ionic probes, lays a robust foundation for the accurate and real-time monitoring of pesticides, employing a strategy based on synergism and competitive coordination.

A molecularly imprinted ratiometric fluorescent sensor for visual detection of 1-naphthol based on fluorescence-enhanced CdTeS QDs via APTES modification

CdTeS quantum dots (CdTeS QDs) were synthesized using the hydrothermal method and subsequently modified with (3-aminopropyl)triethoxysilane (APTES). This modification resulted in a significant enhancement of the fluorescence intensity, which was observed to be five times stronger than that of unmodified CdTeS QDs at 597 nm. Only after the fluorescence enhancement by APTES modification, the material showed a response to 1-naphthol (1-NP). Based on this, the molecularly imprinted polymers (MIPs) with ratiometric fluorescence were developed for the detection of 1-NP, that is, the synthetic raw material and the metabolite of the pesticide carbaryl. Under the excitation of 365 nm UV, the bright orange-red fluorescence (597 nm) of CdTeS QDs encapsulated in MIPs was quenched by 1-NP in the suspension, and 1-NP showed a gradually increasing blue emission (460 nm) with the increase of its concentration. This sensor has a good linear relationship between fluorescence intensity ratio (F460/F597) and 1-NP concentration (C1-NP) in a large concentration range (6.0-140.0 µM, LOD=0.45 µM, RSD<4.41%). It exhibits a visible fluorescence change from orange-red to blue-purple. Excellent recoveries in real samples were obtained by simulating carbaryl metabolism and demonstrated its potential in detection of 1-NP and carbaryl.

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.