A Review on Recent Trends and Future Developments in Electrochemical Sensing

Electrochemical methods and devices have ignited prodigious interest for sensing and monitoring. The greatest challenge for science is far from meeting the expectations of consumers. Electrodes made of two-dimensional (2D) materials such as graphene, metal-organic frameworks, MXene, and transition metal dichalcogenides as well as alternative electrochemical sensing methods offer potential to improve selectivity, sensitivity, detection limit, and response time. Moreover, these advancements have accelerated the development of wearable and point-of-care electrochemical sensors, opening new possibilities and pathways for their applications. This Review presents a critical discussion of the recent developments and trends in electrochemical sensing.

In-situ quantitative prediction of pesticide residues on plant surface by ATR-FTIR technique coupled with chemometrics

Pesticide residues on plant surfaces pose a severe threat to food security, yet most research has focused on monitoring the liquid matrix, with few reports conducting in-situ analysis of the residues. This study was the first to attempt to utilize portable attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for in-situ characterization of broad-spectrum fungicide boscalid residues on plant surfaces. ATR-FTIR scanning of tomato fruits with pre-determined concentrations of boscalid residues was conducted without any pre-treatment, and the obtained spectra were then processed using chemometrics methods. The results demonstrated a negative correlation between the residual concentrations and their corresponding absorption intensities of several well-resolved peaks from the spectra, resulting in a high accuracy of 93.33% for the classification model created by probabilistic neural network (PNN) coupled with principal component analysis (PCA). By employing correlation analysis and the interval partial least squares method (iPLS), quantitative analysis was conducted on the wavenumber ranges of 1000-1800 cm-1 and 2700-2900 cm-1 from the spectra. The regression model, established through partial least squares regression (PLSR), demonstrated exceptional performance with an R2 value of 0.80, RMSE of 1.02 μg/cm2, RPD of 2.0, and RPIQ of 2.1 for validation. Meanwhile, the detection limit (LOD) of the model was calculated as 3.06 μg/cm2. This report highlights the potential of using portable ATR-FTIR for conducting qualitative and quantitative monitoring of pesticide residues both in-situ and on-site. It also provides references for other measuring techniques.

Improved magnetic solid-phase extraction based on magnetic sorbent obtained from sand for the extraction of pesticides from fruit juice

BACKGROUND

A combination of magnetic solid-phase extraction using an efficient and cheap magnetic sorbent obtained from sand and dispersive liquid-liquid microextraction has been developed for the extraction of nine multiclass pesticides (clodinafop-propargyl, haloxyfop-R-methyl, fenoxaprop-P-ethyl, oxadiazon, penconazole, diniconazole, chlorpyrifos, fenazaquin, and fenpropathrin) from commercial fruit juices (sour cherry, pomegranate, grape, watermelon, orange, apricot, and peach juices). The enriched pesticides were determined by gas chromatography-flame ionization detector and gas chromatography-mass spectrometry. The sorbent was natural iron oxide entrapped in silica along with some impurities. In this method, to extract the analytes from the samples, an appropriate amount of the magnetic sorbent (at mg level) is added. Then the sorbent particles are isolated from the solution using an external magnetic field and the adsorbed analytes are desorbed from the sorbent by acetone. In the following, a dispersive liquid-liquid microextraction procedure is carried out to concentrate the analytes more and to reach low limits of detection.

RESULTS

Under optimized extraction conditions, the method revealed satisfactory repeatability (relative standard deviation ≤8% for intra-day and inter-day precision), reasonable extraction recovery (43.3-55.9%), high enrichment factors (433-559), and low limits of detection (0.45-0.89 μg L^-1 ).

CONCLUSION

The method was applied in the analysis of pesticides in various fruit juices. Chlorpyrifos was found in peach juice at a concentration of 27 ± 2 μg L^-1 (n = 3) using a gas chromatography-flame ionization detector. To verify the results, the peach juice was also injected into gas chromatography-mass spectrometry after applying the proposed extraction method. © 2022 Society of Chemical Industry.

Research and Application of In Situ Sample-Processing Methods for Rapid Simultaneous Detection of Pyrethroid Pesticides in Vegetables

A novel rapid and cost-effective pre-processing method for the simultaneous determination of pyrethroid pesticides in vegetables has been developed and validated. The process of pesticide extraction was carried out by the QuEChERS (quick, easy, cheap, effective, rugged and safe) method combined with filtration by filter paper, and cleanup was carried out by the multi-plug-filtration-cleanup (m-PFC) method with no centrifuge program during the whole process. The pre-processing method is optimized for gas chromatography (GC). The process is convenient and time saving, requiring just a few seconds per sample. The recovery rate (70–120%), limit of detection (0.0001–0.007 mg/kg), precision (0.2–9.3%) and accuracy for each analyte were determined in 10 representative vegetables with good results. Finally, the feasibility of the developed method was further confirmed by the successful determination of pyrethroid-pesticide residues in pyrethroid-containing practical samples within the processing method coupled with thin-layer chromatography and a colloidal-gold test strip.

Rationally Designed Ag@polymer@2-D LDH Nanoflakes for Bifunctional Efficient Electrochemical Sensing of 4-Nitrophenol and Water Oxidation Reaction

The rational design and demonstration of a facile sequential template-mediated strategy to construct noble-metal-free efficient bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and electrocatalytic detection of hazardous environmental 4-nitrophenol (4-NP) have continued as a major challenging task. Herein, we construct a novel Ag@polymer/NiAl LDH (designated as APL) nanohybrid as an efficient bifunctional electrocatalyst by a simple hydrolysis method. The well-fabricated APL/GCE exhibited an extensive linear range from 0.1 to 100 μM in optimized conditions. It showed a detection limit (LOD) of 0.0096 μM (9.6 nM) (S/N = 3) for 4-NP in pH 6 by differential pulse voltammetry (DPV). Meanwhile, the newly fabricated APL exhibited outstanding OER activity with a very low overpotential of 259 mV to deliver 10 mA cm^-2 current density (J) at a scan rate of 5 mV/s. The Tafel plot value of APL is low (97 mV/dec) compared to that of the benchmark RuO₂ due to a fast kinetic reaction. Besides, the durability of the electrocatalyst was assessed by a chronoamperometry test (CA) for 36 h at 1.55 mV vs RHE, and the long-term cycling stability was analyzed by using cyclic voltammetry (CV); after 5000 cycles, the electrocatalyst was highly stable. These demonstrated results could lead to an alternative electrocatalyst construction for the bifunctionally efficient electrochemical sensing of 4-nitrophenol and oxygen evolution reaction.

Magnetic solid-phase extraction of pyrethroid and neonicotinoid insecticides separately in environmental water samples based on alkaline or acidic group-functionalized mesoporous silica

In this work, amino- or carboxyl-functionalized magnetic KIT-6 have been synthesized separately. The two nanocomposites were successfully used to enrich pyrethroids and neonicotinoids insecticides from environmental water samples, respectively.

Determination of pyrethroid residues in herbal tea using temperature-controlled ionic liquid dispersive liquid-liquid microextraction by high performance liquid chromatography

A simple and effective method for determining five pyrethroid residues in herbal tea by ultrasound-enhanced temperature-controlled (UETC) ionic liquid dispersive liquid-liquid microextraction (IL-DLLME) coupled with high performance liquid chromatography-diode array detection (HPLC-DAD) was developed. The use of ultrasonication and heating improved the ability of the ionic liquid to extract the analytes. Various parameters that affect the extraction efficiency were investigated and optimized using single factor experiments and response surface design. The optimum conditions of the experiment were 121 µL of [HMIM][PF6] (extraction solvent), 794 µL of acetonitrile (dispersive solvent), a heating temperature of 40°C, a sonication time of 3.6 min and a pH of 2.9. Under optimized conditions, the linearity was in the range of 0.05–5 mg L⁻¹ with correlation coefficients above 0.9993. The limits of detection and quantification were 1.25–1.35 µg L⁻¹ and 5 µg L⁻¹, respectively. The mean recoveries of the five pyrethroids ranged from 74.02% to 109.01%, with RSDs below 9.04%. The proposed method was reliable for the analysis of pyrethroids in Chinese herbal tea.

Low temperature-induced homogeneous liquid–liquid extraction and ternary deep eutectic solvent-based dispersive liquid–liquid microextraction followed by gas chromatography in the assessment of multiclass pesticide residues in cucumbers

In this work, a new DES and liquid nitrogen are used as a preconcentration solvent in DLLME and a phase separation agent in HLLE, respectively.