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Hydrogen peroxide (H₂O₂) plays a key role in a diverse array of cellular signaling pathways, which is closely related to plant health and physiological status. The accurate and efficient monitoring of H₂O₂ in living plant cells has attracted enormous interest. Herein, we developed an electrochemical-colorimetric dual-mode sensor based on the peroxidase-like activity of a polyacrylamide (PAM) -modified copper electrode (Cu-PAM), allowing for the in situ detection of H₂O₂ released from tomato leaves. The co-electrodeposition of unique combination of Cu and polyacrylamide, as well as the active site structure of Cu-centered peroxidases, can enhance adsorption performance by the hydrogen bonds between PAM with H₂O₂, which exhibited excellent electrochemical performance with a low limit of detection (LOD) of 0.0167 mM and a detection range of 0.05-25.31 mM. Meanwhile, a colorimetric signal output of the sensor that can be quantified from 1 μM to 70 μM with a LOD value of 0.33 μM. This work demonstrates a huge potential application prospect of the polyacrylamide-modified copper in the field of biosensors.

In this reasearch, a homogeneous electrochemical sensor based on PCN-224@MB@Apt was fabricated for the ultrasensitive determination of ochratoxin A (OTA). Firstly, nanoscale PCN-224 were synthesized as the nanocarrier to embed the signal probe of methylene blue (MB). Then, the OTA aptamer (Apt) was added and connected to PCN-224@MB via the Zr-O-P bond between Zr metal sites of PCN-224 and phosphate group of Apt as the biogate. When OTA exists, the Apt would preferentially bind with OTA and fall off from PCN-224@MB, leading to the release of MB and generation of differential pulse voltammetry (DPV) response. The DPV response of MB was linearly correlated with the amount of OTA. The optimized PCN-224@MB@Apt sensor showed outstanding detection performance towards OTA with a low detection limit of 2.6 × 10^-5 ng/mL (S/N = 3) and wide linear range (10^-4-10 ng/mL). Meanwhile, the fabricated homogeneous electrochemical sensor exhibited splendid stability, reproducibility, and specificity. To assess the practical applicability, the PCN-224@MB@Apt sensor was applied to detect OTA in real corn samples and desirable recovery rates varying from 83.2 % to 109.6 % were obtained.

Red tide events caused by Akashiwo sanguinea (A. sanguinea) pose a significant threat to ecosystems. However, studies that offer promising approaches for portable and onsite detection with precise identification of A. sanguinea remain insufficient. In this study, we developed an electrochemical biosensor (E-biosensor) for detecting A. sanguinea combined with cascade amplification strategies, termed TDW-E-biosensor. A predictive relationship was also established to predict algal cell density based on electrochemical signals. The experiment results showed that the TDW-E-biosensor was successfully applied for detecting A. sanguinea at the pre-outbreak stage and demonstrated excellent analytical performance, showing a low limit of detection (LOD) of 0.0676 fM and quantitation (LOQ) of 0.102 fM for the three-electrode system, and a low LOD of 6.873 fg μL^-1 and LOQ of 20.460 fg μL^-1 for the portable system. The accuracy of the TDW-E-biosensor was validated through comparison with droplet digital PCR (ddPCR) and Bland-Altman analysis, demonstrating a high level of agreement (a mean difference of 0.132 and a standard deviation of 0.184). The reliability of the predictive relationship was evidenced by controlled laboratory experiments and Bland-Altman analysis. The developed TDW-E-biosensor provides an innovative and promising tool for early warning efforts regarding harmful algae.

The indicator amino acid oxidation (IAAO) technique estimates the physiological requirements for amino acids and proteins in living organisms, including humans. It involves monitoring urinary amino acids and exhaled CO₂ after ingesting 1-¹³C-labeled (carboxy-labeled) amino acids. The most common IAAO indicator amino acid is 1-¹³C-labeled phenylalanine ([1-¹³C]Phe). Its urinary concentration in test subjects ranges from below the detection limit to several μM. A simple analytical method for distinguishing trace amounts of [1-¹³C]Phe in urine from high levels of naturally occurring Phe is crucial for making IAAO tests easier. This study presents a simple and reliable approach for the simultaneous quantification of [1-¹³C]Phe and Phe in human urine using conventional GC-EI-MS. In this method, urinary phenylalanine is reacted with pentafluorobenzyl bromide in a single-phase solvent system of acetone-borate buffer without dehydration or desalting to form disubstituted pentafluorobenzyl (PFB) derivatives, which are then analyzed by GC-EI-MS (SIM). The Phe and [1-¹³C]Phe PFB derivative peaks eluted at the same retention time on the gas chromatogram but could be differentiated on the basis of fragment ions (m/z 434, 435) derived from the loss of the phenyl group ([M - 91]⁺). Correcting the interference of the m+1 isotope peak of Phe in the [M - 91] fragment (m/z 435) of [1-¹³C]Phe using the m/z 434 peak intensity and natural isotope ratio, both Phe and [1-¹³C]Phe could be quantified in the concentration range found in urine. The method was successfully applied to examine the temporal enrichment of [1-¹³C]Phe in urine samples obtained from IAAO subjects following the ingestion of a test meal containing [1-¹³C]Phe.

A simple and efficient effervescence-assisted salting-out assisted liquid-liquid extraction (EA-SALLE) method was developed for the rapid extraction of pyrethroid insecticides in fruit juices and herbal extracts. By integrating effervescence extraction with SALLE, the extraction and phase separation processes were conducted simultaneously, significantly simplifying the experimental procedure and reducing the extraction time to just 3 min. Key factors influencing the method's efficiency were systematically optimized. Combined with gas chromatography with an electron capture detector, enabled the determination of nine pyrethroid insecticides, demonstrating excellent linearity (R² > 0.99), low limits of detection (0.03-0.17 ng/mL), satisfactory accuracy (recoveries ranging from 83.0 % to 107.9 %), and good precision (RSD < 9.1 %). The proposed EA-SALLE method offers a simple, efficient, and cost-effective sample preparation technique. It is characterized by ease of operation, short extraction time, and high sensitivity, providing an effective tool for the monitoring and assessment of pesticide residues in complex samples.