Enhanced sensing performance of carbaryl pesticide by employing a MnO2/GO/e-Ag-based nanoplatform: role of graphene oxide as an adsorbing agent in the SERS analytical performance.

A functional ternary substrate was developed for surface-enhanced Raman scattering (SERS) sensing systems. MnO2 nanosheets were synthesized by a simple and controllable hydrothermal method, followed by the integration of graphene oxide (GO) nanosheets. Subsequently, MnO2/GO nanostructures were decorated with plasmonic Ag nanoparticles (e-AgNPs). The MnO2/GO/e-Ag substrate could enhance the SERS sensing signal for organic chemicals without the assistance of chemical bonds between those analytes and the semiconductor within the ternary substrate, which have been proven to promote charge transfer and elevate the SERS enhancement in previous studies. Instead, GO nanosheets acted as a carpet also supporting the MnO2 nanosheets and e-AgNPs to form a porous structure, allowing the analytes to be well-adsorbed onto the ternary substrate, which improved the sensing performance of the SERS platform, compared to pure e-AgNPs, MnO2/e-Ag, and GO/e-Ag alone. The GO content in the nanocomposite was also considered to optimize the SERS substrate. With the most optimal GO content of 0.1 wt%, MnO2/GO/e-Ag-based SERS sensors could detect carbaryl, a pesticide, at concentrations as low as 1.11 × 10-8 M in standard solutions and 10-7 M in real tap water and cucumber extract.

Magnetoplasmonic photonic arrays for rapid and selective colorimetric detection of chloride ions in water.

The rapid and efficient detection of chloride (Cl-) ions is crucial in a variety of fields, making the development of advanced sensing methods such as colorimetric sensors an imperative advancement in analytical chemistry. Herein, a novel, selective, and straightforward paper-based colorimetric sensing platform has been developed utilizing an amorphous photonic array (APA) of magnetoplasmonic Ag@Fe3O4 nanoparticles (MagPlas NPs) for the detection of Cl- in water. Taking advantage of the highly responsive APA, the key principle of this sensing method is based on the chemical reaction between Ag+ and Cl-, which results in the precipitation of high-refractive index (RI) AgCl. This assay, distinct from typical plasmonic sensors that rely heavily on nanoparticle aggregation/anti-aggregation, is premised on the precipitation reaction of Ag+ and Cl-. In the presence of Cl-, a rapid, distinctive color alteration from royal purple to a dark sky blue is visually observable within a short time of a few minutes, eliminating the necessity for any surface modification procedures. Comprehensive assessments substantiated that these sensors display commendable sensitivity, selectivity, and stability, thereby establishing their effective applicability for Cl- analysis in various technological fields.

Unveiling the effect of crystallinity and particle size of biogenic Ag/ZnO nanocomposites on the electrochemical sensing performance of carbaryl detection in agricultural products.

In this study, bio-Ag/ZnO NCs were synthesized via a microwave-assisted biogenic electrochemical method using mangosteen (Garcinia mangostana) peel extract as a biogenic reducing agent for the reduction of Zn2+ and Ag+ ions to form hybrid nanoparticles. The as-synthesized NC samples at three different microwave irradiation temperatures (Z 70, Z 80, Z 90) exhibited a remarkable difference in size and crystallinity that directly impacted their electrocatalytic behaviors as well as electrochemical sensing performance. The obtained results indicate that the Z 90 sample showed the highest electrochemical performance among the investigated samples, which is attributed to the improved particle size distribution and crystal microstructure that enhanced charge transfer and the electroactive surface area. Under the optimal conditions for carbaryl pesticide detection, the proposed nanosensor exhibited a high electrochemical sensitivity of up to 0.303 µA µM-1 cm-2 with a detection limit of LOD ∼0.27 µM for carbaryl pesticide detection in a linear range of 0.25-100 µM. Overall, the present work suggests that bio-Ag/ZnO NCs are a potential candidate for the development of a high-performance electrochemical-based non-enzymatic nanosensor with rapid monitoring, cost-effectiveness, and eco-friendly to detect carbaryl pesticide residues in agricultural products.

Elucidating the roles of oxygen functional groups and defect density of electrochemically exfoliated GO on the kinetic parameters towards furazolidone detection.

Using electrochemically exfoliated graphene oxide (GO)-modified screen-printed carbon electrodes for the detection of furazolidone (FZD), a nitrofuran antibiotic, was explored. In this study, we designed some GO samples possessing different oxygen functional group content/defect density by using ultrasonic irradiation or microwave techniques as supporting tools. The difference in physical characteristics of GO led to the remarkable change in kinetic parameters (electron transfer rate constant (k s) and transfer coefficient (α)) of electron transfer reactions at K 3/K 4 probes as well as the FZD analyte. Obtained results reveal that the GO-ultrasonic sample showed the highest electrochemical response toward FZD detection owing to the increase in defect density and number of edges in the GO nanosheets under ultrasonic irradiation. The proposed electrochemical nanosensor enabled the monitoring of FZD in the linear range from 1 µM to 100 µM with an electrochemical sensitivity of 1.03 µA µM-1 cm-2. Tuning suitable electronic structures of GO suggests the potentiality of advanced GO-based electrochemical nanosensor development in food-producing animal safety monitoring applications.

Bio-AgNPs-based electrochemical nanosensors for the sensitive determination of 4-nitrophenol in tomato samples: the roles of natural plant extracts in physicochemical parameters and sensing performance.

The present work reports efficient electrochemical nanosensors for the sensitive monitoring of 4-nitrophenol (4-NP) in tomato samples using various biosynthesized silver nanoparticles (bio-AgNPs). Three different bio-AgNP types were synthesized using natural plant extracts, including green tea (GT) leaf, grapefruit peel (GP), and mangosteen peel (MP), aiming to investigate their effects on the formation of bio-AgNPs, as well as the analytical performance of 4-NP. Based on the obtained results, it was found that the phytochemical content in various plant extracts directly influenced the physicochemical parameters of the created bio-AgNPs, such as particle size, crystallinity, and distribution. More importantly, these parameters have decisive effects on the electrocatalytic activity, conductivity, and electrochemical sensing performance of electrodes modified with them for 4-NP detection. Among the three bio-AgNPs evaluated, the GT-AgNPs (using green tea leaf extract) with uniform shape, small size without aggregation, and high crystallinity showed the best analytical performance for 4-NP determination. The electrode-modified GT-AgNPs exhibited a good 4-NP analytical performance with an electrochemical sensitivity of 1.25 µA µM-1 cm-2 and a detection limit of 0.43 µM in the detection range from 0.5 to 50 µM. The practical applicability of the sensor was also studied in tomato samples, promising satisfactory results toward 4-NP detection in other real samples.

Unexpected cases in field diagnosis of African swine fever virus in Vietnam: The needs consideration when performing molecular diagnostic tests.

Background: The first confirmed case of African swine fever (ASF) in Vietnam was reported officially in February 2019. To date, ASF virus (ASFV) have been detected in 63/63 provinces in Vietnam. Currently, real-time polymerase chain reaction (PCR) is considered to be a powerful tool for viral detection in field samples, including ASFV. However, some recent reports have suggested that mismatches in primer and probe binding regions may directly affect real-time PCR qualification, leading a false-negative result. Aim: This study aims to further examine a conflicting result obtained from two OIE recommended methods, conventional PCR and real-time PCR, for ASFV detection. Methods: Two ASF suspected pigs from different provinces in the north of Vietnam were selected for this study based on clinical signs and postmortem lesions. The different results obtained by OIE-recommended conventional PCR and real-time PCR were further analyzed by the Sanger sequencing method and virus isolation in combination with hemadsorption (HAD) test using porcine alveolar macrophages cells. Results: The results showed that when the primer sequence matched perfectly with the sequences of field isolates, a mutation in probe binding region was found, indicating that a single mismatch in the probe binding site may cause a false-negative result by real-time PCR in detecting ASFV in clinical samples in Vietnam. An agreement between conventional PCR, using PPA1/PPA2 primers and two golden standard methods, virus isolation in combination with HAD assay, and sequencing method was observed in this study. Conclusion: A single mismatch in the probe binding site caused a failse-negative result by realtime PCR method in field diagnosis of ASFV. The needs consideration when selecting the appropriate molecular diagnostic methods is based on the current databases of ASFV sequences, particularly for epidemiological surveillance of ASF.

Genetic Characterisation of African Swine Fever Virus in Outbreaks in Ha Nam Province, Red River Delta Region of Vietnam, and Activity of Antimicrobial Products Against Virus Infection in Contaminated Feed.

INTRODUCTION: African swine fever (ASF) was officially reported in Vietnam in February 2019 and spread across the whole country, affecting all 63 provinces and cities. MATERIAL AND METHODS: In this study, ASF virus (ASFV) VN/Pig/HaNam/2019 (VN/Pig/HN/19) strain was isolated in primary porcine alveolar macrophage (PAM) cells from a sample originating from an outbreak farm in Vietnam's Red River Delta region. The isolate was characterised using the haemadsorption (HAD) test, real-time PCR, and sequencing. The activity of antimicrobial feed products was evaluated via a contaminated ASFV feed assay. RESULTS: Phylogenetic analysis of the viral p72 and EP402R genes placed VN/Pig/HN/19 in genotype II and serogroup 8 and related it closely to Eastern European and Chinese strains. Infectious titres of the virus propagated in primary PAMs were 106 HAD50/ml. Our study reports the activity against ASFV VN/Pig/HN/19 strain of antimicrobial Sal CURB RM E Liquid, F2 Dry and K2 Liquid. Our feed assay findings suggest that the antimicrobial RM E Liquid has a strong effect against ASFV replication. These results suggest that among the Sal CURB products, the antimicrobial RM E Liquid may have the most potential as a mitigant feed additive for ASFV infection. Therefore, further studies on the use of antimicrobial Sal CURB RM E Liquid in vivo are required. CONCLUSIONS: Our study demonstrates the threat of ASFV and emphasises the need to control and eradicate it in Vietnam by multiple measures.