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.

A manganese dioxide-silver nanostructure-based SERS nanoplatform for ultrasensitive tricyclazole detection in rice samples: effects of semiconductor morphology on charge transfer efficiency and SERS analytical performance.

Taking advantage of metal-semiconductor junctions, functional nanocomposites have been designed and developed as active substrates for surface-enhanced Raman scattering (SERS) sensing systems. In this work, we prepared three types of nanocomposites based on manganese oxide (MnO2) nanostructures and electrochemically synthesized silver nanoparticles (e-AgNPs), which differed according to the morphologies of MnO2. The SERS performance of MnO2 nanosheet/e-Ag (MnO2-s/e-Ag), MnO2 nanorod/e-Ag (MnO2-r/e-Ag), and MnO2 nanowire/e-Ag (MnO2-w/e-Ag) was then evaluated using tricyclazole (TCZ), a commonly used pesticide, as an analyte. Compared to the others, MnO2-s/e-Ag exhibited the most remarkable SERS enhancement. Thanks to its large surface area and ability to accept/donate the electrons of the semiconductor, MnO2-s acted as a bridge to improve the charge transfer efficiency from e-Ag to TCZ. In addition, the MnO2 content of the nanocomposites was also considered to optimize the SERS sensing performance. With the optimal MnO2 content of 25 wt%, MnO2-s/e-Ag could achieve the best SERS performance, allowing the detection of TCZ at concentrations down to 6 × 10-12 M in standard solutions and 10-11 M in real rice samples.

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.