Paper/GO/e-Au flexible SERS sensors for in situ detection of tricyclazole in orange juice and on cucumber skin at the sub-ppb level: machine learning-assisted data analysis.

Despite being an excellent surface enhanced Raman scattering (SERS) active material, gold nanoparticles were difficult to be loaded onto the surface of filter paper to fabricate flexible SERS substrates. In this study, electrochemically synthesized gold nanoparticles (e-AuNPs) were deposited on graphene oxide (GO) nanosheets in solution by ultrasonication, resulting in the formation of a GO/Au hybrid material. Thanks to the support of GO, the hybrid material could adhere onto the surface of filter paper, which was immersed into a GO/Au solution for 24 h and dried naturally at room temperature. The paper-based materials were then employed as substrates for a surface enhanced Raman scattering (SERS) sensing platform to detect tricyclazole (TCZ), a widely used pesticide, resulting in better sensitivity compared to the use of paper/Au SERS sensors. With the most optimal GO content of 4%, paper/GO/Au SERS sensors could achieve a limit of detection of 1.32 × 10-10 M in standard solutions. Furthermore, the filter paper-based SERS sensors also exhibited significant advantages in sample collection in real samples. On one hand, the sensors were dipped into orange juice, allowing TCZ molecules in this real sample to be adsorbed onto their SERS active surface. On the other hand, they were pasted onto cucumber skin to collect the analytes. As a result, the paper/GO/Au SERS sensors could sense TCZ in orange juice and on cucumber skin at concentrations as low as 10-9 M (∼2 ppb). In addition, a machine learning model was designed and developed, allowing the sensing system to discriminate TCZ from nine other organic compounds and predict the presence of TCZ on cucumber skin at concentrations down to 10-9 M.

Surface ligand modified silver nanoparticles-based SERS sensing platform for ultrasensitive detection of the pesticide thiram in green tea leaves: roles of coating agents in sensing performance.

Silver nanoparticles (AgNPs) have been regarded as a highly promising substrate for surface-enhanced Raman scattering (SERS) sensors. In this study, we focused on the electrochemical synthesis method by developing three kinds of AgNPs using three different electrolytes: citrate (e-Ag-C), oleic acid (e-Ag-O) and fish mint (Houttuynia cordata Thunb.) extract (e-Ag-bio). The as-prepared AgNPs were characterized and then employed as SERS substrates to detect the pesticide thiram. The obtained results show that e-Ag-O exhibits the best SERS performance. The effect of the coating agent was explained by chemical and electromagnetic enhancements (CM and EM). Although thiram could absorb onto e-Ag-C at the highest level, allowing its Raman signal to be best enhanced via the CM, the smallest interparticle distance of e-Ag-O could have resulted in the largest improvement in the EM. Using e-Ag-O to develop SERS-based sensors for thiram, we obtain the impressive detection limit of 1.04 × 10-10 M in standard samples and 10-9 M in tea leaves. The linear ranges are from 10-4 M to 10-7 M and from 10-7 M to 10-9 M, covering the maximum residue levels for plant commodities established by the United States Environment Protection Agency and European Food Safety Authority (2-13 ppm ∼7.7 × 10-6 M to 5 × 10-5 M).

Ultrasensitive detection of crystal violet using a molybdenum sulfide-silver nanostructure-based sensing platform: roles of the adsorbing semiconductor in SERS signal enhancement.

Crystal violet (CV) is an organic dye that is stabilized by the extensive resonance delocalization of electrons over three electron-donating amine groups. This prevents the molecule from being linked to a metal surface, and therefore, reduces the sensitivity of surface-enhanced Raman scattering (SERS) sensors for this toxic dye. In this work, we improved the sensing performance of a silver-based SERS sensor for CV detection by modifying the active substrate. Molybdenum sulfide (MoS2) nanosheets were employed as a scaffold for anchoring electrochemically synthesized silver nanoparticles (e-AgNPs) through a single step of ultrasonication, leading to the formation of MoS2/Ag nanocomposites. As an excellent adsorbent, MoS2 promoted the adsorption of CV onto the surface of the substrate, allowing more CV molecules to be able to experience the SERS effect originating from the e-AgNPs. Hence, the SERS signal of CV was significantly enhanced. In addition, the effects of the MoS2 content of the nanocomposites on their SERS performance were also taken into account. Using MoS2/Ag with the most optimal MoS2 content of 10%, the SERS sensor exhibited the best enhancement of the SERS signal of CV with an impressive detection limit of 1.17 × 10-11 M in standard water and 10-9 M in tap water thanks to an enhancement factor of 2.9 × 106, which was 11.2 times higher than that using pure e-AgNPs.

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.

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.