Encapsulation of 3D plasmonic nanostructures with ultrathin hydrogel skin for rapid and direct detection of toxic small molecules in complex fluids

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.

Designing Tough Hydrogel Shells for Glucose Sensing

Conventional hydrogel microcapsules often suffer from inadequate mechanical stability, hindering their use. Here, water-cored double-network (DN) hydrogel shells are designed, formed by polyacrylamide and calcium alginate networks using triple-emulsion templates. These DN hydrogel shells offer robust mechanical stability, optical transparency, and a precisely-defined cut-off threshold. The feasibility of this platform is demonstrated through the development of a fluorometric glucose sensor. Glucose oxidase is enclosed within the water core, while a pH-responsive fluorescent dye is incorporated into the DN shells. Glucose diffuses into the core through the DN shells, where the glucose oxidase converts glucose into gluconic acid, leading to pH reduction and a subsequent decrease in fluorescence intensity of DN shells. Additionally, the pH-sensitive colorant dissolved in the medium enables visual pH assessment. Thus, glucose levels can be determined using both fluorometric and colorimetric methods. Notably, the DN shells exhibit exceptional stability, enduring intense mechanical stress and cycles of drying and rehydration without leakage. Moreover, the DN shells act as effective barriers, safeguarding glucose oxidase against proteolysis by large disruptive proteins, like pancreatin. This versatile DN shell platform extends beyond glucose oxidase encapsulation, serving as a foundation for various capsule sensors utilizing enzymes and heterogeneous catalysts.

Detection of pesticide residues on flexible and transparent fluorinated polyimide film based on surface-enhanced Raman spectroscopy technology

BACKGROUND

Excessive pesticide residues will seriously endanger human health. The complexity and lag of the current popular analytical methods hinder the timeliness of food safety analysis. Surface-enhanced Raman scattering (SERS) was an ultra-sensitive vibration spectroscopy technology with the advantages of less time cost, non-destructive and semi-quantitative detection, which has attracted much attention in the rapid field detection of pesticide residue. It was clear that we need an efficient and convenient substrate for pesticide residue detection based on SRES technology, which needs to be portable, flexible, transparent and easy to detect irregular object surfaces.

RESULTS

A novel SERS sensor was designed to detect single and multi-component pesticide residues on irregular fruit and vegetable surfaces by in-situ growth of silver nanoparticles on a flexible and transparent fluorinated polyimide (FPI) substrate. Among them, Ag NPs were synthesized by liquid phase reduction method (AgNO3-PVP and NaBH4). The results showed that the detection limit of 1-4 BDT was down to 10-10 mol L-1, the enhancement factor (EF) was up to 1.57 × 107, and relative standard deviation (RSD) was 7.49 %. By this method, tricyclazole solution at a concentration of 0.01 mg L-1 was still detectable by the FPI@Ag SERS substrate. The linear quantification was achieved in the range from 100 mg L-1 to 0.01 mg L-1. Two mixed pesticides, tricyclazole and imazalil, were also successfully distinguished.

SIGNIFICANCE

This represents the formation of a flexible, foldable and transparent substrate for rapid on-site detection. Results can be obtained in <5 min by attaching the substrate to the substance to be tested. And the SERS substrate prepared with high sensitivity, stability, portable and convenient analysis, which provided new ideas for efficient and rapid household food safety detection.

Hydrogel-Assisted 3D Volumetric Hotspot for Sensitive Detection by Surface-Enhanced Raman Spectroscopy

Effective hotspot engineering with facile and cost-effective fabrication procedures is critical for the practical application of surface-enhanced Raman spectroscopy (SERS). We propose a SERS substrate composed of a metal film over polyimide nanopillars (MFPNs) with three-dimensional (3D) volumetric hotspots for this purpose. The 3D MFPNs were fabricated through a two-step process of maskless plasma etching and hydrogel encapsulation. The probe molecules dispersed in solution were highly concentrated in the 3D hydrogel networks, which provided a further enhancement of the SERS signals. SERS performance parameters such as the SERS enhancement factor, limit-of-detection, and signal reproducibility were investigated with Cyanine5 (Cy5) acid Raman dye solutions and were compared with those of hydrogel-free MFPNs with two-dimensional hotspots. The hydrogel-coated MFPNs enabled the reliable detection of Cy5 acid, even when the Cy5 concentration was as low as 100 pM. We believe that the 3D volumetric hotspots created by introducing a hydrogel layer onto plasmonic nanostructures demonstrate excellent potential for the sensitive and reproducible detection of toxic and hazardous molecules.