Plasmon-Enhanced Four-Wave Mixing Imaging for Microdroplet-Based Single-Cell Analysis

A robust SERS calibration using a pseudo-internal intensity reference

Surface-enhanced Raman scattering (SERS) with high molecular sensitivity and specificity is a powerful nondestructive analytical tool. Since its discovery, SERS measurements have suffered from the vulnerability of calibration curve, which makes quantification analysis a great challenge. In this work, we report a robust calibration method by introducing a referenced measurement as the intensity standard. This intensity reference not only has the advantages of the internal standard method such as reflecting the SERS substrate enhancement, but also avoids the introduction of competing adsorption between target molecules and the internal standard. Based on the normalized calibration curve, the magnitude of the R6G concentration can be well evaluated from 10^-7 M to 10^-12 M. Furthermore, we demonstrate that this pseudo-internal standard method can also work well using a different type of molecule as the reference. This SERS calibration method would be beneficial for the development of quantitative SERS analysis.

A SERS/fluorescence dual-mode immuno-nanoprobe for investigating two anti-diabetic drugs on EGFR expressions

A surface-enhanced Raman scattering (SERS)/fluorescence dual-mode nanoprobe was proposed to assess anti-diabetic drug actions from the expression level of the epidermal growth factor receptor (EGFR), which is a significant biomarker of breast cancers. The nanoprobe has a raspberry shape, prepared by coating a dye-doped silica nanosphere with a mass of SERS tags, which gives high gains in fluorescence imaging and SERS measurement. The in situ detection of EGFR on the cell membrane surfaces after drug actions was achieved by using this nanoprobe, and the detection results agree with the enzyme-linked immunosorbent assay (ELISA) kit. Our study suggests that rosiglitazone hydrochloride (RH) may be a potential drug for diabetic patients with breast cancer, while the anti-cancer effect of metformin hydrochloride (MH) is debatable since MH slightly promotes the EGFR expression of MCF-7 cells in this study. This sensing platform endows more feasibility for highly sensitive and accurate feedback of pesticide effects at the membrane protein level.

In Situ Monitoring of Hydrogen Peroxide Released from Living Cells Using a ZIF-8-Based Surface-Enhanced Raman Scattering Sensor

Hydrogen peroxide (H₂O₂) widely involves in intracellular and intercellular redox signaling pathways, playing a vital role in regulating various physiological events. Nevertheless, current analytical methods for the H₂O₂ assay are often hindered by relatively long response time, low sensitivity, or self-interference. Herein, a zeolitic imidazolate framework-8 (ZIF-8)-based surface-enhanced Raman scattering (SERS) sensor has been developed to detect H₂O₂ released from living cells by depositing ZIF-8 over SERS active gold nanoparticles (AuNPs) grafted with H₂O₂-responsive probe molecules, 2-mercaptohydroquinone. Combining the superior fingerprint identification of SERS and the highly efficient enrichment and selective response of H₂O₂ by ZIF, the ZIF-8-based SERS sensor exhibits a high anti-interference ability for H₂O₂ detection, with a limit of detection as low as 0.357 nM. Satisfyingly, owing to the enhanced catalytic activity derived from the successful integration of AuNPs and ZIF, the response time as short as 1 min can be obtained, demonstrating the effectiveness of the SERS sensor for rapid H₂O₂ detection. Furthermore, the developed SERS sensor enables real-time detection of H₂O₂ secreted from living cells under phorbol myristate acetate stimulation, as cells can be cultured on-chip. This study will pave the way toward the development of a metal-organic framework-based SERS platform for application in the fields of biosensing and early disease diagnosis associated with H₂O₂ secretion, thus exhibiting promising potential for future therapies.