Selenium Vacancies and Synergistic Effect of Near- and Far-Field-Enabled Ultrasensitive Surface-Enhanced Raman-Scattering-Active Substrates for Malaria Detection

Abstract

Defect engineering with the active control of defect states brings remarkable enhancement on surface-enhanced Raman scattering (SERS) by magnifying semiconductor–molecule interaction. Such light-trapping architectures can increase the light path length, which promotes photon–analytes interactions and further improves the SERS sensitivity. However, by far the reported semiconductor SERS-active substrates based on these strategies are often nonuniform and commonly in the form of isolated laminates or random clusters, which limit their reliability and stability for practical applications. Herein, we develop self-grown single-crystalline “V-shape” SnSe2‑x (SnSe1.5, SnSe1.75, SnSe2) nanoflake arrays (SnSe2‑x NFAs) with controlled selenium vacancies over large-area (10 cm × 10 cm) for ultrahigh-sensitivity SERS. First-principles density functional theory (DFT) is used to calculate the band gap and the electronic density of states (DOS). Based on the Herzberg–Teller theory regarding the vibronic coupling, the results of theoretical calculation reveal that the downshift of band edge and high DOS of SnSe1.75 can effectively enhance the vibronic coupling within the SnSe1.75–R6G system, which in turn enhances the photoinduced charge transfer resonance and contributes to the SERS activity with a remarkable enhancement factor of 1.68 × 107. Furthermore, we propose and demonstrate ultrasensitive (10–15 M for R6G), uniform, and reliable SERS substrates by forming SnSe1.75 NFAs/Au heterostructures via a facile Au evaporation process. We attribute the superior performance of our SnSe1.75 NFAs/Au heterostructures to the following reasons: (1) selenium vacancies and (2) synergistic effect of the near and far fields. In addition, we successfully build a detection platform to achieve rapid (∼15 min for the whole process), antibody-free, in situ, and reliable early malaria detection (100% detection rate for 10 samples with 160 points) in whole blood, and molecular hemozoin (<100/mL) can be detected. Our approach not only provides an efficient technique to obtain large-area, uniform, and reliable SERS-active substrates but also offers a substantial impact on addressing practical issues in many application scenarios such as the detection of insect-borne infectious diseases.

Metal–Organic-Frameworks-Isolated Au Nanobipyramids as Synergetic Surface-Enhanced-Raman-Scattering Substrates

“…Implied by their names, the origins of these two mechanisms lie in the near electric field and chemical reactions or charge transfer (CT) at the surface of the substrates, respectively. Being the more dominating contributor, EM had attracted almost all attention from scientists and industry insiders until some amazing results were discovered on the prominent enhancement factors (EFs) from CT only and EM + CT synergetic effects based on the significant contribution of CT in some new substrates. − For instance, Zhao et al found out some semiconductor-like zeolitic imidazolate frameworks (ZIFs) exhibited ∼10 6 EFs from CT only, comparable with the result of “hot spots” . Synergetic effects contributed notably from CT have also been witnessed in certain structurally designed metal–semiconductor hybrids like semiconductor nanorods deposited with metal nanoparticles, semiconductor nanoparticles hybridized with nanotubes, metal–semiconductor core–shell SERS substrates, , etc.…”