Mg-Doped ZnO Nanoparticles with Tunable Band Gaps for Surface-Enhanced Raman Scattering (SERS)-Based Sensing

Abstract

Semiconductors have great potential as surface-enhanced Raman scattering (SERS) substrates due to their excellent physiochemical properties. However, they provide low signal enhancements relative to their plasmonic counterparts, which necessitates innovation in their synthesis and application. Substitutional atomic doping is proposed to improve SERS enhancement by controlling electronic properties, such as the band gap. In this work, zinc oxide (ZnO) nanoparticles were synthesized by co-precipitation and doped with magnesium (Mg) at concentrations ranging from 2–10%. Nanoparticle morphology and size were obtained by scanning electron microscopy (SEM). Elemental composition and chemical states were determined using X-ray photoelectron spectroscopy (XPS). Optical properties were obtained with a UV-vis spectrophotometer, while a Raman spectrometer was used to acquire Raman signal enhancements. Stability was assessed by UV-vis spectroscopy, while cytotoxicity was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results showed that the absorption edge of Mg-doped ZnO nanoparticles was red-shifted compared to pure ZnO nanoparticles. The band gap decreased (3.3–3.01 eV) with increasing Mg doping, while the highest Raman enhancement was observed at 2% doping. No significant cytotoxic effects were observed at low concentrations (3–12 μg/mL). Overall, this study provides evidence for the tunability of ZnO substrates and may serve as a platform for applications in molecular biosensing.

Au-Coated ZnO Surface-Enhanced Raman Scattering (SERS) Substrates: Synthesis, Characterization, and Applications in Exosome Detection

“…The synthesized substrates' UV-visible absorption spectra were obtained to determine their optical properties. As shown in Figure 4, all spectra showed an absorption band at 358 nm, corresponding to ZnO [21]. For the ZnO-Au samples, a broad band was observed at 560 nm, corresponding to Au nanoparticles and thereby indicating that the ZnO-Au substrates are active in both the ultraviolet and visible light region [22].…”

“…[23,24,28]. The high-resolution spectrum of O can be split into two Gaussian peaks, as shown in Figure 3d; the peak centered around 530.62 eV corresponds to O −2 on the wurtzite structure of Zn 2+ , while the peak centered around 532.42 eV can be attributed to oxygen vacancies [21]. Overall, the XPS analysis indicated that Au was associated with ZnO, which could thereby provide the electromagnetic contribution towards the enhancement of Raman signal in subsequent applications.…”

“…ZnO nanoparticles were synthesized using a co-precipitation method described in our previous work [21]. In brief, an equal volume of 0.1 M ZnAce and 0.2 M NaOH was added into a 100 mL round bottom flask.…”

Sparked ZnO nanoparticles-based electrochemical sensor for onsite determination of glyphosate residues

“…To confirm the chemical compositions and valence states of the synthesized ZnO-NPs, x-ray photoelectron spectroscopy (XPS) was used as displayed in figures and the 532 eV peak is related to the adsorbed oxygen (chemisorbed oxygen) at the surface [43][44][45][46][47][48][49][50]. It can be observed the initial O 1s peak has FWHM as 2.94 eV after the fit curve it decreases to 1.43 eV for each peak.…”