Electrical Tuning of MoO_x/Ag Hybrids and Investigation of their Surface‐Enhanced Raman Scattering Performance

Abstract

Surface‐enhanced Raman scattering (SERS) technology is a cutting‐edge analytical tool for molecule detection. Attractive SERS performance has been achieved on noble metal nanostructures; however these substrates usually suffer from difficulties of direct adjusting of the physical structures to achieve tunable SERS performance. Studies on semiconductor oxides have revealed that attractive SERS performance can be obtained on them, but strategies of engineering material properties for SERS performance improvement still pose a challenge. Here, an electrically programmable SERS substrate is prepared by depositing hydrothermally synthesized MoOx/Ag hybrids within electrodes as the SERS active region. In the experiment, an electrical field is applied on the electrodes to regulate Ag+ ion migration and redeposition in the MoOx solid electrolyte. Through adjusting the leakage current level, the size of the Ag nanoparticles in the MoOx/Ag hybrids is electrically controlled. The SERS performance of the substrate is evaluated using rhodamine 6G as the Raman reporter. The results evidence that Raman enhancement factors of 1.13 × 105, 4.75 × 105, and 1.04 × 106 can be obtained by programming the leakage current level to 10−7, 10−5, and 10−3 A, respectively. A maximum detection limit of 10−8 m is achieved on the 10−3 A substrate.

2D MoO2/N-Doped-Carbon Nanosheets as SERS Tweezers: A Non-Noble Metal Reusable Substrate for Selective Organic Dye Detection

“…A weak peak accompanied this at 1619 cm −1 , which was attributed to the carbon skeleton vibration of CV (Figure 9c). 47 However, for a similar MB concentration (1 × 10 −4 M) concerning CV (1 × 10 −4 M), the characteristic SERS signal of only MB on the MoO 2 /N-doped-carbon nanocomposite was visible (Figure 9c). Additionally, for a binary mixture composed of 5 times lower MB concentration (1 × 10 −4 M) concerning RhB (5 × 10 −4 M) and MG (5 × 10 −4 M), strong SERS signal characteristics of MB were observed on MoO 2 /Ndoped-carbon nanosheets (Figure 9b,d respectively), which further verified the selective sensing ability of MoO 2 /N-dopedcarbon nanosheets toward MB.…”

“…Similarly, for a binary mixture composed of 5 times lower MB concentration (1 × 10 –4 M) concerning CV (5 × 10 –4 M), strong SERS signal characteristics of MB were observed. A weak peak accompanied this at 1619 cm –1 , which was attributed to the carbon skeleton vibration of CV (Figure c) . However, for a similar MB concentration (1 × 10 –4 M) concerning CV (1 × 10 –4 M), the characteristic SERS signal of only MB on the MoO 2 /N-doped-carbon nanocomposite was visible (Figure c).…”

“…20,21 Alternatively, several semiconductor NMs also possess LSPR properties as well as numerous advantages in comparison with noble metals, such as inexpensive, adaptable synthesis methods, biocompatibility, and superior chemical stability, along with SERS consistency and recyclability. 6,12,22−25 Semiconductor NMs, for example, zinc oxide, 26 titanium dioxide, 27 tungsten oxide, 28−30 molybdenum oxide (MoO 2 , 31−43 MoO 3 , 12,44−46 and MoO x -hybrid 47,48 ), and molybdenum disulfide, 14,46,49 have been shown to be SERSactive. However, to the best of our knowledge, very few are reported for selective and recyclable SERS substrates based on semiconductor NMs because of inadequate separation capability and non-selective performance.…”

“…As typical plasmonic nanomaterials (NMs), different coinage metals, such as Au, Ag, and Cu, including Al, are principally used as SERS substrates due to their tunable localized surface plasmon resonance (LSPR) properties from visible to near-infrared wavelength regions via the control on the NM’s size, shape, and composition. ,− Regardless of their proficient LSPR as well as SERS properties, noble metal NMs undergo several drawbacks; for example, poor biocompatibility, scarcity of usage, and high cost, which undeniably limit their practical applications. , Alternatively, several semiconductor NMs also possess LSPR properties as well as numerous advantages in comparison with noble metals, such as inexpensive, adaptable synthesis methods, biocompatibility, and superior chemical stability, along with SERS consistency and recyclability. ,,− Semiconductor NMs, for example, zinc oxide, titanium dioxide, tungsten oxide, − molybdenum oxide (MoO 2 , − MoO 3 , ,− and MoO x -hybrid , ), and molybdenum disulfide, ,, have been shown to be SERS-active. However, to the best of our knowledge, very few are reported for selective and recyclable SERS substrates based on semiconductor NMs because of inadequate separation capability and non-selective performance. , …”

Facile synthesis of noble metal decorated carbon nanostructure for SERS detection

“…Contributed by the synergetic effect of EM and CM, attractive SERS performance on rGO‐Ag/Au, CNT/Ag, MoO x ‐Ag, and TiO 2 ‐Au has been achieved. [ 27–33 ] Nevertheless, the fabrication of hybrids substrate usually requires multiple steps of chemical synthesis and metal deposition, which complicates the preparation process and also increases the time cost. [ 34 ]…”