Phase- and Morphology-Controlled Synthesis of Tunable Plasmonic MoO_3–x Nanomaterials for Ultrasensitive Surface-Enhanced Raman Spectroscopy Detection

Abstract

The enhancement of the surface-enhanced Raman scattering (SERS) property of the plasmonic metal oxide semiconductor nanostructures by controlling their phase, shape, size, and oxygen vacancy to detect trace amounts of organics is of significant interest. In this study, a simple surfactant-free hydrothermal strategy was proposed to fabricate crystalline h-MoO3–x and α-MoO3–x nanomaterials with tunable plasmonic properties. Herein, the crystal phase, morphology, and oxygen vacancy of MoO3–x nanostructures were precisely controlled under suitable synthetic conditions. The plasmonic properties of the as-synthesized h-MoO3–x and α-MoO3–x micro-/nanostructures were controlled by adjusting the residual volume in the autoclaving chamber. In addition, the plasmonic MoO3–x exhibited SERS activity with a detection limit as low as 1.0 × 10–9 M and the maximum enhancement factor (EF) up to 6.99 × 105 for h-MoO3–x , while for α-MoO3–x , the detection limit was 1.0 × 10–7 M with the corresponding EF up to 8.51 × 103, comparable with plasmonic noble metal nanomaterials without a “hot spot”.

Defect engineering in semiconductor-based SERS

“…Additional to biosensing, therapeutic functions have also been achieved. Particularly, NIR-responsive semiconductors are extensively used in photothermal treatment (PTT) of cancerous cells, including hydrous RuO2, WS2, copper chalcogenides and Mobased materials 72,[118][119][120][121][122] . Photo-tuned MoO2 quantum dots with varied optical response in the NIR region are a good example of dual-functional SERS substrates 122 , with SERS activity towards bioactive molecules phenylalanine and amphotericin, while also showing good PTT performance towards cancer cell HEP G2.…”

“…The monoclinic phase VO 2 (B) which consists of a layered structure was found to exhibit the highest SERS activity due to a higher tendency to accommodate oxygen vacancies. Patil et al 72 developed a series of one-step hydrothermal procedures that produced MoO 3 crystals of different crystal phases, which simultaneously demonstrated the inherent optical response and SERS activity of defective h-MoO 3 and α-MoO 3 .…”

Tunable oxygen deficient in MoO 3 ‐x / MoO 2 heterostructure for enhanced lithium storage properties

“…38 Other two peaks appear when pH = 5 attribute to Mo 5+ (near 231.4 and 234.4 eV), confirming the reduction of ethanol in acid environment. 39 The content of Mo 5+ further increases and even completely transfers to Mo 5+ when pH value comes to 3, as shown in Figure 4D. It is noteworthy that there is still only Mo 5+ when pH = 2 but a little different on the content.…”

Universal and simple MoO3 substrate for identification of SERS enhancement mechanism

“…Furthermore, it can be seen from Figure 4d that the Raman displacements at 1180, 1361 and 1617 cm À1 represent the S O symmetric and asymmetric tensile vibrations and the C N tensile vibrations in MB. [30] The manifestation of this Raman signal of common dye molecules such as R6G, RB and MB on MoO 3 substrate is on resonance Raman enhancement while exhibiting excellent universality.…”