Photoluminescence of CVD-grown MoS₂ modified by pH under aqueous solutions toward potential biological sensing

Transition metal dichalcogenide (TMD) represented by molybdenum disulfide (MoS₂) is a promising platform for versatile applications in biosensing. The semiconducting properties of MoS₂ coupled with its large surface area allows for highly sensitive detection of external environments. Although chemical vapor deposition (CVD) is a promising method for synthesizing large and high quality MoS₂, optical properties of CVD-grown MoS₂ under physiological solution is not clear. Furthermore, understanding of the pH effect on its optical properties is still limited.

Here, we report their photoluminescence (PL) responses to solution pH under aqueous condition by means of PL spectroscopy and imaging. MoS₂ with different Mo sources and additive such as MoS₂, MoO₂ and NaCl were synthesized. It was found that the PL response was highly affected by the Mo sources. While MoS₂ made from MoO₂ showed the highest modulation of PL by solution pH, MoS₂ made from MoS₂ did not show significant response. Furthermore, we demonstrated enhanced pH-sensitivity by UV/O₃ treatments. Spectral analysis on PL and x-ray photoelectron spectroscopy revealed that the PL responses to solution pH were not directly correlated to the defect density (S/Mo ratio) of MoS₂, but likely correlated to its state of defects and initial carrier density. These findings will be a practical guideline to optimize synthesis condition toward developing MoS₂-based optoelectronic biosensing devices. (paper)