Stabilizing photo-induced vacancy defects in MOF matrix for high-performance SERS detection

Photo-induced vacancy defects are employed strategically to imbue semiconductors with enhanced performance characteristics for many important applications such as surface-enhanced Raman scattering (SERS) sensing, photocatalysis, and photovoltaic applications. However, the long-term maintenance and use of photo-induced vacancy defects remain elusive, because of their rapid self-healing upon air exposure. In this study, we demonstrate that photo-induced oxygen vacancy (PIVO) defects can be stabilized by the photoexcitation of metal-organic framework (MOF) materials, which is crucial for SERS analysis. The PIVO defects in MOF materials are stable for at least two weeks in the ambient atmosphere, owing to the combination of steric hindrance and electron delocalization around vacancy defects, which significantly contrasts the short lifetime (within minutes) of PIVO defects in metal-oxide semiconductors. With the formation of stable PIVO defects, a prominent SERS enhancement surpassing that of pristine MOFs is achieved, accompanied with a reduced limit of detection by three orders of magnitude. Moreover, the additional SERS enhancement rendered by PIVO defects can be stably retained and is effective for monitoring various small molecules, such as dopamine and bisphenol A.