Preparation And Performance Of Novel Noble-Metal-Free Surface-Enhanced Raman Scattering Substrates

As a powerful analytical tool,surface-enhanced Raman scattering（SERS）has been widely applied in the fields of life science,chemistry,physics,materials,geology,archaeology and art identification for its high sensitivity,nondestructive detection,and spectroscopic fingerprinting.So far,as the most conventional material for SERS substrates,noble metals show remarkable SERS activity.However,noble-metal SERS substrates carry several inherent shortcomings such as high price,limited material selection,poor stability,complicated“hot spots”regulation,and poor biological compatibility,restricting their further applications.In recent years,noble-metal-free SERS substrates have attracted tremendous attention for their abundant sources,excellent chemical stability,superior biocompatibility and good signal uniformity,which can effectively make up the shortcomings of traditional noble-metal materials and show a great application prospect.At present,in the field of noble-metal-free SERS research,the development of new materials,new technologies,new enhancement strategies and new applications have become research hotspots.Our studies are outlined as followings:An inkjet-printing method to prepare paper-based semiconducting SERS substrates is presented.For the first time,the inkjet-printed paper-based semiconducting SERS substrates are prepared via an inexpensive office inkjet printer with representative two-dimensional Mo O_3-xnanosheets ink.Compared with conventional substrates,these paper-based semiconducting substrates not only could meet the requirements of simple and large-scale preparation,but also realize efficient sample collection by merely swabbing the surface.We obtained the detection limit concentration of rhodamine 6G（R6G）as low as 10^-7M.Furthermore,these flexible paper-based substrates were successfully applied to detect crystal violet（CV）and malachite green（MG）on the fish surface by swabbing.The characteristic peaks of CV and MG could also be observed expressly even when the concentration is down to 10^-6M.A facile and universal approach to fabricate a series of plasmonic metal carbide SERS chips is proposed.This is the first time that tungsten carbide,molybdenum carbide,and niobium carbide are reported as SERS materials with cheap prices.Furthermore,we prove that the high SERS activity of these materials comes from strong localized surface plasmon resonance effects.These metal carbide chips could realize the detection of diverse organic molecules,and the detection limit concentration of R6G was found to be below 10^-8M,which is even lower than some of the noble metal SERS substrates.The high SERS sensitivity,excellent reproducibility and outstanding stability together make metal carbides promising SERS substrates for practical detection.A strategy to improve the SERS performance of metal nitride SERS chips by structural engineering is proposed.A series of planar metal nitride SERS chips are prepared via an ambient temperature sputtering deposition route.Tungsten nitride（WN）and tantalum nitride（Ta N）are used as SERS materials for the first time.These planar metal nitride chips show remarkable Raman enhancement factors（EFs）with 10⁵owing to efficient photoinduced charge transfer process between metal nitride chips and probe molecules.Further,structural engineering of these metal nitride chips is used to improve their SERS activity.Benefiting from the synergistic effect of charge transfer process and electric field enhancement by constructing nanocavity structure,the Raman EF of WN nanocavity chips could be greatly improved to 1.29×10⁷,which is an order of magnitude higher than that of planar chips.Moreover,we also design the WN/monolayer Mo S₂heterostructure chips.With the increase of surface electron density on the upper WN and more exciton resonance transitions in the heterostructure,a 1.94×10⁷level EF and a 5×10^-10M level detention limit could be achieved.Our results provide important guidance for the structural design of ultrasensitive noble-metal-free SERS chips.