Remarkable surface-enhanced Raman scattering of highly crystalline monolayer Ti3C2 nanosheets

As a powerful non-destructive and label-free detection technology, surface-enhanced Raman scattering (SERS) has been widely used in environmental-pollutant detection, biological-tissue sensing, molecular fingerprint analysis and so on. Different from the traditional SERS substrates represented by noble metals and semiconductors, herein, we report a new highly sensitive SERS substrate material with high stability, biocompatibility, and low cost, namely nucleusfree two-dimensional electron gas (2DEG) Ti3C2 monolayer nanosheets. The highly crystalline monolayer Ti3C2 nanosheets with clean surface are synthesized by an improved chemical exfoliation and microwave heating method. The unique structure of nucleus-free-2DEG in Ti3C2 monolayer provides an ideal transport channel without nuclear scattering, which makes the highly crystalline monolayer Ti3C2 nanosheets achieve a Raman enhanced factor of 3.82x10(8) and a 10(-11) level detection limit for typical environmental pollutants such as azo dyes, trichlorophenol, and bisphenol A. Single-molecule imaging is also realized on the surface of the Ti3C2 monolayers, which may be the first time that approximate single-molecule imaging has been achieved on a non-noblemetal SERS substrates. Preliminary toxicological experiments show that the cytotoxicity of this material is very low. Considering the facile synthesis, high biocompatibility, low cost and high chemical stability of carbide nanosheets, these Ti3C2 monolayer nanosheets show significant promise for the design and fabrication of flexible SERS substrates for the sensing of trace substances with ultrahigh sensitivity.