Plasmonic Ag NPs encapsulated in flexible 2D Ti3C2Tx: An ingenious SERS active platform for ultrastable anticounterfeiting in optical steganography.

Optical anticounterfeiting labels based on surface-enhanced Raman scattering (SERS) with enriched molecular "fingerprint" information is not only related to the enhanced sensitive detection but also strongly dependent on excellent long-time stability of nano-platforms. By virtue of in-situ overgrowth of highly dense and close-packed Ag nanoparticles (NPs) on Ti3C2Tx nanosheets, herein, we prepared an extraordinary SERS active nano-substrates with exceptional long-term stability for achieving ultrastable anticounterfeiting tags. The obtained Ag@Ti3C2Tx exhibit a significantly SERS activity with a detection limit of methylene blue (MB) molecules as low at 10-16 M, approaching 0.1 femtomole (fM) ultra-trace level. More importantly, since nearly all active Ag NPs were completely encapsulated in the 2D supports, the unparalleled stability of the resultant Ag@Ti3C2Tx can be undoubtedly verified by immersing them into H2O2 oxidative solution, which is obviously better than that of bare Ag NPs. Then, the hybrid Ag@Ti3C2Tx were subsequently incorporated into polydimethylsiloxane (PDMS) to obtain transparent flexible Ag@Ti3C2Tx@PDMS, giving rise to the ultra-sensitive SERS imaging-based steganographic information. Interestingly, the ultrastable anticounterfeiting capability of the smart SERS nano-platforms is further highlighted by keeping them even after for 400 days storage. The present work holds a great potential for propelling robust SERS-based steganography in many practical real-world scenarios.