Mn Oxide-Silver Composite Nanowires for Improved Thermal Stability, SERS and Electrical Conductivity

Hybridizing Carbon-Based Dot-Capped Manganese Dioxide Nanosheets and Gold Nanoparticles as a Highly Sensitive Surface-Enhanced Raman Scattering Substrate

Surface-enhanced Raman Scattering (SERS) is a sensitive and nondestructive technique that provides fingerprint structural information of molecules. Designing and constructing sensitive and stable SERS substrates is of great significance for the application of the technique. In this study, single-layer carbon-based dots (CDs) are used as capping agents to synthesize gold nanoparticles (AuNPs/CDs) and manganese dioxide nanosheets (MnO₂/CDs), which are then hybridized through a simple cocentrifugation method. After the hybridization, the monodispersive AuNPs/CDs aggregate obviously into some clusters exhibiting strong SERS activity due to the electromagnetic "hot spots" effect, and the MnO₂/CDs also show outstanding SERS activity due to the charge-transfer resonance effect. The obtained nanohybrids (MnO₂/CDs/AuNPs) with robust chemical stability combine well with the electromagnetic enhancement of AuNPs/CDs and chemical enhancement of MnO₂/CDs, leading to an ultrahigh enhancement factor of 3.9 × 10⁸. Based on the novel SERS substrate, a sensitive and rapid sensing system for the detection of malachite green is developed, with a low detection limit of 1 × 10^-9 M. This work provides a valuable model for designing and fabricating high-performance SERS substrates.

"RaMassays": Synergistic Enhancement of Plasmon-Free Raman Scattering and Mass Spectrometry for Multimodal Analysis of Small Molecules

SiO₂/TiO₂ core/shell (T-rex) beads were exploited as "all-in-one" building-block materials to create analytical assays that combine plasmon-free surface enhanced Raman scattering (SERS) and surface assisted laser desorption/ionization (SALDI) mass spectrometry (RaMassays). Such a multi-modal approach relies on the unique optical properties of T-rex beads, which are able to harvest and manage light in both UV and Vis range, making ionization and Raman scattering more efficient. RaMassays were successfully applied to the detection of small (molecular weight, M.W. <400 Da) molecules with a key relevance in biochemistry and pharmaceutical analysis. Caffeine and cocaine were utilized as molecular probes to test the combined SERS/SALDI response of RaMassays, showing excellent sensitivity and reproducibility. The differentiation between amphetamine/ephedrine and theophylline/theobromine couples demonstrated the synergistic reciprocal reinforcement of SERS and SALDI. Finally, the conversion of L-tyrosine in L-DOPA was utilized to probe RaMassays as analytical tools for characterizing reaction intermediates without introducing any spurious effects. RaMassays exhibit important advantages over plasmonic nanoparticles in terms of reproducibility, absence of interference and potential integration in multiplexed devices.