3D-functionalized shell isolated Ag nanocubes on a miniaturized flexible platform for sensitive and selective SERS detection of small molecules

Functionalization of a plasmonic substrate circumvents inadequate analyte localization within the sensing volume, which often threatens the sensitivity of a SERS method. Often nanoplasmonic substrates are functionalized by direct attachment to the host molecule, which affects their SERS activity. Herein, we report 3D-aminofunctionalized Ag@SiO2 nanocubes with ultra-thin silica shell for the detection of small molecules in a flexible platform. The amino groups are introduced by silanizing the ultra-thin silica layer using different aminoslanes which improves sensitivity without sacrificing the colloidal and chemical stability of the core Ag nanocubes. Ag-SHINs functionalized with shorter chain length aminosilanes shows better SERS activity. The amino-functionalization effects a 3-fold SERS signal enhancement enabling label-free aspartame detection down to 71 mu g mL(-1) which is 1.5 times lower LOD than the non-functionalized Ag-SHINs. Analysis of spiked soft drink, as well as a mixture of aspartame and glucose, shows a robust performance signaling the selectivity and sensitivity of the substrate. The improved SERS performance is attributed to the hydrogen bonding induced localization of the analyte within the sensing volume. Added to this, the miniaturized paper platform with its 3D fibrous structure enhances the hotspot density and sample collection efficiency. This substrate can also be extended to other small molecules with the carboxylic group and amino acids as well, replacing the complicated bio-labeled detection schemes.