Facile synthesis of size-controllable gold nanoflowers on carbon nanotube sheets as high-performance flexible SERS sensors

Flexible surface-enhanced Raman spectroscopy (SERS) substrates are assembled by flexible matrices and plasmonic metal nanocrystals. Gold nanoflowers (AuNFs), typically multi-branched nanostructures, show fascinating strong localized surface plasmon resonance (LSPR) properties, but often involve tedious processing strategies. In this work, we report a simple one-pot synthesis approach for AuNF-carbon nanotube (CNT) sheet hybrid composites. By using scanning electron microscopy (SEM)/transmission electron microscopy (TEM)/X-ray diffraction (XRD) characterization, we found that gold nanoflowers consist of a spherical core with highly (111)-oriented plate-like petals, based on which we propose a growth mechanism that branched polyethyleneimine and bromine ions synergistically promote the formation of gold nanoflowers on the CNT support. The SERS platform made of AuNFs-CNT sheets can effectively detect the analyte of Congo Red (CR) at concentrations as low as 10⁻⁸ M with an enhancement factor of 1.1 × 10⁶. Two orders of magnitude of the SERS performance enhancement are attributed to the strong adsorption of molecules by the substrate and the large surface area, spikes and sharp edges of the nanocrystals.