To achieve ultrasensitive detection of trace targets through solution-based surface-enhanced Raman spectroscopy (SERS), direct adsorption of the target molecules on a SERS-active surface is vital. In this work, cetyltrimethylammonium bromide (CTAB)-capped gold nano-bipyramids (Au BPs) with different aspect ratios (ARs) are prepared and the surface is successfully modified by a simple ligand exchange method. Cysteamine-capped gold nanobipyramids (cyst-Au BPs) are obtained by means of replacement of CTAB by cysteamine using Au−S covalent bonding and applied in the solution-based SERS detection of different pigment molecules, which always have weak affinity to the gold surface. The hydrogen bonding between the pigment molecule and cysteamine causes the aggregation of Au BPs to generate local electromagnetic field enhancement. The influence of the AR and concentration of Au BPs on SERS properties is investigated. The SERS detection of weak-affinity molecules to an extremely low limit shows that the cyst-Au BPs are highly sensitive compared to CTAB-capped Au BPs. The limit of detection (LOD) of allura red as low as 0.1 ppb and that of sunset yellow as low as 1 ppb show that the proposed strategy has many advantages due to its simplicity and fast and rapid detection for the sensitivity analysis of weak-affinity molecules.

In this study, we demonstrated a flexible transparent three-dimensional (3D) ordered micro-hemisphere (MHS) array PDMS film with self-assembled Au nanoparticles (NPs) (an Au NP-MHS array film) as a surface-enhanced Raman scattering (SERS) platform for the in situ detection of pesticides in food.

The well-defined silver dendritic nanostructure with a precisely tailored trunk and branches, as well as decorated nanoparticles.

In solution-based surface-enhanced Raman spectroscopy (SERS) detection, plasmonic metal nanoparticles’ controllable assembly and aggregation into highly enhanced electromagnetic coupling nanostructures remains a challenge. In this study, we demonstrate a facile and rapid strategy to control the assembly of poly­(styrene sulfonate) functionalized gold nano-bipyramids (PSS-Au BPs) as highly sensitive SERS substrates for solution-based SERS detection. The assembly process of the PSS-Au BPs was controlled by adding halide ions as aggregation agents under various concentrations in the presence of analytic molecules. In comparison, the citrate-capped spherical gold nanoparticles (Cit-Au NPs) were used to investigate the influence of the shape of NPs and their assembly state on SERS performance. Both in situ ultraviolet–visible (UV–vis) and Raman spectroscopy characterizations revealed that the shape of the NPs and aggregation state are critical to achieving a highly enhanced SERS property. The PSS-Au BPs, owing to the formation of tip-to-tip dimers, have a better electromagnetic enhancement capacity than Cit-Au NP aggregation states. Thus, the PSS-Au BPs display an improved lowest recorded concentration downs to the level of 5 × 10–11 M for crystal violet (CV) molecules, which is 2 or 3 orders of magnitude lower than those of the Cit-Au NPs.

No abstract