Gold nanostar as an ultrasensitive colorimetric probe for picomolar detection of lead ion.

The sensitivity for analytes of interest is vital for environment protection and food safety. Here, we propose an extremely sensitive assay toward Pb by using gold nanostars (GNSs) as probes based on the catalytic activity of Pb on etching gold atoms after being reduced in the presence of 2-mercaptoethanol (2-ME) and sodium thiosulfate. GNSs were prepared by using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid as both the reducing and capping agents, enabling high stability and sensitivity for quantitation of Pb.

A convenient and sensitive colorimetric iodide assay based on directly inducing morphological transformation of gold nanostars.

We propose a convenient and easy colorimetric assay for highly sensitive detection of iodide by using gold nanostars (GNSs) as probes. The assay relies on that iodide directly changes the morphology of GNSs and alters their longitudinal localized surface plasmon resonance (LSPR) without surface modifications and the use of other reagents. Upon increasing iodide concentration, GNSs gradually transformed to sphere gold nanoparticles, the absorbance at longitudinal LSPR decreased, and solution color varied from greenish blue to red, as confirmed by the UV-Vis absorption spectroscopy and transmission electron microscopy.

Precisely tuning the longitudinal localized surface plasmon resonance of gold nanorods additive-regulated overgrowth.

Gold nanorods (GNRs) with desired longitudinal localized surface plasmon resonance (LLSPR) and strong scattering intensity are important for extending their practical applications in bioimaging and sensing. Herein, a simple additive (HCl and NaS)-regulated overgrowth approach has been proposed for preparing GNRs with tunable LLSPR. In this approach, HCl is used to slow down the growth reaction rate by changing chemical equilibrium, while NaS is utilized to halt the reaction when LLSPR is reaching the expected wavelength under monitoring by a UV-Vis spectrometer.