On-Chip
Colorimetric Detection of Cu<sup>2+</sup> Ions
via Density-Controlled Plasmonic Core–Satellites Nanoassembly
- Publication date
- Publisher
Abstract
We
report on an on-chip colorimetric method for the detection and
analysis of Cu<sup>2+</sup> ions via the targeted assembly of plasmonic
silver nanoparticles (2.6 nm satellites) on density-controlled plasmonic
gold nanoparticles (50 nm cores) on a glass substrate. Without any
ligand modification of the nanoparticles, by directly using an intrinsic
moiety (carboxylate ion, COO<sup>–</sup>) surrounded with nanoparticles,
the method showed a high selectivity for Cu<sup>2+</sup>, resulting
in a nearly 2 times greater optical response compared to those of
other metal ions via the targeted core–satellites assembly.
By modulating the surface chemistry, it was possible to control the
density of core gold nanoparticles on the surface, thus permitting
easy tuning of the optical responses induced by plasmon coupling generated
between each core–satellites nanostructure. Using chips with
a controlled optimal core density, we observed the remarkable scattering
color changes of the chips from green to yellow and finally to orange
with the increase of Cu<sup>2+</sup> concentration. The detection
limits of the fabricated chips with controlled core densities (ca.
1821 and 3636 particles/100 μm<sup>2</sup>) are 10 nM and 10
pM, respectively, which are quite tunable and below the level of 20
μM (or 1.3 ppm) defined by the United States Environmental Protection
Agency. The findings suggest that the method is a potentially promising
protocol for detecting small molecules with target selectivity and
the tunability of the detection limits by replacing with ligands and
adjusting core densities