According to recent research, amphiphilic surfactants
can stabilize
metal nanoparticles because of their excellent dispersibility. Therefore,
herein, amphiphilic polyethylenimine (PEI) dendritic polymer nanocapsules
were synthesized by using PEI and poly(urea/malonamide) dendrons of
different generations. Then, silver nanoparticles (AgNPs) were immobilized
on PEI dendritic polymer nanocapsules for surface-enhanced Raman scattering
(SERS) detection. Well-designed amphiphilic PEI dendrons possessed
abundant nucleation sites for AgNP reduction, which could directly
reduce silver ions to AgNPs without additional reducing agents at
room temperature, showing the stronger reducing capability than pristine
PEI. The size and interparticle gap of AgNPs were manipulated by varying
the size of the PEI dendritic polymer and the ratio of PEI dendritic
nanocapsules/AgNO3. As a result, the Ag-PEI-dendritic polymer
was able to perform Raman enhancing capability. Especially, a sample,
namely, Ag-PEI-G0.5, exhibited the strongest Raman enhancement effect,
due to the optimal size and interparticle gap of AgNPs. The Ag-PEI
dendritic SERS nanocapsules could rapidly and reproducibly detect
many kinds of biomolecules (adenine, methylene blue, and beta-carotene)
with a linear calibration curve. The limit of detection (LOD) of adenine
was lower than 10–7 M. Therefore, this facile method
to in situ prepare Ag-PEI dendritic SERS nanocapsules (reducing agent
free) possesses high potential to be applied in rapid SERS detection
for the quantitative analysis of biomolecules.