Au@pNIPAM Colloids as Molecular Traps for Surface-Enhanced, Spectroscopic, Ultra-Sensitive Analysis

Departamento de Química-Física and Unidad Asociada CSIC-Universidade de Vigo, 36310 Vigo, Spain.
Angewandte Chemie International Edition (Impact Factor: 11.26). 01/2009; 48(1):138-43. DOI: 10.1002/anie.200804059
Source: PubMed


Caught in a trap: Colloids of gold nanoparticles coated with a thermally responsive poly‐(N‐isopropylacrylamide) (pNIPAM) microgel can trap molecules in different ways as a function of temperature (see scheme). The porous pNIPAM shells prevent electromagnetic coupling between metal particles, thus providing highly reproducible surface‐enhanced Raman scattering (SERS) signals and intensity.

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    • "Another approach is the physical immobilization of analytes with weak binding affinity onto the surface of the SERS-substrates or within the hot spots of SERS substrates. For example, thermally responsive microgel particles have been coated on Au nanoparticles as molecule traps to drive a non-adsorbable analyte (1-naphthol) towards the Au cores for SERS detection [25] [26], and Ag nanoparticles have been assembled into a multilayered polymer matrix that can immobilize a different analyte with weak binding affinity (dioxin) within the hot spots [27] [28]. Obviously in these approaches , the randomly shaped Au/Ag nanoparticles employed are not optimized for plasmonic enhancement , and the microgel particles completely " isolate " the individual Au nanoparticles, inhibiting the plasmonic interactions between adjacent nanoparticles. "
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    • "In comparison with the R h e[glucose] plots (Fig. 3B), the (I 0 ÀI)/I 0 reveals nearly the same trend towards the change of glucose concentration (Fig. 4B), clearly correlating the glucoseinduced volume change of the microgels to the SPR response of the immobilized Ag NPs. One reason for this SPR response of Ag NP immobilized in the hybrid microgels is associated with the variation of the Rayleigh scattering through the local refractive index change of the surrounding medium of the Ag NPs, induced from the volume phase transition of the gel network [35] [36]. However, this cannot explain the emergence and gradual increase of the long- Fig. 4. (A) Glucose-induced evolution of UVeVis absorption spectra of the imprinted hybrid microgels IHM-1 in PBS of pH ¼ 7.38 and 22 C. Inset is a photograph showing the color of the sample at [glucose] ¼ 0 mM (left) and 20.0 mM (right), respectively. "
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    • "Mostly optical signals are used as read-out because of their ease of detection. However, more sophisticated and sensitive nanosensors which make use of shift in the plasmon peak of gold nanoparticles upon the close presence of analytes have also been described (Alvarez-Puebla et al., 2009; Rodriguez-Lorenzo et al., 2011; Perez-Pineiro et al., 2012). "
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