A Nanostructured SERS Switch Based on Molecular Beacon-Controlled Assembly of Gold Nanoparticles

Abstract

In this paper, highly purified and stable gold nanoparticle (AuNP) dimers connected at the two ends of DNA linkage were prepared by a versatile method. A nanostructured, surface-enhanced Raman scattering (SERS) switching sensor system was fabricated based on the controlled organization of gold nanoparticles (AuNPs) by a DNA nanomachine through the controlled formation/deformation of SERS "hotspots". This strategy not only opens opportunities in the precise engineering of gap distances in gold-gold nanostructures in a highly controllable and reproducible fashion, but also provides a unique ability to research the origin of SERS and sequence-specific DNA detection.

Keywords: gold nanoparticles; molecular beacon sensors; self-assembly; surface-enhanced Raman scattering (SERS); switch.

Figure 1

Characterization of discrete DNA-AuNP conjugates: (a) Electrophoretic analysis (2.5% agarose gel) of ssDNA-bridged AuNP dimers formed from molecular beacon sequences with 15 nm AuNPs. Lane 1: Bare AuNP, as a reference; Lane 2: A mixture of AuNP with the two cyclic disulfide–modified DNA strands. (b) Typical transmission electron microscopy (TEM) image of AuNP dimers separated by agarose gel electrophoresis. (c) Typical TEM image of AuNP-DNA separated by agarose gel electrophoresis. (d) Typical TEM image of AuNP dimers produced by the traditional hybridization method with two complementary AuNP-DNA conjugates.

Scheme 1

Schematic representations of surface-enhanced Raman scattering (SERS) switch through the control of the distance between the two AuNPs by sequential addition of fueling/analytes sequences of F1 and F2.

Figure 2

(a) TEM observation of AuNP dimers at “close” states and (b) AuNPs dimers at “open” states; (c) A histogram of the distance of the open form. The average distance was about 18.2 nm, which is coincident with the theoretical value for DNA 60 bases (~20 nm).

Figure 3

(a) SERS spectra of 4-aminothiophenol (ATP) molecules measured on nanostructured switch devices at “colse” (I) and “open” states (II), respectively. The spectra were recorded by using 633 nm laser lines. (b) A plot of the Raman intensity at 1078 cm⁻¹ for 4-ATP molecules as a function of the number of cycles. High and low Raman absorbance maxima values indicate the devices at the “close” and the “open” states, respectively.

Figure 4

(a) Demonstration of the structural changes of the DNA nanomachine after the addition of F1 and F2. (b) Fluorescence spectroscopy after the addition of F1 (black curve) and F2 (red curve). (c) Fluorescence intensity showing the reversible switching of the DNA nanoswitch.