Metal-Enhanced Fluorescence-Based Core–Shell Ag@SiO₂ Nanoflares for Affinity Biosensing via Target-Induced Structure Switching of Aptamer

Abstract

One of the great challenges in metal-enhanced fluorescence (MEF) technology is the achievement of distance modulation with nanometer accuracy between the fluorophore and metal surface to obtain maximum enhancement. We propose an MEF-based core-shell Ag@SiO2 nanoflare for distance control via the thickness of silica shell with cooperation of DNA hybridization. The nanoflare contains a 50 nm spherical silver nanoparticle (Ag NP) core, a 8 nm silica shell, and cyanine (Cy5)-labeled aptamer hybridized with a complementary DNA (cDNA) immobilized onto the shell surface. The formation of the Cy5-labeled aptamer/cDNA duplex on the Ag@SiO2 NP surface results in the confinement of Cy5 to the shell surface and an increase in the fluorescence of Cy5 with a 32-fold enhancement factor in bulk solution (signal-on). In the presence of affinity-binding targets, the Cy5-labeled aptamers confined onto the Ag@SiO2 NP surface dissociate from their cDNA into the solution because of structure switching. The target-induced release of aptamer leads to a reduction in the enhanced fluorescence signal of the labeled Cy5 moiety (signal-off). Thus, the nanoflare can be used as a sensor for target recognition. Using adenosine-5'-triphosphate (ATP) aptamer, detection of ATP has a linear response from 0 to 0.5 mM and a detection limit of 8 μM. With various types of DNA probes immobilized onto the core-shell Ag@SiO2 NPs, the MEF-based nanoflare has provided an effective platform for the detection and quantification of a broad range of analytes, such as mRNA regulation and detection, cell sorting, and gene profiling.

A fluorescent aptasensor for H5N1 influenza virus detection based-on the core–shell nanoparticles metal-enhanced fluorescence (MEF)

“…1a, the Ag NPs showed an average diameter at 55 ± 3 nm (standard deviation comes from ten independent Ag@NPs measurements) thus the Ag NPs can be expected to indicate highly enhanced fluorescence compared with which reported in the previous researchment (Lu et al, 2014). Fig.1b showed the Ag NPs were coated with silica shell and the silica shell thickness was about 30 ± 1 nm (standard deviation comes from ten independent Ag@SiO 2 NPs measurements) and the silica shell thickness can be adjusted by changing the amount of reagents mentioned in the Ag@SiO 2 NPs preparation section.…”

“…Ag nanoparticles with diameter about 50 nm were synthesized in large scale via a modified method reported by Lu et al (Lu et al, 2014); Ag@SiO 2 NPs were synthesized also according to the literature. Briefly, AgNPs colloid solution was mixed with NH 3 •H 2 O (30%) and TEOS (20%) solution to react for 30 min at room temperature and aged at 4 °C overnight.…”

“…The silica-coated Ag NP suspension was washed three times with a water and ethanol mixture (5:4) and centrifuged at 6000 rpm for 20 min and resuspended in water, and the thickness of the silica shell was determined by TEM. Immobilization of aptamer onto Ag@SiO 2 NPs was performed according to the literature (Lu et al, 2014). The prepared Ag@SiO 2 NPs were mixed with 500 μL of 3-APTS and 1 mL 2,4,6-trichloro-1,3,5-triazine solution (0.2 M) to react for 2 h at room temperature.…”

Recent applications of the combination of mesoporous silica nanoparticles with nucleic acids: development of bioresponsive devices, carriers and sensors

“…This modification allowed a substantial reduction (from 11 to 1) of the overall amount of fluorophore. 191 Moreover, the substitution of the employed SiO 2 NPs by Ag@SiO 2 nanoparticles, enhanced the Cy5 fluorescence while maintaining sensitivity, thus improving neat efficiency.…”

Dual‐Cargo Selectively Controlled Release Based on a pH‐Responsive Mesoporous Silica System

“…[1][2][3][4][5][6][7][8][9][10] MSNs have many unique features, such as homogeneous mesopores, tunable pore size, large surface area, good biocompatibility, and an easily functionalized surface, which has made MSNs one of the most promising drug-delivery vehicles. [11][12][13][14][15] Some smart stimuli-responsive controlled delivery systems release their payloads at targeted organelles or tissues in vitro and in vivo.…”