DNA-capped mesoporous silica nanoparticles as an ion-responsive release system to determine the presence of mercury in aqueous solutions

Abstract

We have developed DNA-functionalized silica nanoparticles for the rapid, sensitive, and selective detection of mercuric ion (Hg(2+)) in aqueous solution. Two DNA strands were designed to cap the pore of dye-trapped silica nanoparticles. In the presence of ppb level Hg(2+), the two DNA strands are dehybridized to uncap the pore, releasing the dye cargo with detectable enhancements of fluorescence signal. This method enables rapid (less than 20 min) and sensitive (limit of detection, LOD, 4 ppb) detection, and it was also able to discriminate Hg(2+) from twelve other environmentally relevant metal ions. The superior properties of the as-designed DNA-functionalized silica nanoparticles can be attributed to the large loading capacity and highly ordered pore structure of mesoporous silica nanoparticles, as well as the selective binding of thymine-rich DNA with Hg(2+) . Our design serves as a new prototype for metal-ion sensing systems, and it also has promising potential for detection of various targets in stimulus-release systems.

Figure 1

(A) SEM image of solid MSN, showing the spherical morphology. (B)TEM image of solid MSN, showing the highly ordered porous structure.

Figure 2

(A) Powder X-ray patterns of the solids: MSN as synthesized and calcined, isocyanate group- functionalized MSN, and Rhodamine 6G-doped MSN-NCO. (B) BET nitrogen adsorption/desorption isotherms of the solids (a) MSN as synthesized and calcined and (b) MSN after dye doping with Rhodamine 6G. (C) BJH pore size distribution of MSN.

Figure 3

(A)Hybridization between Arm-DNA, Fluorophore-Linker-DNA and Complementary-Linker-DNA in the presence of Hg²⁺.(B) Fluorescence intensity of the 100nm Fluorophore-Linker-DNA solution after the addition of the indicated concentrations of Arm-DNA, Hg²⁺and Complementary-Linker-DNA.

Figure 4

(A)Release curve of Rhodamine 6G from Linker-DNA-capped MSN-R6G with different concentrations of Hg²⁺. (B)Fluorescence signal 20 minutes following dye release in the presence of Hg^2+. Laser excitation wavelength: 520nm.

Figure 5

Fluorescence emission signal in the presence of increasing amounts of mercuric ion. Inset: Linear fit of the fluorescence signal, slope=(1.76±0.06)×10⁴ ppb^–1; intercept=(512±44). Excitation at 520 nm; emission at 550 nm.

Figure 6

Fluorescence intensities of the released dye from Linker-DNA-capped MSN-R6G in the presence of 1ppm of different cations. Release time: 20mins.

Scheme 1

(A) Schematic representation of the synthesis , surface modification, dye loading and DNA binding of the MSN, as well as the release of dye via MSN in the presence of mercuric ion. (B) Hybridization of the Arm-DNA and Linker-DNA in the absence and presence of mercuric ion (Green dot: Mercuric ion).