core-shell ag@sio @msio mesoporous nanocarriers for metal ... · core-shell ag@sio2@msio2...

Core-shell Ag@SiO2@mSiO2 mesoporous nanocarriers for

metal-enhanced fluorescence

Jianping Yang a, Fan Zhang a*, Yiran Chen a, Sheng Qian a, Pan Hu a, Wei

Li a, Yonghui Deng a, Yin Fang a, Lu Han a, Mohammad Luqman b,

Dongyuan Zhao a*

a Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and

Innovative Materials, Key Laboratory of Molecular Engineering of Polymers of the

Chinese Ministry of Education, Laboratory of Advanced Materials, Fudan University,

Shanghai 200433, P. R. China

b Chemical Engineering Department, College of Engineering, King Saud University,

Kingdom of Saudi Arabia

Email: [email protected], [email protected]

Tel: 86-21-5163-0205; Fax: 86-21-5163-0307

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2011

Experimental Section

Chemicals. All chemicals were of analytical grade and used without further

purification. AgNO3, ethylene glycol, ammonia aqueous solution (28 wt %), NaCl,

acetone, NH4NO3, tetraethyl orthosilicate (TEOS) and hexadecyltrimethylammonium

bromide (CTAB) were purchased from Sinopharm Chemical Reagent Co. (China).

Polyvinylpyrrolidone (PVP, Mw = 55000), Eosin isothiocyanate (EiTC), Fluorescein

isothiocyanate (FiTC), Rhodamine B (Rh B) and poly(allylamine hydrochloride)

(PAH, Mw = 56000) were obtained from Sigma Aldrich. Deionized water was used in

all experiments.

Synthesis of Ag nanoparticles. Ag nanoparticles with diameter about 50 nm were

synthesized in large scale via a modified method reported by Xia et al.1 2.5 g of PVP

(Mw = 55000) was dissolved in 200 mL of ethylene glycol before 0.5 g of AgNO3

was added. After the three-neck flask was settled in an oil bath, the mixture was then

heated to ~ 130 °C within 25 min under vigorous stirring and maintained at 130 °C

for 1 h to obtain the Ag nanoparticles. The nanoparticles were isolated by

precipitating the solution with acetone (800 mL), followed by centrifugation at 10000

rpm for 3 min, and re-dispersed in 4 mL of ethanol to obtain the 0.05 g (Ag

nanoparticles)/mL solution.

Synthesis of Ag@SiO2 core-shell particles. The Ag@SiO2 particles with different

silica thickness were prepared according to Stöber method. In a typical procedure for

the silica layer coating with the thickness of ~ 3 nm, 2 mL of Ag nanoparticle/ethanol

solution (0.05 g/mL) obtained above was dispersed in the mixture of ethanol (80 mL)

and water (20 mL) and 1 mL of ammonia aqueous solution (28 wt%) under stirring,

then 15 μL of TEOS was added slowly with continuous stirring for 5 sec. The reaction

was continued for 6 h. The Ag@SiO2 particles was separated by centrifugation and

washed by ethanol and water for several times. The thickness of the silica coating

layer could be increased gradually with increasing the TEOS concentration. For

example, silica coating layer with the thickness of ~ 8 nm was obtained using the

procedure similar to the above increasing the TEOS concentration to 60 μL.


Synthesis of Ag@SiO2@mSiO2 core-shell particles. The Ag@SiO2@mSiO2

core-shell particles were prepared through a surfactant-templating sol-gel approach by

using CTAB as a template. In brief, the above synthesized Ag@SiO2 particles were

added into the solution containing 25 mL of water, 15 mL of ethanol, 75 mg of CTAB

and 0.25 mL of ammonia aqueous solution (28 wt %). The mixture was turned to

homo-dispersed solution after being agitated ultrasonically and mechanically for 30

min each. It was followed by the addition of 120 μL of TEOS was added dropwisely

with continuous stirring for about 10 seconds and the reaction was continued for 6 h.

The particles were collected by centrifugation and washed with ethanol and water,

respectively. The CTAB surfactant was removed by solvent extraction method using

60 mL of NH4NO3/ethanol solution (6 g/L) and refluxed at 60 °C for 1 h. This

extraction process was repeated twice. After centrifugating and washing with ethanol

and water, the Ag@SiO2@mSiO2 core-shell nanocarriers were obtained.

Loading of fluorophores in mesoporous silica shells. The dyes including EiTC,

FiTC and Rh B were loaded in the mesoporous silica shells via an impregnation

method. For example, 12 mg of Ag@SiO2@mSiO2 core-shell particles with SiO2

spacer of 8 nm were re-dispersed in 6 mL of ethanol. Brown vials were loaded with

500 μL of Ag@SiO2@mSiO2/ethanol solution and 500 μL of ethanol, followed by

addition of 5, 10, 15, 20 μL of EiTC/ethanol solution (0.5 mg/mL), respectively. After

being stirred for 24 h, 500 μL PAH (2 mg/mL) ethanol solution was injected and kept

stirring for 3 h. The products were collected by centrifugation and washed with

ethanol for 3 times. Finally, the products were re-dispersed in 4 mL ethanol to obtain

the 0.25 mg/mL solution. FiTC and Rh B were loaded in the mesopore channels of the

Ag@SiO2@mSiO2 nanocarrier using the same procedure as that of EiTC.

Loading of FiTC-EiTC in the mesoporous silica shells. 500 μL of the

Ag@SiO2@mSiO2 ethanol solution (2 mg/mL) with SiO2 spacer of 8 nm was diluted

with 500 μL of ethanol. 15 μL of EiTC/ethanol solution (0.5 mg/mL) was injected and

stirred for 24 h, followed by adding different amount of 3, 6, 9, 12 and 15 μL of FiTC

(0.5 mg/mL) was added and continuous stirring for another 6 h, respectively. 500 μL

of PAH (2 mg/mL) ethanol solution was injected and kept stirring for 3 h. The


particles were separated by centrifugation and washed with ethanol, and then diluted

to 4 mL with ethanol (0.25 mg/mL) for use.

Dissolving Ag core from Ag@SiO2@mSiO2 (control sample). The Ag cores in the

core-shell structured Ag@SiO2@mSiO2 particles could be removed by NaCl

solution.2-3 For example, 200 μL of the above-mentioned EiTC-, FiTC-, Rh B- and

EiTC/FiTC-loaded Ag@SiO2@mSiO2 composite particles in ethanol solution (0.25

mg/mL) were dispersed into 3.8 mL of NaCl solution (250 mM) and kept stirring for

one day, respectively. Thus the hollow particles without Ag cores (control sample)

were obtained without washing and centrifugation. The corresponding compared

Ag@SiO2@mSiO2 nanocarrier was also diluted with 3.8 mL water to ensure

concentration of dyes in the Ag@SiO2@mSiO2 nanocarrier and control sample are the

same.

Characterization. Transmission electron microscopy (TEM) measurements were

carried out on a JEOL 2011 microscope (Japan) operated at 200 kV. All samples were

first dispersed in ethanol and then collected using copper grids covered with carbon

films for measurements. Scanning electron microscopic (SEM) images were obtained

on a Philip XL30 microscope (Germany). A thin film of gold was sprayed on the

sample before this characterization. Field-emission scanning electron microscopy

(FESEM) images were obtained on a Hitachi S-4800 microscope (Japan). Powder

X-ray diffraction (XRD) patterns were recorded on a Bruker D4 X-ray diffractometer

(Germany) with Ni-filtered Cu Kα radiation (40 kV, 40 mA). Nitrogen sorption

isotherms were measured at 77 K with a Micromeritcs Tristar 3000 analyzer (USA).

Before measurements, the samples were degassed under vacuum at 180 °C for at least

6 h. The Brunauer-Emmett-Teller (BET) method was utilized to calculate the specific

surface areas (SBET), using adsorption data in a relative pressure range from 0.04 to

0.2. The pore volume and pore size distributions were derived from the adsorption

branches of isotherms using Barrett-Joyner-Halenda (BJH) model. The total pore

volume, Vt, was estimated from the amount adsorbed at a relative pressure P/P0 of

0.995. Fluorescence spectra were recorded on an F-4500 spectrofluorometer (Hitachi

High-Technologies). FiTC, EiTC and Rh B were excited at 485, 520 and 540 nm,


respectively. The bandpass was set at 5 nm both excitation and emission, scan speed

at 2400 nm/min and PMT voltage at 700 V for all measurements. UV-Vis absorption

spectra were measured on a Jasco spectrophotometer (V-550) (Japan). Confocal

luminescence images were made with an Olympus FV1000 (Japan), with λex = 515 nm

as the excitation source and emissions were collected in the range of λ = 535 – 555

nm. All the measurements were carried our in the same condition.

References

1. Y. G. Sun and Y. N. Xia, J. Am. Chem. Soc., 2004, 126, 3892.

2. M. L.-Viger, M. Rioux, L. Rainville and D. Boudreau, Nano Lett., 2009, 9, 3066.

3. M. L.-Viger, D. Brouard and D. Boudreau, J. Phys. Chem. C, 2011, 115, 2974.


Fig. S1 SEM images (a, c, e) and FESEM images (b, d, f) of the Ag nanoparticles (a,

b), the core-shell Ag@SiO2@mSiO2 nanocarrier with the silica spacer in the thickness

of 3 nm (c, d) and 8 nm (e, f).


Fig. S2 TEM image of the core-shell Ag@SiO2@mSiO2 nanocarrier with the SiO2

spacer in the thickness of 3 nm (left). Powder XRD patterns (right) of the

Ag@SiO2@mSiO2 nanocarrier with the silica spacer in the thickness of 3 nm (a) and

8 nm (b).


Fig. S3 Absorption spectra of (a) EiTC-loaded Ag@SiO2@mSiO2 nanocarrier and (b)

after dissolving the silver nanoparticles (inset). The thickness of the silica spacer is 8

nm and the concentration of EiTC is 10.5 x 10-6 mol/L.


Fig. S4 Fluorescence emission spectra of the FiTC-loaded Ag@SiO2@mSiO2

nanocarrier with the silica-spacer in the thickness of 3 nm (a) and 8 nm (b), in which

the FiTC concentration increases from 6.4 x 10-6 to 19.2 x 10-6 mol/L. Fluorescence

spectra of the FiTC-loaded Ag@SiO2@mSiO2 nanocarrier with the silica spacer

thickness of 3 nm (c) and 8 nm (d) and after dissolving the silver nanoparticles. The

excited wavelength is 485 nm.


Fig. S5 Fluorescence emission spectra of the RhB-loaded Ag@SiO2@mSiO2 with the

silica spacer in the thickness of 3 nm (a) and 8 nm (b), in which the RhB

concentration increases from 5.2 x 10-6 to 20.8 x 10-6 mol/L. Fluorescence spectra of

the RhB-loaded Ag@SiO2@mSiO2 nanocarrier with the silica spacer thickness of 3

nm (c) and 8 nm (d) and after dissolving the silver nanoparticles. The excited

wavelength is 540 nm.


Fig. S6 Fluorescence spectra of (a) FiTC (donor)/EiTC (acceptor) (red line) and EiTC

(acceptor)-only (black line) loaded in Ag@SiO2@mSiO2 nanocarrier, (b) FiTC

(donor)/EiTC (acceptor) loaded Ag@SiO2@mSiO2 nanocarrier before (red line) and

after (black line) dissolving the silver nanoparticles. The loading amounts of EiTC

and FiTC are 10.5 x 10-6 and 19.2 x 10-6 mol/L, respectively. Fluorescence spectra of

FiTC (donor)/EiTC (acceptor) loaded Ag@SiO2@mSiO2 nanocarrier before (c) and

after (d) dissolving the silver nanoparticles, while the concentration of EiTC (acceptor)

is kept constant at 10.5 x 10-6 mol/L. The thickness of the silica-spacer layer is 8 nm

and the excitation wavelength is 485 nm for (a-d).


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