Electronic Supplementary Information
Enzyme-free colorimetric determination of virus EV71 using
3D-MnO2-PEG nanoflower and 4-MBA-MA-AgNPs
Chengchao Chu,‡a Shengxiang Ge,‡b
Jing Zhang,b Huirong Lin,
a Gang Liu
a*,
Xiaoyuan Chen c
a State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics &
Center for Molecular Imaging and Translational Medicine School of Public Health
Xiamen University Xiamen 361102, China E-mail: [email protected]
b National Institute of Diagnostics and Vaccine Development in Infectious Disease,
School of Public Health, Xiamen University Xiamen 361102, China
c Laboratory of Molecular Imaging and Nanomedicine, National Institute of
Biomedical Imaging and Bioengineering (NIBIB), National Institutes of Health (NIH),
Bethesda, MD 20892, USA
‡These authors contributed equally to this study.
Reagents and apparatus
All reagents were of analytical grade and used without further purification.
Solutions were prepared using high pure water with a resistance of 18.5 MΩ.cm.
4-mercaptobenzoic acid (4-MBA), melamine (MA), meso-2,3-Dimercaptosuccinic
acid (DMSA), poly(ethylene glycol)bis(amine) (NH2-PEG-NH2; M.W. 3400), and
oleic acid were purchased from Sigma (USA). Silver nitrate (AgNO3), sodium
borohydride (NaBH4), potassium permanganate (KMnO4), oxalic acid, citric acid,
glutathione and Vitamin C were purchased from Xiamen Luyin Reagent Glass
Instrument Co., Ltd. Phosphate buffered solutions (PBS) were prepared by 0.01 mol/L
KH2PO4 and 0.01 mol/L Na2HPO4. The EV71, EV71-Ab1 and EV71-Ab2 were
provided by National Institute of Diagnostics and Vaccine Development in Infectious
Diseases (Xiamen University).
The UV-vis spectra were obtained from a Thermo Scientific Microplate Reader.
The transmission electron microscope (TEM) images were acquired on an H-7500
Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2016
(Hitachi, Japan) at 80 kV. The size and zeta potential were characterized by Zeta sizer
Nano ZS (Marvins). FT-IR was obtained from a BRUKER GC-FT-IR. The pH of the
solutions was measured with PB-10 pH meter (Sartorius, 91 Germany).
Preparation of 4-MBA-MA-AgNPs
The 4-MBA-MA-AgNPs was obtained according to the reported procedure.1
Firstly, AgNPs was prepared by a simple NaBH4 reduction procedure. Briefly, under
vigorously magnetic stirring, 10 mg NaBH4 was added rapidly into 100 mL fresh
aqueous solution of AgNO3 (10-4
mol/L), and a light yellow color appeared. After the
reaction was carried for 10 min, the AgNPs was obtained.
Furthermore, to the prepared AgNPs solution, 2 mL of 10-4
mol/L 4-MBA and 4
mL of 10-4
mol/L MA were added at the same time. Then, the solution was stirred for
30 min making sure the 4-MBA and MA were assembled on the surface of AgNPs.1
The excess 4-MBA and MA were reduced by ultrafiltration.
Preparation of 3D-MnO2-PEG
In this experiment, 250 mg of KMnO4 was added into 125 mL water and stirred
for 30 min to obtain a dissolved solution. At vigorous stirring rate, 2.5 mL of oleic
acid was added into the solution and a steady emulsion was appeared. The emulsion
was further stirred for 24 h at room temperature, and brown-black bulk was obtained.
The result 3D-MnO2 was centrifuged at 8000 rpm and washed with ethyl alcohol for
three times to remove any possible residual reactants. Finally, dry 3D-MnO2 NPs was
obtained by freeze drying in vacuum.2
To obtain 3D-MnO2-PEG, the 3D-MnO2 nanospheres was first reacted with
DMSA to modify their surface with -COOH groups. Briefly, 100 mg 3D-MnO2 NPs
was dispersed in 10 mL toluene. Then, 200 mg DMSA and 200 mg NaHCO3
dispersed in 100 mL acetone were added into the solution. The reaction mixture was
stirred and refluxed at 80 °C for 6 h. The DMSA modified 3D-MnO2 NPs was then
centrifuged at 8000 rpm and washed with acetone for three times, and re-dissolved in
water to obtain a 3D-MnO2 NPs solution (1 mg/mL).
To 1 mL 3D-MnO2-DMSA solution, newly prepared EDC/NHS solution (EDC
20 mg/mL, NHS 10 mg/mL) was added and reacted for 30 min. The excess
EDC/NHS was removed by centrifugation and washed with water. Then, 0.5 mL
NH2-PEG-NH2 (1 mg/mL) was added to the solution and reacted for another 30 min.
The final 3D-MnO2-PEG was obtained by centrifugation and washed with water.
To test the reaction between the 3D-MnO2-PEG and reducing agents (oxalic acid,
citric acid, glutathione or Vitamin C), 100 μL reducing agent solution (1 mM) was
added into 100 μL 3D-MnO2-PEG solution (50 μg/mL). The mixed solution was
photographed and investigated by UV-Vis absorption after the reaction carried for 1, 2,
4, 6, 8, 10, 12, 14, 16, 18 and 20 min.
Preparation of 3D-MnO2-Ab2
The preparation procedure for 3D-MnO2-Ab2 is shown in Fig. 1 (reaction A).
Briefly, 1 mL of freshly prepared EDC/NHS solution (EDC 20 mg/mL, NHS 10
mg/mL) and 2 mL of EV71-Ab2 solution (20 μg/mL, pH 7.4) were mixed with 2 mg
of 3D-MnO2-PEG. After the mixture had been shaken for 10 min, it was transferred to
a refrigerator at 4 °C for 2 h. Then, the excess EDC/NHS and Ab2 were removed with
the help of centrifugation and was washed with PBS (pH 7.4). To block the excess
nonspecific group on the nanoparticles, 2 mL of BSA (1%) was added and the mixture
was incubated at 4 °C for 2 h. After the excess BSA had been removed, the final
3D-MnO2- Ab2 was diluted with PBS (pH 7.4) to a volume of 2 mL and stored at 4 °C
until use.
Procedure of 3D-MnO2 NPs-Based EV71 assay
The EV71 assay was performed in 96-well polystyrene (PS) plates. Firstly,
EV71-Ab1 (4 μg/mL) in bicarbonate buffer (100 mM, pH 9.6) was added into the
wells in the PS plate and incubated at 4 °C overnight. After rinsing with PBS for 3
runs, 1% BSA in PBS was added into each well as a blocking agent. Secondly, EV71
PBS solutions at different concentrations were added into the plates. The plates were
kept at 37 °C for 1 h and washed with PBS for 3 runs. Thirdly, 100 μL of MnO2-Ab2
solution was added into each well, and incubated for 30 min. The excess MnO2-Ab2
was wiped off and rinsed with PBS for 3 runs. Fourthly, 100 μL of Vc solution was
added into each well and incubated for 5 min. Fifthly, 100 μL of 4-MBA-MA-AgNPs
was added each well and incubated for another 5 min. At last, photographs were taken
and the corresponding absorbances at 408 nm and 550 nm were recorded.
Figure S1 The UV–vis spectra of AgNPs (a), 4-MBA–AgNPs (b), 4-MBA-MA–AgNPs modified
with different ratio of 4-MBA and MA (c, 1: 0.5; d, 1: 1; e, 1: 2) when adding 100 nM Mn2+
solution.
Figure S2 The Zeta potential of the AgNPs and 4-MBA-MA–AgNPs.
Figure S3 (A) Photographic images of 4-MBA-AgNPs in the presence of metal ions. A408 nm/A550
nm of 4-MBA-MA–AgNPs in the presence of metal ions (B, 100 nM; C,10 μM; D, 1mM).
Figure S4 The MnO2-DMSA and MnO2-PEG dispersed in toluene/water mixed solution (left:
MnO2-DMSA; right: MnO2-PEG)
Figure S5 The Zeta potential of the 3D-MnO2, 3D-MnO2-NHS, NH2-PEG-NH2 and
3D-MnO2-PEG.
Figure S6 The dispersibility of 3D-MnO2, 3D-MnO2-DMSA and 3D-MnO2-PEG in water, NaCl
solution and PBS.
References
1 Y. Zhou, H. Zhao, C. Li, P. He, W. Peng, L. Yuan, L. Zeng and Y. He, Talanta, 2012, 97,
331.
2 M. Su, Y. Zhang, X. Song, S. Ge, M. Yan, J. Yu and J. Huang, Electrochimica Acta,
2013, 2013, 333.
