SUPPORTING INFORMATION for
Real Time Study of Interactions between Cytosine–Cytosine Pairs in
DNA Oligonucleotides and Silver Ions Using Dual Polarization
Interferometry
Yu Zheng, a,b Cheng Yang, a,b Fan Yang, *,a and Xiurong Yang*,a
a
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, China
b
University of Chinese Academy of Sciences, Beijing 100039, China
* Corresponding author. Tel.: +86 431 85262056; fax: +86 431 85689278.
E-mail address: [email protected], [email protected]
S-1
DPI instrumentation and Principle: DPI mainly consists of a helium-neon laser
emitting light at 632.8 nm, a controller to switch plane polarized light (transverse
magnetic (TM) and transverse electric (TE)), a multiple-layer optical sensing
waveguide consisting of sensing layer and reference layer (sensing layer stacked on
top of reference layer) separated by a central glass clad region, an array photodiode
and a fluidics system. The fluidic system consists of a Rheodyne HPLC injector Valve
and an external pump (Harvard Apparatus, PHD2000) to provide a controlled
continuous fluid flow over channels on the chip surface. When the polarized light
from the He-Ne laser is coupled in at one end of the waveguide, guided through the
sensing and reference light path and combined with each other in the far-field,
Young’s Interference fringes will be formed. Changes in the fluid should affect the
interface of the sensing layer while the reference layer remains unaffected, which
results in the phase change of the sensing light path output, thus the positions of
Young’s Interference fringes will move. The two polarizations TE and TM give two
independent phase shift response. After the analysis of the changes of both TE phase
and TM phase, the real-time thickness, refractive index, density and mass values of
the surface layers are obtained, which are closely related to the solution flown over
the sensing surface.
General procedure for AFM experiment: AFM measurements were performed on
the silicon wafer with Veeco Instruments Nanoscope in tapping mode. The cleaned
silicon wafer was first dipped in 0.003 mg/mL PEI solution for 10 min. Then, the
wafer was rinsed with 10 mM Tris-HClO4 buffer solution (pH 7.0, 200 mM NaClO4)
three times for 5 min each. After it was carefully dried by nitrogen to remove the
buffer from the surface, the wafer was dipped in 12 µM T30 solution for 10 min,
followed by another three-time rinsing with buffer solution. After the wafer was dried
by nitrogen, it was dipped into 5 µM probe solution for 10 min. After the wafer was
rinsed again with buffer solution three times and dried by nitrogen, it was dipped into
10 mM Ag+ solution to make Ag+ interact with the probe. Then, the wafer was rinsed
with buffer solution and dried by nitrogen, waiting for measurement.
S-2
Figure S1. Mass (A), thickness (B) and density (C) value changes of the
probe/T30/PEI layer (black lines) and control DNA/ T30/PEI layer (red lines) after the
addition of different concentrations of Ag+ ranging from 10 nM to 8 µM in 10 mM
Tris-HClO4 buffer solution (pH 7.0, 200 mM NaClO4). The error bars represent the
standard deviation of three measurements.
S-3
Table S1. Determination of the concentration of Ag+ in drinking water samples.
Mass
Added (µM)
0.05
0.5
Thickness
5
Measured (µM) 0.045 0.627 5.577
Recovery (%)
90
125.4
111.5
0.05
0.054
108
S-4
0.5
Density
5
0.05
0.5
0.467 4.417 0.063 0.062
93.4
88.4
126
124
5
5.997
120
Figure S2. Mass (A), thickness (B) and density (C) value changes of the
probe/T30/PEI layer (Method A) (black bars) and probe/PEI layer (Method B) (red
bars) after the addition of different concentrations of Ag+ in 10 mM Tris-HClO4 buffer
solution (pH 7.0, 200 mM NaClO4). The error bars represent the standard deviation of
three measurements.
S-5
Figure S3. Selectivity of the biosensor for Ag+ over other metal ions: K+, Ca2+, Na+,
Mg2+, Zn2+, Mn2+, Ni2+, Pb2+. The concentration of all the metal ions is 20 µM in 10
mM Tris-HClO4 buffer solution (pH 7.0, 200 mM NaClO4).
S-6
Figure S4. AFM images of PEI layer (A), T30/PEI layer (B), probe/T30/PEI layer (C)
and Ag+/probe/T30/PEI layer (D).
A
B
C
D
S-7
Figure S5. Mass (A), thickness (B) and density (C) value changes of the
probe/T30/PEI layer after the addition of different concentrations of cysteine ranging
from 500 nM to 10 µM in the presence of 10 µM Ag+ in 10 mM Tris-HClO4 buffer
solution (pH 7.0, 200 mM NaClO4). The error bars represent the standard deviation of
three measurements.
S-8
Figure S6. Selectivity of the biosensor for cysteine over the mixture of other amino
acids: Ala, Gln, Gly, Pro, His, Leu, Val, Phe and Arg. The concentration of all the
amino acids is 6 µM in the presence of 3 µM Ag+ in 10 mM Tris-HClO4 buffer
solution (pH 7.0, 200 mM NaClO4).
S-9