Supporting Information
of “A manual-slide-engaged switch-on-chip 3D multilayer paper chip for parallel
SERS-immunoassay measurement of clenbuterol from swine hair”
Fan An, Tingting Zheng, Zhigang Gao, Yong Luo, Xianming Liu, Weijie Zhao, Bingcheng Lin
SERS nanoprobes
Figure S1 SERS spectra of nanoprobe-grafted CL antibody(a)and pure SERS nanoprobes (b)
In our experiment, 4-mercaptobenzoic(4-MBA) was chosen as the Raman reporter due to its two
function groups: the-SH and the –COOH. The availability of the –SH can be found in the MBA
entities which were grafted to Au nanoparticles via Au-S bonds; the –COOH was the function
groups attached to the CL antibody. The measured SERS spectra of MBA are showed in Figure S1.
It is found that the characteristic bands of MBA located at 1587 cm-1 and 1078 cm-1 are identical to
those reported in the literature[1]. In Fig. S1, it can also be found that, after antibody was added
onto the-MBA-labeled GNPs, those peaks remained at the same positions in SERS spectra without
any visible shift. It indicates that the addition of antibody on the SERS nanoprobes would not
change the wavenumbers of their SERS spectra. the two peaks at 1078 cm -1 and 1588 cm-1 can be
assigned to the immune SERS nanoprobe-grafted CL antibody under our experimental setup.
Considering that the peak at approximately 1100 cm-1,which is attributed to the paper substrate,
might interfere with the peak 1078 cm -1, we focus our attention on the peak at 1588 cm-1.
Figure S2. (a)SERS signal intensity obtained from 0.01 mMMBA standard solutions of different
volumes reacted with GNPs;(b)SERS signal intensity obtained from 0.01 mMMBA standard
solutions reacted with GNPs in different times. The Raman intensities are those of the bands at
1588cm-1 of MBA,error bars representthe standard deviations from three independent
measurements.
Firstly, to prepare proper SERS nanoprobes, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 μL 0.1 mM MBA were
added into 1.0 mL GNPs respectively, and then these solutions were incubated at room
temperature for 90 min. Fig. S2(a) shows that as the volume of the added MBA solutions increases
from 0.5 to 2.5 μL, the Raman signal gets stronger. And then the GNPs started to aggregate when
more than 2.5 μL MBA solution was added. Consequently, the proper volume of the added MBA
solution should be ca. 2.5 μL. Secondly, the proper incubation time of GNPs with MBA was also
studied. Fig. S2(b) shows the SERS calibration curves obtained at different incubation times (10,
30, 50, 70, 90, 110 and 130 min) with MBA solutions of the same volume were added. From Fig.
S2, (b), it can be seen that the SERS intensities increase as the incubation time increases from 10
to 90 min. However, when the incubation time reaches 90 min, the signal gets weaker. This
suggests that the binding sites on GNPs were occupied by MBA, and excessive incubation time
may lead to aggregations to some extent, so the proper incubation time was considered to be ca.
90 min.
SERS homogeneity of paper chip
Fig. S3 Intensity distribution of the 1587 cm-1 peak in 15 spectra
SERS signals were collected from 15 different locations of the detection zone. Our data suggest
that the intensities of their Raman signals at 1587 cm-1 are close to each other with mean RSD of
8.77%, which is smaller than that reported in the literature[2], as 13.9%.
Paper substrate optimization
Fig.S4 SERS spectra obtained from immune SERS probes on different cellulose substrate.
Immune SERS nanoprobe solutions at the same concentration, were droped onto ten different
kinds of paper and ten spectra are obtained.The ten papers are as follow: Paper1, Whatman No. 1
filter paper;Paper2, slow qualitative filter;Paper 3, rapid quantitative filter;Paper 4, slow
quantitative filter;Paper 5, rapid qualitative filter;Paper6, newspaper;Paper 7, kraft paper; Paper 8,
quatitative miedium speed filter;Paper 9, tissue paper;Paper10, A4 print paper. It can be told from
the Fig. S4 that the Raman sigals from Whatman No. 1 filter paper demonstrated the strongest
intensity. Therefore, it was chosen as the paper substrate for chip fabrication in our study.
Parallel test
Fig. S5 SERS signals of three parallel detection zone where same reagents dropped.
The design of our SoCM-uPad allows us to conduct three parallel experiments on one chip. Fig.
S5 shows a high parallelism in results. Clenbuterol samples at the same concentration were added
onto the three units on one chip. In each unit, Raman spectra were collected for three times and
their average intensities were compared. The three Raman signals turned out to be identical to
each other.
1. J. Ni, R. J. Lipert, G. B. Dawson and M. D. Porter, Analytical Chemistry, 1999, 71, 4903-4908.
2. L. L. Qu, Q. X. Song, Y. T. Li, M. P. Peng, D. W. Li, L. X. Chen, J. S. Fossey and Y. T. Long,
Analytica Chimica Acta, 2013, 792, 86-92.