Supporting information for
Multiple usage of ultrafast laser induced copper substrates for
explosives detection using surface enhanced Raman scattering
Syed Hamad, 1 G. Krishna Podagatlapalli, 2 Md. Ahamad Mohiddon, 3
S. Venugopal Rao 2,*
1
2
School of Physics, University of Hyderabad, Prof. C. R. Rao Road, Hyderabad
500046, India.
Advanced Center of Research in High Energy Materials (ACRHEM), University
of Hyderabad, Prof. C. R. Rao Road, Hyderabad 500046, India.
3
Centre for Nanotechnology, University of Hyderabad, Prof. C. R. Rao Road,
Hyderabad 500046, India.
*
Author
for correspondence
soma_venu@yahoo.com
Telephone Number: +91-040-23138811
e-mail:
svrsp@uohyd.ernet.in
OR
Raman Intensity (a.u.)
900
535
800
(a)
700
525
600
500
520
400
515
300
510
200
505
100
500
0
300
(b)
530
600
900
1200
1500
500
1000
1500
Raman Shift (cm-1)
FIGURE 1 Normal Raman spectra of (a) ANTA and (b) TNT were recorded on plain silicon at the excitation
wavelength 532 nm. The time of integration was 5 s.
Enhancement factor calculations:
In the calculation of Enhancement factor, NSERS and NRaman can be determined by the following
equations
𝑁𝑆𝐸𝑅𝑆 = 𝜂 𝑁𝐴 𝐶𝑎𝑙 𝑉𝑎
𝐴𝑙𝑎𝑠𝑒𝑟
𝐴𝑁𝑆
𝑁𝑅𝑎𝑚𝑎𝑛 = 𝑁𝐴 𝐶𝑎ℎ 𝑉𝑎 𝐴
𝐴𝑙𝑎𝑠𝑒𝑟
𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒
(1)
(2)
here NA is the Avogadro’s number (6.023×1023), Cal is the lower concentration of the analyte
(500 μM) on the enhanced surfaces, Cah is the higher concentration of the analyte (0.1M) on the
enhanced surfaces, Va is the volume (10 μl) of analyte placed on substrate, Alaser is the effective
area of laser spot (1.32 × 10-12 m2) on the substrate, ANS is the NS area drawn by the laser on Cu
substrate is different for MCuNSs and SCuNSs (5×5 = 25 mm2) and A
substrate
is the area
occupied by the liquid on silicon surface (52 = 25 mm2). For our convenience, the combined form
of equations (2), (3) and (4) can be written as following
𝐸. 𝐹 =
𝐼𝑆𝐸𝑅𝑆 𝑁𝑅𝑎𝑚𝑎𝑛
𝐼𝑅𝑎𝑚𝑎𝑛 𝑁𝑆𝐸𝑅𝑆
=
𝐼𝑆𝐸𝑅𝑆
𝐶𝑎ℎ ×𝐴𝑁𝑆
(3)
𝐼𝑅𝑎𝑚𝑎𝑛 𝜂 × 𝐶𝑎𝑙 × 𝐴𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒
Adsorption factor calculations (
The procedure we followed was proposed by Langmuir in Langmuir isotherm and the adsorption
factor calculations were adapted from earlier reports [1-4]. Accordingly, we recorded SERS
spectra of ANTA and R6G for different concentrations which were adsorbed on MCuNS3 and
MCuNS4, respectively, and plot a graph in between SERS intensity and concentration.
𝐾𝑐
To interpret and fit data with the equation 𝑁 = 𝑁0 (1+𝐾𝑐) -------- (4)
Where N = number of molecules adsorbed, N0 = number of molecules adsorbed at saturation, c =
concentration of analyte and K= binding equilibrium constant.
Raman intensity is proportional to N at different concentrations and to N0 at saturation level [4].
12000
10000
(a)
N0 =10263
10000
8000
Experimental data
Langmuir Theoretical fit
6000
4000
4
K =8.8×10 M
-1
2000
SERS Intensity (N)
SERS Intensity (N)
14000
(b)
Experimental data
Langmuir Theoretical fit
N0 =5306
5000
3
K =1×10 M
-1
0
0
0
5000
10000
15000
20000
Concentration (nM)
0
1000
2000
3000
4000
Concentration (M)
FIGURE 2 Langmuir adsorption isotherm plots of (a) R6G and (b) ANTA molecules which were adsorbed on laser
machined copper NSs such as MCuNS4 and MCuNS3, respectively.
From the above plots, the best fits provide binding equilibrium constant (K) are of 8.8×104 M-1
and 1×103 M-1 for R6G and ANTA, respectively.
The critical characteristic of the Langmuir isotherm [1-4] can be expressed in the form of
adsorption factor which is defined as 𝜂 =
1
1+Κ𝑐0
--------- (5), where c0 is the initial
concentration at saturation level is of 15 µM for R6G and 1 mM for ANTA.
Substitute K and c0 values in equation (5) and we obtained the adsorption factor (values are of
~0.43 and ~0.5 for R6G and ANTA, respectively.
1. ANTA molecule for the mode of 1340 cm-1
(i)
MCuNS1
Enhanced Raman intensity ISERS = 11865
Normal Raman intensity IRaman ~10
Adsorption factor  ~ 0.5
Substitute in equation (3)
11865
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 1.2 × 106
10
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
(ii)
MCuNS2
𝐸. 𝐹 =
(iii)
310
0.25𝑀 × 25𝑚𝑚2
×
= 3.1 × 104
10 0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
MCuNS3
731
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 7.3 × 104
10 0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
(iv)
MCuNS4
707.5
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 7.1 × 104
−6
2
10
0.5 × 500 × 10 𝑀 × 25𝑚𝑚
(v)
SCuNS1
𝐸. 𝐹 =
(vi)
1441.5
0.25𝑀 × 25𝑚𝑚2
×
= 1.4 × 105
10
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
SCuNS2
𝐸. 𝐹 =
(vii)
SCuNS3
365
0.25𝑀 × 25𝑚𝑚2
×
= 3.6 × 104
10 0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
715
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 7.1 × 104
10 0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
(viii)
SCuNS4
𝐸. 𝐹 =
2.
710
0.25𝑀 × 25𝑚𝑚2
×
= 7 × 104
10 0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
R6G molecule for the mode of 1360cm-1
(i)
MCuNS1
Enhanced Raman intensity ISERS = 259
Normal Raman intensity IRaman ~ 49
Adsorption factor  ~ 0.43
Substitute in equation (3)
259
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 6.2 × 105
49 0.43 × 5 × 10−6 𝑀 × 25𝑚𝑚2
(ii)
MCuNS2
𝐸. 𝐹 =
(iii)
3847
0.25𝑀 × 25𝑚𝑚2
×
= 9.1 × 106
49
0.43 × 5 × 10−6 𝑀 × 25𝑚𝑚2
MCuNS3
1077
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 2.6 × 106
49
0.43 × 5 × 10−6 𝑀 × 25𝑚𝑚2
(iv)
MCuNS4
7367
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 1.8 × 107
−6
2
49
0.43 × 5 × 10 𝑀 × 25𝑚𝑚
(v)
SCuNS1
𝐸. 𝐹 =
(vi)
SCuNS2
𝐸. 𝐹 =
(vii)
194.7
0.25𝑀 × 25𝑚𝑚2
×
= 4.6 × 105
49
0.43 × 5 × 10−6 𝑀 × 25𝑚𝑚2
SCuNS3
492
0.25𝑀 × 25𝑚𝑚2
×
= 1.1 × 106
49 0.43 × 5 × 10−6 𝑀 × 25𝑚𝑚2
383
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 9.1 × 105
49 0.43 × 5 × 10−6 𝑀 × 25𝑚𝑚2
(viii)
SCuNS4
𝐸. 𝐹 =
159.3
0.25𝑀 × 25𝑚𝑚2
×
= 3.8 × 105
49
0.43 × 5 × 10−6 𝑀 × 25𝑚𝑚2
3. TNT molecule for the mode of 1360 cm-1
(i)
MCuNS1
Enhanced Raman intensity ISERS = 209
Normal Raman intensity IRaman ~ 5
Adsorption factor  ~ 0.5 (Assumption)
Substitute in equation (3)
209
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 4.2 × 104
−6
2
5
0.5 × 500 × 10 𝑀 × 25𝑚𝑚
(ii)
MCuNS2
384.5
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 7.7 × 104
5
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
(iii)
MCuNS3
𝐸. 𝐹 =
(iv)
MCuNS4
𝐸. 𝐹 =
(v)
1071
0.25𝑀 × 25𝑚𝑚2
×
= 2.2 × 105
5
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
78.5
0.25𝑀 × 25𝑚𝑚2
×
= 1.6 × 104
5
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
SCuNS1
1243.5
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 2.5 × 105
5
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
(vi)
SCuNS2
𝐸. 𝐹 =
(vii)
SCuNS3
289
0.25𝑀 × 25𝑚𝑚2
×
= 5.8 × 104
5
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
985.5
0.25𝑀 × 25𝑚𝑚2
𝐸. 𝐹 =
×
= 1.9 × 105
5
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
(viii)
SCuNS4
𝐸. 𝐹 =
257
0.25𝑀 × 25𝑚𝑚2
×
= 5.2 × 104
5
0.5 × 500 × 10−6 𝑀 × 25𝑚𝑚2
References
1. K. R. Hall, L. C. Eagleton, A. Acrivos, and T. Vermeulen, I & EC Fundamentals, 5,
212 (1966)
2. N. Ahalya, R.D. Kanamadi, and T.V. Ramachandra, Ind. J. Chem. Tech. 13, 122 (2006),
3. K.Y. Foo, and B.H. Hameed, Chem. Eng. Journal 156, 2 (2010)
4. J. He, S. Hong, L. Zhang, F. Gan, and H. Yuh-Shan, Fres. Env. Bul. 19, 2651 (2010);
(http://www.hood.edu/uploadedFiles/Hood_College/Home/Academics/Departments/Che
mistry_and_Physics/Thermo.Lab.Manual.Adsorption.pdf) with title “Adsorption of
Pyridine Measured with SERS”.