Matter, Volume 2
Supplemental Information
Investigation of Cortisol Dynamics
in Human Sweat Using
a Graphene-Based Wireless mHealth System
Rebeca M. Torrente-Rodríguez, Jiaobing Tu, Yiran Yang, Jihong Min, Minqiang Wang, YuSong, You Yu, Changhao Xu, Cui Ye, Waguih William IsHak, and Wei Gao
Matter, Volume 2
Supplemental Information
Investigation of Cortisol Dynamics
in Human Sweat Using
a Graphene-Based Wireless mHealth System
Rebeca M. Torrente-Rodríguez, Jiaobing Tu, Yiran Yang, Jihong Min, Minqiang Wang, YuSong, You Yu, Changhao Xu, Cui Ye, Waguih William IsHak, and Wei Gao
Figure S1. Schematic of modification procedure of the graphene electrode for cortisol sensing.
LGE
PPAPolymerization
BSA blocking
Cortisol recognition
EDC/Sulfo-NHSactivation
Ab immobilization
Figure S2. Characterization of the graphene sensor. Differential pulse voltammetry (DPV) in
2.0 mM of K4Fe(CN)6/K3Fe(CN)6 (1:1) after each modification step.
0
10
20
30
40
50
60
-0.2 0 0.2 0.4
-I (µ
A)
E (V)
Bare
pPPA
CAb
BSA
Cortisol-HRP
Figure S3. Electrochemical cortisol sensor optimization. Effect of cortisol-HRP dilution factor
on amperometric signals. Data are represented as mean ± SD (n = 3).
0.0
1.0
2.0
3.0
4.0
0
100
200
300
400
500
1/300 1/200 1/100
I 0.0/
I 10.0
-I (n
A)
Cortisol-HRP dilution
Blank 10 ng mL-110.0 ng/mL0.0
Figure S4. Performance characterization of the graphene-based electrochemical sensors.
Effect of various pHs (A), ionic strengths (B), and presence of interferential molecules (5.0 ng/mL)
(C). PBST, phosphate buffered saline with Tween® 20.Data are represented as mean ± SD (n = 3).
A B C
0.0
0.5
1.0
1.5
2.0
2.5
0
100
200
300
400
0.1X 1X 5X 10X
I 0.0/
I 5.0
-I (n
A)
PBST concentration
Blank 5.0 ng mL-15.0 ng/mL0.0
0.0
0.5
1.0
1.5
2.0
2.5
0
100
200
300
400
7.4 5.5 4.1
I 0.0/
I 5.0
-I (n
A)
pH
Blank 5.0 ng mL-15.0 ng/mL0.0
0.0
0.5
1.0
1.5
2.0
2.5
0
100
200
300
400
I 0.0/
I 5.0
-I (n
A)
Blank 5.0 ng mL-15.0 ng/mL0.0
Figure S5. Stability test of the graphene-based electrochemical sensors. Variation of
amperometric responses for 0.0 and 5.0 ng/mL cortisol with time. Data are represented as mean ±
SD (n = 3).
0.0
0.5
1.0
1.5
2.0
2.5
0
100
200
300
400
day 0 day 1 day 2 day 4 day 5 day 7 day 10 day 26 day 35
I 0.0/
I 5.0
-I (n
A)
Blank 55.0 ng/mL0.0
Figure S6. Optimization of platform design. 3-channel amperometric signals obtained with two
platform designs in 1,000,000X diluted HRP-cortisol, 2.0 mM HQ and 1.0 mM H2O2 in 50 mM
phosphate buffer (pH 6.0). The platform with asymmetric working-to-reference design (A)
displays larger variations in signals obtained as compared with a symmetric design (B).
0
250
500
750
1000
1250
0 50 100 150
E (m
V)
Time (s)
WE1
WE2
WE312
3
0
250
500
750
1000
1250
0 50 100 150
E (m
V)
Time (s)
WE1WE2WE3
A B
12
3
Figure S7. Proportional error evaluated for the GS4 based on real sample recovery studies.
0.0
2.0
4.0
6.0
8.0
10.0
0.0 2.0 4.0 6.0 8.0 10.0
Rec
over
ed c
ortis
ol (n
g/m
L)
Actual cortisol (ng/mL)
Measured value
Figure S8. Thermal image of the sensor patch on human forearm.
Figure S9. Influence of temperature on sensor performance. Amperometric responses for 0.0,
1.0 and 5.0 ng/mL cortisol incubated at room temperature (25 °C), 31 °C and 37 °C. Data are
represented as mean ± SD (n = 3).
0
100
200
300
400
25 37
-I (n
A)
31Temperature (oC)
Blank
1.0
5.0
ng/mL
ng/mL
0.0
Figure S10. Iontophoresis based sweat sampling. Illustration of iontophoresis-assisted sweat
stimulation on a subject’s forearm, and principles of sweat stimulation and cortisol excretion in
sweat.
Figure S11. Influence of time of exercise in cortisol variation. Cortisol level evaluated in sweat
and its relative percentage change of two healthy subjects before and after physical exercise
conducted in the morning (AM) and in the afternoon (PM).
0
20
40
60
80
100
0.0
2.0
4.0
6.0
8.0
AM PM
% C
hang
e
Cor
tisol
(ng/
mL)
Time of exercise
10 min 50 minSubject 1
0
50
100
150
200
250
0.0
1.0
2.0
3.0
AM PM
% C
hang
e
Cor
tisol
(ng/
mL)
Time of exercise
10 min 50 minSubject 2
A B
Figure S12. Salivary cortisol at several time points across the cold pressor test for four subjects
(C1-C4) from the human study presented in Figure 5.
0.0
2.5
5.0
7.5
10.0
Sal
ivar
y co
rtiso
l (ng
/mL)
C1
C2
C3
C4
CPT +
8 min
CPT +
16 mi
n
CPT +
24 mi
n