Supporting Information
Real-time, Sensitive Electrical Detection of Cryptosporidium Parvum Oocysts based on
Chemical Vapor Deposition-Grown Graphene
Jen It Wong1,2, Lu Wang3, Yumeng Shi2, Tomás Palacios4, Jing Kong4, Xiaochen Dong1,a), and
Hui Ying Yang2,b).
Graphene growing and transfer process:
A mixture of methane and hydrogen was used as the carbon source to grow graphene film
with single-layered domains on a Ni film (~500 nm thick, evaporated on SiO2 / Si wafer) by
utilizing chemical vapor deposition (CVD) method at ~1000 ºC. After that, poly(methyl
methacrylate) (PMMA) dissolved in chlorobenzene was spin-coated on the as-grown
graphene, followed by baking at 120 ºC for 20 min. Subsequently, the Ni film was etched
away by the HCl solution (HCl : H2O = 1 : 10) over a period of 8 h and the PMMA/ graphene
sheet was then put on a quartz substrate after deionized (DI) water rinsing. After drying in air,
a small amount of liquid PMMA / chlorobenzene solution was dropped onto it to dissolve the
PMMA, followed by acetone cleaning to remove PMMA. Finally, the PMMA/ graphene film
on quartz substrate was annealed at 450 ºC for 20 min in H2/Ar atmosphere to remove any
remaining PMMA.
Micro-channel fabrication procedures:
To fabricate graphene field-effect device, layers of titanium (10 nm) and gold (40 nm)
were evaporated to form the source and drain electrodes at the two ends of the graphene sheet,
which defined an active graphene device area of 3 × 3 mm. Subsequently, a home-built flow
cell (channel length=3mm, width=10mm, height=1mm) made from Polydimethylsiloxanes
(PDMS, Dow Corning Sylgard 184) block was placed on top of the device, with the silicone
rubber (Dow Corning 3140 RTV coating) as the adhesive layer which isolated and protected
the electrodes from contacting the test solutions.
1
Measurement :
All electrical measurements were conducted using Keithley 4200 semiconductor
characterization system at room temperature.
38
After functionalization
measured in buffer solution
Id (A)
36
1st sweep
2nd sweep
3rd sweep
4th sweep
34
32
30
28
-1.0
-0.5
0.0
0.5
1.0
Vg (V)
Figure S1. Transfer curves of the graphene field-effect device after biofunctionalization. The
transport properties were measured by sweeping the liquid gate voltage from 1.0 V to -1.0 V.
The liquid gate voltage was applied through a Ag/AgCl wire that was in contact with the
buffer solution covering the device. Three additional sweeps were carried out to show the
stability of the device.
2
(a) Non-functionalized device
230
Id (A)
225
5
10
220
3
10
4
10
2
10
buffer
(initial)
215
210
-1.0
-0.5
0.0
0.5
1.0
Vg (V)
220
(b) Non-functionalized device (zoom in)
218
Id (A)
216
3
10
2
10
214
buffer
(initial)
212
5
10
4
10
210
-0.2
0.0
0.2
0.4
0.6
Vg (V)
(c) Functionalized device (zoom in)
33
6
10
Id (A)
32
5
10
31
4
10
3
10
30
29
-0.2
0.0
0.2
buffer
(initial)
0.4
0.6
Vg (V)
Figure S2. Transfer curves in response to Cp. oocyst solutions of different concentrations for
the non-functionalized device (a) and its zoom-in view (b) as compared to the zoom-in view
3
of the functionalized device (c). 102, 103, 104, 105, 106 represent the concentrations of the Cp.
oocyst in terms of counts per 4mL buffer solution.
4
Table S1. Comparison on the transfer curve characteristics of the non-functionalized device
vs. the functionalized device in response to Cp. oocyst solutions of different concentrations:
(1) the voltage shift (V) of the minimum conductance point from that measured in buffer and
(2) the slope (/V) change of the transfer curve.
Concentration
of Cp. oocyst
(count/4mL
solution)
Slope (/V) of the transfer curve and the
percentage increase from the slope measured in
buffer*
Voltage shift (V) of the
minimum conductance point
Non-functionalized device
Functionalized device
Nonfunctionalized
device
Functionalized
device
0 (pure buffer)
--
--
102
0.072
--
103
0.128
0.002
Average: 20%
Average: 25%
104
0.167
0.031
20.51(11%) 14.25(35%)
Average: 23%
10.17(41%) 5.69(53%)
Average: 47%
20.61(11%)
12.07(67%)
105
0.192
0.041
106
--
0.041
p-branch
18.56
n-branch
p-branch
10.54
7.26
19.69 (6%) 12.77 (21%)
Average: 14%
20.46(10%)
--
13.61(29%)
14.60(39%)
8.67(20%)
Average: 25%
--
--
n-branch
3.73
-4.81(29%)
6.67(79%)
Average: 73%
12.28(75%) 6.41(72%)
Average: 74%
* The slope value was taken in the linear regime of the transfer curve and around 0.4V away
from the minimum conductance point, and the number in the parenthesis after the slope value
is the percentage increase of the slope compared to that in the pure buffer.
5