Transcript october 2015 WSU results with other references

[48] N.J. Kybert, G.H. Han, M.B. Lerner, E.N. Dattoli, A. Esfandiar, A.T.C. Johnson, Scalable
arrays of chemical vapor sensors based on DNA-decorated graphene, Nano Res. 7 (2014)
95–103.
Figure is as seen in review article by N. Green and M. Norton – review article text below
measured ambient/dry
Histogram of 56 devices
4.1. Back-gated GFETs:
Back gated GFETs are less frequently employed as DNA
sensors, likely due to the difficulties associated with
producing devices requiring small gate voltages (VG) rather
than the more commonly and readily prepared higher gate
voltage devices, which require VG on the order of tens to
hundreds of volts [51] to achieve significant gain. However,
back-gated GFETs have clear sensing advantages over
liquid-gated assemblies in conditions in which the analyte
solution composition may vary, and in situations where the
analyte is not in a solution matrix, e.g., vapor detection [52].
Kybert et al. have recently reported the use of DNAdecorated graphene for arrays of chemical vapor sensors
which demonstrated a significant shift in the VG required to
observe the minimum in the device conductance (VG, min)
after DNA deposition [48]. ssDNA was adsorbed onto the
surface of graphene, which allowed for chemical vapor
sensing down to parts-per-billion as analyte binding further
shifted the VG, min. Fig. 7 shows the device setup, current
voltage curves demonstrating the value of VG, min, which is
also termed the Dirac voltage, for the back-gated GFETs
before and after the addition of DNA, a mobility histogram
and the dispersion of VG, min values observed for an array
of devices. These authors explain the positive shift in VG,
min as counter- acting the negative field produced by the
phosphate backbone of the adsorbed ssDNA. The gate
voltage shifts positive to overcome the negative field induced
by DNA in order to maintain a similar charge state for
graphene after adsorption. Shifts of VG, min in the direction
of a more positive gate voltage were previously reported by
the same group (Fig. 8) [48]. Generally, back-gated GFETs
show relatively large VG, min shifts compared to liquid-gate
schemes discussed in the next section. Similar electronic
principles apply to liquid-gated GFETs but generally require
lower potentials compared to back-gated devices.
All measurements
are performed with a source–drain voltage of VSD = 50 mV.
The Dirac point is observed at ∼2 V, indicating that the
transfer scheme is relatively clean. The deviation from the
ideal Dirac point at 0 V (unmodified gfet - dn) could result
from a combination of
trapped charges in the oxide and the substrate [24] as well as
the graphene quality.
Upon rinsing under running water and drying, the DNA
entirely desorbs from the graphene (see supplementary
section 2). The biosensors have a detection limit of 11 pM for
poly-l-lysine and 8 pM for λ DNA. This is calculated from
three times the standard deviation3 of the Dirac peak voltage
shift at zero concentration, which are 1.4 V and 1.2 V for
poly-l-lysine and DNA respectively.
~50umx50um gfets
+ charged
amino acids
- charged
nucleic acids
Detection of DNA and poly-l-lysine using
CVD graphene-channel FET biosensors
Aniket Kakatkar1, T S Abhilash2, R De Alba2, J M Parpia2 and
H G Craighead1
Nanotechnology 26 (2015) 125502 (5pp)
measured ambient/dry
10-5-2015 at WSU – device 08262015-5
Summary of recordings done at WSU by david neff Weidong zhang and elloitt brown
on October 6 2015 using Phi’s chip number 08262015-5
I do not have the recordings of this device as measured by Phi before sending to Weidong.
I believe that Weidong has these plots and that they match closely with our pre-modification measurements.
This chip was fabricated by Phi on Si (doped? resistivity? – WZ says high resistivity) with a 90nm oxide layer.
-OTS monolayer on the SiO2 before applying graphene – YES To prevent ‘doping’ of graphene by SiO2.
-Benzimidazole NOT used on graphene before applying to SiO2/OTS (can see in the relatively low Dirac
point of ~30V, not 100V as Phis says is case in doped samples
08262015-5
10-5-2015 at WSU – device 08262015-5
Previous expts. (in adsorption
kinetics) done by M.Rahman –
concentration here is .3nM
dna origami ON HOPG
back gate
2.0nM
source
drain
0.3nM
These origami are
somewhat different design
(arm anchors present)
than those used in GFET
expts. at WSU 10-5-2015
THz/GFET
transmission
setup at
WSU
Ids (amps) at Vds = 0.05V
All plots show THz transmission and DC
measurements of device prior to any analyte
treatment.
Ids (amps) at Vds = 0.05V
Blue vertical line shows Dirac point of
device prior to any solution exposure.
Ids (amps) at Vds = 0.05V
Rinsed GFET –
settling time 25
minutes
THz transmission AU
2.0nM dna
origami added to
GFET - settling
time 17 minutes
THz transmission AU
Water added to
GFET - settling
time 3 minutes
THz transmission AU
10-5-2015 at WSU – device 08262015-5
All measurements taken after GFET
is blown dry. Multiple plots at each
stage represent multiple scans
through Vgs 15-35V. Scans were
repeated until the GFET response
stopped trending with time. Buffer
control (not shown) prior to dna
addition showed much quicker (3
minutes) settling time than seen
with dna addition.
10-5-2015 at WSU – device 08262015-5
0.4um x 0.4um
DNA ON SURFACE BETWEEN SOURCE AND DRAIN AFTER RINSING
10-5-2015 at WSU – device 08262015-5
After return to Marshall U, we measured the same device for DC response. We varied the relative humidity of the
air over the GFET from 2% - 30% with no apparent effect on DC current measurements at Vsd = 0.05 and Vgs = 5V.
About 1 hour was given for the GFET to equilibrate with atmosphere at each RH.
AFM images reveal that the rinsed GFET is still covered with much dna origami. This extensive coverage does not
seem to affect electronic properties of graphene as profoundly as is seen in some literature:
N.J. Kybert, G.H. Han, M.B. Lerner, E.N. Dattoli, A. Esfandiar, A.T.C. Johnson, Scalable arrays of chemical vapor sensors based on DNA-decorated graphene, Nano Res. 7 (2014)
95–103 and Detection of DNA and poly-l-lysine using CVD graphene-channel FET biosensors Aniket Kakatkar1, T S Abhilash2, R De Alba2, J M Parpia2 and H G Craighead1
Nanotechnology 26 (2015) 125502 (5pp)
The devices in these studies were <100um in any dimension.
David Neff will visit Brown lab at WSU this week (12-16-2015) while Phi is there to repeat measurements with new
devices.
Norton lab (Abhijit R.) is performing experiments to determine if Mg++ is protective against the dissolution seen
when dna origami adsorbs to HOPG/graphene. Also we are eploring ways to reverse dna binding to
HOPG/graphene.
These studies are in part to answer reviewers