An MXene–graphene
field-effect transistor (FET) sensor for
both influenza virus and 2019-nCoV sensing was developed and characterized.
The developed sensor combines the high chemical sensitivity of MXene
and the continuity of large-area high-quality graphene to form an
ultra-sensitive virus-sensing transduction material (VSTM). Through
polymer linking, we are able to utilize antibody–antigen binding
to achieve electrochemical signal transduction when viruses are deposited
onto the VSTM surface. The MXene–graphene VSTM was integrated
into a microfluidic channel that can directly receive viruses in solution.
The developed sensor was tested with various concentrations of antigens
from two viruses: inactivated influenza A (H1N1) HA virus ranging
from 125 to 250,000 copies/mL and a recombinant 2019-nCoV spike protein
ranging from 1 fg/mL to 10 pg/mL. The average response time was about
∼50 ms, which is significantly faster than the existing real-time
reverse transcription-polymerase chain reaction method (>3 h).
The
low limit of detection (125 copies/mL for the influenza virus and
1 fg/mL for the recombinant 2019-nCoV spike protein) has demonstrated
the sensitivity of the MXene–graphene VSTM on the FET platform
to virus sensing. Especially, the high signal-to-viral load ratio
(∼10% change in source-drain current and gate voltage) also
demonstrates the ultra-sensitivity of the developed MXene–graphene
FET sensor. In addition, the specificity of the sensor was also demonstrated
by depositing the inactivated influenza A (H1N1) HA virus and the
recombinant 2019-nCoV spike protein onto microfluidic channels with
opposite antibodies, producing signal differences that are about 10
times lower. Thus, we have successfully fabricated a relatively low-cost,
ultrasensitive, fast-responding, and specific inactivated influenza
A (H1N1) and 2019-nCoV sensor with the MXene–graphene VSTM.
Two-dimensional transition metal carbides (MXenes) have attracted a great interest of the research community as a relatively recently discovered large class of materials with unique electronic and optical properties. Understanding of adhesion between MXenes and various substrates is critically important for MXene device fabrication and performance. We report results of direct atomic force microscopy (AFM) measurements of adhesion of two MXenes (Ti
3
C
2
T
x
and Ti
2
CT
x
) with a SiO
2
coated Si spherical tip. The Maugis-Dugdale theory was applied to convert the AFM measured adhesion force to adhesion energy, while taking into account surface roughness. The obtained adhesion energies were compared with those for mono-, bi-, and tri-layer graphene, as well as SiO
2
substrates. The average adhesion energies for the MXenes are 0.90 ± 0.03 J m
−2
and 0.40 ± 0.02 J m
−2
for thicker Ti
3
C
2
T
x
and thinner Ti
2
CT
x
, respectively, which is of the same order of magnitude as that between graphene and silica tip.
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