Carbon nanotubes (CNTs) have been exploited for the development of electrochemical and biological
sensors because of their excellent electrochemical properties, large surface area, ballistic electron transport
and high mechanical strength. In addition to enhanced electrochemical reactivity, CNT-modified
electrodes can be employed to immobilize biomolecules and to minimize surface fouling effects [60].
Moreover, CNT-based electrochemical transducers offer substantial improvements in the performance of
amperometric enzyme electrodes, immunosensors and nucleic-acid sensing devices. Recent studies have
demonstrated that CNT can be used to enhance the electrochemical reactivity of important biomolecules,
and can be utilized to promote the electron-transfer reactions of proteins such as cytochrome c, ascorbic
acid, xanthine oxidase, catalase, tryptophan and dopamine [61]. Further, CNT’s exceptional properties
such as small size, great strength, high electrical and thermal conductivity, and large specific surface area
make them excellent amplification platforms to increase the number of signal-generating molecules [52].
Carbon nanotubes (CNTs) considered as a suitable candidate to be used in paper based sensing
devices due to effective deposition characteristics using carbon nanotubes-based ink and excellent
electronic transduction properties. For instance, Shim et al. took advantage of cotton yarns to build a
SWCNT based chemiresistor for protein detection [62]. Wang et al modified filter paper with carbon
nanotube and antibodies for amperometric detection of microcystin-LR toxin [63]. Similarly Pozuelo et al
fabricated a conductive paper by simply painting paper filter with SWCNT ink. This platform was further
utilized for human immunoglobulin G detection[64]. Zang et al reported electrochemical Immunoassay on
3D microfluidic paper-EDVHG GHYLFH IRU GHWHFWLRQ RI YDULRXV FDQFHU ELRPDUNHU VXFK DV Į-fetoprotein,
carcinoma antigen 125, carcinoma antigen 199 and CEA [65]. For this purpose they modify paper surface
with carbon paste, wax, carbon nanotubes, chitosan with the help of wax and screen printing technique. In
another work, a battery-triggered microfluidic paper-based multiplex electrochemiluminescence
immunodevice based on potential-resolution strategy was demonstrated for the diagnosis of four cancer
markers (r-fetoprotein (AFP), CA 153, CA 199 and CEA [66]. For this purpose carbon nanotube, chitosan
and glutardehyde modified paper zone were used for antibody immobilization which are connected with
screen printed carbon working electrode and Ag/AgCl auxillary electrode through the paper channel.
Further, Wang et al proposed a microfluidic paper-EDVHG DQDOWLFDO GHYLFH ȝ3$'V $ ZD[-patterned
microfluidic paper-based three-dimensional electrochemical device (3D-ȝ3(' ZDV GHPRQVWUDWHG EDVHG
on the multi-ZDOOHG FDUERQ QDQRWXEHV 0:&17V PRGLILHG ȝ3$' 8VLQJ +53-O-PhenylenediamineH2O2
electrochemical system, a sandwich immunoassay on this 3D-ȝ3(' IRU VHQVLWLYHGLDJQRVLVRIWZR
tumor markers simultaneously in real clinical serum samples was developed with a linear range of 0.001–
75.0 U mLí1 for cancer antigen 125 and 0.05–50.0 ng mLí1 for CEA [67]. In this work different printing
technique (screen printing, wax printing etc), costly conducting ink or sophisticated design were used for
biomolecule detection.
We used composites of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)
and carbon nanotube (CNT) for fabrication of the conducting paper by simple dip coating method[68].
Itwas found that the conductivity of formic acid treated paper increased by 2 orders of magnitude due to
removal of non-conducting PSS molecule from conducting paper surface leading to conformational
rearrangement. This fabricated paper is electrochemical active, flexible, efficient conductive and can be
easily disposed off by simple incineration (figure 4). Further this platform was utilized for cancer
biomarker (carcinoembryonic antigen, CEA) detection by immobilizing monoclonal antibody against CEA
(anti-CEA). The PEDOT:PSS-CNT based electrochemical paper immunosensor showed sensitivity [7.8
μA(ng/ml)-1cm2
] in a linear detection range of 2–15 ngmL-1 (figure 5) and feasibility of paper electrode
was also validated with CEA concentration in serum sample of cancer patient. It was observed that
incorporation of carbon nanotubes improve heterogenous electron transfer rate constant and linear
detection range of PEDOT:PSS-CNT based conducting paper compare to PEDOT:PSS-RGO based CP.
IJEGMBE 2015 IOP Publishing
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