Highly Uniform, Flexible Microelectrodes Based on the Clean Single

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Functional Nanostructured Materials (including low-D carbon)

Highly uniform, flexible microelectrodes based on clean singlewalled carbon nanotube thin film with high electrochemical activity Nguyen Xuan Viet, Shigeru Kishimoto, and Yutaka Ohno ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b19252 • Publication Date (Web): 23 Jan 2019 Downloaded from http://pubs.acs.org on January 25, 2019

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ACS Applied Materials & Interfaces

Highly Uniform, Flexible Microelectrodes Based on Clean Single-walled Carbon Nanotube Thin Film with High Electrochemical Activity Nguyen Xuan Viet†,1, Shigeru Kishimoto†, and Yutaka Ohno† †Department

‡,*

of Electronics, Nagoya University, Nagoya 464-8603, Japan

‡Institute

of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8603, Japan

KEYWORDS: carbon nanotube, flexible electronics, electrochemical sensor, microelectrode, dopamine, thin film

ABSTRACT: Electrochemical sensors based on carbon nanotubes (CNTs) have great potential for use in wearable or implantable biomedical sensor

applications

flexibility and associated reproducible

with

because

of

their

excellent

biocompatibility. However, the CNT-based

fabrication

on

sensors

is

flexible

plastic

mechanical

main challenge

their

uniform

film.

Here,

and we

introduce and demonstrate a highly reliable technique to fabricate

ACS Paragon Plus Environment

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flexible CNT microelectrodes on a plastic film. The technique involves a process whereby the CNT film is formed by the dry transfer process based on the floating-catalyst chemical vapor deposition. An oxide protection layer, which is used to cover the CNT

thin

film

contamination

during

the

the

surface.

of

fabrication The

process,

fabricated

minimizes

flexible

CNT

microelectrodes show almost ideal electrochemical characteristics for

microelectrodes

with

the

average

value

of

the

quartile

potentials, E = |E3/4  E1/4|, was 60.4 ± 2.9 mV for the 28 electrodes, while ideal value E = 56.4 mV. The CNT microelectrodes also showed the enhanced resistance to surface fouling during dopamine

oxidation

in

comparison

to

carbon

fiber

and

gold

microelectrodes; the degradations of the oxidation current after ten consecutive cycles were 1.8, 8.3, and 13.9 % for CNT, carbon fiber,

and

sensitivity

gold

microelectrodes,

detection

differential-pulse

of

dopamine

voltammetry,

respectively. is

with

also a

The

high-

demonstrated

resulting

limit

with of

detection of ~50 nM. The reliability, uniformity, and sensitivity of the present CNT microelectrodes provide a platform for flexible electrochemical sensors.

INTRODUCTION


2

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Flexible biosensors are advantageous in that they are adaptable to non-planar surfaces such as human organs and are lightweight.1-2 For example, these biosensors have been used for in vivo monitoring of brain activity through the exploitation of conformal contact.1, 3

Among the various materials suitable for flexible biosensors,

single-walled carbon nanotubes (CNTs) have attracted significant research attention since their discovery owing to their remarkable electrical

and

mechanical

performance.4

They

have

also

shown

promise as electrochemical electrodes because of properties such as rapid electron transfer kinetics, a wide potential window, high sensitivity, biocompatibility, and manufacturing versatility,5-7 in addition to their potential for application in flexible devices.8-10 They can be fabricated on plastic film at room temperature and ambient pressure by using a low-cost process such as a printing technique and transfer process. CNT-based flexible electrochemical sensors have been investigated extensively in recent decades.11-15 Previously, CNTs were deposited on conductive materials capable of providing sufficient electrical conductivity to the CNT electrodes. This was achieved via various methods such as direct growth,16 drop-casting,17 and layer-by-layer assembly.18 The electrochemical response in these hybrid electrodes is provided by both the supporting conducting material and the CNTs. Usually, the electrochemical signal from the CNTs is stronger than that from the supporting metal; however, the potential window


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Page 4 of 28

of this supporting conducting material is smaller than that of the CNTs. Moreover, the effect of the background signal from the supporting metal is significant especially at low concentrations in electrochemical analysis. This reduces the signal-to-noise ratio and limit of detection, whereas as-grown CNT possesses a weaker intrinsic background signal and wider potential window compared to typical metals such as Au and Pt.19 Another problem with CNT-based electrochemical sensors is the poor uniformity in their electrochemical behavior. CNT film can be fabricated according to a number of techniques such as chemical vapor deposition (CVD), solution filtration, thermal spray, and microcontact

printing.20

However,

normal

high-temperature

CVD

cannot be used to deposit a thin film of CNT on flexible plastic film and the conventional solution-based process may degrade the performance and the uniformity in electrochemical activity due to the

contamination

associated

with

dispersal

substances.

For

example, the fabrication of reliable and reproducible CNT-based electrodes has been challenging as a result of contamination that occurs during the lithography-based microprocess.21 In this work, we realized the highly reproducible fabrication of a CNT electrochemical microelectrode on a plastic film by using clean and highly conductive CNT thin film without conductive supporting material. The CNT thin film is formed by a dry transfer process based on floating-catalyst (FC) CVD, which provides a


4

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contamination-free and uniform CNT thin film of as-grown singlewalled CNTs on the plastic film at room temperature.22 We also introduced a protection layer to ensure the CNT surface remains clean

during

the

electrochemical electrochemical

microfabrication

process.

microelectrodes with properties

have

As

a

result,

CNT

nearly ideal and uniform been

realized.

The

CNT

microelectrode was evaluated by demonstrating the high-sensitivity detection of dopamine, an important neurotransmitter.

EXPERIMENTAL SECTION The

flexible

CNT

microelectrodes

were

fabricated

on

a

poly(ethylene napthalate) (PEN) film as shown in Figure 1(a). The CNT thin film was formed by a dry transfer process based on FC CVD.7,

23

Single-walled CNTs were grown by using the FC CVD technique

at ambient pressure with CO as the carbon source, wherein the catalyst

nanoparticles

were

produced

by

the

decomposition

of

ferrocene vapor. CO (200 sccm) was passed through a cartridge containing ferrocene powder. Additional CO (200 sccm) and CO2 (3 sccm) were introduced into the furnace. The growth temperature was 850 C. The CNTs grown by FC CVD were collected by a membrane filter for 600 s, resulting in the formation of a uniform CNT thin film on the filter. The average diameter of the CNTs was estimated to

be

1.7

nm

from

an

absorption

spectrum

(see

Supporting


5


Page 6 of 28

Information, Figure S1). The optical transmittance was 95 % at 550 nm, corresponding to an average CNT thickness of ~5 nm. After forming Au/Ti (100/10 nm) contact electrodes on the PEN film

by

conventional

microfabrication

process,

i.e.,

photolithography, electron-beam evaporation, and lift-off process, the CNT thin film was transferred from the membrane filter to the PEN film. The membrane filter with a CNT thin film was placed on the PEN film such that the side with the CNT thin film contacted the top surface of the PEN film, and pressed gently with a finger to transfer the CNT thin film to the PEN substrate.7,

22

Several

droplets of 2-propanol was dropped onto the CNT thin film with a pipette and dried by nitrogen blow to densify the CNT thin film. The dense network structure of the CNT thin film was observed by SEM as shown in Figure 1(b). The CNT thin film was smoothly connected to the top surface of the Au/Ti electrode even though there was a step at the edge of the electrode (see Supporting Information, Figure S2). This is because the length of the bundles of CNTs ( ≳ 2 m) was much longer than the step height. To prevent the CNT surface from contamination by the photoresist, a layer of 50-nm Al2O3 was deposited on top of the CNT thin film by atomic layer deposition (ALD) at low temperature (140 C). It is known that continuous coating of Al2O3 is possible onto bundles of CNTs by ALD because of the existence of interstitial pores between the individual CNTs constituting the bundle.24 In addition,


6

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Al2O3

is

not

active

in

electrochemical

reaction.25

The

Al2O3

deposited using this technique can easily be removed by basic solution because of the low crystallinity. Outside the electrode region, the CNT thin film was etched by oxygen plasma, by using the Al2O3 layer as a mask. A layer of poly(methyl methacrylate) (PMMA) was applied on top of the Al2O3/CNT to prevent direct exposure of the Au/Ti contact to the electrolyte solution during electrochemical measurement.26 The CNT electrode window was opened by etching the PMMA layer with oxygen plasma, and by subsequently etching the Al2O3 in diluted tetramethylammonium hydroxide (TMAH) solution.27 The fabrication process is described in detail in the Supporting Information (Figure S3).


7


(a)

Page 8 of 28

(b) Protection (PMMA/Al2O3)

CNT thin film Contact electrode (Au/Ti)

2 m

PEN film

(c)

(d)

CE

CNT thin film Au/Ti

WE

RE

Figure

1.

Flexible

CNT

microelectrode

on

plastic

film.

(a)

Schematic structure of the CNT microelectrode, (b) SEM image of CNT thin film, (c) photograph of array of CNT microelectrodes and (inset) micrograph of a CNT microelectrode with a size of 70  70 m2. (d) Photogram of measurement setup.

An array of 35 microelectrodes with different sizes from 30 to 150 m was fabricated on the PEN film sized 10 × 15 mm2 as can be seen in Figure 1(c). A micrograph of a typical CNT microelectrode


8

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is shown in the inset. The above-mentioned process enabled a CNT microelectrode with well-defined geometry to be obtained. The active window area was positioned 5 m away from the gold contact to minimize the series resistance of the CNT thin film. The contact electrode was electrically isolated from the electrolyte by the Al2O3 and PMMA layers, such that only the CNT surface is exposed to the solution and electrochemical reaction is due purely to electron transfer on the CNTs. The electrochemical measurements were performed in a 10-mM PBS solution (pH 7.4) or 0.1 M KCl as the supporting electrolyte using a -Autolab type III Potential/Galvanostat (Metroohm) in a threeelectrode system. The experimental setup is shown in Figure 1(d). The flexible CNT microelectrode served as the working electrode (WE), which was connected to the potentiostat via the contact electrode and a needle probe, a AgCl/Ag electrode (World precision instruments, USA) as the reference electrode (RE), and a platinum wire

(BAS-Japan)

as

the

counter

electrode

(CE).

The

CNT

microelectrode array was attached to a PDMS chamber, in which electrolyte was stored during electrochemical measurements.

RESULTS AND DISCUSSION Uniformity in electrochemical activity


9


Page 10 of 28

We evaluated the uniformity in terms of the electrochemical activity of the surface of the fabricated CNT microelectrodes by observing electrochemically deposited Au nanoparticles. The gold nanoparticles were deposited by subjecting a solution containing HAuCl4 (0.5 mM in a 50-mM PBS solution) to cyclic voltammetry in the potential range from -0.7 to 0.4 V vs. the AgCl/Ag reference electrode at a scan rate of 50 mV/s for three consecutive cycles.21 The SEM images in Figure 2(a) confirm that the Au nanoparticles are

uniformly

deposited

on

the

entire

surface

of

the

CNT

microelectrode. The magnified SEM images in Figure 2(b) show that the Au nanoparticles are approximately uniform in size. This is in contrast to previous work,14 in which a CNT thin film was prepared by a solution-based process and the resultant Au nanoparticles showed a poorer uniform distribution than our CNT microelectrodes. There is no significant variation in the size and density of Au nanoparticles between the center and edge of the CNT electrode, showing that the voltage drop from the edge to the center of the CNT

microelectrodes,

which

was

often

observed

in

previous

research, is negligible.28


10

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(b)

(a)

5 m

20 m

Figure

2.

SEM

images

of

Au

nanoparticles

electrochemically

deposited on the CNT microelectrode: (a) entire surface of the microelectrode and (b) magnified image.

Electrochemical characteristics Electrochemical characterization of the CNT microelectrodes was carried out by using cyclic voltammetry to observe the redox reaction of ferri/ferro cyanide in K3[Fe(CN)6] (0.1 mM) solution with KCl (0.1 M) as the supporting electrolyte. Figure 3(a) shows the

cyclic

voltammograms

for

the

28

as-fabricated

CNT

microelectrodes with different electrode sizes (7 electrodes of each size). Typical sigmoidal cyclic voltammograms, as determined by the diffusion-controlled steady state current, were obtained for the CNT microelectrodes with sizes ranging from 30 to 100 m.


11


Page 12 of 28

The average value of the quartile potentials, E = |E3/4  E1/4|, was 60.4 ± 2.9 mV for the 28 electrodes. This value closely approximates the ideal value of 56.4/n (mV) (Tomeš criterion) for a reversible system with one electron (n = 1).29 This means that the CNT microelectrodes have a high electron transfer rate. The diffusion-controlled steady state current (iss) at a disk microelectrode can be estimated by28 iss = 4nrFDC,

(1)

where n is the number of electrons transferred per redox event, F is the Faraday constant, r is the radius of the disk electrode, and C and D are the concentration and diffusion coefficient of the electroactive species, respectively. Assuming r to be the length of the side of the square-shaped CNT microelectrode, the measured and calculated iss values are in good agreement, as shown in Figure 3(b). An almost identical electrochemical response, i.e., a high electron transfer rate and ideal iss value, was obtained for all the

fabricated

CNT

electrodes.

Furthermore,

reproducible

electrochemical characteristics were achieved for the different CNT microelectrodes not only within the same batch, but also among different batches. The standard deviation of iss was as small as ~3 % for each size of CNT electrode within the same fabricated batch

and

~7

%

among

the

different

batches

of

fabricated

electrodes.


12

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(a)

(b)

i = 4nrFDC ss

Figure 3. (a) Cyclic voltammograms of 0.1-mM solution measured with six CNT microelectrodes for each electrode size. (b) Steady state current versus electrode size. The red dots and blue line show the measured and calculated data by Eq. (1), respectively.

In

addition,

we

evaluated

the

dependence

of

iss

on

the

concentration of K3[Fe(CN)6] in the range from 0.025 to 1 mM in 0.1-M KCl solution with a microelectrode with a diameter of 50 m (see Supporting Information, Figure S4). Even though the E values increased slightly from 57.2 to 74.3 mV as the concentration increased from 0.025 to 1 mM, a high electron transfer rate was obtained for a wide range of K3[Fe(CN)6] concentrations. The iss values and their linear fitting indicate a good linearity of iss


13


with

K3[Fe(CN)6]

concentration

(R2

=

Page 14 of 28

0.998).

The

diffusion

coefficient of K3[Fe(CN)6] inferred from the slope of the plot was D = 7.4  10-6 cm2/s. This value is close to the value of 7.6  10-6 cm2/s reported previously.29 Further enhancement of the electron transfer rate was achieved by

oxidizing

the

electrochemical

surface.

We

examined

the

electrochemical oxidation of CNTs in sulfuric acid solution (2.0 M) by cyclic voltammetry in the potential range of 0~1.8 V vs. AgCl/Ag for five cycles at a scan rate of 100 mV/s. The value of the quartile potential E recorded in 1-mM K3[Fe(CN)6] solution was reduced from 74.3 mV for the as-fabricated electrode to 54.6 mV for the oxidized electrode (see Supporting Information, Figure S5). This result is consistent with those reported for conventional acid-oxidized CNT electrodes.30-31 Interestingly, the oxidized CNT electrodes did not show a significant increase in their background current compared with the as-fabricated electrodes. This behavior differed from that in a previous report on multi-walled CNTsheathed carbon fiber,32 but is consistent with reports on pristine single-walled CNT.31,

33

Detection of dopamine Next, we examined the detection of dopamine (DA) which is an important neurotransmitter and plays a significant role in the function of the mammalian central brain.34 Real-time monitoring of DA has been a long-standing goal because it has been proven to be


14

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a very effective route toward detecting some brain diseases such as

Parkinson’s

disease,35

which

is

characterized

by

the

near

depletion of DA in the synaptic cleft, and schizophrenia,36 which is associated with an abnormally high concentration of DA in the brain. Flexible electrochemical sensors have been considered one of the most promising approaches to realizing real-time monitoring of DA in the brain. This is because their mechanical flexibility allows them to be easily embedded with minimal damage to soft tissues.

In

addition,

they

are

highly

sensitive

toward

the

detection of DA and offer simplicity of implementation. Figure

4(a)

shows

the

cyclic

voltammograms

of

various

concentrations of DA in the range 1 ~ 250 µM, which were measured with an oxidized CNT microelectrode 50 m in diameter. Here, DA was solubilized in 10-mM PBS (pH = 7.4). The CV curves have welldefined sigmoidal shapes. The DA oxidation was irreversible and the quartile potential was E = 50.0 mV at 100 µM, hence far exceeding the ideal value of 28.4 mV for the two-electron transfer of

the

DA

oxidation

reaction.

However,

this

result

is

an

improvement compared to the value of multi-walled carbon nanotubes on a carbon fiber microelectrode, 99.1 mV.37 Good linear fitting with R2 = 0.998 was obtained for the calibration curve for a wide range of DA concentration of 1 ~ 250 M as shown in Figure 4(b). The linear response region covers the DA concentration in a region


15


Page 16 of 28

of the brain known as the caudate nucleus (~50 M if the caudate nucleus were considered as a homogeneous phase).38 (a)

(b)

Figure 4. Detection of DA with CNT microelectrode. (a) Cyclic voltammograms for various DA concentrations from 1 to 250 M, (b) calibration curve.

In addition, the measurement of DA was additionally investigated by using the differential-pulse voltammetry technique39 because of its

enhanced

sensitivity

compared

to

cyclic

voltammetry.

The

measurement conditions are as follows: increasing potential 4mV, amplitude 5 mV, pulse width 50 ms, sampling width 16.7 ms, pulse period

0.2

s,

and

quiet

time

2

s.

The

differential-pulse

voltammograms for low DA concentrations of 50 ~ 250 nM are shown


16

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in Figure 5(a). The signal current also showed good linearity as shown in Figure 5(b). The limit of detection was ~50 nM for the flexible CNT microelectrodes, which is comparable with the DA concentration in the extracellular fluid of the caudate nucleus, 26 nM (nucleus accumbens) or 40 nM (striatum).40 (a)

Figure

(b)

5.

Differential-pulse

voltammograms

of

DA

with

CNT

microelectrode. (a) Voltammograms for DA concentration from 0.05 to 1.0 µM, (b) signal current as a function of DA concentration.

Anti-fouling property In practical sensor applications, especially for implantable sensors, the anti-fouling properties of the electrode surface during long-term analysis are important. The products of the DA


17


Page 18 of 28

oxidation process are known to cause considerable fouling of the surface of carbon-based electrodes.37, repeated

cyclic

voltammetry

41

We therefore carried out

measurements

of

DA

at

a

high

concentration of 0.5 mM with flexible CNT microelectrodes. The cyclic

voltammograms

of

ten

consecutive

measurements

with

an

oxidized microelectrode are shown in Figure 6(a). The positive shift

in

the

half

height

of

the

oxidation

potential

(E1/2)

indicates the existence of the fouling phenomenon.42 The values of E1/2 are plotted against the number of cycles in Figure 6(b). For comparison, the same experiments were conducted with a carbon fiber microelectrode (33 µm, BAS) and a Au microelectrode (50  50 µm2, custom made). The values of E1/2 were 39.8 and 55.2 mV for the asfabricated and

oxidized CNT microelectrodes, respectively. In

contrast, larger E1/2 values were observed for carbon fiber (88.3 mV) and the Au microelectrode (102.5 mV) after ten consecutive measurements

(see

demonstrating

that

Supporting the

Information,

anti-fouling

properties

Figure of

the

S6), CNT

microelectrode are more effective. In addition, degradation of the signal current of DA oxidation after the 10th measurement was also much less for the CNT oxidized microelectrode (1.8%) than for the carbon fiber (8.3%) and Au (13.9%) microelectrodes, confirming the good reliability of the CNT microelectrodes.


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(a)

(b)

Figure 6. (a) Ten consecutive cyclic voltammograms of the CNT microelectrode

repeatedly

measured

in

10-mM

PBS

solution

containing 0.5-mM dopamine, (b) shift of E1/2 during repeated cyclic voltammetry

for

as-fabricated

CNT,

activated

CNT,

commercial

carbon fiber, and Au microelectrodes.

CONCLUSIONS We developed a reproducible technique to fabricate a flexible CNT microelectrode

with

uniform

electrochemical

properties

on

a

plastic substrate. The technique is based on the dry transfer process

and

floating-catalyst

CVD.

The

standard

deviation

of

signal currents measured using cyclic voltammetry of K3[Fe(CN)6] was as small as ~3 % for the same fabricated batch and ~7 % among


19


Page 20 of 28

different batches of fabricated electrodes. The clean and highly conductive

CNT

thin

film

exhibited

ideal

electrochemical

characteristics for microelectrodes with a high electron transfer rate. The CNT microelectrodes exhibited enhanced stability to electrode surface fouling during oxidation of DA in comparison with carbon fiber and gold microelectrodes. In addition, the CNT microelectrodes showed high sensitivity toward the detection of DA with a detection limit of ~50 nM when using differential-pulse voltammetry. CNT microelectrodes based on the present technique provide a platform for the fabrication of flexible electrochemical sensors with excellent electrochemical properties.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Absorption spectrum of CNT thin film, SEM image in the vicinity of

the

contact

electrode,

fabrication

process,

dependence

of

cyclic voltammograms on concentration of K3[Fe(CN)6], effect of electrochemical

oxidation

of

the

CNT

microelectrode,

cyclic

voltammograms of ten consecutive measurements of dopamine with carbon fiber and Au electrodes


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Present Addresses 1Present

address: Department of Physical Chemistry, Faculty of

Chemistry, VNU University of Science, Hanoi, 19 Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam Funding Sources This work was partially supported by JST/CREST (JPMJCR 16Q2) and MEXT KAKENHI Grant Numbers JP15H05867 and JP26107521. Notes Any additional relevant notes should be placed here.


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References (1) Kim, D.-H.; Viventi, J.; Amsden, J. J.; Xiao, J.; Vigeland, L.; Kim, Y.-S.; Blanco, J. A.; Panilaitis, B.; Frechette, E. S.; Contreras, D. Dissolvable Films of Silk Fibroin for Ultrathin Conformal Bio-Integrated Electronics. Nat. Mater. 2010, 9, 511517. (2)

Hsu,

M.-S.;

Chen,

Y.-L.;

Lee,

C.-Y.;

Chiu,

H.-T.

Gold

Nanostructures on Flexible Substrates as Electrochemical Dopamine Sensors. ACS Appl. Mater. Interfaces 2012, 4, 5570-5575. (3) Viventi, J.; Kim, D.-H.; Vigeland, L.; Frechette, E. S.; Blanco, J. A.; Kim, Y.-S.; Avrin, A. E.; Tiruvadi, V. R.; Hwang, S.-W.; Vanleer, A. C. Flexible, Foldable, Actively Multiplexed, High-Density Electrode Array for Mapping Brain Activity in Vivo. Nat. Neurosci. 2011, 14, 1599-1605. (4) De Volder, M. F.; Tawfick, S. H.; Baughman, R. H.; Hart, A. J. Carbon

Nanotubes: Present

and Future

Commercial

Nanostructuring

Electrodes

Applications.

Science 2013, 339, 535-539. (5)

Gooding,

Nanotubes:

A

J.

J.

Review

on

Electrochemistry

and

with

Carbon

Applications

for

Sensing. Electrochim. Acta 2005, 50, 3049-3060. (6) Vashist, S. K.; Zheng, D.; Al-Rubeaan, K.; Luong, J. H.; Sheu, F.-S. Advances in Carbon Nanotube Based Electrochemical Sensors


22

Page 23 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for Bioanalytical Applications. Biotechnol. Adv. 2011, 29, 169188. (7) Fukaya, N.; Kim, D. Y.; Kishimoto, S.; Noda, S.; Ohno, Y. OneStep

Sub-10

m

Patterning

of

Carbon-Nanotube

Thin

Films

for

Transparent Conductor Applications. ACS Nano 2014, 8, 3285-3293. (8) Sun, D.-M.; Timmermans, M. Y.; Kaskela, A.; Nasibulin, A. G.; Kishimoto, S.; Mizutani, T.; Kauppinen, E. I.; Ohno, Y. Mouldable All-Carbon Integrated Circuits. Nat. Commn. 2013, 4, 2302. (9) Wang, C.; Chien, J.-C.; Takei, K.; Takahashi, T.; Nah, J.; Niknejad, A. M.; Javey, A. Extremely Bendable, High-Performance Integrated Circuits Using Semiconducting Carbon Nanotube Networks for Digital, Analog, and Radio-Frequency Applications. Nano Lett. 2012, 12, 1527-1533. (10) Sun, D. M.; Timmermans, M. Y.; Tian, Y.; Nasibulin, A. G.; Kauppinen, E. I.; Kishimoto, S.; Mizutani, T.; Ohno, Y. Flexible High-Performance

Carbon

Nanotube

Integrated

Circuits.

Nat.

Nanotechnol. 2011, 6, 156-161. (11) Yan, X. B.; Chen, X. J.; Tay, B. K.; Khor, K. A. Transparent and Flexible Glucose Biosensor Via Layer-by-Layer Assembly of Multi-Wall Carbon Nanotubes and Glucose Oxidase. Electrochem. Commun. 2007, 9, 1269-1275. (12) Lee, J.-Y.; Park, E.-J.; Lee, C.-J.; Kim, S.-W.; Pak, J. J.; Min, N. K. Flexible Electrochemical Biosensors Based on O2 Plasma Functionalized Mwcnt. Thin Solid Films 2009, 517, 3883-3887.


23


Page 24 of 28

(13) Bui, M.-P. N.; Pham, X.-H.; Han, K. N.; Li, C. A.; Kim, Y. S.; Seong, G. H. Electrocatalytic Reduction of Hydrogen Peroxide by Silver Particles Patterned on Single-Walled Carbon Nanotubes. Sensors Actuators B: Chem. 2010, 150, 436-441. (14)

Ngoc

Bui,

M.-P.;

NamáHan,

K.; AiáLi, C.; HunáSeong,

G.

Electrochemical Patterning of Gold Nanoparticles on Transparent Single-Walled Carbon Nanotube Films. Chem. Commun. 2009, 55495551. (15) Koh, J.; Yi, M.; Lee, B. Y.; Kim, T. H.; Lee, J.; Jhon, Y. M.;

Hong,

S.

Directed

Assembly

of

Carbon

Nanotubes

on

Soft

Substrates for Use as a Flexible Biosensor Array. Nanotechnology 2008, 19, 505502. (16) Okuno, J.; Maehashi, K.; Matsumoto, K.; Kerman, K.; Takamura, Y.;

Tamiya,

E.

Single-Walled

Carbon

Nanotube-Arrayed

Microelectrode Chip for Electrochemical Analysis. Electrochem. Commun. 2007, 9, 13-18. (17) Luo, H.; Shi, Z.; Li, N.; Gu, Z.; Zhuang, Q. Investigation of the Electrochemical and Electrocatalytic Behavior of Single-Wall Carbon Nanotube Film on a Glassy Carbon Electrode. Anal. Chem. 2001, 73, 915-920. (18)

Zhang,

M.;

Gong,

K.; Zhang, H.;

Mao,

L. Layer-by-Layer

Assembled Carbon Nanotubes for Selective Determination of Dopamine in the Presence of Ascorbic Acid. Biosens. Bioelectron. 2005, 20, 1270-1276.


24

Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19) Rosenblatt, S.; Yaish, Y.; Park, J.; Gore, J.; Sazonova, V.; McEuen, P. L. High Performance Electrolyte Gated Carbon Nanotube Transistors. Nano Lett. 2002, 2, 869-872. (20) Liu, H.; Takagi, D.; Chiashi, S.; Homma, Y. Transfer and Alignment of Random Single-Walled Carbon Nanotube Films by Contact Printing. ACS Nano 2010, 4, 933-938. (21) Viet, N. X.; Ukita, Y.; Chikae, M.; Ohno, Y.; Maehashi, K.; Matsumoto, K.; Viet, P. H.; Takamura, Y. Fabrication of New SingleWalled Carbon Nanotubes Microelectrode for Electrochemical Sensors Application. Talanta 2012, 91, 88-94. (22) Kaskela, A.; Nasibulin, A. G.; Timmermans, M. Y.; Aitchison, B.; Papadimitratos, A.; Tian, Y.; Zhu, Z.; Jiang, H.; Brown, D. P.; Zakhidov, A. Aerosol-Synthesized Swcnt Networks with Tunable Conductivity and Transparency by a Dry Transfer Technique. Nano Lett. 2010, 10, 4349-4355. (23) Moisala, A.; Nasibulin, A. G.; Brown, D. P.; Jiang, H.; Khriachtchev, L.; Kauppinen, E. I. Single-Walled Carbon Nanotube Synthesis Using Ferrocene and Iron Pentacarbonyl in a Laminar Flow Reactor. Chem. Eng. Sci. 2006, 61, 4393-4402. (24)

Grigoras,

Kauppinen,

E.

K.; I.;

Zavodchikova, Ernnolov,

V.;

M.

Y.;

Nasibulin,

Franssila,

S.

A.

Atomic

G.;

Layer

Deposition of Aluminum Oxide Films for Carbon Nanotube Network Transistor Passivation. J. Nanosci. Nanotechnol. 2011, 11, 88188825.


25


Page 26 of 28

(25) Diaz, B.; Harkonen, E.; Swiatowska, J.; Maurice, V.; Seyeux, A.; Marcus, P.; Ritala, M. Low-Temperature Atomic Layer Deposition of Al2O3 Thin Coatings for Corrosion Protection of Steel: Surface and Electrochemical Analysis. Corros. Sci. 2011, 53, 2168-2175. (26) Heller, I.; Kong, J.; Heering, H. A.; Williams, K. A.; Lemay, S. G.; Dekker, C. Individual Single-Walled Carbon Nanotubes as Nanoelectrodes for Electrochemistry. Nano Lett. 2005, 5, 137-142. (27) Oh, J.; Myoung, J.; Bae, J. S.; Lim, S. Etch Behavior of ALD Al2O3 on HfSiO and HfSiON Stacks in Acidic and Basic Etchants. J. Electrochem. Soc. 2011, 158, D217-D222. (28) Dumitrescu, I.; Unwin, P. R.; Wilson, N. R.; Macpherson, J. V. Single-Walled Carbon Nanotube Network Ultramicroelectrodes. Anal. Chem. 2008, 80, 3598-3605. (29)

Bard,

A.

J.;

Faulkner,

L.

R.

Electrochemical

Methods:

Fundamentals and Applications, 2nd. Hoboken: Wiley and Sons 2001. (30) Gong, K.; Chakrabarti, S.; Dai, L. Electrochemistry at Carbon Nanotube Electrodes: Is the Nanotube Tip More Active Than the Sidewall? Angew. Chem. Int. Ed. 2008, 47, 5446-5450. (31)

Nishimura,

K.;

Ushiyama,

T.;

Viet,

N.

X.;

Inaba,

M.;

Kishimoto, S.; Ohno, Y. Enhancement of the Electron Transfer Rate in Carbon Nanotube Flexible Electrochemical Sensors by Surface Functionalization. Electrochim. Acta 2019, 295, 157-163. (32) Xiang, L.; Yu, P.; Hao, J.; Zhang, M.; Zhu, L.; Dai, L.; Mao, L. Vertically Aligned Carbon Nanotube-Sheathed Carbon Fibers as


26

Page 27 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Pristine Microelectrodes for Selective Monitoring of Ascorbate in Vivo. Anal. Chem. 2014, 86, 3909-3914. (33) Miller, T. S.; Macpherson, J. V.; Unwin, P. R. Electrochemical Activation of Pristine Single Walled Carbon Nanotubes: Impact on Oxygen Reduction and Other Surface Sensitive Redox Processes. PCCP 2014, 16, 9966-9973. (34)

Bowirrat,

A.;

Oscar ‐ Berman,

M.

Relationship

between

Dopaminergic Neurotransmission, Alcoholism, and Reward Deficiency Syndrome. Am. J. Med. Genet. B. 2005, 132, 29-37. (35) de la Fuente-Fernández, R.; Sossi, V.; Huang, Z.; Furtado, S.; Lu, J.-Q.; Calne, D. B.; Ruth, T. J.; Stoessl, A. J. LevodopaInduced

Changes

in

Synaptic

Dopamine

Levels

Increase

with

Progression of Parkinson's Disease: Implications for Dyskinesias. Brain 2004, 127, 2747-2754. (36) Sawa, A.; Snyder, S. H. Schizophrenia: Diverse Approaches to a Complex Disease. Science Signaling 2002, 296, 692. (37) Harreither, W.; Trouillon, R.; Poulin, P.; Neri, W.; Ewing, A. G.; Safina, G. Carbon Nanotube Fiber Microelectrodes Show a Higher Resistance to Dopamine Fouling. Anal. Chem. 2013, 85, 74477453. (38) Wightman, R. M.; May, L. J.; Michael, A. C. Detection of Dopamine Dynamics in the Brain. Anal. Chem. 1988, 60, 769A-793A. (39) Yue, H. Y.; Huang, S.; Chang, J.; Heo, C.; Yao, F.; Adhikari, S.; Gunes, F.; Liu, L. C.; Lee, T. H.; Oh, E. S. Zno Nanowire


27


Page 28 of 28

Arrays on 3d Hierachical Graphene Foam: Biomarker Detection of Parkinson’s Disease. ACS Nano 2014, 8, 1639-1646. (40) Perry, M.; Li, Q.; Kennedy, R. T. Review of Recent Advances in

Analytical

Techniques

for

the

Determination

of

Neurotransmitters. Anal. Chim. Acta 2009, 653, 1-22. (41) Tse, D. C.; McCreery, R. L.; Adams, R. N. Potential Oxidative Pathways of Brain Catecholamines. J. Med. Chem. 1976, 19, 37-40. (42) Dumitrescu, I.; Edgeworth, J. P.; Unwin, P. R.; Macpherson, J.

V.

Ultrathin

Carbon

Nanotube

Mat

Electrodes

for

Enhanced

Amperometric Detection. Adv. Mater. 2009, 21, 3105-3109.

TOC graphic:

Dry-transferred CNT thin film Protection

Contact electrode

CNT thin film Au/Ti

PEN film

 Flexible  Uniform & reproducible characteristics  Neary ideal electrochemical properties  Excellent anti-fouling property


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Highly Uniform, Flexible Microelectrodes Based on the Clean Single

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