Cat‐Tail‐Like Mesostructured Silica Fibers Decorated with Gold Nanowires: Synthesis, Characterization, and Application as Stretchable Sensors

Abstract

Gold‐nanowires (AuNWs)‐coated mesostructured silica fibers that have the appearance of a cat's tail have been successfully designed and synthesized. The silica fibers had a Brunauer‐Emmett‐Teller (BET) surface area of 347 m² g⁻¹ and Barret‐Joyner‐Halenda (BJH) pore size of 3.8 nm. Negatively charged gold seeds could be anchored onto the surface of mesoporous silica fibers through electrostatic attraction. Further treatment with growth solution (including HAuCl4, 4‐mercaptobenzoic acid, and ascorbic acid) enabled successful growth of vertically aligned AuNWs with controllable lengths on the silica fiber surfaces. These coaxial mesostructured silica microfibers conjugated with AuNWs exhibit excellent stability and real‐time response with high durability (≥2500 cycles) as a sensitive flexible microelectronic material. The fabricated device is able to detect the human pulse (measured at the wrist), as well as small‐amplitude finger motion.

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Cat-Tail-Like Mesostructured Silica Fibers Decorated with
Gold Nanowires: Synthesis, Characterization, and
Application as Stretchable Sensors
Zhijia Zhang,[a, b, c, d] Lim Wei Yap,[b, c] Dashen Dong,[b, c] Qianqian Shi,[b, c] Yan Wang,[b, c]
Wenlong Cheng,*[b, c] and Xiaojun Han*[a]
Gold-nanowires (AuNWs)-coated mesostructured silica fibers
that have the appearance of a cat’s tail have been successfully
designed and synthesized. The silica fibers had a Brunauer-
Emmett-Teller (BET) surface area of 347 m2g1and Barret-
Joyner-Halenda (BJH) pore size of 3.8 nm. Negatively charged
gold seeds could be anchored onto the surface of mesoporous
silica fibers through electrostatic attraction. Further treatment
with growth solution (including HAuCl4, 4-mercaptobenzoic
acid, and ascorbic acid) enabled successful growth of vertically
aligned AuNWs with controllable lengths on the silica fiber
surfaces. These coaxial mesostructured silica microfibers con-
jugated with AuNWs exhibit excellent stability and real-time
response with high durability (2500 cycles) as a sensitive
flexible microelectronic material. The fabricated device is able
to detect the human pulse (measured at the wrist), as well as
small-amplitude finger motion.
Introduction
The design and development in non-evasive assessment and
quantification of human body motion using electrical signals
are the attractively new trend for soft wearable electronics.[1]
The balance between electrical performance and mechanical
robustness is critical for reliable stretchable sensor. To date, a
diverse set of nanomaterials such as graphene,[2] carbon nano-
tubes (CNTs),[3] reduced graphene oxide (R-GO),[4] metallic
nanowires,[5] carbon black (CB),[6] and conductive polymers[7]
have been widely used in designing a series of strain sensors.
Ag nanowires are considered as an excellent candidate for soft
optoelectronic devices including transparent electrode,[8] touch
panel,[9] heater,[10] and stretchable sensor.[11] For example, the
wearable strain sensor based on the Ag nanowires/polyolefin
elastomer nanofibrous composite yarn showed the practicabil-
ity in the application of human motion detections.[12] In
addition, due to its excellent chemical inertness, biocompati-
bility, and facile surface modification, etc., gold has been the
prime material of choice in stretchable electronics, namely
elastronics.[13] In particular, ultrathin gold nanowires (AuNWs)
have been successfully used to design highly sensitive pressure
sensors and highly stretchable strain sensors for a wide range
of applications.[5b,d] More recently, we have also demonstrated
the use of elastomer-bonded standing AuNWs for strain and
electrochemical biosensors.[14]
On the other hand, fibers are crucial materials with
numerous technical applications ranging from textile products,
membrane filtration,[15] catalysis,[16] tissue engineering,[17] and
flexible electronics.[18] Previously, methods for preparing meso-
porous silica fibers include electrospinning,[19] template
method[20] and spontaneous growth.[21] While each method has
its own advantages and disadvantages, spontaneous growth
offers merits of simplicity for generating mesoporous silica
fibers by wet chemistry method. It only requires a single phase
solution and the process is non-toxic without involving high
voltage, special instruments or any complex process.
Multiscale hierarchical configurations have exhibited partic-
ularly desirable performance for increased surface area and
energy conversion efficiency, which can be applied in solar
cell[22] and multifunctional electrochemical sensor.[23] However,
there are few reports to date in the literature using nano-
structure multiscale hierarchical configuration for stretchable
electrochemical biosensors.
Here, inspired by cat tails, we combine standing AuNWs
growth technology with spontaneous mesoporous fibers fab-
rication to design hierarchical nanofiber-on-microfiber struc-
tures for stretchable sensors. Highly conductive AuNWs serve as
active sensing elements, whereas, supporting mesoporous silica
[a] Dr. Z. Zhang, Prof. X. Han
MIIT Key Laboratory of Critical Materials Technology
for New Energy Conversion and Storage
State Key Laboratory of Urban Water Resource and Environment,
School of Chemistry and Chemical Engineering
Harbin Institute of Technology
92West Da-Zhi Street, Harbin, 150001 (P. R. China)
E-mail: hanxiaojun@hit.edu.cn
[b] Dr. Z. Zhang, Dr. L. W. Yap, Dr. D. Dong, Dr. Q. Shi, Dr. Y. Wang,
Prof. W. Cheng
Department of Chemical Engineering
Faculty of Engineering
Monash University
Clayton, VIC 3800 (Australia)
E-mail: wenlong.cheng@monash.edu
[c] Dr. Z. Zhang, Dr. L. W. Yap, Dr. D. Dong, Dr. Q. Shi, Dr. Y. Wang,
Prof. W. Cheng
The Melbourne Centre for Nanofabrication
Clayton, VIC 3800 (Australia)
[d] Dr. Z. Zhang
Key Laboratory of Superlight Material
and Surface Technology of Ministry of Education
College of Material Science and Chemical Engineering
Harbin Engineering University, Harbin 150001 (P. R. China)
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cplu.201900043
Full Papers
DOI: 10.1002/cplu.201900043
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fibers offer flexible yet robust scaffolds. Such novel composite
fibers could be used for designing wearable sensors for
detecting human wrist pulse and tiny motion of finger. The
entire fabrication process is solution-based, exhibiting potential
applications in future soft elastronics.
Results and Discussion
The fabrication of the hierarchical composite fibers has three
steps as illustrated in Figure 1(a). Firstly, Cationic surfactant was
used as structure directing agent to construct mesostructured
silica fibers under strongly acidic conditions by a one-phase
route[24] . TEM image of mesostructured silica fibers was shown
in Figure 1(b). The mean diameter of mesoporous silica fibers
was 246 67 nm and the length was up to millimetres (Fig-
ure S1 in the Supporting Information). The cloudy silica micro-
fibers was seen to be suspended in ethanol solution as shown
at the bottom right corner in Figure S1 (a). Secondly, meso-
porous silica fibers were functionalized with amino group by
using (3-Aminopropyl) trimethoxysilane (APTMS) enabling an
amine-functionalized surface to facilitate subsequent adsorp-
tion of Au seeds following our modified process reported
earlier.[25] Then, amine-functionalized mesoporous silica fibers
were mixed with citrate-stabilized gold seeds (size is 3.5 
0.7 nm). The morphology and UV-vis spectrum of the prepared
Au seeds were characterized (Figure S2 (a) and (b)). The TEM
image (Figure 1(c)) shows the surface of mesoporous silica
fibers were covered with gold seeds after washing several times
with milliQ water. Strong electrostatic attraction between the
positively charge amine group and negatively charged citrate
allows anchoring of Au seeds onto silica microfibers (Figure S2
(c), (d) and (e)). Lastly, AuNWs were grown on the surface of
mesoporous silica fibers.[26] By using 4-mercaptobenzoic (MBA)
binding ligand, Au seeds anchored on the surface of silica
microfibers led to the growth of the standing AuNWs. As
revealed by SEM (Figure 1(d)), the AuNWs were observed to
have grown on the surface of mesoporous silica fibers in the
vertically aligned configuration.
The yield of mesoporous silica fibers synthesized using
cetyltrimethylammonium bromide (CTAB) as the template in
HCl solution was found to be above 90 %. The concentration of
CTAB played a key role to construct mesoporous silica fibers by
one phase method. Because the extent of micellization, the
concentration of the surfactant plays an important role both on
the formation of the micelle and aggregation into liquid
crystals. At a low concentration of CTAB in water (below
50 mM), individual CTAB molecules aggregated as small
spherical shapes (Figure S3 (a)). These spherical aggregates
could amalgamate at higher concentration (100 mM) to con-
struct elongated cylindrical shapes. These two structures
corresponding to liquid crystalline were observed in CTAB-silica
powders, showing in Figure S3 (b) and (c). By using 200 mM
CTAB as templating agent, pure mesoporous silica fibers were
obtained (Figure S3 (d)).
In order to study the meso-channel of mesoporous silica
fibers, both mesoporous silica fibers and AuNWs-functionalised
fibers were measured. The meso-channels were clearly seen
from the TEM images in Figure 2 (a) and (b). The mean diameter
of meso-channels was 1.2 0.2 nm (Figure S4). Brunauer-Em-
mett-Teller (BET) surface area from nitrogen adsorption-desorp-
tion isotherms revealed that both mesoporous silica fibers and
AuNWs-functionalised fibers have typical type-IV branches with
a large hysteresis (Figure 2c). The naked mesoporous silica
fibers had a Barret-Joyner-Halenda (BJH) pore size of 3.8 nm
and a surface area of 168 m2g1and the AuNWs-functionalised
fibers had a BJH pore size of 3.8 nm and a surface area of
347 m2g1. The AuNWs on the surface of mesoporous silica
fibers contributed to the increase of the surface area. Compar-
ing mesoporous silica fibers (black line in Figure 2(d)), the BJH
(Barret-Joyner-Halenda) pore size distribution plot of the
Figure 1. (a) Schematic illustrating the specific conditions used for synthesis of cat-tail-like gold-nanowires (AuNWs)-coated mesostructured silica fibers. TEM
images of (b) mesoporous silica fibers and (c) Au seeds anchored on the surface of mesoporous silica fibers. (d) SEM image of AuNWs-coated mesostructured
silica fibers.
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adsorption curve showed two peaks (red line) indicating that
the parallel AuNWs formed meso-channel.
To prove that Au seeds were anchored on the surface of
mesoporous silica fibers, the catalytic reduction of 4-NP to 4-AP
by NaBH4was employed. The schematic of the reduction
process of 4-NP to 4-AP is shown in Figure 3 (a). The electrons
from the BH4
-donor and the acceptor 4-NP surrounded on the
surface of Au nanoparticles and transferred surface hydrogen,
leading to the swift occurrence and completion from 4-NP to 4-
AP reduction reactions. The Figure S5 (a) as a blank test shows
the pure 4-NP aqueous solution exhibited a strong UV-vis
adsorption at 319 nm, however, this peak shifted to 400 nm
due to the formation of 4-nitrophenolate ions immediately after
the reducer NaBH4was added. Without the addition of Au
catalysts, there is no obvious change of the adsorption intensity
at 400 nm even with an excessive amount of NaBH4in 2 hours
(shown in Figure S5 (b)). With the addition of the mesoporous
silica fibers into the mixture, the miniscule changes of the peak
at 400 nm from 0 to 60 min in Figure 3(b) indicated that naked
mesoporous silica fibers don’t have the catalytic performance.
When mesoporous silica fibers@Au seeds were added into the
mixture, Figure 3(c) reveals that the peak progressively decrease
at 400 nm and a gradual increase of 4-AP adsorption at 300 nm.
It was verified by the complete disappearance of the pristine
strong peak at 400 nm after 14 min, and the initial luminous
yellow solution turn to colourless, indicating that the catalytic
reduction of 4-NP had completed. Figure 3 (d) displays a linear
relationship of ln(Ct/C0) versus reaction time, and the rate
constant k of the pseudo-first-order kinetics is 0.1403 min1. The
above results proved that Au seeds adsorbed on the surface of
mesoporous silica fibers. It is worth noting that the catalytic
performance of Au is directly associated with the particle size
according to the previous literature.[27] However, the catalytic
activity will be gradually decreased by the freely dispersed Au
aggregation. Au seeds anchored on mesoporous silica fibers
providing an efficient strategy to circumvent the block.
In our system the adsorption of Au seeds on the surface of
mesoporous silica fiber was the key process. Because AuNWs
cannot grow without substrate in the solution by our method.
When free Au seeds were used without being adsorbed to any
substrate, the seeds simply grew larger with spherical bramble
shape without forming nanowires (Figure S6). Hence, the
presence of the substrate was clearly essential for shifting the
spherical growth mode transfer to the nanowires growth.
The concentration of HAuCl4played an important role on
controlling the growth of AuNWs. To grow the AuNWs, the
mesoporous silica fibers @Au seeds were immersed in the
water/ethanol growth solution including MBA, HAuCl4and L-
ascorbic acid with the exact ratio. When the concentration of
HAuCl4was below 0.1 mM, no AuNWs was observed on the
surface of mesoporous silica fibers (Figure 4(a)). However, when
the concentration increased to 1 mM, it could be clearly
observed that the AuNWs were paralleled to each other on the
surface of mesoporous silica fiber with uniform width and
height from the crevice of AuNWs in Figure 4(b), S7 (a) and (b).
Figure 2. TEM images of (a) mesoporous silica fibers and (b) the meso-
channels of mesoporous silica fibers. (c) Nitrogen adsorption-desorption
isotherms of mesoporous silica fibers (black line) and AuNWs-functionalised
fibers (red line). (d) Pore size distribution obtained from the adsorption curve
of the sorption isotherm.
Figure 3. (a) Schematic illustration of conceivable mechanism of reduction of
4-NP to 4-AP by Au seeds on the surface of mesoporous silica fibers. UV-vis
adsorption spectra at different time points for the conversion of 4-NP over
(b) mesoporous silica fibers and (c) mesoporous silica fibers@Au seeds with
excess NaBH4in aqueous media at room temperature. (d) Plot of ln(Ct/C0)
as a function of time for the conversion. The concentration of 4-NP (Ct) and
C0(initial concentration) is directly related to the UV-vis adsorption intensity
at 400 nm.
Figure 4. SEM images of AuNWs-functionalised fibers. The AuNWs were in
green and the silica fiber was in red pseudo color, respectively. The
concentration of HAuCl4was (a) 0.1 mM (b) 1 mM (c) 5 mM.
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The growth of AuNWs was more remarkable when the
concentration of HAuCl4was increased to 5 mM, as shown in
Figure 4(c), S7 (c) and (d). Compared with the typical single-
crystalline nanowires, these AuNWs were not straight perfection
despite roughly parallel to each other.
A SEM image with the corresponding energy dispersive X-
ray spectroscopy (EDS) and EDS elemental mapping images of
silicon (Si), gold (Au) and oxygen (O) from AuNWs-functional-
ised fibers were shown in Figure 5. The EDS spectrum (Fig-
ure 5(b)) displays silicon element and gold element of the
AuNWs-functionalised fibers. C and O belong to the carbon and
oxygenated functional groups, and Cu is from the substrate of
copper grid. The different atomic percentages were 85.15 % (C),
11.47 % (C), 0.87% (Si), 1.12 % (Cu) and 1.39% (Au), respectively.
EDS mapping images (Figure 5(c), (d) and (e)) confirm the
location of Si, Au and O, respectively. It can be concluded that
Au nanowires have been homogeneously grown on the surface
of the mesoporous silica fiber.
Au nanowires plays a key role in determining the electrical
conductivity of fibers. To evaluate their conductivity, we
fabricated a stretchable sensor using the elastic materials as
supporting substrates. The fabrication process is illustrated in in
Figure S8 (a). The AuNWs-decorated silica fiber solution was
concentrated to ~ 5 mg/mL and the stretchable sensor was
prepared following the previously published protocol.[28] The
polymeric substrate (uniform nitrile rubber or latex film with
strong adhesion) was first placed in the middle between a glass
slide and a polyimide mask (the size of rectangular hole was
15 × 5 mm2). Subsequently, 200 μL of AuNWs-functionalised
fibers solution was droped onto the open area of the polymeric
substrate. The fabrication of conductive AuNWs-functionalised
fibers stretchable sensor was completed after sealing the
polymeric substrate with a transparent adhesive film connect-
ing with two conductive threads. The thickness of the
conductive AuNWs-functionalised fibers film was about 10 μm
(Figure 6 (a), bottom left), with a resistance of 1.35 0.68 kΩ.
SEM image from the top surface showed a cat tails-like
morphology, i. e., a Si fiber entangled by densely aligned Au
nanowires (Figure 6 (a), top left). The sensing schematic of our
AuNWs-functionalised fibers stretchable sensor was shown in
Figure 6 (b). When the sensor was stretched, some AuNWs-
functionalised fibers were separated to have cracks or gaps,
which decreased the conductive pathways and increase the
electrical resistance of the sensor. Those cracks or gaps were
recovered when the strain was released, which reduced the
electrical resistance of our AuNWs-functionalised fibers sensor.
To study the strain-electrical behaviours of the AuNWs-
functionalised fibers based sensor, we incorporated the device
in a LED circuit and observed its brightness while under strain,
as shown in Figure S9. The yellow light in LED light circuit under
voltage of 9 V indicates AuNWs-functionalised fibers stretchable
sensor was conductive. The LED got darker as the device was
stretched (Figure S9(a)), and then became brighter again during
the releasing process (Figure S9(b)). The strain sensitive prop-
erty indicates its potential to be used as stretchable gauge
sensors.
To further estimate the sensing mechanism of our AuNWs-
functionalised fibers stretchable sensor, the morphology
change during strain-release process were investigated using
optical microscopic characterizations (see Figure S10). When the
AuNWs-functionalised fibers sensor was stretched to 30 % strain,
some cracks or gaps occurred, as highlighted with the red circle
of Figure S10 (b). These cracks or gaps decrease the conductive
pathways, which are responsible for the increase of the
electrical resistance of our AuNWs-functionalised fibers sensor.
As releasing the sensor, some minor cracks were repaired.
Though larger cracks or gaps appeared under high strain (e. g.,
30 %), there were still connected with each other to maintain its
conductivity. Note that those cracks were recovered when strain
was released. The reversible property of cracks under stretch-
ing/releasing process illustrated the excellent durability of our
AuNWs-functionalised fibers stretchable sensor. This self-re-
paired mechanism of our AuNWs-functionalised fibers sensors is
similar to our previous research of AuNWs stretchable
sensors.[29]
To confirm the durability of the AuNWs-functionalised fibers
stretchable sensor, electrical responses during cycling test of
stretching/releasing were collected by electrochemical work-
station (the Parstat 2273). Two sides of the AuNWs-functional-
ised fibers sensor were assembled on a mechanized moving
stages and the data of stretching/releasing cycles was collected
by a computer-based user interface. The electrical resistance
changes curves were shown in Figure 6(c) under a 0 %–0.1 %–
0 % stretching-releasing process at 0.5 Hz. The AuNWs-function-
alised fibers stretchable sensor still kept an excellent stability
and reproducibility after 2500 cycles, which is evidenced by the
negligible change of current after 2500 cyclic test, Figure 6(d).
The SEM images of AuNWs-functionalised fibers latex film strain
sensor morphology before and after been stretched/released
for 2500 cycles were shown in Figure S11 (a) and (b). No
significant damage of the AuNWs-functionalised fibers sensor
was observed, which indicated the high stability of the sensor.
We further investigated the lower strain limit of AuNWs-
Figure 5. Element mapping of AuNWs-functionalised fibers via EDS: (a) SEM
image of AuNWs-functionalised fibers; (b) EDS spectrum of complete
element distribution (the substrate is copper grid); images of element
sensitive of (c) silicon, (d) gold and (e) oxygen.
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functionalised fibers sensors. Figure 6(e) presents the electrical
resistance response versus time under low strain level. It is
remarkable that the electrical responses could be well main-
tained with cyclic stretching-releasing process of 0 %–0.005 %–
0 % strain. Besides that, the minimum shift of the AuNWs-
functionalised fibers sensor was only 0.75 μm, corresponding to
a resistance increase of 1.4 kΩ(Figure 6(f), indicating the high
sensitively and reproducibility of the sensor.
Figure 6. (a) Photographs of the AuNWs-functionalised fibers on nitrile rubber (left) and latex film (right). The inset is the top view SEM images of the AuNWs-
functionalised fibers on the nitrile rubber substrate. (b) The schematic of the AuNWs-functionalised fibers sensor. (c) The durability test with 0.1 % stretching-
releasing process (stretch frequency: 0.5 Hz). The 50 times stretch-release cycles data of the resistance changes were record after each 500 cycles.(d) Zoomed
the resistance change curve in (c) after 2500 cycles. (e) Electrical resistance changes versus times at a frequency of 0.5 Hz under different stretch (0.005%,
0.01 %, 0.1 %, 0.5 %, 1 %). (f) Electrical resistance changes versus times with 0.005 % stretching by 0.75 μm/s. (g) Human wrist pulse detection. 70 beats/min. (h)
Electrical resistance changes as the fast and slow bending-unbending motion of the finger.
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The sensitivity of the AuNWs-functionalised fibers stretch-
able sensor, combined with their reproducible stretchability
and simple fabrication method, make it extraordinarily fascinat-
ing for the development of stretchable sensors. As a typical
application demonstration, the AuNWs-functionalised fibers
stretchable sensor was used for monitoring human wrist pulse.
Arterial stiffening is an independent predictor of cardiovascular
disease. Pulse wave analysis, as an economical, easier, faster,
non-invasive method, is one of the most efficient methods used
to assess arterial stiffness. The AuNWs-functionalised fibers
sensor was attached to the wrist of a male graduate student to
detect the periodic radial artery pulses wave in Figure 6(g). In
addition, our AuNWs-functionalised fibers stretchable sensor
with latex film can be constructed as a soft substrate to detect
the tiny bending motion of fingers (Figure 6(h)). When the
finger was bent, accompanied with the latex stretching, the
resistance of AuNWs-functionalised fibers sensor decreased. As
the finger moved back, the resistance of the AuNWs-functional-
ised fibers sensor recovered to its original state. Our AuNWs-
functionalised fibers sensor was comparable with some pre-
viously reported wearable sensors in the detection
performances.[11,30] The sensitivity of our AuNWs-functionalised
fibers sensor (0.005 %) was better than that of Ag nanowires-
based sensor (0.065 %).[12] Based on the outstanding perform-
ance of the AuNWs-functionalised fibers stretchable sensor, we
believe its great potentiality in next generation wearable
electronic devices.
Conclusion
In summary, we successful designed and fabricated bio-inspired
cat’s tail like golden mesoporous silica fibers for stretchable
sensor. The concentration of CTAB was a key role to fabricate
mesoporous silica fibers. Au seeds were anchored on the
surface of mesoporous silica fibers which provided a platform
to catalyse the reduction of 4-NP to 4-AP. A 3D structure
stretchable sensor made from AuNWs-functionalised fibers
exhibited reliable resistance signals in real-time and in situ
response to radial artery blood pulse and finger bending
motions. Our work reinforces the idea of smart material
hybridization and may offer a novel material for in real-time
and in situ wellness and health applications.
Experimental Section
Materials
Tetraethyl orthosilicate (TEOS), gold (III) chloride trihydrate
(HAuCl4· 3H2O), sodium borohydride (NaBH4), 4-nitrophenol (4-NP),
hexadecyltrimethylammonium bromide (CTAB), (3-Aminopropyl)
trimethoxysilane (APTMS), 4-Mercaptobenzoic acid (4-MBA), triso-
dium citrate, L-ascorbic acid, silver paste and silicon wafers were
purchased from Sigma-Aldrich. Hydrochloric acid (HCl, 32 wt%) was
obtained from AJAX. Ethanol and methanol were purchased from
Merck KGaA. All chemicals were used as-received unless otherwise
indicated. Demineralized water was further purified with a Milli-Q
system (Millipore). All glassware were cleaned by freshly prepared
aqua regia and was rinsed thoroughly by MilliQ H2O before use.
Nitrile rubber was bought from MEDIflex industries. Stainless
conductive thread was obtained from Adafruit industries. Sprayable
latex was purchased from Dalchem. Smith & Nephew OpSite Flexifix
transparent film was purchased from Smith & Nephew.
Synthesis of Mesostructured Silica Fibers
The fabrication process of mesostructured silica fibers was occurred
in strongly acidic aqueous solutions of CTAB as structure directing
agent and TEOS as silica species.[24] A certain amounts of CTAB,
43 mL demineralized water and 7 mL concentrated HCl were added
in a glass bottle. 200 μL TEOS was added into the mixture after all
chemicals were dissolved completely. The resulting solution was
sonicated for 10 min at room temperature and then transferred to
an isothermal oven at 70 °C for ~ 2 days. The suspension solution
was cooled to room temperature, and then the upper layer white
cloudy fibers were collect from the solution carefully. These
samples were washed with MilliQ water and ethanol three times,
respectively.
Surface Amino Functionalization of Mesoporous Silica Fibers
Mesostructured silica fibers were functionalized by APTMS. The
mesoporous silica fibers (0.1 g) and APTMS (20 μL) were dispersed
in 10 mL methanol. The reaction mixture was sonicated at 70°C for
2 h. The resulting functionalized fibers were collected by centrifu-
gation, washed with ethanol at least 3 times, and dispersed in
water before use.
Adsorption of Au Seeds onto Mesoporous Silica Fibers
Firstly, for the preparation of Au seeds, the aqueous solution
(20 mL) including 0.25 mM HAuCl4and 0.25 mM tri-sodium citrate
was mixed with a freshly prepared, ice-cold NaBH4solution (0.6 mL,
0.1 M) under strong stirring for 5 min. To release the excess
borohydride in water, the Au seeds solution was stored at 4 °C for
3 h before use. Then they were used for adsorbing onto the
APTMS-functionalized mesoporous silica fibers. Typically, the func-
tionalized mesoporous silica fibers (1 mg) were added into the
seeds solution (30 mL) with stirring for 2 h. The resulting sample
was collected by centrifugation.
Catalytic Reduction of 4-NP
Fresh NaBH4solution (0.5 mL, 20 mM), 4-nitrophenol aqueous
solution (0.1 mL, 2.5 mM) and H2O (2.5 mL) were mixed into a
quartz cell. Mesoporous silica fibers or Au-seed-coated-fiber sample
solution (0.1 mL, 0.5 wt.%) was added to the cell. Changes of 4-NP
reduction were monitored by UV-vis spectra under room temper-
ature until the colour of reaction solution gradually vanished.
Growth of Au Nanowires on Mesoporous silica Fibers
The growth of Au Nanowires depended on Au seeds on the surface
of mesoporous silica fibers. The mesoporous silica fibers@Au seeds
sample were mixed a HAuCl4aqueous solution (1.7 mM) with a
MBA solution (0.7 mM) in a glass bottle, and then an ascorbic acid
solution (3.6 mM) was added immediately. After a rapid mixing, the
reaction solution kept standing at room temperature for at least
15 min, washed with ethanol, and dispersed in water before future
use.
Full Papers
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Fabrication of Stretchable Sensor
Using a “sandwich” model, latex film or nitrile rubber was in the
middle of a glass slide and polyimide mask (the rectangular size
was 15 × 5 mm2). The concentrated AuNWs-functionalised fibers
solution (200 μL) was drop onto the surface of latex film or nitrile
rubber. Then the glass slide and the mask were removed when the
solution was dried. The conductive threads were firmed on the
both sides of AuNWs-functionalised fibers strips by silver paste.
Smith & Nephew OpSite Flexifix transparent film was covered on
top of silver paste and permanently sealed the AuNWs-functional-
ised fibers film to conductive thread.
Characterization
The morphology were observed through transmission electron
microscope (TEM, FEI Tecnai G2 T20 TWIN LaB6 TEM operating at
200 kV), Scan electron microscope (SEM, FEI Helios Nanolab 600
FIB-SEM operating at 5 kV and 86 pA) and energy dispersive X-ray
spectroscopy (EDX, Oxford). Optical photographs were picked by
Nikon ECLIPSELV150 microscope with a Nikon Digital Sight DS-Fi1
camera. The absorption spectra of Au seeds in water was detected
by an Agilent 8453 UV-vis spectrophotometer. The motorized
moving stages (THORLABS Model LTS150/M) was used to test the
samples stretching-releasing cycles, and the data were collected by
a computer-based user interface (Thoelabs APT user). Nitrogen
adsorption/desorption isotherms were determined with a BET
QUADRASORB SI automated surface area&pore size analyser. The
pore size distributions (BJH model) were calculated from the
adsorption curves of isotherms.
Acknowledgements
This work was financially supported by the Discovery Grant
(DP120100170 and DP140100052), National Natural Science
Foundation of China (Grant No. 21773050, 21528501, 51803041),
the Fundamental Research Funds of the Central University
(HEUCFJ181006) and the Natural Science Foundation of Heilong-
jiang Province for Distinguished Young Scholars (JC2018003). This
work was performed in part at the Melbourne Centre for Nano-
fabrication (MCN) in the Victorian Node of the Australian National
Fabrication Facility (AFNN). Z.Z. gratefully acknowledges the
financial supporting from Chinese Scholarship Council (CSC).
Conflict of Interest
The authors declare no conflict of interest.
Keywords: gold ·mesoporous silica ·nanostructures ·
nanowires ·stretchable sensors
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FULL PAPERS
The cat‘s pyjamas: Gold nanowires
(AuNWs)-coated mesostructured
silica fibers were designed and fabri-
cated. The vertically aligned AuNWs
were grown on the silica fiber
surfaces with controllable length. The
aligned coaxial mesostructured silica
microfibers and Au nanowires
exhibits excellent stability and real-
time response with high durability as
a sensitive flexible microelectronic
material.
Dr. Z. Zhang, Dr. L. W. Yap, Dr. D.
Dong, Dr. Q. Shi, Dr. Y. Wang, Prof. W.
Cheng*, Prof. X. Han*
1 – 9
Cat-Tail-Like Mesostructured Silica
Fibers Decorated with Gold
Nanowires: Synthesis, Characteriza-
tion, and Application as Stretchable
Sensors
Full Papers
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