Supporting information:
A Non-Contact Strategy for Precisely Controlled
Enrichment, Manipulation and Separation of Carbon
Nanotubes by Surface Acoustic Waves
Qian Zeng, Lili Li, Horse L. Ma, Junhua Xu, Yunshan Fan and Hao Wang*
*Corresponding Author e-mail: wanghao@nanoctr.cn
DEVICE FABRICATION
The SAW device fabrication involved two major steps, as shown in Fig. S1: (1)
the fabrication of interdigital transducers (IDTs), and (2) the fabrication of
polydimethylsiloxane (PDMS) (SYLGARD184, Dow Corning) channel. Fig. S1 A-D
shows the fabrication of the IDTs. A double-layer metal (Cr/Au, 5 nm/80 nm) was
deposited on a Y+128° X-propagation lithium niobate (LiNbO3) wafer using an
e-beam evaporator (Auto 500). A layer of photoresist (S 1813, MicroChem) was
spin-coated on the wafer, patterned by a UV light source, and developed in a
photoresist developer (MF-321, Microposit). And then, metal wet etching solutions
were used to form the IDTs, acetone was used to remove photoresist. The PDMS
microchannels were fabricated using standard soft-lithography. The silicon substrate
for the microchannel mould was patterned by photoresist (SU-8 3050, MicroChem).
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PDMS were prepared by mixing at a 1:10 weight ratio, cast onto the silicon mould,
and cured at 80 o C for 4 h. After curing, the PDMS pattern was peeled off from the
silicon mould and drilled for the inlet and outlet. The microchannel height is 50 μm.
Finally, the IDTs substrate and PDMS were aligned and assembled together. The
width of the electrode finger used in our setup is 50 μm, corresponding to SAW
frequency is 19 MHz. The aperture of the IDTs is 1.5 cm. The applied AC signal was
generated using a function generator (33522A, Agilent).
OXIDATION OF MWNTS
MWNTs (purity >95%, diameter within 5-10 nm, Nacen Nanotechnologiese)
were purified by refluxing in an aqueous HNO3 of 2.6 M at 70 o C for 45 h. The
nanotube suspension was diluted and washed with double-distilled water by filtering
through a 0.8-μm polycarbonate membrane. The samples were dried at 80 o C under
vacuum. The purified MWNTs were further oxidized in the 3:1 concentrated
H2SO4:HNO3 mixture for 12 h. The nanotube suspension was diluted and washed
with double-distilled water by filtering through a 0.45-μm polycarbonate membrane.
The samples were dried at 80 o C under vacuum.
PREPARATION OF SWNTS SUSPENSION
20 mg of the SWNTs ((purity >90%, diameter within 1-2 nm, Beijing DK Nano
technology) were dispersed in 100 mL of de-ionized water with 1 g (1 weight %) of
Sodium Dodecyl Sulfate (SDS) in a bath-type sonicator (200 W) for 4 h, the dispersed
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SWNT solution was centrifuged (Sigma1-14, SIGMA) at 14800 rpm for 2 h, and the
supernatant was carefully decanted.
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Supporting Figures
Fig. S1. Device fabrication processes. (a-d) Fabrication of the IDTs, including a metal
deposition process and a following wet etching process. (e-g) Fabrication of PDMS
channel using soft-lithography process. (h) The combination of the substrate and the
channel.
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Fig. S2. CNTs enrichment and alignment by SAW in 1D condition. (a) CNTs
enrichment in the whole channel by SAW. (b-e) Aligned CNTs position is varied by
adjusting the relative phase. Scale bar is 50 μm.
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Fig. S3. CNTs enrichment and alignment by SAW in 2D condition. (a) CNTs aligned
in different angle at different wave nodes. (b, c) CNTs in one wave node change angle
by phase change. (d) A single CNTs bundle at the wave node. Scale bars are 20 μm.
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Movie S1. Enriching and releasing of MWNTs (0.1 mg/mL) in microfluidic channel.
The flow rate is 1 μL/min, applied AC signal at 24 dbm, 19 MHz. The time scale in
this movie has been compressed by a factor of twenty. (This material will be
provided upon request)
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