When a focused light illuminates the photothermal nanoparticles near the liquid–air interface, heat is generated and transferred from the PNPs to the surrounding liquid within tens of nanoseconds, which significantly accelerates the liquid evaporation from the interface and produ...
Optofluidic control using photothermal nanoparticles
NATURE MATERIALS, no. 1 (2006): 27.0-32
Photothermal metallic nanoparticles have attracted significant attention owing to their energy-conversion properties(1-4). Here, we introduce an optofluidic application based on a direct optical-to-hydrodynamic energy conversion using suspended photothermal nanoparticles near the liquid-air interface. Using light beams with submilliwatt p...更多
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- The authors use gold nanocrescent particles with a strong absorption band around 780 nm as the photothermal nanoparticles (PNPs).
- Using light beams with submilliwatt power, the authors can drive and guide liquid flow in microfluidic channels to transport biomolecules and living cells at controlled speeds and directions.
- We use gold nanocrescent particles with a strong absorption band around 780 nm as the photothermal nanoparticles (PNPs)
- We introduce an optofluidic application based on a direct optical-to-hydrodynamic energy conversion using suspended photothermal nanoparticles near the liquid–air interface
- A variety of methods for controlling microscale liquid flow have been developed owing to the increasing interest for microfluidics-based biochemical analysis systems
- When a focused light illuminates the PNPs near the liquid–air interface, heat is generated and transferred from the PNPs to the surrounding liquid within tens of nanoseconds, which significantly accelerates the liquid evaporation from the interface and produces vapour
- The PNPs are drawn towards the new contact line because of the liquid motion and convection
- A water solution containing 100 μM fluorescein, 1 M N-2-hydroxyethylpiperazine-N -2 ethanesulphonicacid (HEPES) buffer and 1 nM PNPs were illuminated by a 20 mW, 785 nm focused laser spot near the liquid–air interface for 1 s
- It shows a much higher flow speed as the vapour and droplets are bound within the channel and contribute to the liquid advance only along the channel direction and the minimized vertical convection in microchannels favours the heat concentration at the liquid–air interface.
- The liquid remains stationary in the hydrophobic channel without the light guide owing to the balanced surface energy, and no thermocapillary flow is seen when the light spot illuminates the interior of the liquid.
- The maximal optofluidic flow speeds in these two channels are different because the introduced liquids have different PNP concentrations.
- As the light illumination power, microchannel dimension and PNP concentration are three major tunable factors to determine the rate of droplet formation and coalescence, the authors characterized the optofluidic flow speed .
- The optofluidic flow speed remains almost the same after the liquid enters the chosen branch, even with sharp turns, because most of the PNPs near the liquid–air interface will follow the direction of the guiding light and be drawn to the advancing liquid–air interface.
- For the sample of thermochromic microcapsules in PNP suspension, the authors used a 10 mW, 785 nm focused laser spot to illuminate the liquid–air interface.
- The authors observed that most the magenta and dark-blue thermochromic microcapsules remained the same colour while water was boiling at the liquid–air interface, even when they were only a few micrometres away from the laser spot.
- The PDMS microfluidic chip was made by the following procedure: first, a replication mould consisting of 5-μm-high ridges was photolithographically patterned on a silicon wafer using SU-8 2005 nature materials VOL 5 JANUARY 2006 www.nature.com/naturematerials a1 b (i) negative-tone photoresist (MicroChem, Massachusetts); second, the 10:1 mixture of PDMS monomer and curing agent (Dow Corning) was cast on the SU-8 mould to become a 500-μm-thick film, which was cured in an oven at 90 ◦C for 10 min; after the PDMS film was completely solidified, it was peeled off from the mould and recessed grooves in the same pattern as the mould generated on the PDMS surface.
- The authors gratefully acknowledge financial support from the Defense Science Office of the Defense Advanced Research Projects Agency, USA
- J.K. was supported by a grant (05K1501-02810) from the Center for Nanostructured Materials Technology under the 21st Century Frontier R&D Programs of the Ministry of Science and Technology, Korea
data sets: 3
Optofluidic control in straight microfluidic channels. a, Illustration of the experimental system configuration. b, Optofluidic control in a 40-μm-wide channel. The video prints show that the flow of the 0.5 nM PNP-suspended 1X PBS buffer solution follows the optical guiding of a 10 mW, 785 nm laser spot at a speed of ∼50 μm s−1 (frames 1–5) and stops otherwise (frame 6). c, Optofluidic control in an 80-μm-wide channel. The 1 nM PNP water solution is guided by a 10 mW, 785 nm laser spot at a speed of ∼50 μm s−1. d, Simultaneous optofluidic controls of 1 nM PNP water solutions in two parallel 10-μm-wide channels by a focused laser line with sub-milliwatt illumination power on each channel. Other channels are intentionally left empty for better image contrast. Frames 1 and 2 show the channels respectively before and after the light translation at a speed of ∼10 μm s−1. e, Optofluidic control of four different liquids. From top to bottom, 0.2 nM and 1 nM PNP water solution, pure deionized water and 60-nm Au colloidal nanospheres are introduced into the 10-μm-wide channels, respectively. Frames 1 and 2 show the channels respectively before and after the light translation at a speed of ∼10 μm s−1. Maximal flow speed by optofluidic control. a, Maximal flow speed of the 1 nM PNP water solution versus the illumination optical power. The open square, circle and triangle correspond to the microchannels with widths of 10, 40 and 80 μm, respectively. The solid, dashed and dotted lines represent the linear fits of the above three data sets, respectively. b, Maximal flow speed versus the PNP concentration for the optofluidic control with a 20 mW laser spot. The symbols and lines have the same representations as those in a. The error bars in both plots represent the standard deviation of the five measurements for each data point. Optofluidic control at two adjacent T-shaped channel junctions. a, Video prints showing that a 1 nM PNP water solution introduced from the right channel is optically guided into the left channel after two sharp turns without filling the other two channels. b, Optofluidic control of liquid flow into three distinct paths at the two junctions without filling undesired channels. c, Optofluidic mixing of three separate liquid streams into one. All scale bars are 50 μm
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