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Fabrication of spiral-shaped microfluidic channels in glass by femtosecond laser
Materials Letters 64 (2010) 1427–1429
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Fabrication of spiral-shaped microfluidic channels in glass by femtosecond laser Yan Li, Shi-liang Qu ⁎ Department of Optoelectronics Science, Harbin Institute of Technology at Weihai, Weihai 264209, China
a r t i c l e
i n f o
Article history: Received 3 February 2010 Accepted 16 March 2010 Available online 24 March 2010 Keywords: Laser processing Microstructure Surfaces
a b s t r a c t Long spiral-shaped microfluidic channels in glass have been fabricated by femtosecond laser direct writing. After hydrofluoric acid etching and post baking, the laser modified regions in glass formed hollow microstructures. The diameter size and the screw-pitch of the channels can be set freely. The experimental results showed that the etched internal surface of the microchannel by hydrofluoric acid will become smoother after the subsequent baking. The incident laser power and scanning speed can also influence the channel quality. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction The trend of fabrication of lab-on-a-ship demands the use of true three-dimensional (3D) microchannels. These channels can have potential applications in the field of chemical and biological analyses [1]. Although some microchannels can be achieved by soft lithography [2], wet etching [3] and the bonding technology [4], these methods have major challenges in true 3D microchannels fabrication. However, femtosecond laser direct-writing technique can resolve this question. People have fabricated precisely the 3D microfluidic channels in transparent materials by the technique. The surface or interior of transparent materials can be modified with micrometer precision by femtosecond laser [5,6]. The femtosecond laser can deposit energy into the transparent materials to form local ablation by nonlinear absorption. So it has become a unique micromachining tool to fabricate microfluidic structures in glass. Marcinkevicius et al. have fabricated H-shaped channel in silica glass using femtosecond laser [7,8]. The experiment was carried out according to the following steps: firstly write a preprogrammed pattern into silica glass by using laser pulses and then etch the modified regions of sample in a 5% aqueous solution of hydrofluoric(HF) acid in an ultrasonic bath [9]. Cheng et al. demonstrated 3D integration of microchannels, microchambers and micromirrors in a glass chip to create functional devices, namely, microfluidic dye lasers that were three-dimensionally embedded in photoetchable glass. In addition, Cheng et al. fabricated a Y-shaped microchannel using femtosecond laser direct writing, followed by baking and successive chemical etching [10–12]. Using this method, many researchers have fabricated different microstructures in recent years. However, there are few reports on the fabrication of spiral-shaped microchannels in glass or other
⁎ Corresponding author. Fax: + 86 631 5687036. E-mail address: [email protected] (S. Qu).
materials. In order to make a full chemical reaction we can let the solution flow through a longer path in the limited length of two microcomponents. The spiral-shaped microchannels can be used to connect two microcomponents. Recently, we fabricated 3D microfluidics in glass by femtosecond laser direct-writing technique followed by chemical etching and post baking. In this letter, we demonstrate the fabrication of a spiralshaped microchannel by femtosecond laser direct writing in glass. Hollow microstructures can be fabricated after hydrofluoric acid etching and post baking. The experimental results showed that the etched internal surface of the microchannel becomes smooth after the subsequent baking. The incident laser power and scanning speed can also influence the processing quality. 2. Experimental setup The glass samples used in this work are commercially available silica glass (70SiO2·20Na2O·10CaO). The experiments are carried out at a Ti: sapphire regenerative amplified laser system (Coherent Inc.). The repetition rate, wavelength and pulse width of the femtosecond laser are 1 kHz, 800 nm, and 120 fs, respectively. The experimental process includes three main steps. First, a linearly polarized Gaussian laser beam is focused onto the rear surface of the sample by using an optical microscope (LMPLFL 20×/0.45, Nikon) at a normal incidence angle. Then the preprogrammed pattern is fabricated in the silica volume by the tightly focused femtosecond laser beam. Second, the glass is etched in a 5% aqueous solution of HF acid in an ultrasonic bath for selective removal of the modified regions. Then the hollow microstructures are formed. Finally, the etched sample is baked for smoothing the internal surfaces of the fabricated hollow microstructures. We set the baking temperature at 200 °C, 400 °C, 600 °C and 800 °C, respectively. After 4 h, the better internal surfaces of the hollow microstructures are formed at 600 °C. So in the follow-up experiments, we have been using the baking temperature at 600 °C for 4 h.
0167-577X/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.03.040
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Y. Li, S. Qu / Materials Letters 64 (2010) 1427–1429
Fig. 1. The experimental setup for fabrication of spiral-shaped microfluidic channels.
Fig. 1 shows a schematic drawing of the experimental setup. The laser beam is focused in the glass sample placed on a computercontrolled XYZ translation stage (precision: 100 nm). A charge coupled device (CCD) connected to a personal computer is used to monitor the whole direct-writing process in real time. A mechanical shutter with 100 ms response time is employed to select the appropriate ablation time. We first focused the femtosecond laser beam on the rear surface of the glass sample and then moved the sample along a spiral-shaped trace to front surface. The Z direction parallels to the direction of laser incidence. 3. Results and discussion In order to obtain the optimal microchannels, we investigated the dependence of processing quality on laser power and scanning speed. Fig. 2(a) shows the maximum length of the laser modified regions related to the laser power when the scanning speed of X–Y direction is kept at 200 µm/s. As can be seen, the higher the power of the laser is, the longer the modified regions are. In addition, the diameter of the spiral-shaped channels is larger after etching in a solution of 5% HF acid diluted with water in an ultrasonic bath. Fig. 2(b) shows the dependence of the maximum length on the scanning speed when keeping the laser average power at 6 mW. As can be seen, the scanning speed has little influence on the maximum length of the laser modified regions. Considering the processing time and quality, the scanning speed can be kept at 200 µm/s and the z-step maximum distance between two adjacent points on the circle can be set at 30 µm which is still able to ensure regional connectivity of the laser modified. According to the experimental results described above, choosing appropriate laser power and scanning speed are required to fabricate spiral-shaped microchannels. In this experiment, the laser average power, the scanning speed, the screw-pitch and the diameter of circle were set at 6 mW, 200 µm/s, 1000 µm and 500 µm, respectively, and the z-step distance was kept at 5 µm. Fig. 3(a) shows the schematic view of the spiral-shaped microchannel formed by moving the sample along spiral trace from rear surface to front surface. And then the laser modified microstructure was etched in a solution of 5% HF acid in an ultrasonic bath to form a hollow microstructure, as can be seen in Fig. 3(b). From Fig. 3(b), we also can obviously see that the etched microchannel had a very rough internal surface. However, after baking the sample at 600 °C for 4 h, the internal surface of the hollow microstructure becomes smooth, as shown in Fig. 3(c). In addition, we have investigated the cross-section of the microchannel. The real post
Fig. 2. (a) Dependence of the maximum length of the laser modified regions on the laser average power when the scanning speed is set 200 µm/s. (b) Dependence of the maximum length of the laser modified regions on the scanning speed when the laser average is kept at 6 mW.
baked cross-sectional profile is shown in Fig. 3(d), where the height of cross-section is about 80 µm. The etching time, the diameter of the laser modified region and the incidence laser power have influence on the diameter of the channel. We are continuously optimizing the experimental parameters to improve the quality of microchannel and reduce the channel diameter. The curvature of the cross-section is related to the diameter of the circle and the screw-pitch. After etching, the diameter of the opening area of the spiral-shaped microchannel is larger than that of the middle area. Fig. 3(e) shows the cross-sectional profile of the opening area. Furthermore, we test the microchannel by injecting a solution with blue ink. A higher pressure was applied to a capillary tube connected to the inlet, so that the blue solution is driven into the microchannel. Fig. 4 shows four stages flowing process of the solution captured by CCD with the time before the solution entered into the channel, the solution entered into the channel one third, two third, and the solution flow out of the spiral-shaped microchannel, respectively. CCD captured images at 25f/s and the video images displayed on the interception of liquid flowing through the ∼3000 µm long spiralshaped microchannel. On the right of the microchannel, the rough internal surface also can be seen from Fig. 4, when the solution flowed into the channel. The formation of these marks is attributed to irregular border of laser modified region caused by laser irradiating in local non-uniform glass and HF acid enlarging the irregular edge.
Y. Li, S. Qu / Materials Letters 64 (2010) 1427–1429
1429
Fig. 3. (a) Schematic view of the spiral-shaped microchannel. (b) Side view of the etched spiral-shaped microchannel by HF acid inside the glass. (c) Side view of the spiral-shaped microchannel after baking of the etched sample at 600 °C for 4 h. (d) The cross-section of the post baked microchannel. (e) The cross-section of the channel at the opening area.
500 µm, respectively. The total length of spiral-shaped microchannel is ∼3000 µm. The experimental results show that the internal surface of microchannel becomes smooth after post baking and the liquidity of the channel is well. The incident laser power and scanning speed also have influence on the channel quality. It is expected that this technique will be applied to fabricate 3D microfluidic components. Acknowledgement We thank Harbin Institute of Technology at Weihai for supporting this work. References
Fig. 4. Side view of blue solution flowing through the spiral-microchannel.
4. Conclusion In summary, we have fabricated the spiral-shaped microchannel in glass by using femtosecond laser direct writing and the subsequent baking. The screw-pitch and the diameter of circle are 1000 µm and
[1] Ahn CH, Jin-Woo Choi, Beaucage G, Nevin JH, Jeong-Bong Lee, Puntambekar A, et al. Disposable smart lab on a chip for point-of-care clinical diagnostics. Proc IEEE 2004;92:154–73. [2] Kavcic B, Babic D, Osterman N, Podobnik B, Poberaj I. Magnetically actuated microrotors with individual pumping speed and direction control. Appl Phys Lett 2009;95:023054. [3] Hnatovsky C, Taylor RS, Simova E, Rajeev PP, Rayner DM, Bhardwaj VR, et al. Fabrication of microchannels in glass using focused femtosecond laser radiation and selective chemical etching. Appl Phys A 2006;84:47–61. [4] Martynova L, Locascio LE, Gaitan M, Kramer GW, Christensen RG, Maccrehan WA. Fabrication of plastic microfluidic channels by imprinting methods. Anal Chem 1997;69:4783–9. [5] Davis KM, Miura K, Sugiomto N, Hirao K. Writing waveguides in glass with a femtosecond laser. Opt Lett 1996;21:1729–31. [6] Bellouard Y, Dugan M, Said A, Bado P. Fabrication of high-aspect ratio micro-fluidic channels and tunnels using femtosecond laser pulses and chemical etching. Opt Express 2004;12:2120–9. [7] Cheng Y, Sugioka K, Midorikawa K, Masuda M, Toyoda K, Kawachi M, et al. Control of the cross-sectional shape of a hollow microchannel embedded in photostructurable glass by use of a femtosecond laser. Opt Lett 2003;28:55–7. [8] Sugioka K, Masuda M, Hongo T, Cheng Y, Shihoyama K, Midorikawa K. Threedimensional microfluidic structure embedded in photostructurable glass by femtosecond laser for lab-on-chip application. Appl Phys A 2004;78:815–7. [9] Marcinkevicius A, Juodkazis S, Watanabe M, Miwa M, Matuso S, Misawa H, et al. Femtosecond laser-assisted three-dimensional microfabrication in silica. Opt Lett 2001;26:277–9. [10] Cheng Y, Sugioka K, Midorikawa K. Microfluidic laser embedded in glass by threedimensional femtosecond laser microprocessing. Opt Lett 2004;29:2007–9. [11] Cheng Y, Sugioka K, Midorikawa K. Microfabrication of 3D hollow structures embedded in glass by femtosecond laser for lab-on-a-ship applications. Appl Surf Sci 2005;248:172–6. [12] He F, Cheng Y, Xu Z, Liao Y, Xu J, Sun H, et al. Direct fabrication of homogeneous microfluidic channels embedded in fused silica using a femtosecond laser. Opt Lett 2010;35:282–4.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Fabrication of spiral-shaped microfluidic channels in glass by femtosecond laser Yan Li, Shi-liang Qu ⁎ Department of Optoelectronics Science, Harbin Institute of Technology at Weihai, Weihai 264209, China
a r t i c l e
i n f o
Article history: Received 3 February 2010 Accepted 16 March 2010 Available online 24 March 2010 Keywords: Laser processing Microstructure Surfaces
a b s t r a c t Long spiral-shaped microfluidic channels in glass have been fabricated by femtosecond laser direct writing. After hydrofluoric acid etching and post baking, the laser modified regions in glass formed hollow microstructures. The diameter size and the screw-pitch of the channels can be set freely. The experimental results showed that the etched internal surface of the microchannel by hydrofluoric acid will become smoother after the subsequent baking. The incident laser power and scanning speed can also influence the channel quality. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction The trend of fabrication of lab-on-a-ship demands the use of true three-dimensional (3D) microchannels. These channels can have potential applications in the field of chemical and biological analyses [1]. Although some microchannels can be achieved by soft lithography [2], wet etching [3] and the bonding technology [4], these methods have major challenges in true 3D microchannels fabrication. However, femtosecond laser direct-writing technique can resolve this question. People have fabricated precisely the 3D microfluidic channels in transparent materials by the technique. The surface or interior of transparent materials can be modified with micrometer precision by femtosecond laser [5,6]. The femtosecond laser can deposit energy into the transparent materials to form local ablation by nonlinear absorption. So it has become a unique micromachining tool to fabricate microfluidic structures in glass. Marcinkevicius et al. have fabricated H-shaped channel in silica glass using femtosecond laser [7,8]. The experiment was carried out according to the following steps: firstly write a preprogrammed pattern into silica glass by using laser pulses and then etch the modified regions of sample in a 5% aqueous solution of hydrofluoric(HF) acid in an ultrasonic bath [9]. Cheng et al. demonstrated 3D integration of microchannels, microchambers and micromirrors in a glass chip to create functional devices, namely, microfluidic dye lasers that were three-dimensionally embedded in photoetchable glass. In addition, Cheng et al. fabricated a Y-shaped microchannel using femtosecond laser direct writing, followed by baking and successive chemical etching [10–12]. Using this method, many researchers have fabricated different microstructures in recent years. However, there are few reports on the fabrication of spiral-shaped microchannels in glass or other
⁎ Corresponding author. Fax: + 86 631 5687036. E-mail address: [email protected] (S. Qu).
materials. In order to make a full chemical reaction we can let the solution flow through a longer path in the limited length of two microcomponents. The spiral-shaped microchannels can be used to connect two microcomponents. Recently, we fabricated 3D microfluidics in glass by femtosecond laser direct-writing technique followed by chemical etching and post baking. In this letter, we demonstrate the fabrication of a spiralshaped microchannel by femtosecond laser direct writing in glass. Hollow microstructures can be fabricated after hydrofluoric acid etching and post baking. The experimental results showed that the etched internal surface of the microchannel becomes smooth after the subsequent baking. The incident laser power and scanning speed can also influence the processing quality. 2. Experimental setup The glass samples used in this work are commercially available silica glass (70SiO2·20Na2O·10CaO). The experiments are carried out at a Ti: sapphire regenerative amplified laser system (Coherent Inc.). The repetition rate, wavelength and pulse width of the femtosecond laser are 1 kHz, 800 nm, and 120 fs, respectively. The experimental process includes three main steps. First, a linearly polarized Gaussian laser beam is focused onto the rear surface of the sample by using an optical microscope (LMPLFL 20×/0.45, Nikon) at a normal incidence angle. Then the preprogrammed pattern is fabricated in the silica volume by the tightly focused femtosecond laser beam. Second, the glass is etched in a 5% aqueous solution of HF acid in an ultrasonic bath for selective removal of the modified regions. Then the hollow microstructures are formed. Finally, the etched sample is baked for smoothing the internal surfaces of the fabricated hollow microstructures. We set the baking temperature at 200 °C, 400 °C, 600 °C and 800 °C, respectively. After 4 h, the better internal surfaces of the hollow microstructures are formed at 600 °C. So in the follow-up experiments, we have been using the baking temperature at 600 °C for 4 h.
0167-577X/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.03.040
1428
Y. Li, S. Qu / Materials Letters 64 (2010) 1427–1429
Fig. 1. The experimental setup for fabrication of spiral-shaped microfluidic channels.
Fig. 1 shows a schematic drawing of the experimental setup. The laser beam is focused in the glass sample placed on a computercontrolled XYZ translation stage (precision: 100 nm). A charge coupled device (CCD) connected to a personal computer is used to monitor the whole direct-writing process in real time. A mechanical shutter with 100 ms response time is employed to select the appropriate ablation time. We first focused the femtosecond laser beam on the rear surface of the glass sample and then moved the sample along a spiral-shaped trace to front surface. The Z direction parallels to the direction of laser incidence. 3. Results and discussion In order to obtain the optimal microchannels, we investigated the dependence of processing quality on laser power and scanning speed. Fig. 2(a) shows the maximum length of the laser modified regions related to the laser power when the scanning speed of X–Y direction is kept at 200 µm/s. As can be seen, the higher the power of the laser is, the longer the modified regions are. In addition, the diameter of the spiral-shaped channels is larger after etching in a solution of 5% HF acid diluted with water in an ultrasonic bath. Fig. 2(b) shows the dependence of the maximum length on the scanning speed when keeping the laser average power at 6 mW. As can be seen, the scanning speed has little influence on the maximum length of the laser modified regions. Considering the processing time and quality, the scanning speed can be kept at 200 µm/s and the z-step maximum distance between two adjacent points on the circle can be set at 30 µm which is still able to ensure regional connectivity of the laser modified. According to the experimental results described above, choosing appropriate laser power and scanning speed are required to fabricate spiral-shaped microchannels. In this experiment, the laser average power, the scanning speed, the screw-pitch and the diameter of circle were set at 6 mW, 200 µm/s, 1000 µm and 500 µm, respectively, and the z-step distance was kept at 5 µm. Fig. 3(a) shows the schematic view of the spiral-shaped microchannel formed by moving the sample along spiral trace from rear surface to front surface. And then the laser modified microstructure was etched in a solution of 5% HF acid in an ultrasonic bath to form a hollow microstructure, as can be seen in Fig. 3(b). From Fig. 3(b), we also can obviously see that the etched microchannel had a very rough internal surface. However, after baking the sample at 600 °C for 4 h, the internal surface of the hollow microstructure becomes smooth, as shown in Fig. 3(c). In addition, we have investigated the cross-section of the microchannel. The real post
Fig. 2. (a) Dependence of the maximum length of the laser modified regions on the laser average power when the scanning speed is set 200 µm/s. (b) Dependence of the maximum length of the laser modified regions on the scanning speed when the laser average is kept at 6 mW.
baked cross-sectional profile is shown in Fig. 3(d), where the height of cross-section is about 80 µm. The etching time, the diameter of the laser modified region and the incidence laser power have influence on the diameter of the channel. We are continuously optimizing the experimental parameters to improve the quality of microchannel and reduce the channel diameter. The curvature of the cross-section is related to the diameter of the circle and the screw-pitch. After etching, the diameter of the opening area of the spiral-shaped microchannel is larger than that of the middle area. Fig. 3(e) shows the cross-sectional profile of the opening area. Furthermore, we test the microchannel by injecting a solution with blue ink. A higher pressure was applied to a capillary tube connected to the inlet, so that the blue solution is driven into the microchannel. Fig. 4 shows four stages flowing process of the solution captured by CCD with the time before the solution entered into the channel, the solution entered into the channel one third, two third, and the solution flow out of the spiral-shaped microchannel, respectively. CCD captured images at 25f/s and the video images displayed on the interception of liquid flowing through the ∼3000 µm long spiralshaped microchannel. On the right of the microchannel, the rough internal surface also can be seen from Fig. 4, when the solution flowed into the channel. The formation of these marks is attributed to irregular border of laser modified region caused by laser irradiating in local non-uniform glass and HF acid enlarging the irregular edge.
Y. Li, S. Qu / Materials Letters 64 (2010) 1427–1429
1429
Fig. 3. (a) Schematic view of the spiral-shaped microchannel. (b) Side view of the etched spiral-shaped microchannel by HF acid inside the glass. (c) Side view of the spiral-shaped microchannel after baking of the etched sample at 600 °C for 4 h. (d) The cross-section of the post baked microchannel. (e) The cross-section of the channel at the opening area.
500 µm, respectively. The total length of spiral-shaped microchannel is ∼3000 µm. The experimental results show that the internal surface of microchannel becomes smooth after post baking and the liquidity of the channel is well. The incident laser power and scanning speed also have influence on the channel quality. It is expected that this technique will be applied to fabricate 3D microfluidic components. Acknowledgement We thank Harbin Institute of Technology at Weihai for supporting this work. References
Fig. 4. Side view of blue solution flowing through the spiral-microchannel.
4. Conclusion In summary, we have fabricated the spiral-shaped microchannel in glass by using femtosecond laser direct writing and the subsequent baking. The screw-pitch and the diameter of circle are 1000 µm and
[1] Ahn CH, Jin-Woo Choi, Beaucage G, Nevin JH, Jeong-Bong Lee, Puntambekar A, et al. Disposable smart lab on a chip for point-of-care clinical diagnostics. Proc IEEE 2004;92:154–73. [2] Kavcic B, Babic D, Osterman N, Podobnik B, Poberaj I. Magnetically actuated microrotors with individual pumping speed and direction control. Appl Phys Lett 2009;95:023054. [3] Hnatovsky C, Taylor RS, Simova E, Rajeev PP, Rayner DM, Bhardwaj VR, et al. Fabrication of microchannels in glass using focused femtosecond laser radiation and selective chemical etching. Appl Phys A 2006;84:47–61. [4] Martynova L, Locascio LE, Gaitan M, Kramer GW, Christensen RG, Maccrehan WA. Fabrication of plastic microfluidic channels by imprinting methods. Anal Chem 1997;69:4783–9. [5] Davis KM, Miura K, Sugiomto N, Hirao K. Writing waveguides in glass with a femtosecond laser. Opt Lett 1996;21:1729–31. [6] Bellouard Y, Dugan M, Said A, Bado P. Fabrication of high-aspect ratio micro-fluidic channels and tunnels using femtosecond laser pulses and chemical etching. Opt Express 2004;12:2120–9. [7] Cheng Y, Sugioka K, Midorikawa K, Masuda M, Toyoda K, Kawachi M, et al. Control of the cross-sectional shape of a hollow microchannel embedded in photostructurable glass by use of a femtosecond laser. Opt Lett 2003;28:55–7. [8] Sugioka K, Masuda M, Hongo T, Cheng Y, Shihoyama K, Midorikawa K. Threedimensional microfluidic structure embedded in photostructurable glass by femtosecond laser for lab-on-chip application. Appl Phys A 2004;78:815–7. [9] Marcinkevicius A, Juodkazis S, Watanabe M, Miwa M, Matuso S, Misawa H, et al. Femtosecond laser-assisted three-dimensional microfabrication in silica. Opt Lett 2001;26:277–9. [10] Cheng Y, Sugioka K, Midorikawa K. Microfluidic laser embedded in glass by threedimensional femtosecond laser microprocessing. Opt Lett 2004;29:2007–9. [11] Cheng Y, Sugioka K, Midorikawa K. Microfabrication of 3D hollow structures embedded in glass by femtosecond laser for lab-on-a-ship applications. Appl Surf Sci 2005;248:172–6. [12] He F, Cheng Y, Xu Z, Liao Y, Xu J, Sun H, et al. Direct fabrication of homogeneous microfluidic channels embedded in fused silica using a femtosecond laser. Opt Lett 2010;35:282–4.