For devices such as bio-/chemical sensors in microfluidic systems, flow fluctuations result in noise in the sensor output. Here, we demonstrate in-line monitoring of flow fluctuations with a cantilever-like sensor integrated in a microfluidic channel. The cantilevers are fabricated in different materials (SU-8 and SiN) and with different thicknesses. The integration of arrays of holes with different hole size and number of holes allows the modification of device sensitivity, theoretical detection limit and measurement range. For an average flow in the microliter range, the cantilever deflection is directly proportional to the flow rate fluctuations in the microfluidic channel. The SiN cantilevers show a detection limit below 1 nL/min and the thinnest SU-8 cantilevers a detection limit below 5 nL/min. Finally, the sensor is applied for in-line monitoring of flow fluctuations generated by external pumps connected to the microfluidic system.
References
[1]
Jakeway, S.C.; de Mello, A.J.; Russell, E.L.; Fresen, J. Miniaturized total analysis systems for biological analysis. J. Anal. Chem. 2000, 366, 525–539.
[2]
Beebe, D.J.; Mensing, G.A.; Walker, G.M. Physics and applications of microfluidics in biology. Ann. Rev. Biomed Eng. 2002, 4, 261–286.
[3]
Mogensen, K.B.; Klank, H.; Kutter, J.P. Recent developments in detection for microfluidic systems. Electrophoresis 2004, 25, 3498–3512.
Ashauer, M.; Glosch, H.; Hedrich, F.; Hey, N.; Sandmaier, H.; Lang, W. Thermal flow sensor for liquids and gases based on combinations of two principles. Sens. Actuators A 1999, 73, 7–13.
[10]
Van Oudheusden, B.W. The determination of the effective ambient temperature for thermal flow sensors in a non-isothermal environment. Sens. Actuators A 1999, 72, 38–45.
[11]
Van Kuijk, J.; Lammerink, T.S.J.; de Bree, H.E.; Elwenspoek, M.; Fluitman, J.H.J. Multi-parameter detection in fluid flows. Sens. Actuators A 1995, 47, 369–372.
[12]
Ernst, H.; Jachimowicz, A.; Urban, G.A. High resolution flow characterization in Bio-MEMS. Sens. Actuators A 2002, 100, 54–62.
[13]
Petrak, D.; Rauh, H. Micro-flow metering and viscosity measurement of low viscosity Newtonian fluids using a fibreoptical spatial filter technique. Flow Meas. Instrum. 2009, 20, 49–56.
[14]
Koenig, J.; Voigt, A.; Buettner, L.; Czarske, J. Precise micro flow rate measurements by a laser Doppler velocity profile sensor with time division multiplexing. Meas. Sci. Technol. 2010, 21, 074005.
[15]
Richter, M.; Wackerle, M.; Woias, P.; Hillerich, B. A Novel Flow Sensor with High Time Resolution based on Differential Pressure Principle. Proceedings of the Twelfth IEEE International Conference on Micro Electro Mechanical Systems, Orlando, FL, USA; 1999.
Boillat, M.A.; van der Wiel, A.J.; Hoogerwerf, A.C.; de Rooij, N.F. A Differential Pressure Liquid Flow Sensor for Regulation and Dosing Systems. Proceedings of the IEEE Conference on Micro Electro Mechanical Systems (MEMS'95), Amsterdam, The Netherlands, 29 January–February 2 1995; pp. 350–352.
[18]
Liu, Z.; Hong, T.; Zhang, W.; Chen, H. Novel liquid flow sensor based on differential pressure method. Rev. Sci. Instrum. 2007, 78, 015108.
[19]
Collins, J.; Lee, A.P. Microfluidic flow transducer based on the measurement of electrical admittance. Lab Chip 2004, 4, 7–10.
[20]
Kim, D.-K.; Majumdar, A.; Kim, S.J. Electrokinetic flow meter Sens. Actuators A 2007, 136, 80–89.
[21]
Wang, J.; Sullivan, M.; Hua, S.Z. Electrolytic-bubble-based flow sensor for microfluidic systems. J. Microelectromech. Syst. 2007, 16, 1087–1094.
[22]
Ezkerra, A.; Fernandez, L.J.; Mayora, K.; Ruano-Lopez, J.M. Fabrication of SU-8 free-standing structures embedded in microchannels for microfluidic control. J. Micromech. Microeng. 2007, 17, 2264–2271.
[23]
Radhakrishnan, S.; Lal, A. Scalable microbeam flowsensors with electronic readout. J. Micromech. Syst. 2005, 14, 1013–1022.
[24]
Lien, V.; Vollmer, F. Microfluidic flow rate detection based on integrated optical fiber cantilever. Lab Chip 2007, 7, 1352–1356.
[25]
Nezhad, A.S.; Ghanbari, M.; Agudelo, C.G.; Packirisamy, M.; Bhat, R.B.; Geitmann, A. PDMS microcantilever-based flow sensor integration for lab-on-a-chip. IEEE Sens. J. 2013, 13, 601–609.
[26]
Zhang, Q.; Ruan, W.; Wang, H.; Zhou, Y.; Wang, Z.; Liu, L. A self-bended piezoresistive microcantilever flow sensor for low flow rate measurement. Sens. Actuators A 2010, 158, 273–279.
[27]
Noeth, N.; Keller, S.; Boisen, A. Fabrication of a cantilever-based microfluidic flow meter with nL min ？1 resolution. J. Micromech. Microeng. 2011, 21, 015007.
[28]
Keller, S.; Haefliger, D.; Boisen, A. Optimized plasma-deposited fluorocarbon coating for dry release and passivation of thin SU-8 cantilevers. J. Vac. Sci. Technol. B. 2007, 25, 1903–1908.
[29]
Keller, S.; Blagoi, G.; Lillemose, M.; Haefliger, D.; Boisen, A. Processing of thin SU-8 films. J. Micromech. Microeng. 2008, 18, 125020.
[30]
Keller, S.; Haefliger, D.; Boisen, A. Fabrication of thin SU-8 cantilevers: Initial bending, release and time stability. J. Micromech. Microeng. 2010, 20, 045024.
[31]
Van Rijn, C.J.M.; Elwenspoek, M.C. Microfiltration Membrane Sieve with Silicon Micromachining for Industrial and Biomedical Applications. Proceedings of the IEEE Conference on Micro Electro Mechanical Systems (MEMS'95), Amsterdam, The Netherlands, 29 January– February 2 1995; pp. 83–87.
[32]
Van Rijn, C.J.M.; Veldhuis, G.J.; Kuiper, S. Nanosieves with microsystem technology for microfiltration applications. Nanotechnology 1998, 9, 343–345.
[33]
Stoffel, A.; Kovacs, A.; Kronast, W.; Mueller, B. LPCVD against PECVD for micromechanical applications. J. Micromech. Microeng. 1996, 6, 1–13.
[34]
Keller, S.S.; Gammelgaard, L.; Jensen, M.P.; Schmid, S.; Davis, Z.J.; Boisen, A. Deposition of biopolymer films on micromechanical sensors. Microelec. Eng. 2011, 88, 2297–2299.
