Abstract
Despite recent progresses in the field of microfluidics, the effect of liquid pressure on the detection accuracy has been rarely studied. Here, we perform a quantitative analysis of such effect, by utilizing the sensitive optical responses of graphene to the refractive index (RI) change of its surrounding environment. We utilize a reflection coupling configuration by combining the total internal reflection (TIR) and ultrasonic waves. The high-performance graphene is processed on common glasses by using the solution-processable oxidation-reduction method. We find that the RI change of water caused by a pressure as small as 500 Pa generated by the liquid level change in the microfluidics can be measured directly. The detection accuracy and response time limits are approximately 280 Pa and 100 ns, respectively. The Maxwell's boundary conditions, Fresnel's law, and Pascal's law are used in theoretical analyses. This work highlights the importance of liquid pressure in microfluidics and provides guidance in designing and accurate detection of microfluidic devices.
Highlights
Microfluidic, called the “lab-on-a-chip,” is an exciting field that offers manageable and sustainable implementation of chemical and biological processes (Mark et al, 2010)
We developed an effective method for ultrasensitive optical detection of water pressure in a microfluidic chip with high-performance reduced graphene oxide on regular glass (Fowler et al, 2009; Zhou et al, 2009)
No doping by other chemical elements illustrates that the uniform crystal structure of reduced graphene oxide (rGO) is not damaged during the preparation (Ismach et al, 2010)
Summary
Microfluidic, called the “lab-on-a-chip,” is an exciting field that offers manageable and sustainable implementation of chemical and biological processes (Mark et al, 2010). Because of the small diameter and the inevitable enlarged contact area of a microfluidic channel, the liquid flow inside possesses different physical properties compared to that in the fluid systems at macroscopic scales (Anna et al, 2003; Sun et al, 2008). The phenomena such as capillary, laminar, and mixture flows should be taken into consideration, which are all closely related to liquid pressure (Cristini and Tan, 2004; Liu et al, 2006). The existence of only theories without experimental verification may cover up the accurate detection of microfluidic systems and the precise control of micro-reactions
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