Development of microfluidic LED sensor platform
© Kim et al.; licensee Springer. 2015
Received: 30 December 2014
Accepted: 18 January 2015
Published: 17 June 2015
We developed the microfluidic light emitting diode (LED) sensor for methanol detection. The linear gradient-generating microfluidic device consists of two inlet and four outlet microchannels. The concentration gradients of methanol were stably generated in the microfluidic platform in a temporal and spatial manner. The methanol harvested from microfluidic platforms was analyzed by measuring electrical conductivity, showing that currents were decreased with the methanol content. The methanol in the microfluidic device was also observed by LED sensor. Therefore, this microfluidic LED device could be a powerful platform for methanol sensor applications.
KeywordsLED sensor Microfluidic gradient device Methanol detection Electrical conductivity
Methanol, the simplest alcohol and organic solvent, has widely been used for fuel cell and biochemical applications [1-3]. The direct methanol fuel cell is of great benefit for portable electronic devices, because it enables increase of power density and decrease of operating temperature [4-6]. The physical and chemical properties of methanol are also similar to gasoline, showing that methanol is a good candidate as a fuel cell in automotive engines [7-9]. Despite many methanol-based industrial applications, the major problem is still remained, such as methanol toxicity, which can cause severe disease of metabolic acidosis, nerve disorder, olfactory mucosa, and blindness . Although small amount of methanol is inhaled, methanol becomes toxic formic acid via formaldehyde as previously described . In general, the volatile organic compound (e.g., methanol), which can be conventionally detected by gas chromatography technique, has low boiling point and high reactive property. Thus, the development of the platform technology to detect the methanol at room temperature has become imperative .
Microfluidic devices have previously been developed to generate concentration gradients and detect biomolecules [13-15]. Recently, an integrated microfluidic device has been developed to quantify methanol concentrations . The methanol and methanol oxidase infused into the poly(methyl methacrylate) (PMMA)-based microfluidic device. The injected solutions were heated at 45°C to generate formaldehyde and methanol concentrations were subsequently observed by ultraviolet (UV) spectrophotometer. The accuracy of microfluidic device-based methanol detection was approximately 93% compared to gas chromatography method. Integrated microfluidic device has been developed to detect methanol concentrations . The system consisted of light emitting diode (LED) photometer, PMMA-based microfluidic device, photodiode, voltmeter, and temperature controller. The samples were loaded and were subsequently mixed by a vortex stirrer in the microfluidic device. The colorimetric reaction of the mixtures was performed by thermoelectric cooler and micro-hotplate systems. LED photometer system detected methanol concentrations in the microfluidic device. Furthermore, microfluidic device has been developed for direct methanol fuel cell applications . For the fuel cell, methanol and oxygen was employed as an anode and cathode, respectively. The microfluidic device containing anode flow fields enabled the generation of liquid–gas meniscus. It showed that the interfacial mass-transfer resistance was largely generated by evaporation of the small meniscus, resulting in inhibition of methanol delivery to anode catalyst layers. The flow field enabled the formation of passive direct methanol fuel cells containing higher methanol concentrations. However, previous approaches have used complex integrated microfluidic devices to detect methanol gas at high temperature. To overcome these limitations, we developed the linear gradient-generating microfluidic device to monitor and quantify the methanol at room temperature using programmed microcontroller, LED sensor, and electrical conductivity analysis. Therefore, this microfluidic LED device could be a powerful tool for methanol sensor applications.
2.1 Fabrication of the microfluidic device to generate methanol concentration gradients
2.2 Experimental set-up
The microfluidic device containing two inlets and four outlets allowed streams of solutions to generate laminar flow in parallel without any convective mixing. To generate concentration gradients in the microfluidic device, the methanol and buffer solutions were injected with a uniform flow rate (66 μl/min) using a syringe pump (Harvard Apparatus, USA). The methanol was analyzed by measuring current–voltage (I-V) curve using source meter and Labview programming.
2.3 Computational simulation
C is the concentration, u is the velocity vector calculated by the Navier–Stokes equations (1) and (2). D is the diffusion coefficient (2.19 × 10−9) at the condition of 0.1 MPa and 298.5 K . The number of elements of mesh used in this simulation was approximately 116,632. Consequently, the optimal flow rate (66 μl/min) generated by a syringe pump was calculated.
2.4 Electrical circuit diagram for LED sensor
3 Results and discussion
Analog/digital (A/D) conversion voltage used in a microcontroller
A/D voltage (V)
A/D voltage (V)
We developed the microfluidic LED sensor for methanol detection. The linear gradients of methanol were generated in the microfluidic device. The methanol harvested from the microfluidic device was analyzed by electrical conductivity and LED sensor. We demonstrated that the electrical conductivity was decreased with increasing the methanol and each percentage of the methanol was also observed by LED sensor. Therefore, this microfluidic LED device for methanol detection could be a powerful tool for methanol sensor applications.
This research was supported by BioNano Health-Guard Research Center funded by the Ministry of Science, ICT & Future Planning (MSIP) of Korea as Global Frontier Project (Grant number H-GUARD_2014M3A6B2060503), Republic of Korea. This work was also supported by Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) (2013K1A4A3055268) and the Sogang University Research Grant of 2014 (Grant Number SRF-201414001).
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