Elsevier

Microelectronic Engineering

Volume 88, Issue 8, August 2011, Pages 1798-1800
Microelectronic Engineering

An integrated on chip organic optical source based on electrochemiluminescence

https://doi.org/10.1016/j.mee.2010.12.083Get rights and content

Abstract

We report here on an original “glass-PDMS-glass” electrochemiluminescence optofluidic device that integrates 32 electrodes on a large surface. This organic electrically powered light source has been integrated on chip using an alternative process based on a photopatternable silicone resist. Under a continuous flow rate, this device allows electrogenerated chemiluminescence for several minutes which would be very useful for future μTAS systems.

Introduction

Since optofluidics was introduced in the early 2000s, a lot of devices combining microfluidics and optics have been developed such as L2 waveguides, adaptive liquid lenses, microdroplet optical mixing, or lensless optofluidic microscopes [1], [2], [3], [4], [5]. Most of them need an external optical source. Optofluidic integrated light sources generally refer to dye laser or light emission occurring within the liquid dye core of the L2 waveguides. Both systems offer major advantages that are the flexibility and the tunability of the emission wavelength simply obtained by changing the composition of the gain medium or of the liquid core. Nevertheless, those systems still rely on external bulky optics that have to be carefully coupled to the microfluidic chip [6].

To reach the portability of microfluidic systems, electrically powered light sources have to be developed. Electrochemiluminescence (ECL) which consists in producing light from excited states of an organic luminophore appears as a promising alternative. Moreover, ECL also has direct analytical applications like clinical assays [7]. In 1998, Horiuchi group demonstrated laser action driven by ECL [8]. However, their work was done before microfluidic emergence and some issues like time stability could not be resolved. A recent example of ECL used in microfluidics was reported by Pittet et al. [9] who detected hydrogen peroxide with luminol ECL based on printed circuit board electrodes. The purpose of this work is to implement an optical source based on ECL annihilation embedded in an integrated microfluidic device which can be simply controlled and monitored by external voltage and for which no optical elements are needed. We thus report here on a new “glass-PDMS-glass” ECL optofluidic device that integrates a 4 × 4 array of 16 optical sources on a large surface (33.75 cm2).

Section snippets

Experimental

Instead of using a standard “glass-PDMS-glass” process [10], we have developed a novel one based on photopatternable PDMS (the silicone WL-5150 resist from Dow Corning). The technological steps are presented in Fig. 1. Two hundred nanometer thick platinum microelectrodes with different separation distances (d=2-16μm) were first patterned on the lower glass substrate (D263 Borosilicate) by conventional UV lithography and lift-off processes (Fig. 1a and b). The 16 μm thick microfluidic channel was

Results and discussion

At an upper voltage of 3.2 V, the ground-state DPA molecules are oxidized and reduced at each electrode producing anionic and cationic radicals. After diffusion of radicals, an excited state DPA is produced and light is emitted when the excited state DPA returns to its initial state. Fig. 3 shows a ECL spectrum recorded at a flow of 0.5 μL/s, which exhibits a maximum of intensity at the same wavelength as the DPA fluorescence emission (430 nm).

To study the role of the electrode distance d, cyclic

Conclusion

In conclusion, we have demonstrated that ECL can be successfully implemented in an integrated microfluidic device with electrodes spaced from few microns working at low flow rate. Since such fluidic organic optical source can be simply electrically powered, it is of high potential for future portable μTAS with embedded electronics.

Acknowledgments

The authors would like to thank the LPN and ISMO staff for technical assistance in both laboratories, and in particular Dr. Damien Lucot for microwires bonding and Dr. Antoine Pallandre. S. Méance is financially supported by the French Ministry for Higher Education and Research and the University of Paris-Sud 11.

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