Cocaine detection by a mid-infrared waveguide integrated with a microfluidic chip

A germanium (Ge) strip waveguide on a silicon (Si) substrate is integrated with a microfluidic chip to detect cocaine in tetrachloroethylene (PCE) solutions. In the evanescent field of the waveguide, cocaine absorbs the light near 5.8 mm, which is emitted from a quantum cascade laser. This device is ideal for (bio-)chemical sensing applications.

Mid infrared waveguide spectroscopy for cocaine detection in liquid environments

Yu-Chi Chang, Nico de Rooij, Joab Di Francesco, Hans Peter Herzig, Lubos Hvozdara, Vincent Paeder, Peter Van der Wal, Philip Wägli

A germanium strip waveguide on a silicon substrate is integrated with a microfluidic chip to detect cocaine in tetrachloroethylene solutions. In the evanescent field of the waveguide, cocaine absorbs the light at 5.8μm, which is emitted from a quantum cascade laser. The lowest measured concentration is 100μg/ml.

2012

Design, Fabrication and Characterization of Mid-Infrared Strip Waveguide for Laser Spectroscopy in Liquid Environments

Yu-Chi Chang

Optical sensors based on the interaction between molecular vibrations and mid infrared radiations attracted high attentions in the last decades. In this study, we present the development of a waveguide evanescent field sensor based on the absorption spectroscopy in liquid environments. The device consists of a single mode strip waveguide integrated with a microfluidic system. With a quantum cascade laser at the wavelength of 5.8 μm, we demonstrate the detection of cocaine dissolved in tetrachloroethylene (PCE). Mid infrared germanium waveguides on silicon have been proposed but not experimentally demonstrated. Here we realize this new type of waveguide with a monocrystalline germanium layer on a silicon substrate (Ge-on-Si) with standard photolithography and reactive ion etching. It is designed to be singlemode in transverse magnetic polarization at 5.8 μm. We used a method based on the Fabry-Perot resonance to measure the propagation loss, and the achieved lowest loss is 2.4 dB/cm. The bending loss was measured to be 0.12 dB per 90∘bend with the radius of 115 μm. A microfluidic chip made from a UV-curable adhesive is integrated to the Ge-on- Si waveguide. This is the first integration of this waveguide with a microfluidic system. Solutions of cocaine in PCE flow in the microfluidic channel and absorb the light in the evanescent field. A reference waveguide and an integrated Y- junction eliminate the noise from coupling fluctuations, and the limit of detection is calculated to be 5 μg/ml. Mid infrared photonics can be further developed based on the platform of Ge-on- Si waveguides. We demonstrate a detection of refractive index changes with a Mach-Zehnder interferometer integrated with a microfluidic system. Subwavelength structures for antireflection of the waveguide facets are also experimentally tested. We foresee an increasing development and applications based on this waveguide in the mid infrared.

EPFL2012

Microfluidic Droplet-Based Liquid–Liquid Extraction and On-Chip IR Spectroscopy Detection of Cocaine in Human Saliva

Yu-Chi Chang, Nico de Rooij, Hans Peter Herzig, Lubos Hvozdara, Philip Wägli

We present a portable microsystem to quantitatively detect cocaine in human saliva. In this system, we combine a microfluidic-based multiphase liquid-liquid extraction method to transfer cocaine continuously from IR-light-absorbing saliva to an IR-transparent solvent (tetrachloroethylene) with waveguide IR spectroscopy (QC-laser, waveguide, detector) to detect the cocaine on-chip. For the fabrication of the low-cost polymer microfluidic chips a simple rapid prototyping technique based on Scotch-tape masters was further developed and applied. To perform the droplet-based liquid-liquid extraction, we designed and integrated a simple and robust droplet generation method based on the capillary focusing effect within the device. Compared to well-characterized and commonly used microfluidic H-filters, our system showed at least two times higher extraction efficiencies with potential for further improvements. The current liquid-liquid extraction method alone can efficiently extract cocaine and pre-concentrate the analytes in a new solvent. Our fully integrated optofluidic system successfully detected cocaine in real saliva samples spiked with the drug (500 mu g/mL) and allowed real time measurements, which makes this approach suitable for point-of-care applications.

Amer Chemical Soc2013

Design, Fabrication and Characterization of Mid-Infrared Strip Waveguide for Laser Spectroscopy in Liquid Environments

Yu-Chi Chang

EPFL2012