Absorption spectroscopy in microfluidic flow cells using a metal clad leaky waveguide device with a porous gel waveguide layer

Broadband absorption spectroscopy is advantageous because the full spectral profile of an analyte can permit identification of species. This work for the first time investigates the feasibility of a metal clad leaky waveguide (MCLW) device to obtain an absorption spectrum of an analyte of interest, methylene blue, using a white light source in a microfluidic flow cell. The MCLW device comprises a porous low refractive index gel, agarose, deposited on a titanium coated glass slide. The device was capable of detecting 2.3 μM of methylene blue at a wavelength of 650 nm. The corresponding minimum detectable absorbance is 1.6 × 10−1 cm−1. In comparison to commonly used detection devices the MCLW is simpler, robust, easier to fabricate and can be easily interfaced to microfluidic devices. It was also possible to store the MCLW devices dry for up to a year and rehydrate them in 30 s to a working condition.