A novel leaky waveguide grating (LWG) device for evanescent wave broadband absorption spectroscopy in microfluidic flow cells

Evanescent wave (EW) broadband absorption spectroscopy is commonly interfaced with a range of analytical systems, including microfluidic flow cells, for identification and quantitation of species. A miniaturised spectrometer integrated with a microfluidic flow cell is useful to permit on-site analysis of samples. This work reports a novel leaky waveguide grating (LWG) device, which is able to obtain an absorption spectrum of an analyte of interest (in this case, methylene blue) without an external spectrometer. At 600 nm, the spectral resolution and the minimum detectable absorption coefficient of the LWG device is 49.5 nm and 1.65 cm−1, respectively. The LWG can be fabricated on birefringent substrates such as plastics because the performance of the device is independent of the polarisation of the excitation source. The LWG device was fabricated using microcontact printing and hence can be easily mass produced.