Experimental set-up and recorded spectra of NMA adsorbed to the waveguide.
(a) Artist’s impression of the experimental set-up based on butt-coupled broad-band illumination of a waveguide system by a supercontinuum NIR source and recording of the transmittance spectra with use of OSA (See Methods). Tear-sized droplet of a liquid has been dripped onto the waveguide for the spectroscopy analysis. (b) photograph of the chip during the measurement, NMA has been dripped in Hex solution onto PDMS liquid reservoir using micropipette; in the photograph, two waveguides are illuminated by coherent red and green light sources for demonstration of potential multi-array detection. (c) Transmittance spectra (solid curves) recorded using the waveguide while dripping volume of 0.1 mL and concentration of 66.7% NMA diluted in Hex mixture. The spectra are registered at time intervals of about 1 min with time increasing from the top to the bottom of the figure. The blue solid curve corresponds to the min 0 in the subplot (d). The red curve corresponds to the transmittance decrease by 18 dB. Other curves have been shifted vertically for clarity. N-H and aryl C-H absorption bands are indicated by the arrows; (d) Experimental transmittance modulation depth of (N-H)-bond stretching band shown as a function of time.