Photothermal microfluidic sensor based on an integrated Young interferometer made by ion exchange in glass

We present the planar co-integration of an ion-exchange Young interferometer with a microfluidic sensing chamber for photothermal analyte detection. Being exclusively fabricated and packaged in borosilicate glass, the sensor is well suited for a vast range of applications in chemical analysis, including ionizing environments. Local absorption of a pulsed excitation laser by the analyte in the fluid generates a change of the fluid refractive index which translates to a shift of the interference pattern. The detection limit of fringe movement was measured to be 1.8 × 10−3 × 2π and the corresponding refractive index resolution was Δn = 7.5 × 10−6. Absorption measurements of cobalt(II) nitrate in ethanol yielded a detection limit of c = 6 × 10−4 M, equivalent to an absorption coefficient of α = 1.2 × 10−2 cm−1 and a minimum detectable absorbance of K = 1.4 × 10−5. At a probed volume of 20 pl, a quantity of 12 fmol of Co(II) was detected.