In situ μ-printed optical fiber-tip CO₂sensor using a photocrosslinkable poly(ionic liquid)

Carbon dioxide (CO2) sensors play important roles in our daily life and production activities. However, it remains a challenge to develop a tiny device with remote sensing capability for detection of CO2concentration and related parameters. Here we present a new optical fiber-tip CO2sensor for simultaneous measurement of CO2concentration and temperature. A photocrosslinkable poly(ionic liquid), i.e. poly(1-allyl-3-vinylimidazolium bromide) (PAVB), with selective CO2adsorption capability was synthesized to fabricate miniature sensors via an in situ optical μ-printing technology. We directly printed several micrometer-scale Fabry–Pérot interferometers (FPIs) on the end face of a multicore optical fiber using the PAVB and SU-8 epoxy, respectively. We have demonstrated that the PAVB FPI sensor can measure CO2concentration with a sensitivity up to ∼35 pm/% in a wide range of 0%–75%, and its rise and fall dynamic response times are about 6.1 and 8.0 min, respectively. Meanwhile, the SU-8 FPI sensor is able to measure temperature with a sensitivity 0.059 nm/°C. Such a tiny CO2sensor can remotely and simultaneously measure CO2concentration and temperature in very small spaces and is thus promising for many applications ranging from waste gas detection to food quality control.