In situ μ-printed optical fiber-tip CO2 sensor using a photocrosslinkable poly(ionic liquid)

•A photocrosslinkable poly(ionic liquid), i.e. poly(1-allyl-3-vinylimidazolium bromide) (PAVB), with a large number of imidazolium functional groups has been synthesized for reversible adsorption of CO2 gas.•An in situ optical μ-printing technology has been established to directly print microscale polymer Fabry–Pérot interferometers (FPIs) on the small end faces of optical fibers.•Two kinds of microscale FPIs using the PAVB and SU-8 epoxy have been fabricated on the end face of a multicore optical fiber for simultaneous measurement of CO2 concentration and temperature, respectively.•In addition to the excellent sensing performances (e.g. good selectivity, high sensitivity, and extremely wide dynamic operation range), the novel optical fiber-tip sensor has unique capabilities to remotely measure CO2 concentration and temperature in very small spaces. 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 CO2 concentration and related parameters. Here we present a new optical fiber-tip CO2 sensor for simultaneous measurement of CO2 concentration and temperature. A photocrosslinkable poly(ionic liquid), i.e. poly(1-allyl-3-vinylimidazolium bromide) (PAVB), with selective CO2 adsorption 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 CO2 concentration 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 CO2 sensor can remotely and simultaneously measure CO2 concentration and temperature in very small spaces and is thus promising for many applications ranging from waste gas detection to food quality control.