Fig. 1. Main components of the sensing instrument for simultaneous collection of the spectral responses from a multiple polymer microresonator. The excitation laser, wavemeter, and components for the fluid selection and pumping are not depicted.

Fig. 2. Overview of the multiplexed sensor with 100 microresonators taken by the measuring system camera. Inset demonstrates an SEM image of the individual microresonator.

Fig. 3. Numerical results of the optimization of the coupling-limited Q factor for the right-angle prism coupling scheme. (a) Impact of the incident angle αin on the sensitivity and Qrad/V ratio for the modes (circle, TE; cross, TM polarization) of different orders excited in the microcavity around 680 nm. Insets demonstrate distribution of the EM field for TE modes phase matched at αin=37°, 40°, and 45°. (b) Variations of the coupling-limited Q factor (Qcoup, solid line) and absorption-limited Q factor (Qabs, dashed line) for different gaps between the coupling unit and microresonator.

Fig. 4. Results of the numerical estimations of the deviations of the polymerization voxel characteristic length for different thicknesses of the water-matched adhesive film (0, 200, 400, 600 nm) between the substrate and photosensitive material in the 2PP process.

Fig. 5. Spectral resonance properties of the 2PP toroid microresonator fabricated on a sample with a 400 nm gap to the substrate. (a) Overview of the resonance lines for the exemplary microresonator within the 10 nm spectral range measured in water. (b) Zoom into the resonance line with a sharp peak. (c) Statistics on the measured loaded quality factor in a water environment for 100 microresonators on a single sample.

Fig. 6. Evidence of the 4D sensing enabled by exemplary sample of the multiplexed sensor with 529 units of 2PP microresonators in the form of the long-term dynamics of the spectral shift for the periodically varied environment between water (WTR) and phosphate buffered saline (PBS). The solid line shows the spectral shift mean value; shaded area is the 95% confidence interval.

Fig. 7. Spectral response of the multiplexed 4D microresonator sensor in the form of the scaled PC1 value (PC1 score) for a 10 ppm PFOA solution followed by the pure water (WTR) flushing.

Fig. 8. Dynamical variations of the generalized sensor response in the form of the scaled PC1 for different concentrations of continuously pumped water-based solutions containing different PFAS at varied concentrations. Each variation is measured after the PBS pumping phase for 6000 s. The spectral shift dynamics in pure water before (WTR1) and after (WTR2) the measurements of PFAS are added to each curve. (a) Reaction of the PFOA solutions with concentrations from 10 ppb to 20 ppm. (b) Reaction of the PFBS solutions with concentrations from 1 ppb to 1 ppm.