Figure 1.

Preparation of the bioresorbable fluorescence pH sensor. a) Sketch of the pH sensor architecture and operation principle. The sensor consists of a micrometer‐thick nanostructured porous silicon oxide (nPSiO₂) membrane coated with a nanometer‐thick pH‐responsive stack of two polymers labelled with Rh fluorophores (PAH:Rh and PMAA:Rh). b) Main fabrication steps of the pH sensor on PLGA substrate: 1) preparation of a ≈5‐µm‐thick nPSi membrane via two‐steps electrochemical silicon etching; 2) thermal oxidation of the nPSi membrane to nPSiO₂; 3) transfer‐printing of nPSiO₂ membrane onto a ≈40‐µm‐thick PLGA film; 4) layer‐by‐layer conformal coating of the nPSiO₂ scaffold with a nanometer‐thick multilayer stack of PAH:Rh and PMAA:Rh. c) 1) Picture of the bioresorbable pH sensor highlighting the Rh‐coated nPSiO₂ membrane (pink area) on the PLGA foil; 2) bright‐field and 3) fluorescence optical microscope images of the cross‐section of the nPSiO₂ scaffold LbL‐coated with Rh‐labelled polyelectrolytes. Scale bar is 10 µm. d) Photoluminescence intensity at 580 nm versus number of Rh‐labelled polyelectrolyte layers assembled in the nPSiO₂ scaffold either transfer‐printed on PLGA foil or left on the native Si chip, as well as on flat SiO₂ substrate used as control. The inset highlights the photoluminescence intensity measured on flat SiO₂ substrate (n = 3 samples for each polyelectrolyte architecture). e) Ratio of the photoluminescence intensity (at 580 nm) achieved on nPSiO₂ scaffolds and flat PSiO₂ substrate (i.e., PL_nSiO2/PL_SiO2) versus number of Rh‐labelled polyelectrolytes of the multilayer stack (n = 3 samples for each polyelectrolyte architecture). All data are presented as mean (± s.d).