Fig. 3. Analysis of individual cells. (A) Upper left: AFM topography of a [2Fe]^adt–HydA1-containing E. coli cell. Lower left: sSNOM image mapped at v₁ = 1660 cm⁻¹ (amide I absorption). Lower right: sSNOM image mapped at v₂ = 1710 cm⁻¹ (topography artifact). Upper right: v₁ − v₂ sSNOM difference image. The protein is clearly localized to the cellular environment see Fig. S6 and S7† for additional examples. (B) Nano-FTIR near-field phase spectrum from 2000–1300 cm⁻¹. Spectra were recorded on the cell (spot 1, blue) and next to the cell (spot 2, red) in the AFM topography (panel A). (C) ATR FTIR difference spectra showed an HDO band (2515 cm⁻¹) increase in the presence of D₂ (exposure time 0–90 s increasing from black to purple). Inset: a simultaneous enrichment of H_red (1891 cm⁻¹) over H_ox (1940 cm⁻¹) was observed.