Fig. 3. SM-SERS spectra of hemin bound (A) Au DONAs and (B) Ag DONAs under laser excitation of 633 nm and 488 nm, respectively (inset shows SEM image of the corresponding DONAs; scale bar = 125 nm; measurement condition – obj: 100×; power: 250 μW (Au) and 80 μW (Ag); acc time: 4 s. (i) and (ii) in (A) and (B) represents two individual DONA spectra. Statistical distribution of vibrational bands corresponding to spin and oxidation state drawn from different single DONAs is shown in (C) and (D) for Au and Ag DONAs. (E) SERS spectra of hemin (153 μM) adsorbed on Au NPs (60 nm) surface (laser: 633 nm, objective: 50×, acquisition time: 10 s, laser power: 0.9 mW). (F) Contour plot of time evolution SERS spectra of hemin recorded from single Ag DONA (shown in inset; image size: 300 nm × 300 nm). Condition – laser: 488 nm; power: 80 μW; acquisition time: 0.5 s; objective: 100× (Zeiss). Temporal fluctuation in SERS intensity and spectral wandering in the vibrational modes characteristic of hemin can be seen of which most important are the ν₃ (1497 cm⁻¹) and ν₁₀ (1611 cm⁻¹) modes which signifies the high spin Fe(iii) state of hemin. White box highlights the peak wandering of ν₁₀ band in the range of 1602–1616 cm⁻¹ over time.