Fig. 4. Secondary structure determination from ORS-nanoIR absorption spectra.

Structures and morphologies of a apoferritin³³ (red cross) and b thyroglobulin (blue cross)²⁹. c, d Average IR spectrum of three different protein molecules and comparison with bulk IR spectra. e, f Deconvolution of the structural contributions in the amide band I by second-derivative analysis (Savitzky–Golay smoothed, second order, 7 pt) and comparison with bulk FTIR spectra. Comparison of the measured secondary structure by bulk FTIR and single-molecule AFM-IR of g apoferritin and h thyroglobulin. The experimental error arises from the sum of the s.e. of the mean of three spectra averaged and the fit convolution fit error. Source data are provided as a Source Data file.