Fig. 1.

Exemplar spectra collected for (a) and (b) 2 × 10⁻²% AO staining followed by 3 washing cycles (c) and (d) 2 × 10⁻³% AO staining followed by two washing cycles and (e) and (f) 2 × 10⁻⁴% AO staining for 0–10⁵ CFU ml⁻¹ E. coli in (a, c and e), and for 10⁶−10⁸ CFU ml⁻¹ E. coli in (b, d and f). Spectra are coloured by concentration: blue 10⁸, green 10⁷, red 10⁶, grey 10⁵, mint green 10⁴, magenta 10³, cyan 10², black 0 CFU ml⁻¹