In the case of Mb, the absorbance at 280 nm in the second fraction was quantified, with ε = 13.98 mM -1 cm -1 , from its sequence, as of (N of tryptophan residues*5.5) + (N of tyrosine residues*1.5). 92 For β-gal, the protein absorbance at 280 nm was likewise calculated, using the expected content of Mb as blank, with ε= 191.95 mM -1 cm -1 . The measurements were conducted in a Cary 60 UV-Vis spectrophotometer (Agilent, USA). FITC-labelled polystyrene microbeads (2 µm diameter) were added to the reaction mixture (10 µL directly from the suspension) and then directly imaged via CLSM.