Moth wing scales as optical pH sensors

We embed individual wing scales from Chrysiridia rhipheus (sunset moth) into pH sensitive interpenetrating polymer network (IPN) of chitosan and PVA to generate novel pH sensors based on “biological physical dye”. The immobilized wing scales’ visible reflectance is responsive to pH conditions, owing to their inner microstructural changes induced by the IPN volume change in the swelling/deswelling process of hydrogel. In neutral and acidic environments, the in situ reflectance peaks of wing scales slightly shift ∼27 nm around 730 nm for pH 1.00–7.07, while in basic environments the peaks obviously blueshift ∼260 nm from ∼730 nm at pH 7.07 to ∼470 nm at pH 13.74. Such prominent pH sensitivity of “moth scale indicators” in week basic conditions (pH 7.95–9.99) promises a bio-sensing pH monitor that can be used in bio-medical and bio-controlled applications.