Filter paper photography and fluorescence analysis

Filter paper preparation: Two sprays with a pure water atomiser were used to re-humidify the filter papers (Fig ​(Fig11c).

Photography environment: To create fluorescein excitation, filter papers were photographed under a LED bulb lamp. The emitted light was white with a 475 nm short pass filter (Edmund Optics, York, UK). Light was received using a long pass filter at approximately 500 nm (Hoya F3 yellow lens filter, Hoya Vision Care Company, Bangkok, Thailand; Fig ​Fig11d).

Camera settings: A Canon EOS 700D camera with 18–55 mm lens (Canon Inc, Tokyo, Japan) was used for photography. The camera settings were ISO 1,600; shutter speed 0.25 seconds; aperture F=8.0; and white balance ‘halogen’.

Fluorescence quantification: The photograph was split into the red/green/blue (RGB) stack and the green channel selected using the Fiji distribution of ImageJ.27 The technique described by Hammond was adapted to calculate total fluorescence (TF; Fig ​Fig11d).28