La1422 a

On-field experiments were realized thanks to carry-on detection equipment. It consists in two blue LEDs (Thorlabs – M490L3–490 nm) combined with a first lense (Thorlabs ACL25416U-A), two filters (Thorlabs FES0500 – Thorlabs M497-16) and a second lense (Thorlabs LA1422-A) to light the paper. The signal emitted by the biological reaction on paper is collected by a linear camera (Thorlabs LC-100) through a first lense (Thorlabs ACL3026-A), a FITC dichroic filter (Thorlabs MD499), a filter (Thorlabs FELH0500) and a second lense (Thorlabs ACL25416U-A). The paper device is positioned on a chip holder heated by a PTC heater (DBK HP05), controlled by a platine thermic element (RS Components PT 1000ohms) and a temperature controller (Carel IR33). A home-made Microsoft Office 2007 macro program enables to extract data from the linear camera recording software (Splicco), to detect the position of the maximum fluorescence intensity for each paper rectangular area and to monitor the mean intensity around each maximum over time.

To obtain the fluorescence image of the illuminated area, the fluorescent light that is emitted from the sample is collected by the expander system and imaged to infinity. A bandpass filter (ET525/36m or ET585/20m, Chroma, VT, USA) is used for green emission or red emission. Then, light is focused onto the camera (iDS 3060cp), which captures an image of the fluorescent sample. As the detectable sample is the same size as the illumination area (4 × 4 mm²), an extra lens system is designed for the macroimaging of small size objects, which requires high-resolution and well-corrected chromatic aberration from red to green, which is a spectral range that cannot be corrected by a regular lens or even an achromatic lens. The elaborate achromatic system (see Fig. 2), which has an effective focal length of f = 30 mm, is composed of three spherical singlet lenses (LC2679-A, LB1757-A, and LA1422-A, Thorlabs, NJ, USA) and the air spaces are optimized (see the electronic supplementary material).