Fig. 1. Diagram representing the working principle of the LC-based sensors.

Fig. 2. The process of functionalizing the glass slides is represented in this diagram, where every step before glueing is represented [15].

Fig. 3. Diagram of the polarized optical microscope configuration.

Fig. 4. Finalized prototype, with the components fitted in an encasing.

Fig. 5. 3D model of the final version encasing for the setup: (a) complete box with lid; (b) light source section, with LED slot; (c) lens section of the box; and (d) sensor support.

Fig. 6. (left) Representation of the frame alignment relative to the support. (right) Image captured by positioning the lens at an optimal distance, for an E. coli sensor with a concentration of 2.69×103  CFU/mL.

Fig. 7. Region of detection for an E. coli biosensor with a concentration of 3.84 CFU/mL and a width of 6.4 mm: (a) without and (b) with the width adjustment.

Fig. 8. Fit for the selected batch of E. coli biosensors, for the concentration with the percentage of colored pixels. The X axis is on a logarithmic scale.

Fig. 9. Detection of the sensors for (a) E. coli ATTC35218 (E8); (b) Bacillus (O26); and (c) Acinetobacter (D6).

Fig. 10. Bar graph for the average percentage for Bacillus (O26), Acinetobacter (D6), and E. coli (E8).

Fig. 11. (a) Portion of the 3D-printed box design to let sunlight reach the sample. (b) Equipment used to conduct the testing outdoors.

Fig. 12. Graph displaying the percentage of colored pixels detected at 8:30 and 13:30 concerning the box’s angle of inclination.

Fig. 13. Example of the analysis with the GUI. (a) Lower concentration E. coli sensor (2.12×10−1  CFU/mL, corresponding to 36.55%). (b) Control sensor. (c) Higher concentration E. coli sensor (4.20×108  CFU/mL).