Lensless imaging has recently attracted a lot of attention as a compact, easy-to-use method to image or detect biological
objects like cells, but failed at detecting micron size objects like bacteria that often do not scatter enough light. In order
to detect single bacterium, we have developed a method based on a thin wetting film that produces a micro-lens effect.
Compared with previously reported results, a large improvement in signal to noise ratio is obtained due to the presence
of a micro-lens on top of each bacterium. In these conditions, standard CMOS sensors are able to detect single
bacterium, e.g. E.coli, Bacillus subtilis and Bacillus thuringiensis, with a large signal to noise ratio. This paper presents our sensor optimization to enhance the SNR; improve the detection of sub-micron objects; and increase the imaging
FOV, from 4.3 mm2 to 12 mm2 to 24 mm2, which allows the detection of bacteria contained in 0.5μl to 4μl to 10μl, respectively.