Water is fundamental for developing and sustaining life and is largely used for agricultural and industrial activities. Water quality is an important condition for preserving human health. Many diseases occur when bacterial strains contaminate it. This work aims to design, fabricate, and test a low-cost, miniaturized sensing system utilizing a microfluidic optical cell exploiting the chemiluminescent reaction between luciferin and adenosine triphosphate (ATP), the energy unit in biological systems, to measure the concentration of ATP in water and consequently the bacterial concentration. The ATP– luciferin chemiluminescent solution is introduced in a 3D printed lab-on-chip microfluidics (LoC) system and is coupled to a silicon photomultiplier (SiPM) for highly sensitive real-time detection. The chemiluminescent reaction between Luminol and hydrogen peroxide has been used in this study to perform some preliminary …