Evanescent waveguide lab-on-chip for optical biosensing in food quality control

Optical biosensing systems are commonly developed assembling a source, a light–sample interaction area, and a detector as distinct stand-alone elements. We present a compact, inexpensive, and easy-to-use glass chip that monolithically integrates both the interaction and detection elements in a 1 cm2 overall surface. The device working principle is based on evanescent wavelight interaction with the complex refractive index of a liquid mixture, being the index influenced by the mixture’s physical and chemical features. We describe the manufacture of a prototype able to perform investigations on food quality and subsequent tests on the detection of fat content in milk. Theoretical investigations are reported as well as measurements performed on samples in the green spectrum. A sensitivity of about 139 fA/(g/dL) and a limit of detection of 14 ppm have been achieved, better than those of current commercial devices.