Optoelectronic integrated waveguide devices based on optical materials for biosensing applications

In this communication we present our recent developments on optoelectronic devices based on waveguides and optical materials for biosensing applications. Two prototypes of evanescent waveguide biosensors with on-chip detection have been demonstrated, where light interacts with a droplet of biological solution. In both devices an optical waveguide and a thin-film photodiode are integrated on the same glass substrate to detect a given analyte’s presence and concentration in a biological sample. A first prototype based on an ion-exchanged glass waveguide diffused in a borosilicate BK7 glass substrate coupled with a hydrogenated amorphous silicon (a-Si:H) photodiode has been fabricated and characterized at 532 nm. A first application of the device in determining cholesterol concentration showed a limit of detection (LoD) of 0.2 ppm, close to current commercial devices. A second prototype made of a SU-8 polymer channel waveguide and an a-Si:H detector has been fabricated and demonstrated at 532 nm. Preliminary experimental results on the detection of fat concentration in milk demonstrated a LoD equal to 14 ppm, one order of magnitude lower than industrial devices. Another system based on Au-plasmonic nanostructures (PNs) built on an ion-exchanged glass waveguide has been demonstrated for applications in fluorescence and Raman scattering. Depending on the relative value of the PNs’ array periodicity and the wavelength of light propagating through the waveguide, it is possible to control the direction of the light scattered by the nanostructures. The proposed device can be successfully employed in integrated biochip microsystems for sensing applications.