A method and an apparatus for carrying out in vitro diagnostic analysis of biological samples by analyzing the spectrum of light radiation transmitted through the sample, using innovative components for this analysis was developed. The in-vitro analysis systems currently available, for example for the ELISA (enzyme-linked immunosorbent assay) test, usually employ a halogen lamp or LEDs as a light source, optical fibers as transmission media for the optical path, a set of mechanically selectable optical filters, and photo-sensors for reading the signal intensity. In particular, interference filters and inorganic solid state photodiodes are commonly used. These systems, usually, have the following restrictions to be respected: maximum reading range from 0 to 3 Optical Density (OD), 5 different probing wavelengths: 405nm, 450nm, 492nm, 550nm, 620 nm, bandwidth for each wavelength around 10nm. The system proposed in our work is based on Organic Light-Emitting Diodes (OLEDs) with broad emission spectrum for white light and on a series of Photonic Crystals (PCs) that selects the needed probe wavelengths (405 nm, 450 nm, 492 nm, 550 nm, 620 nm) and a bandwidth of around 10 nm around the peaks, for an acquisition sensitivity from 0 to 3 OD. A very compact optical path has been designed. The detection of the signal is carried out using an Organic Photodiode (OPD) having an appropriate photoresponse. The design of the proposed system gives the opportunity to reduce the overall dimensions of the analyzer, compared to the systems existing on the market, avoiding the use of additional optical fibers, interference filters and optical losses. © 2021 META Conference. All rights reserved.