The detection of cancer at the dysplasia stage is one of the most important goals in biomedical research. Optical techniques, specifically diffuse reflectance and intrinsic fluorescence, may improve the ability to detect gastrointestinal (GI) cancers, since they have exquisite sensitivity to some intrinsic biomarkers present on the tissues. This work follows the research that has been done towards the implementation of a spectroscopy microsystem for the early detection of GI cancers. For that purpose, the behavior of the fluorescence signal, at different temperatures and considering the most important biomarkers in GI malignancy detection, was studied and presented. ; This work is funded by FEDER funds through the "Eixo I do Programa Operacional Fatores de Competitividade (POFC) QREN, project references COMPETE: FCOMP-01-0124-FEDER-020241 and FCOMP-01-0124-FEDER-022711 (PEst-C/FIS/UI0607/2013) and by FCT – Fundação para a Ciência e a Tecnologia, project reference PTDC/EBB-EBI/120334/2010. S. Pimenta thanks the FCT for the SFRH/BD/87605/2012 PhD grant.