This article compares two different immunosensors developed for important food analytical and environmental problems. The label-free detection techniques were the piezoelectric quartz crystal rnicrobalance Measurement (QCM) and the optical waveguide lightmode spectroscopy (OWLS). Immobilizing anti-Escherichia coli IgG onto the gold electrode of QCM, E. coli bacterial cells were measured. Resonant frequency responses of the sensor system were determined at various concentrations of E coli (1.7 x 10(5)-8.7 x 10(7) CFU/ml). The same antibody,was immobilized onto the amino silanized sensor of OWLS by glutaraldehyde covalent coupling. The measuring range was between 3 x 104 and 3 x 107 CFU/ml. Chloramphenicol (CAP) antibiotic was measured in standard solutions with immunosensor based on label-free techniques to study the possibility of direct sensing of molecules with low Molecular weight. Anti-chloramphenicol antibody immobilization have been performed onto the gold surface of the crystal by using 3-mercaptopropionic acid (MPA) and dimethylaminopropyl-ethylcarbodiimide-hydroxysuccinimide ester (EDC-NHS) chemistry. The linear measuring range was found between 5 x 10(-6) and 5 x 10(-2) M chloramphenicol. Experiments were performed for measuring chloramphenicol with the same method with OWLS detection. After glutaraldehyde cross-linker immobilized the antibody, the signal measured was proportional to the analyte content in the range of 10(-7)-10(-3) M. (c) 2005 Elsevier B.V. All rights reserved.