This paper presents a fault analysis applied to a novel optical, label-free sensors array for DNA detection. The IFA approach to extract and model the possible defects has been used. A critical equivalent resistance for the possible faults has been defined and it allowed to define the threshold values of current to discriminate the occurrence of the failures mechanisms. Particularly critical is the shorts occurrence: in this failure mode the current changes can generate a wrong information that can be confused with the current reduction due to DNA detection. At the end a test strategy for structural test is proposed.