Defects form in materials through a variety of mechanisms and can dramatically affect the performance of those material. Crystal defects such as vacancies are inherent in metals and semiconductors and affect conductivity and other properties. Dislocations and grain boundaries form where there are interruptions to the periodicity of crystalline structures. Larger defects, such as cracks, or chemical defects, such as variations in the composition of a material, also affect the everyday performance of the material and can also lead to dramatic failures. Specificity is a hallmark of biological interactions. In natural systems, biomolecules are able to differentiate individual target molecules from thousands of competitors. Mimicking this specificity represents a challenge in some inorganic systems where the target is diffuse and inseparable from a large, competing background. Thus, it is desirable to exploit the specificity of biological interactions to detect defects and other inhomogeneities in a surface before the material is put into service or before it fails while in service.