Diffraction-based diagnostic devices

A method of making a biosensor, comprising the steps of:

• forming a receptive material layer generally uniformly over a surface of a substrate member, the layer containing a receptive material specific for an analyte of interest;
• defining at least one active area and at least one inactive area of the receptive material in a masking process wherein a blocking agent is used to render the receptive material inactive in the defined inactive area;
• and
• wherein when the biosensor is exposed to a medium containing the analyte of interest, the analyte binds to the receptive material in the active areas and facilitates subsequent diffraction of transmitted light or reflected light in a diffraction pattern corresponding to the active areas.