A varifocal optical system includes a substantially circular membrane deposited on a substrate, and a ring-shaped PZT thin film deposited on the outer portion of the circular membrane. The optical imaging lens comprises six lens elements positioned sequentially from an object side to an image side. The IO module is associated with a controllable energy source via which the field device is supplied with energy. The assay specifically detects the molecular target that binds the nucleic acid ligand with high affinity and specificity. The mask layer is patterned, and a number of bar-shaped protruding structures is formed on a surface of the mask layer, a lot is defined between each of two adjacent bar-shaped protruding structures of the number of protruding structures to expose a portion of the base. By integrally processing the external contact terminals, bonding wires may be affixed using a single wire bonding process.