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The electro-optical properties of organic and bio-molecules have been previously investigated that have potential for selectively filtering and controlling the transmission of electromagnetic signals with carrier frequency in the THz band. Specifically, retinal isomers have been studied because they exhibit the type of THz characteristics needed for the design of molecular electronic devices. Here, the goal is to define bio-molecular filters that have utility in integrated platforms for sensing THz spectral signatures. According to our calculations, retinal isomers demonstrate the type of properties needed for the design of molecule-based optically-controllable filters in THz region. An initial challenge for this type of bio-architecture is the integration of the retinal-based components into conventional semiconductor devices. This paper presents a potential methodology for achieving such integrated sensor components. In particular, by modifying one end of retinal with a thiol linker, it is possible to chemically graft the retinal to gold surfaces. Therefore, since two-dimensional gold nanostructure arrays can be produced by depositing gold onto pit-patterned highly oriented pyrolytic graphite (HOPG) surface or semiconductor substrates, this approach could be applied to achieve large-scale integration of bio-molecular devices. This paper will report on simulations of ground state and metastable state energies, along with the associated THz spectra of the retinal isomeric molecule connected to a gold atom via the link of a cysteine molecule. In addition to the retinal isomers, this paper also investigates another isomer trans- and cis- stilbene and presents results suggesting that stilbene may also be a good candidate for molecular electronics. Hence, this paper provides results for the THz spectral characteristics and required optical excitations for a novel type of bio-device for sensing.
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