The concept of optical antennas in physical optics is still evolving. Like the antennas used in the radio frequency (RF) regime, the aspiration of optical antennas is to localize the free propagating radiation energy, and vice versa. For this purpose, optical antennas utilize the distinctive properties of metal nanostructures, which are strong plasmonic coupling elements at the optical regime. The concept of optical antennas is being advanced technologically and they are projected to be substitute devices for detection in the millimeter, infrared, and visible regimes. At present, their potential benefits in light detection, which include polarization dependency, tunability, and quick response times have been successfully demonstrated. Optical antennas also can be seen as directionally responsive elements for point detectors. This review provides an overview of the historical background of the topic, along with the basic concepts and parameters of optical antennas. One of the major parts of this review covers the use of optical antennas in biosensing, presenting biosensing applications with a broad description using different types of data. We have also mentioned the basic challenges in the path of the universal use of optical biosensors, where we have also discussed some legal matters.

The design and prototyping of a dual port planar printed quad band/Ultra wide band (UWB) patch antenna, with octagonal ring shaped metasurface structure (MSS) assimilated at the back to reduce mutual coupling between antenna elements, is presented. The proposed MSS incorporated UWB antenna has been designed and fabricated on a high permittivity (ε_r= 15) ceramic filled biopolymer based sandwich structured dielectric substrate. Substantial reductions of mutual coupling(S21) between the dual port array elements of the proposed antenna has been achieved by assimilating a 6 × 9 octagonal ring shaped metasurface structure with near zero refractive index (NZRI) in the ground plane. Measurement results show that the proposed antenna with MSS loading has achieved the reflection co-efficient (S11 <-10 dB) bandwidths of 1.25(2.25-3.5) GHz, 1 (4-5) GHz, 0.7 (5.9-6.6) GHz and 1.75 (7.7-9.45) GHz. Stable radiation patterns, with gains of 3.18 dBi, 2.96 dBi, 3.34 dBi and 9.61 dBi, have been measured at resonant frequencies of 2.85 GHz, 4.4 GHz, 6.2 GHz and 8.75 GHz.