Several developed low-cost, highly sensitive, and simple to realize and to use plasmonic sensor configurations are here presented. In particular, the presented sensor configurations are based on polymer waveguides, such as polymer optical fibers and planar waveguides, that excite the plasmonic phenomena in nanofilms, continuous on nanostructured. These plasmonic sensor chips are monitored using a simple experimental setup based on a white light source and spectrometer. Moreover, they can be combined with chemical and biological receptors in several application fields. In these cases, we can obtain the selectivity to the substances of interest via the use of specific Molecular Recognition Elements (MRE) in contact with the plasmonic sensing surfaces, such as those based on molecularly imprinted polymers (MIPs), antibodies, aptamers, nanoMIPs, etc. The substances that can be measured with the proposed approach are pollutants, viruses, bacteria, toxic metals, pesticides, or other molecules of interest to detect in aqueous solutions. So, the advantages and disadvantages of each biochemical sensor system are presented in detail. More specifically, plasmonic extrinsic optical fiber sensor and intrinsic optical fiber sensor types will be reported in terms of plasmonic characteristics and application fields. For instance, these selective plasmonic optical fiber sensor systems (intrinsic or extrinsic schemes) can be used for "Smart Cities" applications, as in water quality monitoring, through an IoT (Internet of Thing) approach, or, alternatively, they can be used onboard of simple robots, based on an autonomous guide, to follow increasing concentrations of pollutants in rivers or sea to identify the point of interest (the source), etc.