Optical chemical sensors are widely applied in many fields of modern analytical practice, due to their simplicity in preparation and signal acquisition, low costs, and fast response time. Moreover, the construction of most modern optical sensors requires neither wire connections with the detector nor sophisticated and energy-consuming hardware, enabling wireless sensor development for a fast, in-field and online analysis. In this review, the last five years of progress (from 2017 to 2021) in the field of optical chemical sensors development for persistent organic pollutants (POPs) is provided. The operating mechanisms, the transduction principles and the types of sensing materials employed in single selective optical sensors and in multisensory systems are reviewed. The selected examples of optical sensors applications are reported to demonstrate the benefits and drawbacks of optical chemical sensor use for POPs assessment.

The interest in assembling porphyrin derivatives is widespread and is accounted by the impressive impact of these suprastructures of controlled size and shapes in many applications from nanomedicine and sensors to photocatalysis and optoelectronics. The massive use of porphyrin dyes as molecular building blocks of functional materials at different length scales relies on the interdependent pair properties, consisting of their chemical stability/synthetic versatility and their quite unique physicochemical properties. Remarkably, the driven spatial arrangement of these platforms in well-defined suprastructures can synergically amplify the already excellent properties of the individual monomers, improving conjugation and enlarging the intensity of the absorption range of visible light, or forming an internal electric field exploitable in light-harvesting and charge-and energy-transport processes. The countless potentialities offered by these systems means that self-assembly concepts and tools are constantly explored, as confirmed by the significant number of published articles related to porphyrin assemblies in the 2015–2019 period, which is the focus of this review.

Recent studies evidence the interplay between the photosensitivity and the gas sensitivity in porphyrin-functionalized ZnO nanorods. These effects are critically governed by the transport phenomena of electronic charge across the interfaces of organic and inorganic structures. Then the surface potential is a useful quantity to investigate the mutual relationship between these two phenomena. For this scope, Kelvin probe measurements of porphyrin-ZnO structures were performed in the dark, under visible light and exposed to organic vapors. Results show a synergic effect of gas sensitivity and photosensitivity for free base porphyrins, while in the case of metalloporphyrins, the coordinated metal ion alters the cooperation between the two effects, as observed in the Zn complex, where the exposure to light increases the adsorption of gases, but the photovoltage is reduced during the exposure to the gas.