As illustrated in section 2.3, small molecules such as CO2 can easily adsorb within the MOF microporosity. However, as molecular size increases, diffusion through the porous matrix becomes hindered and sieving effects must be taken into account. Among others effects, diffusion becomes relevant for the sensing of aromatic and polycyclic aromatic hydrocarbons (PAH). For example, naphthalene and nitrobenzene represent a serious hazard towards human health and the environment, and are widely used in industrial activities. Nitrobenzene is involved in the synthesis of widely used chemical such as pharmaceuticals and pesticides, it is involved in the petrochemical industry activities, and its emission has even been detected even from small laundry facilities. Naphthalene can also be found in emissions from several industrial activities, ranging from metal production to plastic, pesticides and surfactants synthesis, and present a severe risk to human health. Therefore, to develop suitable platforms for fast detection of this family of compounds is of particular interest. Towards this aim, Zheng et al. employed single-core(metal) -shell(MOF) NPs (Figure ), for the detection from aqueous solutions of 4-nitrobenzenethiol (NBT) and 1naphtalenethiol (NAT). In their work, they pre-synthesize Au/Ag nanorods to later encapsulate them in ZIF-8 by LPE method. As shown in Figure -ii, both NBT (5.95 Å kinetic diameter) and NAT (7.20 Å kinetic diameter) can be detected by both bare Ag/Au NPs and Ag/Au@ZIF-8 particles; however, larger molecules like Malachite Green Isothiocyanate dye (MGI, 13.45 Å kinetic diameter) are not able to reach the surface of the plasmonic core due the sieving effect imposed by the porous framework of ZIF-8, with 11.6 Å pore diameter. It is worth noticing that access to the ZIF-8 micropore is restricted by a 3.4 Å rings, which in principle should prevent the access of NAT and NBT as well. Short-lived ligan vacancies (i.e., partial and temporal disruption of the coordinative bonds) and the framework's flexibility were attributed to the ability of the molecules to penetrate into ZIF-8, although constructional porosity probably played a significant role as well. ) and naphthalene (δCH at 786 cm -1 ) intensity ratio. Reproduced with permission from Phan-Quang et al. Copyright 2019, American Chemical Society.