## 1 Introduction  
Polymeric nanoparticles (NPs) may exhibit unique physical properties that differ from the properties of their counterparts in the macroscale. The differences are mainly based on the smaller object size, leading to a higher surface-area-to-volume ratio, a better dispersion stability, a larger diffusibility, and mobility. This dispersion allows the NPs to be generally more interactive with the external media than micro- and macroparticles [1; 2; 3; 4]. Preparation of polymeric NPs with a narrow distribution allows for reliable and reproducible results for their applications, and heterophase polymerization of (almost) water-insoluble monomers through emulsion polymerization (EP) and mini-emulsion polymerization (miniEP) are widely-employed methods to achieve monodisperse size distributions. Surfactant-based approachesmay be used in both EP and miniEP systems in order to prevent the coalescence of monomer droplets via electrostatic and/or steric stabilization. In the case for EP, micellar nucleation is prevalent and the surfactants are usually used above the critical micelle concentration (CMC) [5; 6]. In contrast, in miniEP the surfactant is generally used below its CMC, in order to prevent micellar nucleation, and the nano-sized droplets are formed by high shear forces, favoring an equal dissemination of surfactants among the monomer droplets. This mini-emulsification process leads to critically stabilized droplets, and their size is connected with the type and concentration of the surfactant used, because it affects the interfacial area between the water and the monomer phase and, consequently, the number and size of the monomer droplets. In miniEP the particle nucleation takes place in the stabilized monomer droplets and the particle size characteristics post polymerization are related to the droplet size characteristics prior to polymerization, hence, they are often referred to as \"nanoreactors\". The uniform density of surfactant molecules at the droplet surfaces achievable via miniEP, results in the production of NPs with a narrow size distribution and with adjustable average diameters between 50 and 500 nm [7]. Concerning the choice for surfactant, sodium dodecyl sulfate (SDS) has been used as the standard anionic surfactant in miniEP systems and the use of cationic surfactants, such as cetyltrimethylammonium bromide (CTAB) is fairly recent, but their efficiency is comparable to that of SDS [8]. In order to make use of the large surface-area-to-volume ratio of polymer NPs, the NP surface is often decorated with groups which bear a chemical, physical or biological function. Such NPs can be regarded as functional NPs. Developing efficient ways to synthesize functional polymer NPs has been a notable field of study in chemistry and biotechnology [9; 10; 11; 12; 13; 14]. Such functionalized particles find use in bioconjugation [15] and bioseparation of selective biomolecules [2], labeling and immunoassay [2; 10; 16], and biosensors [17; 18; 19; 12]. Functionalized polymeric NPs can also present interesting opto-electrical [2; 20] (lenses and colloid crystals) or rheological applications (coatings, viscosity control, and film-formation) [2; 21; 22]. The most common approach for the generation of NP surfaces presenting defined functional groups is chemical modification after NP preparation. However, this post-polymerization approach often relies on multi-step reactions and a need for rigorous and time-consuming purification [9; 12]. These drawbacks of post-polymerization modifications can be overcome if the desired functional groups are already present at the NP surface during preparation. This can be achieved, e.g., by making use of the characteristics of the miniEP process. For droplet stabilization in miniEP, different surfactants can be used.