**1. Introduction**

Across the globe, there is a great interest in the field of polymers and polymerbased nanoparticles followed by their nanotechnology-based applications. However, polymeric nanoparticles (PNPs) are under a wide range of utilization in various fields. Especially researchers and scientists are trying to design various nanoparticles (NPs) and capsules with surface modifiable character features [1]. The polymer nanoparticles do obey and endorse the aforementioned sentence with existing literature which shows numerous nanoparticles with modifiable size, shape, and their surface properties. For example, quantum dots (QDs) carbon nanotubes (CNTs), cellulose NPs and fibers [2] iron oxide nanoparticles (FeONPs), gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), cobalt nanoparticles (CNPs), zinc oxide nanoparticles (ZnONPs), SnO2 nanoparticles, protein-based nanoparticles, amino acid-based nanoparticles, silica (SiO2) nanoparticles,

graphene nanosheets, titanium-based nanoparticles, core-shell nanoparticles, hollow core-shell (hCS) nanoparticles, hollow polymer-polymer nanoparticles (HPPNPs), polymer-metal nanoparticles (PMNPs), polymer-metal blends (PBs), polymer-silica nanocomposites (PSiNCs), polymeric micelles (PMs), solid-lipid nanocapsules (SLPNCs), liposomal nanoparticles, albumin-based nanoparticles, chitosan-based nanoparticles, platinum-based nanoparticles (PtNPs), ceramic nanoparticles, carbohydrate nanoparticles, etc. are reported and corroborated in the literature [2–5]. Furthermore, a significant interest in the synthesis and characterization of polymers followed by the design and development of polymeric nanoparticles (PNPs) with surface tunable properties has become an essential due to the various applications. For example, the amino acid-based polymer is much more suitable for the preparation of nanoparticles because of its biosafety and nontoxic and biodegradable nature. Similarly, thermosensitive polymer, for example, poly-Nisopropyl acrylamide (PNIPAM), shows lower critical solution temperature (LCST) at ~32°C, and it is much more useful to prepare the nanoparticles or capsules with thermally tunable morphology and other futuristic characteristic properties [6]. However, the main advantage to polymer scientists is they can easily synthesize the polymer to engineer the nanoparticles followed by the significant functionalization and surface modifications by changing the solvents, concentration, and stirring methods or by changing the functional groups which are present in the synthesized polymer complex. Similarly, the ionic (cationic and anionic) polymers referred to as polaxomers can help to modify the surface of the particles. Polymeric nanoparticles are under a wide range of utilization in the field of biomedical, nanobiotechnology, nanobiopharma, and other pharmaceutical domains. For example, they are very much used in the field of drug delivery systems (DDSs), gene delivery systems (GDSs), protein delivery systems (PDSs), cell delivery systems (CDSs), and tissue engineering followed by plastic surgery, etc. [7, 8]. However, polymers have numerous industrial applications as well, such as cell phone manufacturing companies, soft drink and water bottle industries, electronics and electrical engineering departments, automobile industries, and many other industrial usages based on the requirements. Interestingly, polymeric nanoparticles with porosity have multidirectional usages such as drug or nanomedicine loading and its target specific release. The nanoparticles with ~200 nm (in diameter) are the ideal size for the biomedical applications. The pore size with ~100 nm in the polymer nanoparticles or capsules is much more suitable for drug delivery and cancer therapeutics. According to International Union of Pure and Applied Chemistry (IUPAC) definition, the microparticle size should be <2 nm, (in diameter) and meso-particles or mesoporous particle and capsule size *ca.* 2–50 nm, and nanoparticles (particle size 50–200 nm) have been referred for various applications [6–8]. The effective and potential working capacity of nanoparticles has been defined by their size, shape, morphology, porosity, and other thermal properties. However, the qualitative quantification of use of polymer-based nanoparticles and their potential applications completely depends on the characteristic features like surface modification, size, and shape tenability. For example, many properties like color and atomic orientation are differing from the sizes of bulk to nanoscale [9, 10].
