PE is a very recalcitrant polymer, resistant to degradation process due to the presence of the linear backbone of carbon atoms, degree of crystallization and high molecule weight, hydrophobicity, and insolubility in water and remains in the environment for several years even after exposure to moist soil or water . Several studies have been carried out on microorganisms and enzymes capable of PE polymer degradation and their mechanisms. However, the resistant structure of PE eludes short term analysis . NPE particles are beneficial and convenient in tests for rapid screening of microorganism involved in plastic degradation and relevant enzyme assays. Native degrading microorganisms can easily colonize, form biofilms and hence degrade resistant polymer films or their fragments, but engineered bacteria carrying genes coding for relevant hydrolytic enzymes do not have the potential for attachment and biofilm formation and hence the use of NPE particles is recommended for the study of heterologous enzymes. For example, Wei and coworkers used nanoPET particles for the enzymatic hydrolysis assay of polyethylene terephthalate (PET) . Danso and colleagues used nanoPET to test engineered bacteria with synthetic genes obtained from metagenomics databases for PET degradation function detection .
On the other hand, plastic particles with a size of <5 mm released in terrestrial and marine environments eventually enter the food chain and cause ecotoxicological problems in living organisms [27, 28] and therefore, the exploitation of these nanoparticles could be valuable in the design of various evaluation experiments .
Synthesis of PE magnetic nanoparticle using decalin solvent and tetraglyme as a nonsolvent emulsion and high temperature for generating crystallization by ultrasonication as well as CTAB surfactant for drug delivery has been previously reported . Kolb and colleagues used a solution of nickel complex as a catalyst in small amount of solvent and surfactant for diaper ethylene in the aqueous medium under temperature and pressure to form lattices with average sizes 100 nm to 1 µm . A method for PE microplastics was developed by Balakrishnan and coworkers dissolving the polymer in toluene after which it was emulsified in water and surfactant, and particles were dispersed by ultrasonication. Nanoparticles were then used to evaluate the toxicological effect of PE microplastics on marine biota . In our study, surfactants as additives were excluded from experiments since the effects of PE on bacterial growth was being assessed. On the other hand, xylene was used as a solvent as it is volatile and is rapidly removed from particles. This method is simple and reliable and does not necessitate any specific instrumentation.
Polymeric nanoparticles are defined in the size range of 1-1000 nm [10, 32] and as the results from DLS and SEM analysis indicate, NPE particles show a size range between 70 and 1005 nm, and a PDI of 0.88 which signifies a wide range of size distribution and polydispersity. Since these particles are hydrophobic, they tend to bind together and therefore, it is deemed possible smaller particles join to form larger particles seen as two peaks in the DLS result (Fig. 2a). These peaks represent two population of particles with two different sizes of 507.65 nm and 810.35 nm which are predominantly present in the sample.
Reducing the size of the polymer increase available surfaces for biodegradation . Based on the results obtained from XRD and SEM analysis, NPE particles have amorphous forms making them more vulnerable and accessible to degradation compared to the crystalline structure [33, 34].
As results from this analysis indicate, the technique presented in this paper for the production of nano-PE particles dispersed in water is simple, easy, and cost-effective and could be exploited for the implementation of experiments investigating the toxic effects of nano-PE on living organisms. Furthermore, these particles could be valuable in the detection and efficient use of microbial cell factories to convert PE plastic wastes into high-value biopolymers such as biopolymers (PHA), providing an alternative to conventional recycling and hence, promoting the wellbeing of the environment [35, 36].