Table 3.

General characterization techniques of LRNs.

Parameter	Method	Comment	Ref
Particle size	Dynamic light scattering (DLS)	Based on the scattering of light caused by the Brownian movement of the particles.	[139]
	Scanning electron microscopy (SEM)	Observe the morphological state by direct visualization.	[140,141,142]
	Transmission electron microscopy (TEM)
	Atomic force microscopy (AFM)
Shape	Microscopy techniques (SEM, TEM, AFM)	Generate images of individual NPs to characterize their shape, size, and location.	[141,143]
	Energy-dispersive X-Ray spectroscopy (EDS)	An electron beam hits the sample, exciting an electron in an inner shell, causing its ejection and forming an electron-hole in the electronic structure of the element.	[140,144]
	X-ray photoelectron spectroscopy (XPS)	Irradiate a material with a beam of X-rays such as a typical Al Kα or Mg Kα source while simultaneously measuring the kinetic energy and number of electrons that escape from atoms on the surface of the material being analyzed.	[145]
	X-ray diffraction analysis (XRD)	It is produced by constructive interference of a monochromatic beam of X-rays scattered at specific angles from each set of lattice planes in a sample. The peak intensities are determined by the atomic positions within the lattice planes.	[141,146,147]
Surface charge	Electrophoretic light scattering (ELS)	It is measured through the mobility of the charged particles under an electric field that indirectly correlates with the surface charge.	[147]
Surface properties	AFM, contact angle measurement (CAM)	CAM has long been used as a criterion of static hydrophobicity of solid surfaces. It is a simple-to-adopt method for surface hydrophobicity analysis based on the sessile drop Young–Laplace method. AFM has been shown to reveal surface energies and hydrophilic or hydrophobic characteristics of the interacting surfaces.	[148]
	Nuclear magnetic resonance spectroscopy (NMR)	It can be defined as an indispensable tool that applies a magnetic field to an atomic nucleus (e.g., the most common stable isotopes 1H, 13C, 15N) and radiofrequency pulses to characterize the resonant frequency of that atomic nucleus according to its chemical or environmental surroundings.	[149]
Thermodynamic properties	Differential scanning calorimetry (DSC) Thermogravimetry (TG)	Give information about the crystallographic structure, chemical composition, and physical properties.	[150]
Encapsulation efficiency, cargo release	Ultraviolet-visible spectrophotometry (UV-Vis), high-performance liquid chromatography (HPLC) Ultracentrifugation, ultrafiltration, gel filtration	Use classical quantification methodologies according to the characteristics of the drug to be encapsulated.	[151]