Orange
wood biomass is an interesting lignocellulosic material,
but its lignin has been little explored. As a structural macromolecule
present in the plant cell wall, lignin has been used in nanoencapsulation
and nanomedicine, standing out as a good drug carrier. In this study,
lignin was extracted by soda pulping process and used to produce nanoparticles
for curcumin encapsulation and subsequent application in photodynamic
therapy (PDT). The nanoparticles were synthesized by the solvent shifting
process and characterized with UV–vis, fluorescence, dynamic
light scattering (DLS), ζ-potential, and scanning electron microscopy
(SEM). The lignin was soluble in organic solvent and presented an
extraction yield of 20.6 ± 2%. The Fourier transform infrared
(FTIR) spectroscopy and NMR signals showed that the lignin presents
hardwood-type characteristics. The lignin nanoparticles were easily
obtained and presented average sizes of 284 ± 60, 287 ±
60, and 502 ± 100 nm for pure lignin, 1% curcumin, and 5% curcumin
nanoparticles, respectively. They exhibited a negative ζ-potential
of about −42 ± 5 mV. The formulations were evaluated for
30 days and remained stable in phosphate-buffered saline (PBS). The
curcumin encapsulation yields were high, above 90% in all formulations.
Scanning electron microscopy (SEM) images showed that the nanoparticles
are spherical and homogeneous. Studies using hepatocarcinoma (HTC)
and HepaRG cells showed that the lignin nanoparticles were nontoxic
within 4 h of incubation, and for nanoparticles containing 5% curcumin,
toxicity was observed upon application of light in PDT experiments.