Lambda 35

Diffuse reflectance UV–Vis spectra were obtained using a spectrophotometer Perkin Elmer Lambda 35, equipped with an integrating sphere. The measurements were carried out in the range of 1100–250 nm, using Spectralon as a reference. The reflectance measurements were converted to absorption spectra using the Kubelka–Munk function, F(R). For determining the UV–Vis light absorption properties of the gels, the scattered transmission was measured using the same instrument (Perkin Elmer, Lambda 35). The sample was placed in micro-cuvettes (Brand: 12.5 mm × 12.5 mm × 45 mm, center height: 8.5 mm, 230–900 nm, Roth) and introduced in the transmission port of the integrating sphere. The transmitted and forward scattered light was collected and measured by the sphere (during the measurements the Spectralon was placed in the reflectance port of the instrument).

According to Wang’s method [35 (link)] with slight modification, the standard curve of CA (Y = 0.01439 X + 0.0061, R² = 0.9996) was established. CA was dissolved in ethanol to prepare standard solutions (10 µg/mL~50 µg/mL). The absorbance of the solution at 276 nm was determined by a UV spectrophotometer (Lambda 35, Perkin Elmer, Waltham, MA, USA); ethanol was used as a blank control group. Then, the standard curve equation of CA concentration (X)—absorbance value (Y) was fitted.
Afterward, 4 mL of freshly prepared composite NPs dispersion was mixed with 16 mL petroleum ether, and the mixture was vortically oscillated for 10 min. Then, 0.5 mL organic phase was taken and placed in the fume hood for 30 min to make the petroleum ether completely volatilized. Subsequently, 4 mL of anhydrous ethanol was added to the reagent flask. The absorbance of the solution at 276 nm was determined by a UV spectrophotometer (Lambda35, Perkin Elmer). The EE was then calculated according to (1): $$\mathrm{EE}\left(\%\right)=\frac{{\mathsf{\lambda }}_1–{\mathsf{\lambda }}_2}{{\mathsf{\lambda }}_1}\times 100\%$$
where λ₁ represents the total mass of CA, and λ₂ represents the free mass of CA in the dispersion.

The measurement of encapsulation efficiency was carried out according to Wang’s method [13 (link)], with a slight modification. The standard curve of CA was first established. A certain concentration of CA solution (10 µg/mL~50 µg/mL) was prepared with ethanol as a solvent. UV spectrophotometer (Lambda 35, Perkin Elmer, Waltham, MA, USA) was used to measure the absorbance at a wavelength of 276 nm. Taking the concentration of CA as the abscissa and the absorbance value as the ordinate, the equation of the standard curve is fitted as Y = 0.01439X + 0.0061 (R² = 0.9996).
Afterwards, 4 mL of the fresh composite nanoparticles were mixed with 16 mL of petroleum ether and stirred well for 10 min. Then, 0.5 mL of the upper organic-solvent phase was transferred to a 25 mL reagent bottle, and the bottle was left in a fume hood for 30 min to completely evaporate the petroleum ether. Subsequently, 4 mL of absolute ethanol was added to dissolve CA in the reagent bottle. The absorbance was measured at 276 nm using a UV spectrophotometer (Lambda 35, Perkin Elmer), and ethanol was used as the blank control group. The encapsulation efficiency was then calculated using the following formula: $$\mathrm{EE}\left(\%\right)=\frac{m_1-m_2}{m_1}\times 100\%$$
where $m_1$ represents the total mass of CA in the formula and $m_2$ represents the dissociative mass of CA.