UCNPs Application Fields

Biomedicine: The near-infrared excitation of UCNPs (such as 808/980 nm) can penetrate tissues to a depth of 3-5 cm, and the tissue autofluorescence background is reduced to 1/20 of the visible light excitation, which has been used for deep imaging of liver cancer in situ tumors.

Integrated diagnosis and treatment: UCNPs loaded with zinc phthalocyanine (ZnPc) can synchronously release singlet oxygen (¹O₂, photodynamic therapy) and produce photothermal effect (ΔT≈15℃) under the triggering of 660 nm red light. Animal experiments have shown that the system has a tumor inhibition rate of 92% for breast cancer, and the side effects are significantly lower than traditional chemotherapy.

Energy conversion: UCNPs are integrated into dye-sensitized solar cells (DSSCs) as a spectral conversion layer, which can convert low-energy infrared light (~980 nm) into visible light, extending the light response range of DSSCs to the near-infrared region. Studies have shown that co-sensitization strategies (such as ADEPA-1/LEG4 dye combination) combined with UCNPs can increase battery efficiency from 7.2% to 14.3%. Silver nanoparticles (AgNPs) modified TiO₂ photoanode further enhance light capture through the localized surface plasmon resonance (LSPR) effect, increasing the short-circuit current density by 35%.

Security coding: Time-space resolution coding technology based on multicolor luminescence has been applied to high-end anti-counterfeiting. For example, NaYF₄:Yb/Tm/Er nanoparticles can emit blue-green-red tricolor light by regulating the excitation power density, and can achieve a dynamic coding combination of 10⁶ in combination with pulsed laser modulation, which has been used in drug traceability systems.

Application of Dynamic Light Scattering (DLS) in Surface Modification of UCNPs

Particle size and dispersibility analysis: PEI modification increases the hydrated particle size of Upconverting Nanoparticles (UCNPs) from 20 nm to 35 nm, and the particle size distribution index (PDI) decreases from 0.25 to 0.12, indicating that surface charge repulsion improves dispersion stability. When pH>8, the deprotonation of PEI causes the particle size to increase sharply to 50 nm and is accompanied by aggregation, which is closely related to the decrease of Zeta potential from +35 mV to +18 mV.

Zeta potential evaluation: Surface positive charge (such as +35 mV modified by PEI) can significantly improve cell uptake efficiency. Flow cytometry showed that the internalization rate of positively charged UCNPs in HepG2 cells was 3.2 times that of neutral particles, but excessive charge (>+40 mV) would trigger lysosomal escape barriers and needed to be regulated to +20-30 mV through PEGylation to balance efficiency and safety.