Table 5.

Table summarizing the key differences in toxicity profiles, biodistribution, and regulatory challenges between UCNPs and other nanoparticles

Nanomaterial	Toxicity profile	Biodistribution	Regulatory challenges	References
Upconversion nanoparticles (UCNPs)	Generally lower toxicity; potential for lanthanide ion release causing oxidative stress. Biocompatible surface coatings often mitigate cytotoxicity.	Accumulate primarily in the liver and spleen; influenced by surface modifications.	Evolving frameworks due to novel properties and limited long-term data.	[35,66,136,183]
Silver nanoparticles (AgNPs)	Higher toxicity; induces oxidative stress and apoptosis; and affects gene expression related to oxidative stress. Accumulates in various organs; hepatobiliary toxicity noted.	Primarily deposited in the mononuclear phagocyte system (MPS); widespread organ distribution was noted.	Heavily regulated due to toxic components; extensive safety data required for biomedical applications.	[184–186]
Gold nanoparticles (AuNPs)	Moderate toxicity; size-dependent effects on cellular response, with smaller sizes causing necrosis or apoptosis. Primarily stored in the liver; lower systemic toxicity compared to AgNPs.	Accumulation in the liver, spleen, kidney, heart, lungs, testis, brain, and thymus; size influences distribution.	Regulatory scrutiny due to potential environmental impact; safety assessments needed.	[187–192]
Copper nanoparticles (CuNPs)	Higher doses are required for toxicity; sex-related differences observed in response. Major accumulation in liver, kidney, and spleen; bio persistence concerns.	Notable accumulation in liver, kidney, and spleen; gastrointestinal exposure leads to higher public risk.	Increasing scrutiny due to health risks associated with copper exposure; requires thorough evaluations.	[193–195]
Titanium dioxide nanoparticles (TiO2 NPs)	Size-dependent toxicity; smaller TiO2 NPs cause more oxidative stress and DNA damage. Potential lung toxicity upon inhalation; chronic exposure risks identified.	Biodistribution is influenced by size and shape; smaller particles show higher organ distribution	Regulatory concerns regarding inhalation risks and environmental persistence; ongoing assessments are needed.	[196]
Quantum dots (QDs)	Higher toxicity due to heavy metals (e.g., cadmium); can cause significant cytotoxic effects. Toxicity varies based on size, surface chemistry, and concentration.	Tend to accumulate in the liver and kidneys. Long-term retention raises concerns about chronic toxicity.	Heavily regulated due to toxic components (e.g., cadmium). Extensive toxicity data required for approval in biomedical applications.	[197–200]
Carbon nanotubes (CNTs)	Variable toxicity dependent on structure (SWCNTs vs. MWCNTs) and functionalization; can cause inflammation and cytotoxicity. Inhalation can lead to pulmonary toxicity and potential fibrotic responses.	Can penetrate biological barriers and accumulate in various organs, including the lungs. Persistence in biological systems can lead to long-term health risks.	Increasing scrutiny due to environmental impact and potential health risks. Thorough safety evaluations are needed; addressing concerns over environmental impact and potential health risks.	[201–205]