Table 3.

Advantages and disadvantages of commonly used NPs for siRNA delivery

NP material	Advantages	Disadvantages
Cationic block polymers [84, 85]	Relatively simple synthesis Inexpensive High throughput Large choice of functionalities (e.g. biodegradable units) Stimulus-responsive polymers for “smart” delivery	High polydispersity Variable silencing efficiency Balance between high toxicity (at high MW) and efficient cell transport (also at high MW) Potential for protein corona formation resulting in rapid clearance
Cationic dendrimers [86]	Low polydispersity Large choice of functionalities Molecular architecture and biodistribution can be accurately tuned	Complex synthetic routes Balance required between high toxicity (at high MW) and efficient cell transport (also at high MW) Potential for protein corona formation and rapid clearance
Cationic lipid formulations [87–89]	Ease of formulation Limited synthesis required (self-assembly) Rapid and well-characterised cell internalisation Commercially available materials	Low siRNA loading efficiency High production cost More limited choice of functionalities (cf. polymers) Leakage or degradation of loaded materials Tendency to aggregate Some toxicity
Metallic NPs (Ag/Au) [90]	High control of NP shape and morphology Ease of preparation Ease of surface modification Biocompatibility (Au)	siRNA bound to surface of particle, so limited protection offered Particle aggregation Toxicity (Ag) Non-biodegradable
Quantum dots (QDs) [91]	Inherent fluorescence of QDs enables dual imaging and therapeutic (theranostic) systems	Metal core toxicity More complex surface functionalisation chemistry required (cf. Ag/Au NPs) Particle aggregation
Viral delivery [92]	High silencing efficiency Highly monodisperse	Safety concerns Expensive May trigger immune response, neutralising efficacy