Non-viral carrier systems, especially nanoparticles, have been investigated extensively for siRNA delivery, and may be utilized in clinical applications in the future. So far, a few preliminary clinical trials of nanoparticles have produced promising results. However, further research is still required to pave the way to successful clinical applications. The most important issues that need to be focused on include encapsulation efficiency, formulation stability of siRNA, degradation in circulation, endosomal escape and delivery efficiency, targeting, toxicity and off-target effects. Pharmacology and pharmacokinetic studies also present another great challenge for nanoparticle delivery systems, owing to the unique nature of siRNA oligonucleotides compared with small molecules.

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In this review, we discuss in detail several commonly used and sensitive analytical techniques, including atomic absorption spectrometry, inductively coupled plasma optical emission spectrometry or mass spectrometry, X-ray fluorescence spectrometry, high-performance liquid chromatography, differential pulse polarography, neutron activation analysis and anodic stripping voltammetry. We also provide some application examples of these analytical techniques for heavy metals in herbal medicines.

This study suggests that biodegradable cationic CHT-PLGA nanoparticles possess great potential for efficient and safer siRNA delivery in future clinical applications.