Gold, silica, iron oxide and quantum dots: carriers that can deliver genes and be seen, steered or switched on from outside the body. Gene delivery meets diagnostics.
- Typical size
- 10–100 nm
- Particle
- Nanoplex
- Unique feature
- External triggers
Lipid and polymer reagents laid the foundation of non-viral delivery. Nanoparticle and inorganic reagents are emerging as powerful alternatives, with unique stability, tunability and imaging capability for both in vitro and in vivo work.
These carriers use a biocompatible inorganic core such as gold, silica, iron oxide, quantum dots or calcium phosphate. A cationic coating such as PEI, poly-L-lysine or amino-silane binds the nucleic acid, forming stable complexes called nanoplexes that protect the cargo and enter cells efficiently.
What sets them apart is that the core itself does something. Iron oxide responds to magnets and shows up on MRI, gold converts light into heat, and quantum dots glow. That makes theranostics possible: treating and tracking in the same particle.
Control from outside the body
Magnetic fields
Iron oxide particles can be pulled towards a target tissue with an external magnet.
Light
Gold nanorods heat up under laser light, opening endosomes and releasing cargo on demand.
Ultrasound
Focused ultrasound can trigger release and help particles cross barriers such as the blood–brain barrier.
Real-time imaging
MRI contrast or fluorescence shows where the carrier has gone.
How it works
- 1
Complexation
The negatively charged nucleic acid binds electrostatically to the positively charged particle coating.
- 2
Cellular uptake
Small size, surface charge and optional ligands such as antibodies or folate drive endocytosis into chosen cells.
- 3
Endosomal escape
Proton-sponge coatings or light-triggered heating disrupt the endosome.
- 4
Release and function
The cargo detaches to express a gene, silence a target or edit the genome, optionally on an external trigger.
The main inorganic carriers
| Carrier | Made of | Stand-out feature |
|---|---|---|
| Gold nanoparticles | Colloidal gold with PEI or thiolated polymer coatings | Biocompatible, plasmonic imaging and photothermal release |
| Iron oxide | Magnetite (Fe₃O₄) or maghemite (γ-Fe₂O₃) | Magnetic targeting and MRI contrast |
| Silica | Mesoporous or solid SiO₂ | Large surface area, tunable pores, easy functionalisation |
| Quantum dots | Semiconductor nanocrystals | Fluorescent tracking of delivery |
| Calcium phosphate | Biodegradable mineral crystals | Low cost and safely dissolves; a classic method in nanoform |
| Titanium or zinc oxide | TiO₂, ZnO | Light-triggered release (still experimental) |
Strengths
- High stability. Resistant to enzymatic breakdown and environmental stress.
- Multifunctional. Combines delivery with MRI or fluorescence imaging and targeting.
- On-demand release. Light, magnetic fields or ultrasound control where and when cargo is freed.
- Low immunogenicity. Inorganic cores usually provoke only a minimal immune response.
- Targeted delivery. Surfaces are easy to functionalise with tissue- or cell-specific ligands.
- Guidable. Magnetic particles can be steered and even recovered.
Challenges
- Long-term toxicity. Some materials, such as cadmium quantum dots, may release toxic ions without protective coatings.
- Organ accumulation. Particles can build up in the liver and spleen.
- Complex synthesis. Needs specialised equipment and expertise.
- Batch variability. Size, shape and surface charge must be tightly controlled.
- Regulatory barriers. Novel materials and biodistribution make approval more complex.
- Cost. High-purity nanomaterials and functionalisation can be expensive.
Where it is used
Cancer gene therapy
Targeted delivery of tumour-suppressor genes or siRNA against oncogenes.
Neuroscience
Crossing the blood–brain barrier with magnetic or focused-ultrasound guidance.
CRISPR delivery
Precise transport of Cas9 mRNA and guide RNA.
Theranostics
Gene delivery with real-time imaging, such as MRI-guided transfection.
Vaccines
Gold nanoparticles can act as adjuvants and boost immune responses.
Tissue engineering
Light-activated control of gene expression inside scaffolds.
What comes next
The field is moving towards smart, responsive and personalised delivery systems.
Hybrid nanoparticles
Inorganic cores inside lipid or polymer shells, such as liposome-coated gold.
Biodegradable inorganics
Calcium phosphate and silica designs that safely degrade in the body.
AI-driven design
Machine learning predicts the best particle properties for each cell type.
Clinical translation
Gold- and iron oxide-based systems in preclinical and early clinical trials.
By merging nanotechnology with molecular biology, inorganic carriers deliver genetic material with precision, stability and real-time feedback, making them a powerful toolkit for research, diagnostics and therapy.