Nanoparticles in medicine: heating, imaging, targeting and killing bacteria

Six nanomedicine principles on one page: photothermal therapy with gold nanorods, magnetic hyperthermia with iron oxide, T1 and T2 MRI contrast agents, upconversion nanoparticles for imaging deep in tissue, theranostic particles that leave leaky tumour vessels, and antibacterial silver. Schematics only, with every caption quoted from the cited papers.

1. Photothermal therapy: Gold nanorods with a suitable aspect ratio absorb and scatter strongly in the near infrared (650–900 nm), where the tissue’s own chromophores take away less of the light; anti-EGFR antibody–conjugated rods bound malignant cells, which under a continuous 800 nm laser needed about half the laser energy that nonmalignant cells needed to be destroyed (Huang 2006). In tumours given nanoshells, 820 nm light at 4 W/cm² raised the temperature by ΔT = 37.4 ± 6.6 °C within 4–6 min; without nanoshells ΔT < 10 °C (Hirsch 2003). 2. Magnetic hyperthermia: Superparamagnetic iron oxide nanoparticles (SPIONs) release heat in an alternating magnetic field; Néel and Brownian relaxation dominate and hysteresis losses are negligible (Mehak 2023). Néel relaxation turns the moment inside a fixed particle, Brownian relaxation rotates the whole particle (Jesus 2026). Magnetoliposomes were heated at 40–47 kA/m and 270 kHz to treat pancreatic cancer cells and organoids (Palzer 2021); drug-loaded iron oxide can also be gathered at a tumour by an external magnet (Tietze 2015; Jahangirian 2019). 3. MRI contrast: In gadolinium hydroxide particles, relaxation comes from chemical exchange of protons between the particle surface and bulk water: inner-sphere relaxation (Vuong 2012). Superparamagnetic particles create magnetic inhomogeneities; relaxation of the water diffusing through them is outer-sphere, and the region holding the particles darkens on the image (Vuong 2017). In the animal studies reviewed, USPIO and Gd-based nanoparticles enhanced the T1-weighted signal, while SPIO lowered it in T1- or T2-weighted images (Luo 2020). 4. Upconversion imaging: Upconversion nanoparticles turn near-infrared light into visible emission, with deep tissue penetration, reduced autofluorescence and low phototoxicity; LaF₃:Er,Yb particles emitted green and red light by a two-photon process under 976 nm excitation (Deshmukh 2025). Core/silica-shell probes excited at 980 nm gave signal-to-noise ratios up to 170 at tissue depths up to about 1.0 cm in nude mice; dense tissue lowered the signal (Wang 2015). 5. Theranostic particles: Theranostic nanoparticles accumulate at the tumour through the large gaps in the blood vessels near tumours (Fernandes 2023a); they can carry folate or peptides that target cancer cells and imaging agents to follow the treatment (Fernandes 2023b). Fe₃O₄ cores give MRI and optical imaging plus local heating (Shi 2015); anti-EGFR gold nanorods both lit up and destroyed malignant cells (Huang 2006). 6. Antibacterial silver: Silver nanoparticles release Ag⁺ ions, which bind thiol, amino, phosphate and carboxyl groups; acting on proteins, DNA and membranes at once lowers the risk of resistance but also makes nanosilver toxic to cells; they also generate superoxide and hydroxyl radicals that damage membranes (Morozova 2021). Silver nanoparticles show important activity against bacterial biofilms (Franci 2015).

Huang, El-Sayed, Qian & El-Sayed, “Cancer cell imaging and photothermal therapy in the near-infrared region by using gold nanorods”, J. Am. Chem. Soc. 2006 (doi:10.1021/ja057254a); Hirsch et al., “Nanoshell-mediated near-infrared thermal therapy of tumors under magnetic resonance guidance”, Proc. Natl. Acad. Sci. USA 2003 (doi:10.1073/pnas.2232479100); Mehak, Thummer & Pandey, “Surface modified iron-oxide based engineered nanomaterials for hyperthermia therapy of cancer cells”, Biotechnol. Genet. Eng. Rev. 2023 (doi:10.1080/02648725.2023.2169370); Palzer et al., “Magnetic fluid hyperthermia as treatment option for pancreatic cancer cells and pancreatic cancer organoids”, Int. J. Nanomedicine 2021 (doi:10.2147/IJN.S288379); Vuong et al., “Paramagnetic nanoparticles as potential MRI contrast agents: characterization, NMR relaxation, simulations and theory”, MAGMA 2012 (doi:10.1007/s10334-012-0326-7); Vuong, Gillis, Roch & Gossuin, “Magnetic resonance relaxation induced by superparamagnetic particles used as contrast agents in magnetic resonance imaging: a theoretical review”, WIREs Nanomed. Nanobiotechnol. 2017 (doi:10.1002/wnan.1468); Luo et al., “Molecular magnetic resonance imaging with contrast agents for assessment of inflammatory bowel disease: a systematic review”, Contrast Media Mol. Imaging 2020 (doi:10.1155/2020/4764985); Deshmukh et al., “NIR-excited imaging of cervical cancer cells using biocompatible LaF₃:Er,Yb upconversion nanophosphors”, Luminescence 2025 (doi:10.1002/bio.70269); Wang et al., “The quality of in vivo upconversion fluorescence signals inside different anatomic structures”, J. Biomed. Nanotechnol. 2015 (doi:10.1166/jbn.2015.1947); Fernandes, “Review on metal-based theranostic nanoparticles for cancer therapy and imaging”, Technol. Cancer Res. Treat. 2023 (doi:10.1177/15330338231191493); Fernandes, “Liposomes for cancer theranostics”, Pharmaceutics 2023 (doi:10.3390/pharmaceutics15102448); Shi, Sadat, Dunn & Mast, “Photo-fluorescent and magnetic properties of iron oxide nanoparticles for biomedical applications”, Nanoscale 2015 (doi:10.1039/c5nr01538c); Morozova, “Silver nanostructures: limited sensitivity of detection, toxicity and anti-inflammation effects”, Int. J. Mol. Sci. 2021 (doi:10.3390/ijms22189928); Franci et al., “Silver nanoparticles as potential antibacterial agents”, Molecules 2015 (doi:10.3390/molecules20058856); Jesus et al., “Magnetothermally responsive mesoporous silica nanocarriers: materials design, thermoresponsive gates and controlled drug release”, Nanomaterials 2026 (doi:10.3390/nano16161018); Tietze et al., “Magnetic nanoparticle-based drug delivery for cancer therapy”, Biochem. Biophys. Res. Commun. 2015 (doi:10.1016/j.bbrc.2015.08.022); Jahangirian et al., “A review of small molecules and drug delivery applications using gold and iron nanoparticles”, Int. J. Nanomedicine 2019 (doi:10.2147/IJN.S184723).

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