Description

Gold nanoparticles are used in different applications such as therapeutics, hyperthermia therapy, diagnosis, drug delivery, biological, medical, biotechnology applications, and catalysis. Gold nanoparticles are easy to synthesize and flexible to surface functionalize by organic and biological ligands.
Surface plasmon resonance (SPR): when gold nanoparticles exposed to a specific wavelength of light, the free electrons oscillate collectively by absorbing wavelengths of light resulting in an oscillating electromagnetic field. The oscillating electromagnetic field results in resonant oscillations in the visible light region. The amplitude of the oscillation reaches the maximum at a specific frequency, called surface plasmon resonance.
Nanogold absorbs and scatter light resulting in colors ranging from vibrant red to blue to black and finally to colorless, depending on particle size, shape, refractive index, and aggregation state. By changing the particle size, ligands, the optical and electronic properties of gold particles can be adjusted for different uses.

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Gold nanoparticles show various optical properties depending on their shape. Spherical gold nanospheres have a strong absorbance peak at 500 – 600 nm, whereas gold nanorods show absorbance peaks at 500 – 1200 nm. Such optical properties of nanogold are substantial for biosensors and optical devices. The size of the gold nanoparticles alters the optical properties; for example: when the size of gold particles changes from 10 – 50 nm, the maximum surface plasmon resonance band shifts from 517 to 532 nm in the visible region.

Drug Delivery: Gold nanoparticles can be coated with hundreds of molecules of drugs as targeting agents in drug delivery. Additionally, gold nanoparticles are also used to detect biomarkers in the diagnosis of heart diseases, cancers, and infectious agents. The surface functionality of gold particles allows for specific interactions with cells and the capping ligands play an important role in how the gold particles are internalized into the cell.
Gold nanoparticle conjugated with drugs provides controlled and sustained release properties valuable for drug and gene delivery. Gold nanoparticles show unique properties for imaging, and therapeutic for the targeted drug delivery. Au NPs conjugated with drugs show low toxicity, strong absorption, and binding property with a range of organic and biological molecules. Hence, surface-modified nanogold (Au-NPs) succeed as a carrier for drugs and vaccines to the targeted cells.

Photothermal Therapy: Gold nanoparticles can strongly absorb light as a result of the SPR. The absorbed light can efficiently be converted to heat, which makes nanogold useful agents for the thermal destruction of cancer cells by photothermal therapy. Using the appropriate laser light, gold nanoparticles can be precisely targeting and destroying tumor cells for treatment.

Diagnosis: Gold nanoparticles are used in the diagnosis of heart diseases, cancers, and infectious agents using X-ray technique and used for lateral flow assays based on their optical properties which help detection with the naked eye with good sensitivity.