Gold nanoparticles aid dectection of vitamin D,
which can be absorbed from the Sun

US researchers have developed a nanotechnology-based test to detect the important vitamin D metabolite calcitriol, the deficiency of which is an indicator of kidney failure.

We all get vitamin D from our diet and from our exposure to sunlight. Vitamin D and its metabolites have an important role in our body's health as they regulate calcium and phosphate levels. Excesses and deficiencies have recently been linked to cardiovascular disease, cancer and kidney disease.

Because of this, clinical demand for an easy test for calcitriol has increased significantly. Most of the current methods use immunoassays that require radio- or enzyme-labels that need large amounts of serum sample and produce radioactive waste and can be very complex which limits their use.

Now Marc Porter and colleagues at the University of Utah in Salt Lake City have developed a test based on using surface enhanced Raman scattering (SERS) combined with gold nanoparticles. This new technique requires a much smaller sample volume and has no radioactive waste. 'Our work demonstrates that a simple optical method, when combined with gold nanoparticle labels, can outperform the standard methods heavily used in clinical diagnostic laboratories around the world,' says Porter.

The combination of SERS with an extrinsic Raman label (ERL), in this case modified gold nanoparticles, has produced a competitive assay with a limit of detection of 8.4 pg/mL - matching the sensitivity of previous immunoassay methods. Following exposure to calcitriol, a biotin-labelled analog can be bound to unoccupied antibody sites allowing subsequent ERL binding to complete the assay and the observed response decreases when the concentration of calcitriol increases.

'This paper is a very nice example of the use of SERS for the detection of metabolites in clinically relevant samples,' comments Karen Faulds, at the Centre of Molecular Nanometrology in Strathclyde, UK. Faulds was impressed with the use of SERS for clinical diagnostics and adds that 'this breakthrough using a SERS based competitive assay holds great promise for the future.'
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