SERS Method Could Offer Earlier Screening For Preeclampsia

Preeclampsia, a pregnancy complication involving harmfully high blood pressure, is a leading cause of maternal mortality in the developing world. Unfortunately, early diagnosis there remains a major challenge. Now, researchers have developed a new, portable screening method that uses surface-enhanced Raman spectroscopy to quantify levels of uric acid in urine, a potential early indicator of preeclampsia (Anal. Chem. 2014, DOI: 10.1021/ac503967s).

Among the hallmark signs of preeclampsia are hypertension and protein in the woman’s urine. Currently, the only treatment option is to deliver the baby as early as possible. Traditional diagnostic methods, such as fluorescence-based immunoassays to detect protein in urine, can’t detect preeclampsia until its later stages, can take days to get results, or aren’t portable enough to use in developing countries, says Christa L. Brosseau, an analytical chemist at Saint Mary’s University, in Halifax, Nova Scotia.

So she and her colleagues decided to use a method called electrochemical surface-enhanced Raman spectroscopy to measure urine levels of uric acid. The acid is a marker of hypertension, and scientists increasingly see high levels of it as an early warning sign of preeclampsia.

To aid detection of the molecule, the researchers built a testing surface by layering silver and gold nanoparticles on top of a commercial carbon electrode. Applying a voltage across the electrode boosts uric acid’s interactions with the surface, which then further amplifies the acid’s characteristic Raman signal.

The researchers tested the method on four samples of synthetic urine containing different uric acid concentrations below 1 mM. Uric acid concentrations above 0.4 mM serve as a potential red flag for preeclampsia, Brosseau says. In these preliminary tests, the researchers found a consistently linear relationship between the Raman signal and the uric acid concentration, suggesting that the method could quantify the biomarker.