SERS-based quantitative detection of ovarian cancer prognostic factor haptoglobin

Jayakumar Perumal,1 Ghayathri Balasundaram,1 Aniza P Mahyuddin,2 Mahesh Choolani,2 Malini Olivo1,3 1Bio-Optical Imaging Group, Singapore Bioimaging Consortium, Agency for Science Technology and Research (A*STAR), Helios, Singapore; 2Departments of Obstetrics and Gynecology and Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; 3School of Physics, National University Ireland, Galway, Ireland Abstract: Surface-enhanced Raman spectroscopy (SERS) is increasingly being used for biosensing because of its high sensitivity and low detection limit, which are made possible by the unique Raman ‘fingerprint’ spectra from the biomolecules. Here we propose a novel SERS method for the fast, sensitive, and reliable quantitative analysis of haptoglobin (Hp), an acute phase plasma glycoprotein that is widely gaining application as a prognostic ovarian cancer biomarker. We exploited the peroxidase activity of the hemoglobin–haptoglobin (Hb–Hp) complex formed by the selective and specific binding of Hp to free Hb to catalyze the reaction of 3,3',5,5'-tetramethylbenzidine (TMB) substrate and hydrogen peroxide to result in the final product of strongly SERS-active TMB2+. We observed a linear increase in the SERS signal of TMB2+ with increasing concentrations of Hb–Hp complex from 50 nM to 34 µM. Based on this concentration-dependent SERS spectrum, we quantified Hp in clinical samples. We observed that our inference about the prognosis of the disease coincided with the histology data and that our method was much more sensitive than the enzyme-linked immunosorbent assay method. Keywords: SERS-based biosensing, hemoglobin–haptoglobin complex, ovarian cancer, biomarker detection, 3,3',5,5'-tetramethylbenzidine, peroxidase active substrates