Human haptoglobin phenotypes and concentration determination by nanogold-enhancedelectrochemical impedance spectroscopy

Abstract

Haptoglobin (Hp) is an acute phase protein that binds free hemoglobin (Hb), preventingHb-induced oxidative damage in the vascular system. There are three phenotypes in humanHp, whose heterogeneous polymorphic structures and varying concentrations in plasmahave been attributed to the cause of diseases and outcome of clinical treatments.Different phenotypes of Hp may be composed of the same subunits but different copynumbers, rendering their determination difficult by a single procedure. In this study,we have developed a simple, fast, reliable and sensitive method, using label-freenanogold-modified bioprobes coupled with self-development electrochemical impedancespectroscopy (EIS). By this method, probe surface charge transfer resistance isdetected. The relative charge transfer resistance ratios for Hp 1-1, Hp 2-1 and Hp2-2 were characterized. We were able to determine protein size difference within3 nm, and the linear region of the calibration curve for Hp levels in the range of90 pg ml − 1 and90 µg ml − 1 (∼1 fM to 1 pM). We surmise that similar approaches can be used to investigate proteinpolymorphism and altered protein–protein interaction associated with diseases.