A Tailored Self-Assembling Monolayer for Monitoring Biomarkers in Cell Culture Media Using the liSPR System

Surface plasmon resonance (SPR) spectroscopy is a promising chip-based biosensor technology that can quantify various biomarkers without molecular labels or time-consuming sample preparation. The liSPR spectrometer is an inexpensive, convenient, portable, and robust SPR system. A drawback is that the chips’ sensing surfaces are fragile as they consist of a thin layer of gold sputtered directly on a polymer slide, without the Cr or Ti adhesive layers typically used in other SPR chips. Furthermore, interfering substances, particularly non-target proteins, may adsorb to the gold due to its hydrophobicity. This can lead to non-specific sensor signals or even inactivation of the ligands and hence false SPR signals. Thus, to improve the system’s reliability the bare gold surface must be modified. Here, we present a tailored sensor surface for measuring human serum albumin (HSA) levels of human hepatocytes cultivated in vitro in media containing huge numbers of proteins capable of adsorbing to a bare gold surface. The key feature is a mixed self-assembled monolayer (SAM) comprising two types of alkanethiols: one for covalently attaching ligand molecules – here antibodies – to the chip and one for suppressing non-specific adsorption of interfering sample components. In addition to describing the new sensor surface we present data on its levels of immobilized antibody, non-specific adsorption of cell culture components, and HSA binding capacities. Calibration curves (obtained using HSA-spiked media samples) are also presented showing that the rapid, convenient sensor system provides similar sensitivity and reliability to standard ELISA methodology.