A Physisorbed Interface Design of Biomolecules for Selective and Sensitive Protein Detection

We present a unique immobilization technique via physical adsorption/exchange of biomolecules onto a sensing surface of surface plasmon resonance (SPR). The adsorption/exchange is based on competitive bindings of biomolecules to a surface, which does not require a chemical modification of the biomolecules. SPR sensorgrams show that three human serum proteins, albumin, immunoglobulin G (IgG), and fibrinogen, have different adsorption strengths to the surface and the competitive adsorption of the individuals controls the exchange sequence. A target protein displaces a preadsorbed weak-affinity protein; however, a preadsorbed strong-affinity protein is not displaced by the target protein. In a microfluidic device, we engineer two gold surfaces covered by two known proteins. The sensor allows selective protein detection by being displaced by a target protein on only one of the surfaces. We demonstrate that IgG is selectively detected between albuminand fibrinogen-adsorbed surfaces. Moreover, the physical adsorption without using an additional surface modification can lead to highly sensitive detection in SPR because of the exponential decay of surface plasmon resonance wave (SPW) from the sensing surface. Based on the competitive adsorption and exchange reaction, we