INTRODUCTION

The interface between a sensor surface and the chemical or biological systems to be studied is a vital component of all sensor systems, including label-free biosensors. With the exception of solution-phase systems such as calorimetry or analytical ultracentrifugation, receptors must be attached to some form of solid support to transduce a binding event to the sensor. During this process, receptors must retain their native conformation and binding activity, attachment to the sensor must be stable over the course of the assay, and binding sites must be presented to the solution phase to interact with the analyte to generate a detectable signal. Most importantly, the support must be resistant to nonspecific binding of analyte and other sample components that could mask a specific binding signal.

Many coupling strategies utilize a bespoke chemical linker layer between the sensor and the biological component to achieve these ends. Functionalized alkane thiols and alkoxy silanes, which form stable monolayers on planar surfaces act as ideal linkers. The alkyl termini of these molecules can be derivatized with ethyleneglycol subunits to produce a protein-resistant planar surface or can be mixed with molecules that possess suitable reactivity for receptor capture, for example, –epoxy, –carboxyl, –amino, –biotinyl, –nitrilotriacetic acid. The larger binding partner (e.g., a protein target) is normally immobilized on the surface, and the smaller binding partner (e.g., a drug candidate) is allowed to bind to this surface from free solution.