Characterization of Two-component Organothiol Mixed Monolayers on Gold and Quantification of Nonspecific Adsorption on Mixed Sam Biosensor Platforms Using Electrochemical Enzyme Immunoassay

Abstract

Self-assembled monolayer (SAM) technology provides a simple and useful way to functionalize biosensors. The formation and characterization of SAM monolayers are briefly reviewed in Chapter One. Several selected examples of SAM based biosensors were introduced. Because the sensitivity of a biosensor depends on its nonspecific adsorption of immumoactive organisms, a brief introduction to the principles and methods to inhibit nonspecific adsorption on biosensors is also given in Chapter One. In Chapter Two, the theory governing the formation of two-component SAMs is discussed. The mechanism controlling the final composition of the mixed monolayer can either be kinetically or thermodynamically controled. Two-component SAMs containing alkanethiol/ olig(ethylene glycol) (OEG) thiol, 4-aminothiophenol/alkanethiol and 4-aminothiophenol/olig(ethylene glycol) thiol were characterized using capacitance and coulometry measurements and surface-enhanced Raman spectroscopy. The adsorption isotherms for these mixed SAMs systems were discussed by the model of thermodynamic control in the formation of mixed monolayer. Nonspecific adsorption of immunoactive molecules on a biosensor’s surface is an important way to minimize of nonspecific adsorption on SAM-based biosensor platforms is discussed in Chapter Three. Protein adsorption on mixed SAMs of decanethiol (DT) and tetraethylene glycol thiol (EG4-SH) was quantified using electrochemical enzyme immunoassay. The protein adsorption is reduced more on the OEG-SAM surface than on hydrophobic decanethiol SAM surface. Both thiols were used as blocking agents in immuno-sandwich biosensor platforms with mixed SAMs to confirm that an EG4-SH monolayer inhibits of nonspecific adsorption better than a DT monolayer. Chapter Four provides general conclusions on the characterization of two-component organothiol mixed monolayers on gold and quantification of nonspecific adsorption on mixed SAMs biosensor platforms using an electrochemical enzyme immunoassay.