Maleimide functionalized silicon surfaces for biosensing investigated by in-situ IRSE and EQCM

• In-situ characterization of the electrochemical deposition process
• para-Maleimidophenyl (p-MP) functionalized surfaces for biosensing
• Quantification of results by EQCM and IRSE
• A steric hindrance effect is found for deposition of the p-MP group.
• Optical modeling of in-situ infrared spectroscopic measurements

A quantitative study of the electrodeposition of nominal 3–5 monolayers of p-maleimidophenyl (p-MP) with current transients, electrochemical quartz crystal microbalance (EQCM) and in-situ infrared spectroscopic ellipsometry (IRSE) is presented. In particular maleimide functionalized interfaces are of high interest for specific biosensing. Such surfaces are prepared electrochemically on Au-QCM, micro-crystalline silicon (μc-Si)-coated Au-QCM (μc-Si-Au-QCM) and crystalline silicon (c-Si(111)) surfaces. The electrodeposition of p-MP on μc-Si-Au-QCM is developed and is shown to be similar to that of Au-QCM sensors with a grafting efficiency of 0.5 after the first potential cycle. For subsequent deposition on silicon, the oligomer formation and thickness is limited due to a steric hindrance effect and the molecules size. The combination of used methods enabled the verification of grafted p-MP, evaluation of optical constants and thicknesses, and grafting efficiencies. The presented cooperative multi-method characterization gives a new analytical possibility for in-situ studies of electrochemically functionalized surfaces towards biosensing.

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