Experimental Research of the Polyamidoamine Dendrimer as a Coating Layer For Microfabricated Silicon Biosensors -Edición Única

Abstract

This investigation was conducted towards the development of a sensor that can interact in a biological environment to detect a specific biochemical component. The motivation of this research came upon by the need to reduce the periodical bone marrow biopsies that follow treatment on patients with Leukemia; as well reducing the costs associated with the monitoring phase and improving the quality of life of patients. This biosensor could serve as an early-detection device that monitors the concentration of the Angiotensin Converting Enzyme (ACE) inside bone marrow, to send a wireless signal outside the body, indicating a high probability that the patient is entering relapse. In order to develop this type of biosensor, an active biolayer needs to be constructed on top of the sensing mechanism, to be able to “trap” the desired molecule to be detected. The proposed MicroElectroMechanical System (MEMS) to sense the ACE molecule is an array of microcantilevers connected to a microcircuit for data acquisition and analysis, along with radiofrequency transmission capabilities. This work focuses on creating a selective coating material that can interact with a biological medium and sense a specific molecule to measure its concentration. This research started with an exhaustive literature review to target specific problems such as: selecting the MEMS platform, the coupling agent, the coating material, as well as identifying a possible leukemia relapse biochemical indicator. Once the design parameters were established, an experimental phase was conducted. The first step was to functionalize the silicon structure with γ-aminopropyltriethoxysilane (γ-APS). Next, a series of iterative reactions were performed, alternating between a Michael addition and an amidation reaction, using methyl acrylate and ethylenediemine respectively to construct the poly(amidoamine) (PAMAM) dendrimer to be used as the coating layer. At the end of each reaction a sample was taken for analysis with Fourier transform infrared (FTIR) spectroscopy and with an atomic force microscope (AFM). Results show that the PAMAM dendrimer was successfully grown on top of the silicon wafers, but the attachment was not evenly distributed along the surface. A suggested improvement is to perform an oxidizing reaction to the silicon wafer prior to the γ-APS functionalization, in order increase the –OH groups and obtain a uniform attachment of the PAMAM dendrimer on the surface. This thesis concludes with a “future work” section that lays the groundwork to take the next steps in verifying the validity of the model. Among the suggested experiments, the use of ACE antibodies with fluorescent markers is highly recommended to quantify the amount of ACE molecules that are trapped by the PAMAM biolayer with an ACE inhibitor (Captopril) as the molecular sensor.