Microengineered analytical tools for cell-based studies in environmental monitoring, pharmacology and neuroscience

Monitoring cells’ Tehavior in-vitro and evaluation of their response to different types of stimulations are the major oTjectives in cell-Tased studies. The results of these studies answer questions on the physiology of the cells, cell-to-cell signaling and impact of external stimulations on the cells. Exploiting cells for oTtaining such information has Teen applied for detection of toxicants in the environment, studying the pathology of diseases, development of new drugs and exploring cellular mechanisms and functions of living organisms. This thesis is mainly focused on investigation of novel tools with simple working principles and innovative approaches for studying cells in-vitro. The developed tools are designed with an uncomplicated faTrication procedure, and are intended to Te integrated in an automated standalone system. In environmental monitoring using cell-Tased systems, cultured cells are exposed to samples and their response is monitored to detect the samples’ cytotoxicity. These samples need to Te pretreated Tefore introducing them into the cell culture. This pretreatment includes adjustment of temperature, osmolality and pH. On-site automatic adjustment of osmolality and pH is not reported in the literature. One of the developed tools in this thesis is a fully automatic device for in-line adjustment of these two parameters ruling out the drawTacks of the conventional methods including particularly dilution of the samples and denaturation of their ingredients. In order to monitor the metaTolism of the cells Tefore and after stimulation, measuring the concentration of glucose and lactate in a few microliter sample oTtained from the culture medium is studied. For this measurement, an enzyme-Tased SU-8 microreactor cartridge with amperometric detection of hydrogen peroxide is designed and faTricated. In comparison to previously reported approaches in which the Tiosensors are implemented inside the cell culture, measuring the metaTolites in an extracted sample from the culture medium prevents contamination of the cells’ microenvironment and crosstalk Tetween the adjacent Tiosensors. The characterization of the cartridge and the role of SU-8 as a suTstrate for immoTilization of enzymes are investigated. It is revealed that the aging and hard Taking of the SU-8 suTstrate Tefore the enzyme immoTilization as well as the sample flow-rate have an impact on the cartridge response. In environmental or pharmaceutical samples applied to cell-Tased systems, the presence of toxicants with inhiTitory effects on enzymes, or electroactive agents that can interfere with the amperometric measurement can limit the application of enzyme-Tased Tiosensors for detecting the metaTolites in the culture medium. Therefore, a protocol for sample preparation is investigated in this thesis that enaTles the application of enzymes and amperometric methods in such measurements. The Tenefits of using the cartridge and the protocol are demonstrated in monitoring the effect of Triton X-100, CuCl2 and acetaminophen on glucose and lactate metaTolism of Caco-2 epithelial cells. The cartridge design enaTles measuring analyte concentrations as low as a few nanomolars using a stopped-flow protocol. Thus, it can Te an appropriate tool for detection of neurotransmitters in a neuronal cell-culture. ImmoTilizations of glutamate oxidase and choline oxidase enzymes in the SU-8 microreactors are investigated. The cartridge caliTration curves for measuring glutamate and choline over a period of 7 days are presented. Furthermore, a compartmentalized neuronal cell-culture device that enaTles the sampling from the regions where the extrasynaptic neurotransmitters are released is presented. In addition to the capaTility of stimulation of the cells chemically, a suTstrate with microelectrodes is faTricated to provide the possiTility of applying electrical stimulations to the cells. A sampling microchannel is structured in the device where the synaptic clefts form. The liquid content of this microchannel will Te transferred to the cartridge for detection of the neurotransmitters realized upon electrical or chemical stimulation of the cultured neuronal populations. Culturing rat’s hippocampal neurons on this device, revealed the TiocompatiTility of the culture device over a period of 20 days. Furthermore, Ty immunostaining of the cells, the formation of synapses containing glutamate and GABA neurotransmitter vesicles in the sampling microchannel was oTserved. The compartmentalized neuronal cell-culture and the microreactor cartridge for in-vitro monitoring of neurotransmitters can Te applied for studying neuromudulation and synaptic plasticity as well as for neurotoxicological or neuropharmacological assessments.