Dimitra Valadorou presented successfully her Master’s Thesis entitled “Sensors integrated in Organ-on-a-Chip microfluidic platforms” on March 29, 2023.

ABSTRACT

Preclinical studies for drug development include two types of experiments: cell culture and animal studies. Both of these methods have fundamental limitations in imitating the cellular microenvironment compared to the human body, and as a result they cannot always predict human cellular responses. Organ-on-a-chip (OoC) may be a good solution to overpass this limitation as it uses human cells, like a real human organ, and simulates their physiological microfluidic environment. Although OoC technology is promising in mimicking the complexity of tissues, continuous real-time monitoring of cells is lacking. Thus, one of the biggest limitations of the OoC technology is the lack of biosensors integrated on the microfluidic platform that could provide information about changes in the cell environment upon stimuli. The ultimate target of this work is the relief of this limitation.

An organ that is often affected by drugs is the kidney, which is the second major target of drugs and chemicals, after the liver. For this reason, in this thesis we focused on studies of microfluidic kidney-on-a-chip platforms and fabricated a microfluidic device by soft lithography of PDMS using a mold fabricated by photolithography on PCB. More specifically, the chip made of PDMS consisted of a microchannel and a medium reservoir separated by a porous polyester membrane on which human cells can be cultured.

The biosensor is integrated in series with the OoC platform to avoid cell disruption. A PDMS segment with an embedded microchannel is soldered onto the sensor microchannel sealing it. The bonding is done using a thin layer of liquid PDMS interposed between the two parts. Hence, the nutrient fluid that passes through the OoC platform and thus the cells, then passes through the microchannel of the biosensor enabling the direct and real-time detection of proteins secreted by the cells into the medium. The protein we chose to detect for the first time with these sensors is interleukin 6 (IL-6), which is a known biomarker of inflammation in human body fluids. First, the interleukin 6 detection protocol was optimized by enzyme-linked immunosorbent assay (ELISA). The biosensor used belongs to the group of electrochemical immunosensors, and aims to detect proteins in a solution. The biosensor chip consists of a microchannel with integrated three pairs of electrodes where IL-6 is detected. The chip was designed at INN and manufactured in the PCBs industry, while in the lab we added reduced graphene oxide (rGO) between the electrodes. Then, the anti-IL-6 antibody was immobilized on rGO by two methods: a) direct adsorption on the surface and b) using the streptavidin-biotin complex. The proteins even at very low concentrations show high specificity against the antibodies developed for them, so IL-6 is specifically bound and detected on the surface of the sensor, by measuring its resistance change. A systematic drop in resistance proportional to the concentration of IL-6 in the solution was observed for IL-6 concentrations of the order of μg/ml. However, to enable detection of IL-6 at concentrations that are diagnostically relevant (on the order of pg/ml) further optimization of the sensitivity of the biosensor is required.