Single Cell Dielectric Detection
The analysis of single cells is fundamental to understanding the important processes that underlie the workings of healthy cells and their normal growth and development, as well as in recognizing and tracking down how these processes become disrupted, potentially leading to adverse conditions and disease. Unfortunately, due to heterogeneity of biological cells present even in genetically identical populations, pinpointing these processes is not easy. To quantify the extent of variation between individual cells in a given population, it is necessary to analyse thousands or even tens of thousands of single cells. This daunting task has been made easier with the advance of novel techniques involving microfluidics which allows high throughput delivery of individual cells.
Changes in cells physiology are known to result in changes in their dielectric properties. Dielectric-based methods have emerged as a label-free, non-invasive, and integratable with microfluidic modality to study single cells. We integrate microfluidic platforms with sensitive electrical measurement systems and exploit their ability to characterize various biological phenomena at a cellular level. AC electrokinetics and impedance spectroscopy are the two primary dielectric methods we employ.
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Dielectric Cell Culture Monitoring
Mammalian cell cultures are used extensively in the industrial bioprocesses for production of therapeutic proteins. To ensure maximum productivity of recombinant proteins it is desirable to prolong cell viability during a mammalian cell bioprocess, and therefore important to carefully monitor cell density and viability. Fed-batch culture, an approach in which nutrients required for cell growth and product formation are fed to the bioreactor during cultivation, is pre-dominantly employed to extend the viable and productive phase of a culture. The yield and quality of products is affected substantially by the feeding strategy (time of feeding, concentration of nutrients, and type of nutrient). High concentration of nutrients increases the cellular production of metabolic byproducts notably lactate and ammonia, which are detrimental to protein productivity. Depletion of nutrients leads to starvation-induced apoptosis. An optimal feeding regime can be developed from simple assessment of the metabolic state of the cells during the course of culture in a bioreactor. We work on developing label-free on-line single-cell assessment technologies to continuously monitor the status of cells in pharmaceutical bioreactors. We have found that a noticeable change in cytoplasm conductivity of cells occurs at an early stage of apoptosis which can be employed as a label-free indicator of the event. By interrogating single cells based on their cytoplasm conductivity, we have been able to detect small population of apoptotic cells in a batch culture at an early stage.
In this project we aim to develop a novel single-cell trapping microfluidic device which takes advantage of dielectrophoresis to capture individual cells and uses microstructures in the channel to compartmentalize them. The two-step trapping mechanism is intended to tackle the challenge of trapping single cells at a high efficiency while providing sufficient space for their compartmentalization and long-term temporal studies.
Semiconductor-based sensors are a class of extremely sensitive sensing devices capable of detecting low abundance ions and chemicals in a fluid sample. Field-effect transistors (FET) are commonly used in such sensors where the base of the transistor in contact with a sample-under-test acts as the sensing surface. The interaction of ions and charged molecules at the sample-gate interface impacts the gate electric potential and subsequently the drain current of the transistor. In this research we design and fabricate an extended-gate FET sensor integrated with a microfluidic device for detection of small molecules in biosamples.