The Non-Invasive Miniature Bioreactor for Laboratory Engineering project, better known as NIMBLE, aims to develop an innovative 100mL small-scale lab bench bioreactor that bridges the gap between what's in demand for bioreactors and what's currently available on the market. This product uses a low-cost reusable system that is meant for long term use in conjunction with an even lower-cost non-reusable vessel that allows users to avoid sanitary processes and concerns with contamination. The product features noninvasive sensing capabilities for pH, Optical Density (OD), Dissolved Oxygen (DO), and temperature as well as feedback control systems for pH, DO, and temperature. The system is designed to operate for 2 weeks before a new vessel needs to be used. NIMBLE has several innovative features such as a custom optical sensing architecture used for the OD, DO, and pH measurements. The design uses both a ruthenium-based layer and a polyaniline-based layer placed internally to allow for purely non-invasive optical sensing. This product will serve as a general-use bioreactor for a broad range of applications in laboratories using its ability to maintain such custom conditions with easily disposable vessels.

I was a member of the sensors/electronics team, so contributed to the design and early-stage testing of the non-invasive sensor package: temperature, dissolved oxygen, pH, and optical density. I owned the dissolved oxygen and pH sensors.

To measure the dissolved oxygen (DO) of the reaction, our product uses a sensing layer made of a Tris (4,7-diphenyl-1, 10-phenanthroline) ruthenium(II) Complex in Sol-Gel, which changes fluorescence based on the dissolved oxygen concentration it is exposed to. Fluorescence is the material property of “visible or invisible radiation emitted by certain substances as a result of incident radiation of a shorter wavelength such as X-rays or ultraviolet light” [Oxford]. As the dissolved oxygen concentration increases in contact with the Ru-complex layer, the fluorescent intensity is quenched, and so the emitted light is decreased.

To measure the pH of the reaction, our product uses a polyaniline (PANI) sensing layer, which changes its absorbance based on the pH that it is exposed to.

Optical density (OD) is based on the linear relationship between light absorbance and particle concentration. To measure the OD of the reaction, our product uses an LED, a reference photodiode, and two measurement photodiodes. Light is emitted from the LED and is scattered by the suspended particles in the culture. Some of this scattered light is detected by a photodiode, which measures its incident intensity. As the culture grows, the optical density increases and results in a greater intensity of light being detected by the photodiode due to increased scatter.