A portable sensor for cell optical density measurement in microfluidic chips

Daniel John Whyte,Egan H Doeven,Jayanth Jaya Kumar,Abbas Kouzani,Muhd Nazrul Hisham Zainal Alam

doi:10.1177/0020294018783440

Abstract

This paper presents the development of a smartphone-controlled wireless device for cell optical density sensing in microfluidic chips. The footprint of the device is very compact relative to a classical laboratory spectrophotometer, making it a portable device. The cell optical density sensing device consists of an embedded microcontroller, optical sensing components, and a wireless transceiver performing cell optical density measurements in disposable microfluidic chips fabricated from poly(methylmethacrylate) polymers. The device is controlled by an Android application allowing for true portability and the possibility of remote or field operation of the device. The use of microfluidic chips as the sample carrier for optical density detection instead of a plastic cuvette allows users the flexibility to explore and/or conduct a variety of micro-scale chemical analysis using the device which would be difficult in a cuvette-based system. The function of the device is validated through a series of off-line and online optical density measurements using Saccharomyces cerevisae yeast cultures. The device is low cost, small enough to fit in most laboratory flow hood cabinets, and can be easily integrated into miniature bioreactor systems. Moreover, wireless communication enables the user to operate the device using smartphones or rapidly transfer the measured data to an online repository for analysis or storage.

Highlights

In microbiology, optical density (OD) measurements are a commonly employed method for estimation of suspended cell concentration.[1,2] It is a label-free, noninvasive, straightforward technique to implement for assessing the progress of cells growth
Instruments used in biochemical and/or chemical analysis can be characterized by the device specific response function; that is, an equation relating the instrument output signal to the known analyte concentration
In a microbial/ molecular absorption spectroscopy such as the OD sensor presented in the work, it is anticipated that the device response would follow a typical linear trend of a Beer– Lambert equation with zero intercept to the data (Equation (1))

Summary

Introduction

Optical density (OD) measurements are a commonly employed method for estimation of suspended cell (bacteria cultures) concentration.[1,2] It is a label-free, noninvasive, straightforward technique to implement for assessing the progress of cells growth. OD is defined as the logarithmic ratio of the intensity of transmitted light to the intensity of the incident light.[3] The measurement is based on the amount of light scattered by the suspended cells where a linear correlation between the concentration of the suspended cells and the intensity of light transmitted along a known path length can be obtained via the applicability of the Beer– Lambert’s law.[4,5,6] The only disadvantage is that dead microbial cells and cell debris scatter the light. This technique applies an alternating current (AC) electrical field to the suspended cells and measures cell conductivity as a function of frequency.[7,8] industrial impedance spectroscopy is relatively costly and does not offer much flexibility for integration with other instruments

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Conclusion