A low-cost optofluidic platform for the colorimetric assessment of bacterial activity in domestic wastewater

Optofluidic chips represent a cost-effective platform for the development of miniaturized devices to perform biochemical reactions at a microscale. The dye reduction-based electron-transfer activity monitoring (DREAM) assay is a colorimetric approach that has been adopted for the rapid assessment of bacterial activity in bioreactors used in bioremediation and industrial biotechnology. A three-layered PMMA-based optofluidic chip having laser-machined microchannels coupled with a detection system comprising an LED source and a photodiode interfaced with a microcontroller for automation constituted the experimental setup. Data acquisition was executed using a user-friendly graphical user interface (GUI) that enabled real-time monitoring of bacterial activity. A performance comparison study was performed to assess the viability of replacing expensive spectrophotometers with an inexpensive photodiode for optoelectronic automation. Bacterial activity across different growth phases of a bacterial culture, initiated using untreated domestic wastewater, was assessed by the detector on the basis of voltage readings corresponding to the rate of decrease in the blue color intensity. The highest activity observed corresponded to the log phase of the growth curve. The optimal time for measurement of bacterial activity within the log phase of the growth curve was identified using different dilutions of untreated domestic wastewater. Furthermore, the device showed comparable sensitivities for samples from different time points in a bacterial growth curve and for different dilutions of untreated domestic wastewater samples. The device also demonstrated a linear response in the assessment of bacterial activity as a function of the change in strength of untreated domestic wastewater. This is the first report on colorimetric assessment of bacterial activity using a low-cost photodiode-based device at the microscale constructed using off-the-shelf components.