Detection of size spectrum of microalgae cells in an integrated underwater microfluidic device

•A new microfluidic method for the detection of size of microalgae cells is presented.•Automatic sampling and size spectrum analysis can be accomplished.•A detected particulate is a living microalgae cell or cannot be distinguished.•The developed system is automatic, portable, low cost and easy operated.•The device has great potential for in-situ study of marine ecosystems.

Size spectrum of biological particles directly affects nutrient cycling and energy flow distribution of marine ecosystems. Fast and accurate detection of the size and distribution of marine phytoplankton plays a very important role for in-depth study of physiological characteristics of marine phytoplankton community structure and function. In this paper, a novel detection method and system of size spectrum of microalgae cells on a microfluidic chip is presented. In this device, a microfluidic resistance pulse sensor (RPS) technology is adopted to determine the particle size of microalgae cells; chlorophyll fluorescence intensity is used to judge if a particle is a live microalgae cell or not. Inside a waterproof case, the system mainly comprises a microfluidic chip platform, a sample acquisition module, an optoelectronic detection unit, and a module performing data acquisition, data processing and system control. To demonstrate the performance of the developed system, experiments were conducted with three species of microalgae cells (Isochrysis galbana, Dunaliella salina and Tetraselmis chui), typical phytoplankton cells in marine environments, as samples. Comparison experiments between the developed detection system and a commercial flow cytometer were conducted. The results demonstrate that the developed system is reliable and accurate. The limit of detection of microalgae cell size is 3 μm for the current device and can be improved in the future. The presented microfluidic system provides a very promising method of size spectrum detection of microalgae cells with the advantages such as fast detection, small size and easy operation. It has a great potential for in-situ underwater detection of micro phytoplanktons pending further product development.