Microwell-assisted filtration with anodic aluminum oxide membrane for Raman analysis of algal cells

In this study, rapid and direct Raman analysis of microalgae was demonstrated through measurement of algal cells (or algal paste) prepared by microwell-assisted filtration using an anodic aluminum oxide (AAO) membrane. To obtain the algal paste, an array of polydimethylsiloxane (PDMS) microwells with through holes was placed on top of the AAO membrane, after which a vacuum was initiated and a droplet of algal solution dispensed inside the PDMS microwells for a 5-min filtration process. The results showed that the AAO membrane has the lowest background noise compared to other types of filter papers or membranes. Compared to the droplet evaporation method, the “coffee-ring” effect was effectively suppressed when applying our proposed filtration method. The algal cells became stacked inside the microwells, which led to relatively uniform and strong Raman signals across individual algal paste and consistency among different algal pastes.