Microfluidic preparation of composite hydrogel microparticles for the staining of microalgal cells.

The delivery of lipophilic dyes, such as BODIPY 505/515, to cells is often hindered by their low aqueous solubility, necessitating the use of organic solvents to facilitate the delivery, which unfortunately compromises the viability of the cells. In this work, we demonstrate the generation of novel composite hydrogel microparticles loaded with BODIPY 505/515, which can be used to deliver the dye to microalgal cells to stain the intracellular lipids. The microparticles were prepared by combining polymeric micelles with hydrogel technology to obtain microparticles of enhanced loading capacity. The generated hydrogel microparticles were tested by incubation with Phaeodactylum tricornutum algal cells. The cells were rapidly and successfully stained by the dye-containing microparticles, and their viability was not affected by the staining process. The method can also be used to stain other types of microalgal cells, such as Nannochloropsis gaditana cells. We therefore believe that this work offers a versatile and useful solution to important cell-staining problems in biotechnology.

Droplet-based microfluidic screening and sorting of microalgal populations for strain engineering applications.

The application of microfluidic technologies to microalgal research is particularly appealing since these approaches allow the precise control of the extracellular environment and offer a high-throughput approach to studying dynamic cellular processes. To expand the portfolio of applications, here we present a droplet-based microfluidic method for analysis and screening of Phaeodactylum tricornutum and Nannochloropsis gaditana, which can be integrated into a genetic transformation workflow. Following encapsulation of single cells in picolitre-sized droplets, fluorescence signals arising from each cell can be used to assess its phenotypic state. In this work, the chlorophyll fluorescence intensity of each cell was quantified and used to identify populations of P. tricornutum cells grown in different light conditions. Further, individual P. tricornutum or N. gaditana cells engineered to express green fluorescent protein were distinguished and sorted from wild-type cells. This has been exploited as a rapid screen for transformed cells within a population, bypassing a major bottleneck in algal transformation workflows and offering an alternative strategy for the identification of genetically modified strains.

High-bandwidth detection of short DNA in nanopipettes.

Glass or quartz nanopipettes have found increasing use as tools for studying the biophysical properties of DNA and proteins, and as sensor devices. The ease of fabrication, favourable wetting properties and low capacitance are some of the inherent advantages, for example compared to more conventional, silicon-based nanopore chips. Recently, we have demonstrated high-bandwidth detection of double-stranded (ds) DNA with microsecond time resolution in nanopipettes, using custom-designed electronics. The electronics design has now been refined to include more sophisticated control features, such as integrated bias reversal and other features. Here, we exploit these capabilities and probe the translocation of short dsDNA in the 100 bp range, in different electrolytes. Single-stranded (ss) DNA of similar length are in use as capture probes, so label-free detection of their ds counterparts could therefore be of relevance in disease diagnostics.