Microfluidic systems have become a major area of research during the last few decades, and resulted in the development of easy-to-use and miniaturized platforms for biological and chemical analysis. Their ability to process small qualities of liquids make these systems especially appealing for the design of low-cost, high-throughput assays with enhanced analytical performances, and these platforms are currently in use for DNA sequencing, chemical and biochemical screening, PCR (polymerase chain reaction), protein crystallization, directed evolution of proteins, detection of rare diseases, cell-cell interactions, single cell analysis and similar applications.
Microfluidic devices are required to precisely measure the contents of liquid samples in minute amounts, which is often accomplished by means of optical detection techniques. Electrical droplet sensing, however, can provide a scalable and label-free alternative to conventional methods of microfluidic analysis, and allows the low-cost implementation of multiple sensors within a small area – and Pelin Kübra İşgör and Merve Marcalı, members of the Elbüken group at UNAM, have developed a capacitive sensor just for the task.
The system employs nothing but off-the-shelf electronics and costs a meager $24 in parts, but the whole is far more than its parts: Although previous designs using store-bought parts fell short of the analytical mark, the new, portable integrated circuit system could rival the sensitivities of bench-top analyzers, providing a new record for the literature at a femtoFarad-level detection capacity. Cheap and flexible, the platform could also handle processes such as analyte dilution and in-chip reactions by mixing two liquids at any given ratio.
This system can be used for very precise droplet size and speed detection, as well as droplet counting – also possible is the automated and precise measurement of dielectric content in droplets for biochemical assay monitoring. Being able to effectively characterize the content of microdroplets electrically opens up new avenues for biosensor design, and the team hopes that their research will eventually lead to the impedance spectroscopy of each individual droplet.
This work was funded by the European Union FP7 Marie Curie Career Reintegration Grant (PDB-LOCs, Grant No. CIG-2012-322019). The study has been published in Sensors and Actuators B: Chemical, April 2015, 210, 669-675.