1 research outputs found
Ferrodrop Dose-Optimized Digital Quantification of Biomolecules in Low-Volume Samples
We
present an approach to estimate the concentration of a biomolecule
in a solution by sampling several nanoliter-scale volumes and determining
if the volumes contain any biomolecules. In this method, varying volume
fractions (nanoliter-scale) of a sample of nucleic acids are introduced
to an array of uniform volume reaction wells (100 μL), which
are then fluorescently imaged to determine if signal is above a threshold
after nucleic acid amplification, all without complex instrumentation.
The nanoliter volumes are generated and introduced using the simple
positioning of a permanent magnet, and imaging is performed with a
cellphone-based fluorescence detection scheme, both methods suitable
for limited-resource settings. We use the length of time a magnetic
field is applied to generate a calibrated number of nanoliter ferrodrops
of sample mixed with ferrofluid at a step emulsification microfluidic
junction. Each dose of ferrodrops is then transferred into larger
microliter scale reaction wells on chip through a simple shift of
the external magnet. Nucleic acid amplification is achieved using
loop-mediated isothermal amplification (LAMP). By repeating each nanoliter
dosage a number of times to calculate the probability of a positive
signal at each dosage, we can use a binomial probability distribution
to estimate the sample nucleic acid concentration. Using this approach
we demonstrate detection of lambda DNA molecules down to 25 copies
per microliter. The ability to dose separate nanoliter-scale volumes
of a low-volume sample across wells in this platform is suited for
multiplexed assays. This platform has the potential to be applied
to a range of diseases by mixing a sample with magnetic nanoparticles