Generating Microdroplet Array on Photonic Pseudo-paper for Absolute Quantification of Nucleic Acids.

Here, we propose a new platform for digital nucleic acid assay based on a microdroplet array. The hydrophilic-superhydrophobic property of the pseudopaper photonic nitrocellulose substrate is employed to divide an aqueous sample containing the target nucleic acid into hundreds of microdroplets for loop-mediated isothermal amplification (LAMP). The LAMP reaction leads to the production of fluorescent calcein. By counting the number of microdroplets that are fluorescent, the target nucleic acid (i.e., Staphylococcus aureus DNA) with the copy number ranging from 1 to 1000 can be absolutely quantified without using sophisticated microfluidic devices. The effect of fluorescence enhancement attributed to the photonic nitrocellulose can effectively amplify the detection signal and reduce the amplification time. Thus, we believe that the proposed platform for digital nucleic acid assay based on the microdroplet array is promising for rapid and cost-effective bioanalytical applications.