Culture-free detection of methicillin-resistant Staphylococcus aureus by using self-driving diffusometric DNA nanosensors.

The rapid and robust detection of infectious bacteria is vital in sepsis treatment because of their ability to reveal multi-drug resistance. This study presents culture-free and self-driving DNA nanosensors by combining diffusometry and oligonucleotide probes to rapidly detect a lethal superbug, methicillin-resistant Staphylococcus aureus (MRSA). The DNA nanosensors were synthesized with conjugated fluorescent nanobeads and designed oligonucleotide probes that can recognize the target sequences on MRSA's genomic DNA. The high selectivity and specificity of this binding ensure the accuracy of detection. A DNA fragment tagged with gold nanoparticles (AuNPs) was attached to the same MRSA single-stranded DNA (ssDNA) to form a sandwiched configuration. The protrusive AuNPs surrounding the nanobeads decreased the diffusivity of the complexed nanobeads by increasing the bead size. Accordingly, diffusivity was inversely proportional to the concentration of the target MRSA ssDNA. Each measurement required only 10 s. An optimal limit of detection of 10 pM was achieved. This study successfully developed DNA nanosensors based on diffusometry for the rapid and robust detection of target superbugs and unknown pathogenic microorganisms.