Plasmon-modulated fluorescence nanoprobes for enzyme-free DNA detection via target signal enhancement and off-target quenching

Rapid, sensitive, and reliable nucleic acid assay is crucial for the molecular diagnosis of many diseases. For high sensitivity, conventional techniques require time-consuming, high-cost, and complicated procedures, such as enzymatic gene amplification, labeling, and purification, limiting their applications to point-of-care diagnostics. Herein we report a new DNA nanoprobe based on the dual effects of target-specific plasmon-enhanced fluorescence and off-target plasmonic quenching. Janus gold half-shell/polystyrene nanospheres (hsAu/PSs, ∼150 nm diameter) are tethered with capture single-stranded DNA (ssDNA), coupled with a fluorophore-conjugated reporter ssDNA through sandwich-type hybridization with target DNA, resulting in 5-fold increase through plasmon-enhanced fluorescence. Smaller gold nanoparticles (∼13 nm diameter) are subsequently introduced as quenchers to reduce background fluorescence from unhybridized reporter ssDNA, increasing the sensitivity about 103 times. The limit of detection of the dual-mode plasmonic DNA nanoprobe is 16 pM at room temperature in 1 h for the target gene of Klebsiella pneumoniae carbapenemase. The nanoprobe also exhibits a high selectivity enough to discriminate a single-base difference in the target gene. Our strategy harnesses both of the plasmon-mediated fluorescence enhancement and quenching effects through the sophisticated design of nanoscale colloids, which opens a promising avenue to the enzyme-free, simple, sensitive, and selective detection of pathogenic DNA.