Transition Metal Dichalcogenide Nanosheets for Visual Monitoring PCR Rivaling a Real-Time PCR Instrument.

Monitoring the progress of polymerase chain reactions (PCRs) is of critical importance in bioanalytical chemistry and molecular biology. Although real-time PCR thermocyclers are ideal for this purpose, their high cost has limited their applications in resource-poor areas. Direct visual detection would be a more attractive alternative. To monitor the PCR amplification, DNA-staining dyes, such as SYBR Green I (SG), are often used. Although these dyes give higher fluorescence when binding to double-stranded DNA products, they also yield strong background fluorescence in the presence of a high concentration of single-stranded (ss) DNA primers. In this work, we screened various nanomaterials and found that graphene oxide (GO), reduced GO, molybdenum disulfide (MoS2), and tungsten disulfide (WS2) can quench the fluorescence of nonamplified negative samples while still retaining strong fluorescence of positive ones. The signal ratio of positive-over-negative samples was enhanced by around 50-fold in the presence of these materials. In particular, MoS2 and WS2 nearly fully retained the fluorescence of the positive samples. The mechanism for MoS2 and WS2 to enhance PCR signaling is attributed to the adsorption of both the ssDNA PCR primers and SG with an appropriate strength. MoS2 can also suppress nonspecific amplification caused by excess polymerase. Finally, this method was used to detect extracted transgenic soya GTS 40-3-2 DNA after PCR amplification. Compared with the samples without nanomaterials, the addition of MoS2 could better distinguish the concentration difference of the template DNA, and the sensitivity of visual detection rivaled that from a real-time PCR instrument.