Transition-metal dichalcogenides (TMDs), including molybdenum disulfide (MoS2) and tungsten disulfide (WS2), with appealing properties have recently become promising alternatives to graphene with semimetal and low on/off current ratio properties as the sensing channel in field-effect transistor (FET) biosensors. However, the efficiency of DNA-based FET devices strongly depends on how DNA probes are tethered to the nanomaterial channels. As against covalent attachment, simple DNA physisorption has become increasingly popular, and a DNA sequence with strong affinity for nanomaterials is still highly sought after. Recently, poly-cytosine (poly-C) DNA was found to be strongly adsorbed to many common nanomaterials, including WS2. Herein, a diblock DNA probe containing a (poly-C) (C15) was used to attach to a chemical vapor deposition (CVD)-grown monolayer WS2 surface; meanwhile, the target complementary DNA (cDNA) was hybridized to the other block of the DNA probe. The biosensor developed following this strategy led to a limit of detection down to 3 aM within a concentration range spanning over approximately 7 orders of magnitude (10–16 to 10–9 M), which was lower than those of the previously reported TMDs and a good competitor to graphene FET DNA biosensors. Moreover, the proposed WS2 FET DNA biosensor showed high specificity capable of distinguishing the cDNA from non-cDNA, one-base mismatched DNA, two-base mismatched DNA, and three-base mismatched DNA, making our strategy an exciting avenue for disease diagnosis. The authors are convinced that this work extends the CVD synthesis of WS2 and its promise in biosensing application-based FETs.

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Researchers have recently designed various biosensors combining magnetic beads (MBs) and duplex-specific nuclease (DSN) enzyme to detect miRNAs. Yet, the interfacial mechanisms for surface-based hybridization and DSN-assisted target recycling are relatively not well understood. Thus, herein, we developed a highly sensitive and selective fluorescent biosensor to study the phenomenon that occurs on the local microenvironment surrounding the MB-tethered DNA probe via detecting microRNA-21 as a model. Using the above strategy, we investigated the influence of different DNA spacers, base-pair orientations, and surface densities on DSN-assisted target recycling. As a result, we were able to detect as low as 170 aM of miR-21 under the optimized conditions. Moreover, this approach exhibits a high selectivity in a fully matched target compared to a single-base mismatch, allowing the detection of miRNAs in serum with improved recovery. These results are attributed to the synergetic effect between the DSN enzyme activity and the neutral DNA spacer (triethylene glycol: TEG) to improve the miRNA detection’s sensitivity. Finally, our strategy could create new paths for detecting microRNAs since it obliterates the enzyme-mediated cascade reaction used in previous studies, which is more expensive, more time-consuming, less sensitive, and requires double catalytic reactions.

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