Flexible and ultrasensitive biosensing platforms capable of detecting a large number of trinucleotide repeats (TNRs) are crucial for future technology development needed to combat a variety of genetic disorders. For example, trinucleotide CGG repeat expansions in the FMR1 gene can cause Fragile X syndrome (FXS) and Fragile X-associated tremor/ataxia syndrome (FXTAS). Current state-of-the-art technologies to detect repeat sequences are expensive, while relying on complicated procedures, and prone to false negatives. We reasoned that two-dimensional (2D) molybdenum sulfide (MoS₂) surfaces may be useful for label-free electrochemical detection of CGG repeats due to its high affinity for guanine bases. Here, we developed a low-cost and sensitive wax-on-plastic electrochemical sensor using 2D MoS₂ ink for the detection of CGG repeats. The ink containing few-layered MoS₂ nanosheets was prepared and characterized using optical, electrical, electrochemical, and electron microscopic methods. The devices were characterized by electron microscopic and electrochemical methods. Repetitive CGG DNA was adsorbed on a MoS₂ surface in a high cationic strength environment and the electrocatalytic current of the CGG/MoS₂ interface was recorded using a soluble Fe(CN)₆^-3/-4 redox probe by differential pulse voltammetry (DPV). The dynamic range for the detection of prehybridized duplexes ranged from 1 aM to 100 nM with a 3.0 aM limit of detection. A detection range of 100 fM to 1 nM was recorded for surface hybridization events. Using this method, we were able to observe selectivity of MoS₂ for CGG repeats and distinguish nonpathogenic from disease-associated repeat lengths. The detection of CGG repeat sequences on inkjet printable 2D MoS₂ surfaces is a forward step toward developing chip-based rapid and label-free sensors for the detection of repeat expansion sequences.

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