Label-free Electrochemical Detection of CGG Repeats on Inkjet Printable 2D Layers of MoS.

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 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 (MoS) 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 MoS ink for the detection of CGG repeats. The ink containing few-layered MoS 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 MoS surface in a high cationic strength environment and the electrocatalytic current of the CGG/MoS interface was recorded using a soluble Fe(CN) 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 MoS for CGG repeats and distinguish nonpathogenic from disease-associated repeat lengths. The detection of CGG repeat sequences on inkjet printable 2D MoS surfaces is a forward step toward developing chip-based rapid and label-free sensors for the detection of repeat expansion sequences.