Integration of Ti3C2Tx MXene in the selection of DNA aptamers for FMRP for the diagnosis of fragile X syndrome.

Being the second cause of intellectual disability after Down syndrome, Fragile X Syndrome (FXS) is a X-linked heritable disease. It is caused by a mutation in FMR1 gene consisting of an expansion of CGG repeats causing the absence or reduced expression of Fragile mental retardation protein (FMRP). FXS diagnosis is thus based on molecular techniques studying the FMR1 gene alterations. However, studying the protein is crucial for a better understanding of the FMRP role in brain development and function. This work aims to select a ssDNA aptamer for the detection and quantification of FMRP in blood. SELEX (Systematic Evolution of Ligands by EXponential enrichment) process, with a total of eight rounds of selection, was used to generate three ssDNA sequences able to bind FMRP. Affinity studies were performed by exploring the ability of ssDNA to adsorb to the titanium carbide (Ti3C2Tx) MXene. Dissociation constants were determined based on the capacity of MXene to quench the fluorophore labeling of the aptamers. The aptamer sequence FM1, with the best affinity Kd = 25.35 nM, was employed for the design of a fluorescent assay, where Ti3C2Tx MXene acts as an energy acceptor. Under the optimal conditions, the proposed strategy enabled the FMRP determination within the range of 0.01 to 1000 ng/mL and the low detection limit of 0.038 pg/mL. MXene-based aptamer selection could be an excellent alternative in SELEX to techniques used in traditional SELEX.