Electrografted Laser-Induced Graphene: Direct Detection\nof Neurodegenerative Disease Biomarker in Cerebrospinal Fluid

There\nare more than 50 neurodegenerative disorders, and amyotrophic\nlateral sclerosis (ALS) is one of the most common disorders that poses\ndiagnostic and treatment challenges. The poly glycine–proline\n(polyGP) dipeptide repeat is a toxic protein that has been recognized\nas a pharmacodynamic biomarker of C9orf72-associated (c9+) ALS, a\nsubtype of ALS that originates from genetic mutation. Early detection\nof polyGP will help healthcare providers start timely gene therapy.\nHerein, we developed a label-free electrochemical immunoassay for\nthe simple detection of polyGP in unprocessed cerebrospinal fluid\n(CSF) samples collected from ALS patients in the National ALS Biorepository.\nFor the first time, an electrografted laser–induced graphene\n(E-LIG) electrode system was employed in a sandwich format to detect\npolyGP using a label-free electrochemical impedance technique. The\nresults show that the E-LIG-modified surface exhibited high sensitivity\nand selectivity in buffer and CSF media with limit of detection values\nof 0.19 and 0.27 ng/mL, respectively. The precision of the calibration\nmodel was better in CSF than in the buffer. The E-LIG immunosensor\ncan easily select polyGP targets in the presence of other dipeptide\nproteins translated from the c9 gene. Further study with CSF samples\nfrom ALS patients demonstrated that the label-free E-LIG-based immunosensor\nnot only quantified polyGP in the complex CSF matrix but also distinguished\nbetween c9+ and non-c9– ALS patients.