Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting almost 30,000 individuals in the United States, with 5,000 new cases every year. It was found that uncontrolled G₄C₂ nucleic acid repeat expansions in C9ORF72 gene produces poly-GP dipeptide repeating proteins, which is present in biological fluids of the patients. While, Neurofilament Light chain Nf-L is also recognized as potential biomarker for neurodegenerative diseases including ALS. Current diagnostic techniques require expensive lab equipment and trained workers. Electrochemical biosensing can potentially transform the diagnostic platforms into low-cost portable sensors for point-of-care diagnosis. We propose here an electrochemical immunosensor on modified reduced graphene oxide screen-printed electrode (RGOSPE) to sense two different biomarkers. Experimentally, antibodies of respective biomarkers were immobilized sensor surface through amide bond with carboxylic group electrografted on RGOSPE. Resistance to electrochemical charge transfer was monitored (R_ct) before and after capturing biomarkers protein on the RGOSPE platform in presence of solution-based redox probe, Fe(CN)₆^3-/4- using Metrohm Autolab potentiostat. Increase in R_ct was observed following capturing the biomarkers in the sample. The prepared immunosensors successfully detected poly-GP in the concentration range of 10 - 2500 pg/mL with the limit of detection (LOD) of 39 pg/mL. This sensitivity is sufficient to detect concentration of 500 pg/mL for asymptomatic ALS patients, 800 pg/mL for symptomatic ALS and ALS-FTD patients. The Nf-L immunosensing platform successfully detected Nf-L in the range of 10 -1500 pg/mL with the limit of detection (LOD) 162 pg/mL. The competitive assay for specificity of Poly GP detection in the presence of potential interferents Poly-GR and Poly-GA confirmed that the system is highly selective for poly-GP dipeptide.