In this study, we present the effect of catalytic performance in Mn-MOF upon incorporating varied concentrations of phthalocyanine derivative (H2PcP8OH16) for ascorbic acid detection in an extended gate field-effect transistor (EGFET) configuration. The fabricated Mn-OM-MOF-2/CP electrode demonstrated notable selectivity toward ascorbic acid in physiological conditions of sweat, with a sensitivity of 71.375 μA·mM−1·cm−2, a response time of less than 6 s, and a linear range from 5 to 240 μM. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.26 and 0.78 μM, respectively. Remarkably, the prepared electrodes followed the Michaelis−Menten kinetics. Among them, the Mn-OM-MOF-2/CP electrode demonstrated the highest affinity for ascorbic acid, with a Km value of 0.142 mM. To gain deeper insights into the charge transfer mechanism during ascorbic acid interaction with Mn-OM-MOF-2/CP, we employed the scanning Kelvin probe (SKP) technique and conducted post-FTIR analysis to understand the sensing mechanism. Additionally, post-UV−visible (UV−vis) measurements were performed to explore how the incorporation of the phthalocyanine derivative enhances affinity. Additional studies using standard artificial sweat have confirmed the Mn-OM-MOF-2/CP electrode’s good recovery. Overall, the results of the EGFET method demonstrated the suitability of the Mn-OM-MOF-2/CP electrode for rapid, noninvasive, single-use ascorbic acid detection in 1× phosphate buffer saline (1× PBS).