PCDA-EDA Colorimetric Nanofiber Sensor for Rapid Visual GHB Screening: Linker Reassignment and Scalable Fabrication

γ-Hydroxybutyric acid (GHB), a colorless and odorless central nervous system depressant associated with drug-facilitated sexual assault, demands rapid on-site detection. Polydiacetylene (PDA) colorimetric sensors derived from 10,12-pentacosadiynoic acid (PCDA) conjugates are a promising platform, but the molecular origin of GHB recognition in PCDA-gabazine systems has remained unresolved. Here, we compare a series of structurally related PCDA conjugates to examine how the chemical state of the EDA-derived unit affects the GHB-induced colorimetric response. A side-by-side substituent screen of three PCDA derivatives showed that PCDA-EDA produced the largest colorimetric response (ΔR = 53) within 30 s, the hydrazide analogue gave a moderate response (ΔR = 34), and a simple amide was negligible (ΔR = 12). By contrast, a PCDA-gabazine mat prepared by the same protocol showed only a subtle, barely discernible color shift after several hours and remained predominantly blue even after approximately 24 h, without a visually appreciable blue-to-red transition. This difference suggests that the accessible free primary amine of PCDA-EDA is an important factor contributing to its faster and stronger response. Building on this mechanistic finding, we replaced the previously used PVDF-HFP/PEO matrix with a cellulose/PVDF-HFP formulation processed from DMF and adopted multi-nozzle electrospinning, reducing the fabrication time from approximately 120 to 30 min per sheet, corresponding to a 75% reduction in processing time. The sensor mat showed a clearly distinguishable, dose-dependent visual response across 0.5-3% w/v GHB within 30 s, covering the forensically relevant concentration window. These findings reposition linker architecture as a central design parameter for PDA-based forensic colorimetric sensors.