Tunable Laser-Reduced Graphene Oxide–DNA Aptamer Composite for Rapid Disease Detection

Flexible graphene-derived composites are promising transduction materials for rapid biosensing, but conductivity and surface reactivity must be balanced within the same device. Here, a laser-patterned reduced graphene oxide (rGO)/poly(ethylene terephthalate) (PET) composite was developed for label-free resistive detection of herpes simplex virus type 1 (HSV-1) glycoprotein D (gD). A graphene oxide film was spin-coated on PET and locally reduced at 48.3 mJ cm−2 to form conductive contacts and at 25 mJ cm−2 to create a sensing region retaining carboxyl groups. A 5′-amine-modified 44-nucleotide DNA aptamer was covalently immobilized by carbodiimide coupling. Atomic force microscopy indicated a local film thickness of approximately 62–72 nm, while infrared and Raman spectroscopy supported the intended chemical reduction gradient. Aptamer immobilization increased sensor resistance by approximately 5–7%. Across 15 sensors, gD produced a concentration-dependent response that was clearly separated from albumin; a representative endpoint response was approximately 6.5% for gD and 0.7% for albumin. The lowest demonstrated detection level was approximately 100 pM, without a formal statistical LOD calculation. The approximate semilog-linear interval was 1 nM–1 mM, and the response time was 70–100 s. These results demonstrate that spatially programmed laser reduction can integrate conductive and bioreactive functions in a composite-based biosensor on a flexible substrate.