Reprogramming Photo Paper into a Scalable 3D Biosensing Platform for Label-Free, Time-Resolved Cell Analysis.

Three-dimensional (3D) paper-based cell culture platforms have emerged as attractive low-cost alternatives for developing physiologically relevant in vitro tissue models. However, their widespread adoption remains constrained by the need for substrate modification and complex microfabrication, while monitoring cell growth and viability continues to rely predominantly on optical or destructive endpoint assays. Moreover, these techniques are predominantly qualitative or semiquantitative, often require expensive fluorescent labels or biochemical reagents, and are inherently limited by imaging depth, light scattering, and autofluorescence. Here, we directly repurpose commercially available photo paper into a scalable 3D bioelectronic scaffold by integrating coplanar aluminum electrodes through a lithography-free thermal evaporation process. The cellulose-rich nonglossy surface supported direct attachment and infiltration of L929 fibroblasts (used as the model cell line for concept validation) without additional surface functionalization, while the integrated electrodes exhibited a low fabrication resistance (12.6 ± 3.7 Ω), enabling reproducible electrical measurements. Cytocompatibility was evaluated using complementary live/dead staining, MTT metabolic activity assays, and confocal microscopy, which collectively demonstrated sustained cell viability, attachment, and proliferation on the fabricated platform. Label-free electrical impedance spectroscopy revealed a progressive increase in impedance with culture time, consistent with increasing cell coverage and interfacial barrier formation, and exhibited the same temporal trend as the biological assays. Unlike conventional endpoint techniques, the proposed platform enables nondestructive, time-resolved electrical interrogation of cell growth while combining simple fabrication, low material cost, and compatibility with scalable manufacturing. These findings establish a proof-of-concept photo paper-based bioelectronic scaffold that integrates 3D cell culture with impedance sensing, providing an accessible foundation for future in vitro tissue models, cell-based bioelectronic assays, and low-cost biomedical research platforms.