The low solubility of carbon dioxide (CO₂) in aqueous media leads to significant gas losses during microalgal cultivation, limiting carbon availability and biofixation efficiency. To address this limitation, polymeric nanofibers functionalized with monoethanolamine (MEA) were evaluated as a dual-function system to enhance CO₂ availability and modulate metabolite production in Porphyridium purpureum. Polyacrylonitrile nanofibers with or without MEA were produced by electrospinning and added to the culture medium at 0.1 mg mL⁻¹. Cultivation was carried out for 15 days at 21 ± 1 °C under continuous illumination, with injection of a gas mixture containing 7.5% CO₂ for two minutes every hour. Three experimental conditions were evaluated: control without nanofibers, PAN nanofibers, and MEA-functionalized PAN nanofibers. Released polysaccharides were recovered from the supernatant by ultrafiltration at the end of cultivation. The highest B-phycoerythrin concentration was obtained in the MEA-functionalized nanofiber treatment, reaching 41.3 ± 3.22 mg g⁻¹ dry weight, representing a threefold increase compared to the control. Cultures supplemented with non-functionalized nanofibers showed intermediate values of 24.56 ± 3.22 mg g⁻¹. In addition, released polysaccharides from nanofiber treatments exhibited a 23% increase in purity, while MEA-functionalized nanofibers promoted a 10% increase in acidic sugar content. The enhanced CO₂ availability provided by nanofibers appears to favor glycolytic flux and amino acid precursor supply for phycoerythrin biosynthesis, while also altering polysaccharide composition. Increased production of phycoerythrin and acidic sugars is particularly relevant due to their antioxidant, anti-inflammatory, and bioactive properties. Overall, nanofiber-assisted cultivation represents an effective strategy to intensify pigment production and tailor polysaccharide profiles in Porphyridium purpureum for high-value biotechnological applications. This approach demonstrates strong potential for sustainable bioprocess intensification, improved carbon utilization efficiency, and development of scalable cultivation platforms targeting pharmaceutical, nutraceutical, food, and specialty pigment markets worldwide with reduced harvesting costs and process stability.