Two-Step Air/Water Oxidation Process for the Long-Lasting Photoluminescence and Biological Viability (MTT Assay) of Porous Silicon Particles

Due to their visible photoluminescence (PL) at room temperature, porous silicon particles (PSps) have gained interest for their potential biomedical applications, making them promising biological markers for in vivo or in vitro use. This study explores the PL evolution and stabilization of PSps following a two-step oxidation process involving air annealing and chemical oxidation in deionized water. PS layers were fabricated by electrochemical etching of p⁺-Si wafers and then annealed in air at 300 °C and 600 °C for five minutes. The layers were then stored in deionized water and sonicated to produce PSps. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to analyze the morphology and composition of the particles, and spectrofluorimetry was used to monitor the PL over several weeks. Samples annealed at 300 °C exhibited a transition from nearly complete PL quenching to strong yellow-red emission. In contrast, the 600 °C sample showed no PL emission. The cytotoxicity of the PSps was evaluated using an MTT assay on human endothelial cells (EA.Hy926) with PSps and polyethylene glycol (PEG)-coated PSps at concentrations of (3.5-125 µg/mL) in both serum-free and fetal bovine serum (FBS)-containing media over 24, 48, and 72 h. Cell viability was significantly affected by both exposure time and particle concentration; however, this effect was prevented under conditions mimicking the physiological plasma environment.