Surface-engineered porous silicon nanoparticles amplifying [Ru(bpy)3]2+ electrochemiluminescence for ultrasensitive immunoassay.

Highly sensitive electrochemiluminescence (ECL) systems are essential for the accurate detection of disease-related cytokines. Herein, mildly oxidized porous silicon (MO-PSi) nanoparticles are first employed as a multifunctional modification material to boost the ECL signal of the tris(2,2'-bipyridine)-ruthenium(II) [Ru(bpy)3]2+/tripropylamine (TPrA) system for cytokine immunoassay. Freshly etched PSi was subjected to a one-step mild oxidation treatment to generate mildly oxidized porous silicon (MO-PSi), during which the surface Si-H groups were converted into a SiOx layer enriched with Si-OH groups while preserving the porous silicon framework. Notably, the MO-PSi-modified indium tin oxide (ITO) electrode exhibits a higher ECL response than ITO electrodes coated with PSi or mesoporous silica nanoparticles (MSN). The enhanced performance is primarily attributed to the surface engineering of MO-PSi. Specifically, the Si-OH-terminated SiOx layer endows MO-PSi surface with strong negative charges, enabling efficient electrostatic enrichment of cationic [Ru(bpy)3]2+ at the electrode interface for ECL reaction. Moreover, the mild oxidation treatment passivates surface defects, improving the electrochemical stability of modification layer and facilitating interfacial electron transfer, collectively leading to enhanced ECL emission. As a proof of concept, two types of immunosensor were constructed to detect the cytokines interleukin-1β (IL-1β) and interleukin-6 (IL-6), achieved by covalently immobilizing antibodies onto the Si-OH groups of MO-PSi. This sensing platform demonstrates a wide concentration range from 1 fg/mL to 1 ng/mL for both cytokines, with detection limits as low as 0.9 fg/mL for IL-1β and 0.3 fg/mL for IL-6. This work highlights the feasibility of using the MO-PSi-modified electrode to fabricate high-performance ECL biosensors.