Electro-Photodynamic Visualization of Singlet Oxygen Induced by Zinc Porphyrin Modified Microchip in Aqueous Media

A porphyrin-based electro-photodynamic imaging system was fabricated for monitoring the concentration of oxygen. Distinct from the electrochemiluminescent (ECL) inability of numerous organic species in aqueous solutions, a strong and stable red irradiation at 634 nm could be stimulated electrochemically on zinc(II) meso-tetra(4-carboxyphenyl) porphine (ZnTCPP)/tetraoctylammonium bromide (TOAB) in the physiological condition. In terms of in situ electron paramagnetic resonance and ECL spectroscopies, the nature of ECL was thoroughly investigated, being exactly the chemiluminescence from singlet oxygen (¹O₂) produced during the successive electro-reduction of ZnTCPP. Meanwhile, the excellent film-making capacity of amphiphilic TOAB as a potent ion barrier granted the luminophores a micro-order and patternable electrode modification. Such platform was exceptionally tolerant of pH variation, facilitating a durable solid-state ECL visualization under potentiostatic electrolysis and time exposure in the charge-coupled device (CCD) camera. For flow-injection and real-time detection, a chip-mounted microfluidic cell was customized and manufactured. A sensitive and simple vision-sensing of O₂ was further achieved with a real determination limit as low as a few micromolar level. The developed ECL imaging system is a good prototype and an eco-friendly technique in the cathodic range, and thus, it would supplement the primary anodic imaging library, showing great promise for multiplexed and colorimetric assays as well as oxygen-involved activity studies in the future.