Metalloporphyrins into Mesoporous Photonic Crystals: Towards Nanostructured Sensing Devices

Metalloporphyrins are molecules capable of optically sensing targets due to their specific reactivity. Shifts in metalloporphyrins spectra are usually in the order of 30 nm, requiring a spectrophotometer for transducing the analyte concentration. Mesoporous oxide thin films photonic crystals (PC) act as optical filters, while their pores can host molecular moieties. In this work used a metalloporphyrin, Mn^III meso-tetra(N-methyl-4-pyridyl) porphyrin (MP), to add a recognition functionality to a PC and, at the same time, retain their pore network, in order to develop a versatile and portable sensing device for volatile amines. The hybrid material MP@PC was prepared by immersion of the PC, synthesized from two mesoporous oxides with different refractive index, in an MP solution. The system was characterized by UV-Vis absorption and FTIR spectroscopies, and SEM microscopy. Sensing of small molecules was tested using ethylenediamine (EDA) as a volatile amine model, showing an absorbance increase in the PC spectral window with promising analytical parameters. The hybrid material presents enhanced sensing capabilities compared to MP or PC alone. A prototype device was built, aiming for a future design of simple, low-cost equipment, with a light emitting diode and a light-dependent resistor, including the MP@PC sensor. The device is capable of sensing with only 1.52 μg of MP on a 1 cm² glass slide and it is easily prepared and showed a very small detection limit.