Photodynamic therapy (PDT) is currently an advanced optical technology in medical applications. However, the application of PDT is limited by the detection of photosensitizers. This work focuses on the application of fluorescence spectroscopy and imaging in the detection of an effective photosenzitizer, hematoporphyrin monomethyl ether (HMME). Optical properties of HMME were measured and analyzed based on its absorption and fluorescence spectra. The production mechanism of its fluorescence emission was analyzed. The detection device for HMME based on fluorescence spectroscopy was designed. Ratiometric method was applied to eliminate the influence of intensity change of excitation sources, fluctuates of excitation sources and photo detectors, and background emissions. The detection limit of this device is 6 μg/L, and it was successfully applied to the diagnosis of the metabolism of HMME in the esophageal cancer cells. To overcome the limitation of the point measurement using fluorescence spectroscopy, a two-dimensional (2D) fluorescence imaging system was established. The algorithm of the 2D fluorescence imaging system is deduced according to the fluorescence ratiometric method using bandpass filters. The method of multiple pixel point addition (MPPA) was used to eliminate fluctuates of signals. Using the method of MPPA, SNR was improved by about 30 times. The detection limit of this imaging system is 1.9 μg/L. Our systems can be used in the detection of porphyrins to improve the PDT effect.
Metalloporphyrins with paramagnetism are becoming research focus because their potential use in biomedical field as fluorescence probes and the magnetic resonance imaging (MRI) contrast agents. Divalent manganese metal ion (Mn<sup>2+</sup>) has a half-filled 3d shell with a strong paramagnetic effect. To investigate whether porphyrins coordinated to Mn<sup>2+</sup> can serve as multiple functional probes, hematoporphyrin monomethyl ether coordinated to Mn<sup>2+</sup> (Mn-HMME) was synthesized and its characterization, MRI enhancement property, luminescence property and photosensitivity were studied. Mn-HMME was characterized by UV-visible spectrum and Fourier transform infrared spectrum. It was found that the number of Q bands in the absorption spectrum of Mn-HMME reduced to two compared to free HMME. From the Fourier transform infrared spectrum of Mn-HMME, the characteristic infrared absorption peak of N-H bond in HMME at 970 cm<sup>-1</sup> disappears, but the nitrogen-metal characteristic absorption peaks (1114 cm<sup>-1</sup> and 1093 cm<sup>-1</sup>) were observed. The MRI of Mn-HMME indicates that Mn-HMME has relatively strong MRI enhancement effect. From luminescence spectroscopic analysis, the fluorescence emission of Mn-HMME was weaker than that of free HMME but still detectable. This may be caused by the energy transfer from free HMME to Mn<sup>2+</sup>. The test of photosensitivity of Mn- HMME denotes that the photosensitivity of Mn-HMME disappears. Our results indicate that Mn-HMME has the potential as a multiple functional probe in both fluorescence imaging and MRI.