Yangdong Zheng

Luminescence and photosensitivity of gadolinium labeled hematoporphyrin monomethyl ether

Photodynamic therapy for deep-lying lesions needs an appropriate imaging modality, precise evaluation of tissue oxygen and an effective photosensitizer. Gadolinium based metalloporphyrins Gd(III)-HMME is proposed in this study as a potential multifunctional theranostic agent, as photosensitizer, ratiometric oxygen sensor and MRI contrast agent. The time resolved spectroscopy revealed the luminescence peak of Gd(III)-HMME at 710 and 779 nm with a lifetime of 64 μs in oxygen-free methanol to be phosphorescent. This phosphorescence is strongly dependent on dissolved oxygen concentration. Its intensity in oxygen saturated methanol solution is 21% of that in deoxygenated solution. The singlet oxygen quantum yields ΦΔ of HMME and Gd(III)-HMME in air saturated methanol solution were determined to be 0.79 and 0.40 respectively using comparative spectra method. These phenomena indicate that the oxygen sensibility and production of singlet oxygen of Gd(III)-HMME can fulfill the requirement of PDT treatment.

Fluorescence intensity ratio method for temperature sensing

A thermometry method based on the ratio between the valley intensity formed by fluorescence peak overlap and the peak fluorescence intensity has been developed. Excited by a 405 nm laser, the valley to peak ratio (VPR) of the emissions originating from 5D0 to 7F2 Stark sublevels in Eu3+-doped CaWO4 shows a monotonic change with temperature. Spectrum analysis indicates that this monotonic increase is caused by the homogeneous broadening of the spectral lines as the temperature increases. The relative sensitivity S(r) is in the magnitude of 10(-4)  K(-1) in the experimental temperature range of 303-573 K.

Influence of phase transitions on green fluorescence intensity ratio in Er^3+ doped K_05Na_05NbO_3 ceramic

The fluorescence intensity ratio (FIR) method is a non-contact temperature (T) measurement technique based on thermally coupled levels of rare earth ions in a doped host. Green fluorescence originating from ²H_11/2 and ⁴S_3/2 states of Er³⁺ doped K_0.5Na_0.5NbO₃ (KNN) ceramic are studied in the temperature range of 300 K to 720 K. The fluorescence intensities change dramatically around phase transition points where the crystal symmetry changes, inducing deviation of the FIR from Boltzmanns law. The temperature determined by the FIR method deviates from thermocouple measurements by 7 K at the orthorhombic to tetragonal phase transition (T_O-T) point and 13 K at the Curie point (T_C). This finding gives guidance for developing fluorescent T sensors with ferroelectrics and may also provide a fluorescent method to detect phase transitions in ferroelectric materials.

Comparison study on the influence of the central metal ions in palladium(II)- and gadolinium(III)-porphyrins for phosphorescence-based oxygen sensing

The luminescence and oxygen sensing properties of a series of palladium(II)- and gadolinium(III)-porphyrins were evaluated and compared. Spectral analysis indicates that absorption and luminescence of Gd-porphyrins are red-shifted compared to those of Pd-porphyrins. This demonstrates that the energy levels of excited states in Gd-porphyrins are lower than those in the corresponding Pd-porphyrins. Phosphorescence quantum yield of Pd-hematoporphyrin monomethyl ether (HMME) was about 3-fold higher than that of Gd-HMME due to the decreased non-radiative decay rate of triplet states in Pd-HMME, which was confirmed by the longer phosphorescence lifetime of Pd-HMME. This is attributed to the higher first excited triplet state (T1) in Pd-HMME as compared to that of Gd-HMME. However, the phosphorescence intensity and lifetime responses of Gd-HMME to oxygen were larger than those of Pd-HMME. To understand this difference, oxygen quenching constants (kq) of Gd- and Pd-HMME were evaluated and were found to be 4972.9 and 26.4 s−1, respectively. The huge difference in kq between the two species is responsible for their disparate oxygen responses. We suggest that the greater kq of Gd-HMME results from the better energy matching between its T1 (12 658–14 006 cm−1) and the second excited state (13 123 cm−1) of oxygen, which was demonstrated by the higher singlet oxygen quantum yield of Gd-HMME. The same phenomena (spectral red-shifts, lower phosphorescence quantum yields, shorter lifetimes, and larger oxygen responses) were also observed upon substituting Pd(II) by Gd(III) in other porphyrins studied in this work.

Relative sensitivity variation law in the field of fluorescence intensity ratio thermometry

We study the variation law of relative sensitivity in the field of fluorescence intensity ratio thermometry. It is theoretically demonstrated that there must be only one maximum value of relative sensitivity in the case in which there is a positive offset in fitting function. Moreover, the method to obtain this maximum is proposed. Experimental results, taking the D15/D50 levels of Eu3+ as examples, are in excellent accordance with the conclusion. The mechanism behind is then investigated, and other populating processes imposed on the D15 level, which exert negative outcome on thermal sensitivity, are found to play a key role in determination of this unique variation law.

Photophysical properties of sinoporphyrin sodium and explanation of its high photo-activity

Sinoporphyrin sodium (DVDMS) is a novel photosensitizer with high photodynamic therapy (PDT) effect. Reasons for its high photo-activity were investigated according to the study of photophysical characteristics of DVDMS. Extinction coefficients (e) of DVDMS at 405 nm and 630 nm are 4.36 × 105 and 1.84 × 104 M−1.cm−1; fluorescence quantum yield (ΦF) is 0.026; quantum yield of lowest triplet state formation is 0.94 and singlet oxygen quantum yield (ΦΔ) is 0.92. Although ΦΔ of DVDMS is only 10% higher than that of Photofrin®; (0.83), the extinction coefficient of DVDMS at 630 nm is 10-fold greater than that of Photofrin®;. This leads to its higher singlet oxygen generation efficiency (eΦΔ). The higher eΦΔ of DVDMS can result in an effective reduction of dosage (1/10 of Photofrin®;) reaching the same cytotoxic effect as Photofrin®;. Even though ΦF is approximately equal to that of Photofrin®;, brightness (eΦF) of DVDMS is 10-fold greater than that of Photofrin®; because of the 10-fold greater extinction coeff...

Pressure-sensitive blackbody point radiation induced by infrared diode laser irradiation

Ultrabroadband radiation from Yb(2)O(3) at ambient and low air pressures was investigated under the excitation of a 980 nm diode laser. The radiation was confirmed to be blackbody radiation, and it is sensitive to environmental air pressure in the way that the integrated radiation intensity decreases linearly with increasing air pressure. An ideal gas model may be employed to interpret the linear dependence. The pressure-sensitive radiation characteristic provides a potential method for noncontact measurement of air pressure with high accuracy.

Modified calculation method of relative sensitivity for fluorescence intensity ratio thermometry

The calculation method of relative sensitivity (Sr) for fluorescence intensity ratio (FIR) thermometry is discussed, taking the F33-H63 and H43-H63 transitions of Tm3+ as examples. The value of Sr is calculated using its original definition, and is found to largely deviate from the result obtained using the conventional method that is widely used at present. This deviation is found to stem from the neglect of an offset. A modified expression of Sr is proposed, which shows the true performance of FIR technology and makes it possible to precisely compare the Sr values obtained using various methods.

The effect of imidazole on the enhancement of gadolinium-porphyrin phosphorescence at room temperature

A mechanism for the enhanced room-temperature phosphorescence (RTP) of gadolinium-coordinated hematoporphyrin monomethyl ether (Gd-HMME) in the presence of imidazole and free gadolinium ions (Gd3+) is revealed. Imidazole, the molten solvent used in the synthesis of Gd-HMME, was effective in enhancing the Gd-HMME RTP. In the presence of imidazole, further enhancement of the Gd-HMME RTP was observed upon adding Gd3+. Overall, a 40-fold enhancement of Gd-HMME RTP intensity was achieved by adding both imidazole and Gd3+. In addition, there was an increase in the RTP lifetime. Through spectroscopic analysis, we deduced that a protective medium is formed by the imidazole and the degree of this protection is further increased by Gd3+. The protective medium enhances the Gd-HMME RTP by partially inhibiting energy transfer from the lowest triplet state of Gd-HMME to oxygen. This was demonstrated by the presence of lower levels of singlet oxygen in the Gd-HMME solution after the addition of imidazole. These results indicate that imidazole could have potential application as an RTP enhancer or triplet state protector.

Biomedical Properties of Tantalum Coatings Prepared by Multi Arc Ion-Plating

Ti-50.6 at.% Ni shape memory alloy was coated with tantalum using multi arc ion-plating technique with the aim to increase its radiopacity and biocompatibility. The surface characteristics were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results of XPS survey spectra show that a thin oxide film are formed inside tantalum coating as a result of natural passivation of Ta in atmosphere. The hemocompatibility was evaluated in vitro by clotting time and platelet adhesion measurement. The results of our study showed that the clotting time of tantalum was higher than that of the TiNi alloys and no sign of accumulation and only slight pseudopodium was observed on the tantalum coatings, suggesting that the tantalum coatings can improve the biocompatibility of TiNi alloy.