Fluorolog 2

The evaporation of the samples on quartz substrates was carried out using an Edwards Auto 306 evaporator equipped with a high vacuum chamber (10⁻⁶ mbar) and a frequency thickness monitor (FTM) to check the evaporation rate. The deposition rate was 0.5 nm∙s⁻¹ with a final thickness of 80 nm. The solid state absorption spectra were recorded on a Perkin-Elmer Lamba 900 UV–vis–NIR spectrophotometer, the photoluminescence spectra of Alq₃ and Al(Op)₃ were acquired on a Spex Fluorolog 2. The photoluminescence quantum yield in solid state was estimated by the absolute method using an integrating sphere [44 (link)]. The lifetimes were obtained on a time-correlated single photon counter (TCSPC) equipped with a NanoLED source and a Horiba Jobin-Yvon Fluorohub for the data elaboration.

For the experimental tests presented in this paper, a set of liquid homogeneous phantoms representative of GI tissues was considered, with different concentrations of Hb, polystyrene beads (1 μm diameter), and the fluorophores NADH and Carbostyril 124 (7-amino-4-methyl-2(1H)-quinolinone, representative of collagen). The structures of both fluorophores are shown below (Figure 2). For each phantom created, its diffuse reflectance signal was obtained, between 350 nm and 750 nm, with a commercial UV-Vis-NIR spectrophotometer (Shimadzu UV 3101PC) equipped with an integrating sphere. The fluorescence signal was obtained, between 380 nm and 600 nm (with excitation at 350 nm), using a commercial fluorometer (SPEX^® FluoroLog^® 2), equipped with a temperature controlled cuvette holder. Temperature was kept constant at the chosen value ±0.2 °C. All the fluorescence spectra were corrected for the instrumental response of the equipment (using the correction curve provided by the manufacturer). The influence of intensity fluctuations of the lamp was eliminated by the acquisition system (dividing the sample signal by a reference signal acquired by a photodiode). Therefore, fluorescence signal has no variability for each of the samples at a given temperature.