New insights in the spatially resolved dynamic pH measurement in macroscopic large absorbent particles by confocal laser scanning microscopy

Advanced characterization of immobilized enzymes as heterogeneous biocatalysts

“…A pH drop resulted in this case from the oxidation of d-glucose into d-gluconic acid. Fluorescence lifetime provides advanced measurement capabilities [178,179,186], eliminating signal distortion in dependence of the scanning depth as a known critical problem of intensity-based measurements in CLSM [193]. Internal pH changes at spatial resolution have been monitored in hydrogels and PEG microparticles using fluorescence lifetime microscopy techniques [166,186].…”

Enzymes immobilized in mesoporous silica: A physical–chemical perspective

“…For opto-chemical O 2 sensors quenching of a phosphorescent dye results in a shift in intensity and lifetime of the phosphorescence whereas in pH sensing the absorption or emission properties change depending on the protonation state of the indicator. This technique has also been developed for measurements directly inside various supports [137][138][139]. In order to detect the environment inside the pores, experienced by the protein, either the internal surface of the support or the protein itself needs to be functionalized with a luminescent probe.…”

Model-based experimental analysis of enzyme kinetics in aqueous–organic biphasic systems

“…Therefore, CLSM requires either fluorescent molecules (Tallarek et al, 2003, Cvetkovic et al, 2004, or small fluorescent marker molecules attached to macromolecules to allow for spatially resolved concentration measurements (Kasche et al, 2003). The quantification of concentration based on fluorescence intensity, however, has been demonstrated to be limited by the attenuation of light by the carrier matrix that results in depth-dependent calibration curves and prohibits the evaluation of (fast) dynamic diffusion problems (Heinemann et al, 2004). The impact of light attenuation may be overcome using either two photon excitation (Denk et al, 1990), or fluorescence lifetime CLSM (Kuwana et al, 2004).…”