The dynamic interactions between active molecules and the cell membrane play a crucial role in various fundamental biological processes. In recent years, the emergence of the photovoltage transient technique has provided an insitu, real-time, and non-invasive approach to studying dynamic processes at the membrane interface. This technique utilizes silicon wafers' photoelectric response to generate charges and records voltage transient pulses during the charging and discharging process of phospholipid membranes. These pulses directly reflect the instantaneous structure and properties of the membrane. By analyzing the temporal evolution of voltage pulses, the dynamic changes in membrane structure induced by molecular actions can be elucidated. In particular, this technique offers valuable insights into the timing of transitions between different functional states. This review provides a comprehensive overview of the working principle, equipment setup, and data processing methods employed in photovoltage transient analysis. Furthermore, using supported phospholipid bilayers as model cell membranes, it highlights recent advancements made with this technique in investigating the mechanisms underlying membrane interactions of active molecules such as surfactants, polymers, peptides, and nanoparticles. Finally, an assessment of its strengths and limitations is provided along with future prospects for its development.
The photovoltage transient technique was initially employed to analyze the charging and discharging curves, as well as the hydration process, of single- and multi-layered membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipids. Previously, X-ray diffraction (XRD) and quartz crystal microbalance with dissipation (QCM-D) technology were commonly utilized for real-time monitoring of the swelling process in phospholipid membranes, providing information on changes in mass and thickness of Z-direction layers. In contrast, the photovoltage transient technique offers additional insights into the kinetics of the swelling process and timing of transitions between different stages. This study demonstrated the efficacy of the photovoltage transient technique in real-time monitoring of membrane interface processes; specifically, it quantitatively measured the characteristic τ value of DOPC phospholipid membrane, thereby enabling further development of quantitative analysis methods for this technique. Then, the photovoltage transient technique, in conjunction with giant unilamellar vesicle (GUV) leakage assays, atomic force microscopy (AFM) and QCM-D, was employed to monitor the structural perturbation of surfactants (TTAB) and polymers (Brij35 and PVPk30) on the membranes. Specifically, Brij35 primarily undergoes an adsorption-accumulation-penetration process; whereas PVPk30 exhibits a dynamic equilibrium between molecular adsorption-desorption and/or membrane permeation-healing competing mechanisms. This disparity in membrane action processes elucidates the discrepancy observed in their cytotoxicity during live cell experiments. The ability of photovoltage transient technology to investigate the entire membrane as a research subject along with its high sensitivity enables it to capture fluctuations in data points that reflect the coexistence of competitive mechanisms. Furthermore, photovoltage monitoring revealed the occurrence of peptide-induced membrane permeabilization. The distinct mechanism of action on the membrane between melittin (as a representative antimicrobial peptide) and TAT (a typical cell penetrating peptide) was elucidated. Lastly, the conductive carbon dots (CDs) induced phenomena of membrane overcharging and overdischarging, potentially attributed to charge transfer between the silicon substrate and the embedded conductive CDs.