Formation of controllable pH gradients inside microchannels by using light-addressable electrodes

Actively Driven Light-Addressable Sensor/Actuator System for Automated pH Control for the Integration in Lab-On-A-Chip (LoC) Platforms

“…However, it turns out that after 60 s of illumination, the resulting voltage shifts from the I – V curves were 66, 98, and 129 mV for a width of 0.05, 0.1, and 0.2 mm, respectively. In a previous study, this effect was also shown for smaller illuminated areas (20 × 20 to 100 × 100 μm 2 ) . It was assumed that due to the geometrical restrictions of the microfluidic channel, generated H + -ions at the outer rim of the pH gradient are buffered first.…”

“…1.5 mm was detected by the LAPS system in the channel. This effect can be attributed to H + -ion diffusion as discussed in our previous study, while here the effects of a limited sample volume and space constraints (80 μm in z -direction, orthogonal to the surface) are even more restricting. The channel was finally flushed with buffer solution to ensure that the pH value in the solution was changed.…”

“…Exemplarily, LAPS , was utilized inside microfluidic systems for the detection of ion diffusion, , enzymatic reactions, , or cellular acidification processes. − LAEs were applied to actively adjust the microenvironment through photoelectrochemical reactions. , Examples are light-addressed neuron stimulation, , material deposition, , or pH manipulation , in photoelectrochemical measurement cells. Within microfluidic channels, LAEs were often incorporated for single-cell manipulations as optoelectronic tweezers , and to manipulate pH levels …”

“…Within microfluidic channels, LAEs were often incorporated for single-cell manipulations as optoelectronic tweezers 31,32 and to manipulate pH levels. 33 In numerous applications, it is of great benefit to study (bio)chemical processes not only under equilibrium conditions but also in response to external stimuli, such as the pH-induced effect on the catalytic activity of enzymes 34,35 or changes of the microenvironment of cells. 36,37 In this work, we aim to develop an actively driven sensor/actuator system for automated pH control, designed for integration into a single platform.…”

Light-Addressable Electrochemical Sensors toward Spatially Resolved Biosensing and Imaging Applications

“…Recently, light-addressable electrochemistry or light-activated electrochemistry (LAE), which can drive the Faradaic process in an amperometric fashion, has become another hot research spot in the construction of LAESs. , Based on an electrolyte–semiconductor (ES) structure, LAE allows light-induced local Faradaic currents to cross the electrode/electrolyte interface, which broadens the applications from potentiometric measurements to amperometric detection principles . For instance, LAE has been adopted for electrochemical analysis, − biomolecular sensing, , and live cell imaging. , The fundamental theory, spatial confinement and sensing performance of LAE, has been reviewed by Vogel et al It is noteworthy that another significant concept of photoelectrochemical (PEC) sensing possessing a working principle similar to LAE has also witnessed remarkable progress in the past two decades. − Most of this work benefited from the advantage of the high sensitivity of PEC due to the unique setup consisting of two separate energy forms, that is, using light as the excitation source and electricity as the detection signal. , The light addressability of PEC, however, has been rarely exploited and summarized.…”