Optimization of Cell‐Based Multi‐Chamber LAPS Measurements Utilizing FPGA‐Controlled Laser‐Diode Modules

Abstract

A light-addressable potentiometric sensor (LAPS) is a field-effect-based potentiometric device, which detects concentration changes of an analyte solution on the sensor surface in a spatially resolved way. It uses a light source to generate electron-hole pairs inside the semiconductor, which are separated in the depletion region due to an applied bias voltage across the sensor structure and hence, a surface-potential-dependent photocurrent can be read out. However, depending on the beam angle of the light source, scattering effects can occur, which influence the recorded signal in LAPSbased differential measurements. To solve this problem, a novel illumination unit based on a field programmable gate array (FPGA) consisting of 16 smallsized tunable infrared laser-diode modules (LDMs) is developed. Due to the improved focus of the LDMs with a beam angle of only 2 mrad, undesirable scattering effects are minimized. Escherichia coli (E. coli) K12 bacteria are used as a test microorganism to study the extracellular acidification on the sensor surface. Furthermore, a salt bridge chamber is built up and integrated with the LAPS system enabling multi-chamber differential measurements with a single Ag/AgCl reference electrode.

Effect of Plasma Treatment on the Sensor Properties of a Light‐Addressable Potentiometric Sensor (LAPS)

“…Usually, a drift of this size can be acceptable for cell culture experiments, especially as it appears to be uniform along the sensor surface, which can therefore be compensated by means of the differential measuring principle of the LAPS. [2] 3.3. Annealing Effect on the Sensor Properties of the LAPS For constant photocurrent mode measurement, the recorded signals from the left side (L, treated) and the right (R, control) side of the sensor were plotted in Figure 7.…”

“…Potentiometric sensors based on a semiconductor‐insulator field‐effect structure play an important role in label‐free (bio‐)chemical sensing . The light‐addressable potentiometric sensor (LAPS) is an important subtype of this kind of sensors, which is able to detect the variations of the surface charge in a spatially resolved manner . Figure provides an overview of the working principle of a pH‐sensitive Ta 2 O 5 LAPS.…”

“…Local variations in the surface potential influence the amplitude of the photocurrent in the space‐charge region. In this way, by changing the location of the light source, the generated photocurrent in the particular sensor area can be read out …”

“…[1] The light-addressable potentiometric sensor (LAPS) is an important subtype of this kind of sensors, which is able to detect the variations of the surface charge in a spatially resolved manner. [2] Figure 1 provides an overview of the working principle of a pH-sensitive Ta 2 O 5 LAPS. Depending on the concentration of the H þ ions in the analyte solution, a surface potential is generated on the transducer, superimposed with the DC bias voltage applied between a reference electrode and the semiconductor.…”

“…In this way, by changing the location of the light source, the generated photocurrent in the particular sensor area can be read out. [1][2][3][4][5] Typical current versus voltage plots (I/V curves) can be obtained by sweeping the applied bias voltage and simultaneously illuminating an area of the semiconductor. As shown in Figure 1b, depending on the local analyte concentration in the solution, the I/V curve moves along the horizontal axis.…”