Time-Resolved pH/pO₂ Mapping with Luminescent Hybrid Sensors

Abstract

A method for simultaneous and referenced 2D mapping of pH and pO2 is described. The experimental setup combines a fast gateable CCD camera as detector, a LED as excitation light source and a single-layer sensor membrane as optical transducer. The planar optode comprises a lipophilic fluorescein derivative (lifetime approximately 5 ns) and platinum(II) mesotetrakis(pentafluorophenyl)porphyrin (approximately 70 micros in the absence of a quencher) immobilized in a hydrogel matrix. Depending on the fluorescent pH indicator, a pH transition in the physiological range (pH 6-pH 8) or in the near-basic region (pH 7-pH 9) can be achieved. The measuring scheme involves the time-resolved acquisition of images in three windows during a series of square-shaped excitation pulses. A method allowing the calculation of both parameters from these three images is presented. The pH/pO2 hybrid sensor incorporating the pH indicator 2',7'-dihexyl-5(6)-N-octadecyl-carboxamidofluorescein was characterized in detail. The pH and pO2 were determined with a maximum deviation of 0.03 pH unit and 6.5 hPa pO2, respectively, within the range of pH 7.6-pH 8.7 and 0-200 hPa pO2 in test measurements. The ionic strength (IS) cross-sensitivity was found to be relatively small (pH/IS < 3.5 x 10(-4) mM(-1) and pO2/IS <-0.053 hPa mM(-1) at a transition from 0.5 to 0.1 M IS). Whereas a strong temperature effect on the sensor signal was observed (DeltapH/DeltaT = 0.011-0.034 K-1 and DeltapO2/DeltaT = 1.85-7.17 hPa K-1 in the range from 277 to 308 K). Examples of pH/pO2 images obtained in natural marine sediment are presented.

Functional and structural imaging of phototrophic microbial communities and symbioses

“…While some of these studies showed pronounced light-dependent pH dynamics in sediments with microphytobenthos, a more detailed application of these sensors for photosynthesis studies still needs to be realized. Most recently, combined planar sensors for simultaneous imaging of pH and O 2 have also been used for sediment studies (Schröder et al 2007). Other combined sensor materials and measuring systems have been developed (Nagl & Wolfbeis 2007), e.g.…”

Optical Chemical Sensors:Design and Applications

“…In particular, a determination of the dissolved oxygen is of utmost importance in many fields of science and technology (Papkovsky & O'Riordan, 2005), including biotechnology (Kostov et al, 2001), biology (Schmaelzlin et al, 2005), marine science (Schroeder et al, 2007), and in medicine (Kimura et al, 2007). Recent interest in methods for measuring dissolved oxygen has been focused mainly on optical sensors, due to their advantages over conventional amperometric electrodes in that they are faster and do not consume oxygen (McDonagh et al, 2002).…”

Sensor Paints

“…[4] The paint was deposited on the wall of a kind of aquarium that was filled with sediment and seawater. Schroeder et al [6] have developed a method for sensing both oxygen and pH in marine sediments using a sensor paint that is capable of recording two parameters (pH and O 2 ) simultaneously. One typical result is shown in Figure 2.…”

“…Optical sensorsunlike other types of sensors-can image several parameters simultaneously. Recently, materials have been reported that can sense both pH and oxygen, [6,22] or temperature and oxygen, [16,23] or CO 2 and oxygen.…”