Sensors and Actuators B 147 (2010) 310–315 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb 2D full-field measurement of oxygen concentration based on the phase fluorometry technique that uses the four-frame integrating-bucket method Chen-Shane Chu, Yu-Lung Lo ∗ Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan article info Article history: Received 22 December 2009 Received in revised form 9 March 2010 Accepted 10 March 2010 Available online 17 March 2010 Keywords: Full-field Oxygen sensor Phase fluorometry Pt(II) complex Sol–gel abstract A modulation system for the phase-resolved two-dimensional fluorescence phase imaging of a planar optical oxygen sensor is presented. The proposed system is based on the phase fluorometry technique and uses the four-frame integrating-bucket method. Integrating buckets with multiple frames are achieved using a complex programmable logic device to provide an external trigger to the charge coupled device (CCD). The oxygen-sensitive film is based on microporous film prepared using a sol–gel process with a Pt(II) complex, platinum tetrakis pentafluorophenyl porphine (PtTFPP); the film can be efficiently excited by a laser diode with a central wavelength of 405 nm. The experiment results show that the maximum phase difference between 0% and 100% gaseous oxygen is 22 ◦ . The 2D full-filed O 2 distribution imaging was found to be the most sensitive between 0% and 20% O 2 . The combination of optical sensor technology and phase-resolved imaging allows the determination of the distribution of chemical or physical param- eters in heterogeneous systems, making the proposed system a powerful testing tool for screening and mapping applications. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The two-dimensional (2D) measurement of the distribution of physical and chemical parameters in non-homogeneous samples is of interest in medical and biological research and in clinical diagnosis. The combination of planar optodes and charge coupled device (CCD) technology has led to a significant improvement in the high spatial resolution two-dimensional mapping of single ana- lytes in inhomogeneous samples. This type of sensor has been used to investigate the 2D distributions and dynamics of pO 2 and pH in marine systems [1–3], for noninvasive quantification of oxygen supply engineered tissues [4], and to visualize airflow patterns in wind tunnel research [5,6]. Optical chemical sensor films are ide- ally suited for combination with imaging techniques because planar sensors have an array of numerous independent sensing elements whose response can be read out using CCD cameras [7]. Intensity-based fluorescence imaging methods are commonly used in fluorescence microscopy [8–11]. In optical chemical sens- ing, the analyte (e.g., oxygen) causes a change in the fluorescence intensity of the sensor which is related to the analyte’s concentra- tion. However, the fluorescence intensity (in contrast to the phase shift) depends not only on the actual analyte concentration but also on other factors including: (1) susceptibility to light source ∗ Corresponding author. Tel.: +886 6 2757575x62123; fax: +886 6 2352973. E-mail address: loyl@mail.ncku.edu.tw (Y.-L. Lo). and detector drift, (2) changes in the optical path, and (3) drift due to the degradation or leaching of the fluorescent dye. These fac- tors cause intensity fluctuations and have to be referenced out. It is therefore desirable to sense optical parameters using methods not influenced by these factors, which can be minimized by operating the sensor in the time-domain or frequency-domain instead of the intensity domain. Recently developed fluorescence lifetime imaging techniques have enabled the measurement of fluorescence decay times with high resolution. Both time-domain (pulsed) [12–15] and frequency-domain (phase-resolved) [16–18] methods have been described. The instrumental effort in both techniques increases with decreasing decay time of the fluorophores used. Imag- ing of decay times in the nanosecond time range (which are common for most fluorescence-based optical sensors) requires expensive equipment. Conducting measurements in the frequency- domain offer several advantages over time-domain measurement techniques including relative simplicity and simpler signal detec- tion and processing instrumentation. These are due to the fact that the instrumentation bandwidth can be theoretically reduced by as much as desired at a specific frequency, which significantly increases the signal to noise ratio. In the frequency- domain, the phase shift or amplitude changes can be used to demodulate the fluorescence signal (e.g., to obtain the corre- sponding lifetime) [19,20]. Therefore, simple, low-cost approaches for the 2D distribution of oxygen detection systems are desir- able. 0925-4005/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.03.032