Time Resolved Singlet Oxygen Spectroscopy
A Virtual Experiment
Santi Nonell
Institut Químic de Sarrià
Universitat Ramon Llull
Vía Augusta 390, 08017-Barcelona, Spain
santi.nonell@iqs.url.edu
Time-resolved detection of singlet oxygen, O2(1
g), is usually accomplished by taking advantage of its weak phosphorescence in the infrared region of the electromagnetic spectrum, at 1.27 mm. The intensity of this emission, and therefore of the electrical signal produced by a detector, is proportional to the O2(1g) concentration. Time-Resolved Phosphorescence Detection (TRPD) is used to determine both the magnitude and characteristic rise and decay time rate constants of the signal.
The Simulated Equipment
Here we provide a virtual TRPD simulation that mimics the response that would be obtained from the set-up shown in Fig. 1. The TRPD system consists of 4 primary components:
1. A pulsed laser with emission matching the absorption spectrum of the photosensitizer with pulse duration in the nanosecond, or less, time scale providing about 0.1 to 10 mJ of energy per pulse,
2. Optical elements including neutral density filters or crossed-beam polarizers to attenuate the laser output and cut-off, and interference filters to filter out any sensitizer fluorescence and residual laser light at the detector.
3. A suitable detector that is sensitive in the near infrared region with a rise time less than 1 ms, and
4. A digital oscilloscope or transient recorder with a digitizing frequency equal to or greater than 10 MHz.
Figure 1. The optical set-up that is simulated in the virtual laboratory experiment described here.
The sample in the virtual instrument, shown in the cuvette (light blue) toward the right-hand part of Fig. 1, consists of a solution containing a photosensitizer. The photosensitizer is capable of transferring energy from an excited triplet state to a molecule of oxygen, thus creating excited state singlet oxygen. You select the photosensitizer properties, solvent, and oxygen concentration, and set controls as if you were using a real TRPD apparatus. Results are displayed graphically. Appropriate parameters are also recorded in tabular form for later analysis.
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Simulated Experiments using LabVIEW This simulation is accomplished using LabVIEW software. Since LabVIEW is used to interface real instruments with computers for control and data acquisition, LabVIEW simulations can be constructed to be indistinguishable from a real experiment. Each virtual experiment is downloaded as a VI (Virtual Instrument), a small .exe program file (about 100 KB). Running the VIs as stand-alone programs requires the previous installation of the LabVIEW Run Time Engine (included in the download package). The LabVIEW VI provides the simulated instrumentation to conduct a TRPD experiment to measure singlet oxygen generated by a photosensitizer. Laboratory instructions describing the steps that need to be taken in this process are provided in the accompanying PDF file. Keep these instructions available as a guide in the use of the simulated instrument. LabVIEWTM is a product of National Instruments Corporation. Click on link for additional information. |
Download Options (Windows Only)
All necessary files for using this virtual laboratory can be downloaded from this site. If necessary, an updated LabVIEW Run Time Engine can be downloaded from the National Instruments web site, the originators of LabVIEW.
HINTS:
1) Zip Files: In most cases, you will be downloading zipped files. These are compressed files to make downloading faster. Many operating systems include an unzip program, and many will begin to run when you click on the link below. If so, allow the unzip program to extract the compressed files to a directory that you select. If you accept the default directory, be sure that you know where it is so that you can find your VI.
2) Screen Resolution: These VIs run best when your screen is set to a resolution of 1024 x 768, and the Windows font is set to normal size. If your screen is set to a different resolution, the VI will run, but you may have some problems in viewing some aspects of the display in a convenient manner.
[ Download - 13.1 MB ]
Suggested Readings
C.Schweitzer and R.Schmidt, Physical Mechanisms of Generation and Deactivation of Singlet Oxygen, Chem. Rev., 2003, 103, 1685-1757.
[ Reprint ].
S. Nonell and S. E. Braslavsky, "Time-resolved singlet oxygen detection", in Singlet Oxygen, UV-A and Ozone (L. Packer and H. Sies, Eds.), Methods Enzymol., 2000, 319, 37-49. [ Reprint ].
Jiménez-Banzo, X. Ragàs, P. Kapusta, and S.Nonell. Time-resolved methods in biophysics 7. Photon counting vs analog time-resolved singlet oxygen phosphorescence detection, Photochem. Photobiol. Sci., 2008, 7(9), 1003-1010. [ Reprint ].
10/23/08