A photoluminescence (PL)-based O2 sensor utilizing inorganic light emitting diode (LED) as the light source and a
polymer-based photodetector (PD) is demonstrated. The device structure is compact and the sensor integrates the sensing
element, light source, and organic PD as thin films that are attached such that the sensing element is sandwiched between
the LED and the PD. The sensing elements are based on the oxygen-sensitive dyes Pt-octaethylporphyrin embedded in a
polystyrene matrix. A green inorganic LED (peak emission ~525 nm) light source was used to excite the porphyrin dye,
which emits at ~640 nm. This emission can be measured using P3HT:PCBM bulk heterojunction photodiodes, which
have been shown earlier to have efficient photodetection at this wavelength if the active layer is sufficiently thick. The
time constant associated with sweeping out the photogenerated carriers is found to be ~ 10μs. Such a fast decay of
photocurrent is useful for oxygen monitoring, determined by measuring the Pl decay time rather than the PL intensity, of
the sensing film. This approach can eliminate the need for frequent sensor calibration and optical filters (as pulsed LED
excitation is employed in this mode) which lead to bulkier design.
KEYWORDS: Fluorescence resonance energy transfer, Single walled carbon nanotubes, Luminescence, Molecules, Zinc, Quantum dots, Oxygen, 3D modeling, Ions, Chemical analysis
We have developed conjugates with quantum-dots (QDs) for the purpose of analysis of nanosystems that are organic or inorganic in nature such as DNA and carbon nanotubes. First, by employing Florescence Resonant Energy Transfer (FRET) principles, a hybrid molecular beacon conjugates are synthesized. For water- solubilization of QDs, we modified the surface of CdSe-ZnS core-shell QD by using mercaptoacetic acid ligand. This modification does not affect the size of QDs from that of unmodified QDs. After linking molecular beacons to the carboxyl groups of the modified QDs using 1-Ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride, hybrid molecular beacons are prepared as a DNA probe. After hybridization with specific target DNA and non-specific target DNA, the hybrid conjugates show high specificity to the target DNA with 5-fold increase in the intensity of fluorescence. By developing atomic model of the conjugates, we calculated with 8 numbers of molecular beacons on a single quantum dots, we could increase the efficiency of FRET up to 90%. In other hands, for application of quantum dots to the carbon nanotubes, FRET is a barrier. Thus, after employing 1 % sodium-dodecyl-sulfonate (SDS), single-walled carbon nanotubes are decorated with QDs at their outer surface. This enables fluorescent microscopy imaging of single-walled carbon nanotubes which is a more common technique than electron microscopy. In summary, QDs can be used for analysis or detection of both organic and inorganic based nanosystems.
Conference Committee Involvement (3)
Organic Semiconductors in Sensors and Bioelectronics V
15 August 2012 | San Diego, California, United States
Organic Semiconductors in Sensors and Bioelectronics IV
24 August 2011 | San Diego, California, United States
Organic Semiconductors in Sensors and Bioelectronics III
4 August 2010 | San Diego, California, United States
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