Articles Review

Hand-held thermal-regulating fluorometer [1]

Abstract: This article relates to the construction of a portable, low cost, thermal-regulating light-emitting diode (LED)-based, handheld fluorometer. This regulated fluorometer is based on both a low thermal mass infrared heater, and an orthogonal geometry LED-based filter fluorometer. Power is supplied through an external power supply and data is collected in real time through standard serial interfaces of personal computers or personal digital assistants. Thermal regulation is automatically maintained using temperature sensor feedback control. Optical excitation relies on LED light source(s) and optical detection is made through an adjustable integrating photodetector. With such a handheld system, applications requiring temperature sensitive photometric measurements for real-time analyte detection can be more easily performed in the field

  • Portable, low cost fluorometer using blue LED as excitation source and integrating photo detector as detection element
  • Sample can be thermal regulated using infrared heater and infrared thermometer
  • Software only regulate temperature and changing integration settings, raw data output for further processing
  • Tested using FAM fluorescent dye
  • No comments about performance or accuracy of the fluorometer


Versatile portable fluorometer for time-resolved luminescence analysis [2]

Abstract: A robust, filter-based portable fluorometer was designed, prototyped, and tested for time-resolved luminescence (TRL) analysis. Its flexible optical design allows interchangeable configurations to support three measurement modes: liquid-phase TRL using a sample cuvette, solid-matrix TRL using a sorbent strip, and evanescent-field TRL using a quartz-rod waveguide. A xenon flashlamp is used as the light source and a photomultiplier tube (PMT) as the photodetector. A gating technique was implemented to overcome PMT saturation by the intense xenon lamp flash, therefore higher gains can be set to measure weak luminescence signals. The TRL signal is digitized at a 4μstime resolution and a 12bit amplitude resolution. Individual flashes were monitored by a photodiode and its current was integrated to compensate for source light fluctuation. Using tetracycline as a model analyte, a 0.025ppb limit of detection (LOD) with a typical 2% relative standard deviation, and a 3 orders of magnitude (0.5–300ppb) linear dynamic range (r2=0.9996) were achieved

  • A portable, but not low cost, fluorometer for time resolved luminescence analysis
  • Uses xenon flash lamp with filter as excitation source, and photo multiplier tube with filter as the detection device
  • This device claimed to have better SNR by about 1 order of magnitude than state of the art commercial spectrometer at the time of the writing
  • Intended to detect drugs such as tetracycline
  • Could be used to test different compounds due to the multi wavelength light source


The SLIM Spectrometer [3]

Abstract: A new spectrometer, here denoted the SLIM (simple, low-power, inexpensive, microcontroller-based) spectrometer, was developed that exploits the small size and low cost of solid-state electronic devices. In this device, light-emitting diodes (LED), single-chip integrated circuit photodetectors, embedded microcontrollers, and batteries replace traditional optoelectronic components, computers, and power supplies. This approach results in complete customizable spectrometers that are considerably less expensive and smaller than traditional instrumentation. The performance of the SLIM spectrometer, configured with a flow cell, was evaluated and compared to that of a commercial spectrophotometer. Thionine was the analyte, and the detection limit was ∼0.2 μM with a 1.5-mm-path length flow cell. Nonlinearity due to the broad emission profile of the LED light sources is discussed

  • A portable, low cost colorimeter for remote data logging application
  • Uses "flow cell" ? to allow for unattended sensing
  • Uses multiple LED because the chemical under test can absorb broader wavelength
  • Photo detector with integration and averaging method to detect intensity of light
  • Suffer from non-linearity because of the combination between absorbance profile and LED spectrum
  • Lost to commercial spectrometer in the aspect of wavelength resolution and noise
  • Claimed could easily be changed to fluorometer just by making the detection angle 90 degree to the light source


Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field [4]

Abstract: This report describes the electronics of a portable, low-cost, light-emitting diode (LED)-based photometer dedicated to one-shot optochemical sensors. Optical detection is made through a monolithic photodiode with an on-chip single-supply transimpedance amplifier that reduces some drawbacks such as leakage currents, interferences, and parasitic capacitances. The main instrument characteristics are its high light source stability and thermal correction. The former is obtained by means of the optical feedback from the LEDpolarization circuit, implementing a pseudo-two light beam scheme from a unique light source with a built-in beam splitter. The feedback loop has also been used to adjust the LED power in several ranges. Moreover, the low-thermal coefficient achieved (−90 ppm/°C) is compensated by thermal monitoring and calibration function compensation in the digital processing. The hand-held instrument directly gives the absorbance ratio used as the analytical parameter and the analyte concentration after programming the calibration function in the microcontroller. The application of this photometer for the determination of potassium and nitrate, using one-shot sensors with ionophore-based chemistries is also demonstrated, with a simple analytical methodology that shortens the analysis time, eliminating some calibrating solutions (HCl, NaOH, and buffer). Therefore, this compact instrument is suitable for real-time analyte determination and operation in the field

  • Another portable, low cost, LED based colorimeter to measure disposable, one use test strips
  • What's interesting here is that they used optical feedback to stabilize intensity power from LED. In experiment they measured LED light intensity varies with temperature and time
  • They used digital temperature sensor to compensate global electronic thermal drift. This is in contrast with article "Hand-held thermal-regulating fluorometer" where they regulate the temperature instead of compensating the effect of it
  • The use of integrated photo diode with transimpedance amplifier to reduce some drawbacks such as leakage current, noise pickup, stray capacitance
  • Precise and adjustable bias for LED using low thermal drift voltage reference, DAC, and digital potentiometers


References

  1. A. S. Farmer, D. P. Fries, W. Flannery, and J. Massini, "Hand-held thermal-regulating fluorometer", Review of Scientific Instruments 76(11) pp. 115102 (2005).
  2. G. Chen, "Versatile portable fluorometer for time-resolved luminescence analysis", Review of Scientific Instruments 76(6) pp. 63107 (2005).
  3. K. M. Cantrell and J. D. Ingle, "The SLIM Spectrometer", Anal. Chem. 75(1) pp. 27–35 (2003).
  4. A. J. Palma, J. M. Ortigosa, A. Lapresta-Fernández, M. D. Fernández-Ramos, M. A. Carvajal, and L. F. Capitán-Vallvey, "Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field", Review of Scientific Instruments 79(10) pp. 103105 (2008).
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