An inexpensive flow injection analysis system for determining low concentration levels of nitrite employing the Griess reagent spectrophotometric method is reported. The novel photometric detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based flow detector. This colorimetric detector employs two LEDs, operating one as a light source and the other as a light detector. The emitter LED is forward biased and the detector reverse biased. The emitter and detector LED had a λmax of 530 nm and 623 nm respectively. The emission spectrum of the emitter LED efficiently overlapped with the absorbance spectrum of 9 µM NO2 and Griess reagent complex. A simple timer circuit measures the time taken for the photocurrent generated by the emitter LED to discharge the detector LED from 5 V (logic 1) to 1.7 V (logic 0).
The Griess reagent method employed for nitrite determination is based on the formation of an azo dye, the intensity of which is directly related to nitrite concentration. The linear range, reproducibility and limit of detection were investigated. Detection limits in the nanomolar range were achieved using the Paired Emitter-Detector Diode (PEDD) flow analysis device. For a comparative study the linear range and limit of detection were also investigated using a platewell reader. Higher sensitivity and improved precision were obtained from the PEDD compared to the commercially available plate well reader.
In the last three years, a number of Irish primary schools have been using LEGO Mindstorms technology in order to investigate the use of project-based learning as an alternative teaching tool. This has involved the use of LEGO bricks combined with standard electronic motors and some commercial sensors (e.g. temperature). In order to develop this project into the area of science education, we have developed a range of miniaturized optical sensors, which are compatible with the LEGO platform. This paper describes two such sensors that have been developed and fabricated for use with the LEGO platform, a collaboration between the MIT Media Lab and the National Centre for Sensor Research. In particular a working oxygen sensor has been designed and fabricated. The principal design features were compatibility with the programmable LEGO platforms and robustness for classroom use. This sensor uses the method of intensity quenching to determine oxygen concentration. In addition, simple color sensors have been produced. The aim of developing such sensors is to familiarize students with the concept of colour detection and to introduce them to the basic principles of spectroscopy. The performance of both sensor types and preliminary classroom results are reported.