Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Development of a low-cost colorimeter and its application for determination of environmental pollutants
Graphical abstract
Introduction
Today, the demand for miniature sensors and analyzers is increasing. The advancement in LED sources and photodetector technologies provide an effective solution to analytical instrument miniaturization, low power consumption and low cost [1]. With the ability to detect light quite well, the LED can be used as an inexpensive optical detector for the wide range of applications. Typically, the LED can detect the light at a wavelength shorter than the wavelength it emits, therefore, it can act as a good wavelength selectivity detector [2]. If a LED emits greenish-yellow light at the wavelength of about 555 nm (nm), it detects green light at the wavelength of about 525 nm and over the spectral width of 50 nm [2]. It seems that every LED is capable of detecting a relatively narrow band of wavelengths, with different sensitivity. LEDs have the ability to be coupled to a wide variety of detectors such as phototransistors [3], photomultiplier tubes [4], [5], photodiode-arrays [6], [7], photodiodes [8], [9], light dependent resistors [10]. By far, the most common detector used in LED-based chemical sensors is the photodiode [11]. LED-based sensors do not require optical couplers or monochromators since LEDs emit relatively narrow band of wavelength [1].
LEDs offer a number of advantages compared to existing light sources, including increased lifetime, low cost, low power consumption, higher brightness, enhanced spectral purity and breadth of spectral range from 247 to 1550 nm [11], [12]. Therefore, the use of light emitting diodes (LEDs) as light sources has been successfully applied in chemical sensors and sensing devices to measure transmittance and absorbance in combination with colorimetric analytical methods [11].
Colorimetric techniques have been extensively applied for the detection of chemical and biochemical analytes in food control as well as in environmental, biomedical, and educational domains [13], [14], [15], [16], [17]. Colorimeters are generally used to determine the relative amount of an analyte by measuring the light that is partially absorbed. Typically, colorimeters are equipped with a tungsten lamp light source [18], [19], [20], however, several previous studies have demonstrated that LEDs can be successfully used as a light source instead of a complex optical system [21], [22], [23]. Recently, custom colorimetric systems also have been developed, facilitated by the simplicity of colorimetric techniques, and these systems adhere spectroscopic principles, cost reduction of electronic parts, and amenability to low-cost manufacturing techniques, such as 3D printing. These systems exhibit desirable characteristics including portability, low power consumption, ease of use, data transmission potential, and inexpensive material components.
Herein, an inexpensive method of performing spectrophotometric absorption experiments was developed. The hardware was locally developed based on the general construction principles of colorimeters. A colorimeter with adjustable RGB LED lighting and a photodiode detector was successfully configured to detect environmental contaminants. Comparative studies on the developed colorimeter and conventional devices were also performed.
Section snippets
Chemicals, reagents, and samples
The nitrate, nitrite, ferrous and manganese standard solution were purchased from Merck, Germany. The reagent powder (NitraVer 3 Nitrite, NitraVer 5 Nitrate, Ferrous Iron and Sodium Periodate) and Citrate Buffer powder were purchased from Hach, USA. Tetracyline, Tris buffer, HCl and Eu2O3 were purchased from Sigma-Aldrich.
Electronic components
The RGB LED light WS2812 (CJMCU-2812-61) was supplied from Deng Xia, China. The Arduino Uno R3 and LCD ST7920 - A3H12 were purchased from Sparkfun Electronics (Niwot, CO,
Results and discussion
Because pollutant detection was achieved via the development of coloured products, absorbance at 400–700 nm was expected. To achieve these conditions, RGB LED light with a wavelength adjustable from 380 to 730 nm was selected as the excitation source and tested with model pollutants. Detection was performed using the photodiode BPW21R, the measured output signal was proportional to the intensity of light transmitted through the sample, which is related to the pollutant concentration. The module
Conclusion
A compact and cost-effective colorimeter configuration was developed using RGB LED as a light source and photodiode detector for determining environmental pollutants. The efficiency and reliability of the colorimeter was evaluated by comparison with a commercially available colorimeter. A good correlation was demonstrated by linear regression analysis, indicating that the newly developed colorimeter is a promising replacement for conventional colorimeters for screening and monitoring
CRediT authorship contribution statement
Le Quoc Hoang: Conceptualization, Methodology, Writing - review & editing, Software, Validation. Huynh Bui Linh Chi: Writing - original draft. Dang Nguyen Nha Khanh: Writing - original draft. Ngo Thi Tuong Vy: Writing - original draft. Phan Xuan Hanh: Software, Validation. Truong Nguyen Vu: Software, Validation. Hoang Thuc Lam: Software, Validation. Nguyen Thi Kim Phuong: Conceptualization, Methodology, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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