Multi-ion detection by one-shot optical sensors using a colour digital photographic camera

Abstract

The feasibility and performance of a procedure to evaluate previously developed one-shot optical sensors as single and selective analyte sensors for potassium, magnesium and hardness are presented. The procedure uses a conventional colour digital photographic camera as the detection system for simultaneous multianalyte detection. A 6.0 megapixel camera was used, and the procedure describes how it is possible to quantify potassium, magnesium and hardness simultaneously from the images captured, using multianalyte one-shot sensors based on ionophore-chromoionophore chemistry, employing the colour information computed from a defined region of interest on the sensing membrane. One of the colour channels in the red, green, blue (RGB) colour space is used to build the analytical parameter, the effective degree of protonation (1-α(eff)), in good agreement with the theoretical model. The linearization of the sigmoidal response function increases the limit of detection (LOD) and analytical range in all cases studied. The increases were from 5.4 × 10(-6) to 2.7 × 10(-7) M for potassium, from 1.4 × 10(-4) to 2.0 × 10(-6) M for magnesium and from 1.7 to 2.0 × 10(-2) mg L(-1) of CaCO(3) for hardness. The method's precision was determined in terms of the relative standard deviation (RSD%) which was from 2.4 to 7.6 for potassium, from 6.8 to 7.8 for magnesium and from 4.3 to 7.8 for hardness. The procedure was applied to the simultaneous determination of potassium, magnesium and hardness using multianalyte one-shot sensors in different types of waters and beverages in order to cover the entire application range, statistically validating the results against atomic absorption spectrometry as the reference procedure. Accordingly, this paper is an attempt to demonstrate the possibility of using a conventional digital camera as an analytical device to measure this type of one-shot sensor based on ionophore-chromoionophore chemistry instead of using conventional lab instrumentation.

Spectrophotometric and Digital Colour Colourimetric (DCC) analysis of colour-based indicators

“…The absorption spectrum of a simple simulated dye, with an absorbance, A o , at  max is described by eqn (4). This equation allows the creation of seven absorption spectra, with A o = 1, that span the visible spectrum.…”

“…Wang et al have used a mobile phone's digital camera to probe the colour change associated with a .microchip enzyme-linked immunosorbent assay, ELISA, when exposed to different levels of the ovarian HE4 biomarker in urine [3]. Capitan-Vallvey et al have used colour digital photography for one-shot, multi-ion (potassium, magnesium and hardness) detection [4] and Ozcan et al have used mobile phone microscopy for high resolution pathology imaging [5]. And finally and most recently, photography has been used monitor an epidermal UV colorimetric dosimeter and is now the basis of L'Oreal's 'My Patch' UV dosimeter, which involves monitoring UV dose with a mobile phone digital camera coupled to an App [6].…”

Classification and quantitative optical analysis of liquid and solid samples using a mobile phone as illumination source and detector

“…The strategy employed in this approach was to relate the desired analytical parameter to one of the red, green or blue (RGB) color channels (or in some cases employment of a greyscale 2 conversion) in order to obtain quantitative information. Reagent mediated analyses have been extensively studied in which digital images describing color development of one-shot sensing spots were evaluated [4,6,8,10]. There has also been work done using digital images of solutions based on their spectral properties [11][12][13][14][15][16].…”

“…While inexpensive electronic components in consumer products do not approach the quality necessary for use in commercial analytical instrumentation, they have demonstrated usability for optical measurements despite their limitations [2,3]. Reports of the use of digital cameras for chemical analyses, for example, have recently covered such diverse areas as detection of biogenic amines [4], pH [5], water hardness [6,7], nickel in meteorites [8] and alloy composition [9].…”

A Portable Microcontrolled Pumping Flow System Developed to In Loco Determination of Diuron at Nanomolar Levels Employing a Disposable Biosensor

“…In this context, improvements and upgrades in technologies for hardware, such as microcontroller and microprocessors, have revolutionized the analytical instrumentation [1,2]. Microcontroller is a modern device that presents an inner microprocessor and other peripherals as a clock, memory, lines of command for in/out data, registers, readers and analog-to-digital converter (A/D) [3].…”