The steady advances in technology employed in smartphones, coupled with the high availability and the ease access to these devices, increased the interest in applying it to analytical purposes. The main goal is to develop simple, fast, and low‐cost analytical methods, generating immediate results. Different analytical strategies using smartphones have been proposed to identify or determine different analytes in a wide range of matrices. Some of them use the smartphone to capture the images, to process them, and to provide the analytical results. Others use this device just for image acquisition. In this context, this review aimed to relate previous works that used smartphones to acquire images for analytical purposes, with a special focus on PhotoMetrix application, which is a tool for chemical analysis. This application allows the decomposition of digital images acquired by smartphone cameras and to process them within the same device, allowing in situ chemical analysis.

PhotoMetrix and colorimetric image analysis using smartphones

Simultaneous identification of the wood types in aged cachaças and their adulterations with wood extracts using digital images and SPA-LDA.

Microfluidic paper-based device integrated with smartphone for point-of-use colorimetric monitoring of water quality index

A greener, fast, and cost-effective smartphone-based digital image procedure for quantification of ethanol in distilled beverages

An environment-friendly spot test method with digital imaging for the micro-titration of citric fruits

A simple, accurate, and low-cost analytical procedure for methanol determination in sugarcane spirits (cachaca) employing analysis of digital images is presented. A portable system with cheap materials and lighting system to obtain images from a smartphone was built and an RGB system was used for analytical purposes. The reaction for determination of methanol in beverages consists in methanol oxidation to methanal, and consequent formation of a violet chromophore in the presence of chromotropic acid on heating in an oven at 80 °C for 15 min. From the system optimization, analytical curves that showed good linearity for the green channel (from RGB) was built, with regression coefficient (R
 2) of 0.998. Relevant matrix effect in the samples was not verified, since the recovery percentage ranged from 83 to 110%. The results of methanol concentration in six cachaca samples obtained by the developed method were compared with using the spectrophotometric method with a confidence level of 95% (n = 3). The developed method has some economic and environmental benefits, since it has low reagent consumption with 800 μL per measured spot, as well as, it presents cheap and handle-easy devices, which encourages the quality control of this toxic and undesirable contaminant for smallholders and industries on production of sugar cane spirits.

Smartphone Application for Methanol Determination in Sugar Cane Spirits Employing Digital Image-Based Method

In this work, a simple, low-cost and easy-to-handle analytical procedure based on carbon quantum dots (CQDs) is proposed to check commercially available formulated microbicides that are used to mitigate the transmission of viruses, such as SARS-COV-2, or bacterial diseases. For this purpose, CQDs were synthesized via pyrolysis using citric acid and ethylenediamine as precursors to produce an intense fluorescence that is used to measure the concentration of hypochlorite, an important biocidal agent present in sanitizing mats, by quenching mechanisms. The characterization of the CQDs was performed using IR spectrophotometry, UV-Vis spectrophotometry, spectrofluorometry, thermogravimetric analysis, scanning electron microscopy, dynamic light scattering, X-ray diffraction, energy-dispersive spectroscopy, and zeta potential measurements. For analytical purposes, fluorescence was measured in a UV chamber irradiated using an LED with the maximum emission at 350 nm. A smartphone was coupled to the UV chamber to measure the fluorescence quenching due to the presence of hypochlorite, and further the digital images were decomposed by RGB data using free software. Tests of pH, CQD concentration and stability of the fluorescence emitted were performed. The stability study of the fluorescence emitted by the CQD solution showed a relative standard deviation lower than 5.0%. The fluorescence digital image-based (FDIB) method resulted in a linear range from 17.44 μmol L-1 to 90.0 μmol L-1 with an LOD of 3.30 μmol L-1 for the determination of hypochlorite using a microplate made of PLA (polylactic acid) customized using a 3D printer. Furthermore, the hypochlorite concentration was tested in situ for its compliance in a sanitizing mat, in a real use situation (daily, a group of four people, each one kept their feet on the mat for 30 s). After 2.5 h, the monitored concentration of hypochlorite was 0.04953% (w/v) or 7.63 mmol L-1, and therefore, it was inefficient to act as a sanitizing agent. Thus, for the first time in the literature, an FDIB method with CQDs is used to verify in situ microbicide practices with a fast and low-cost analytical procedure.

Matheus Valentin Maia

Papers

Smartphone Application for Methanol Determination in Sugar Cane Spirits Employing Digital Image-Based Method

A fluorescence digital image-based method using carbon quantum dots to evaluate the compliance of a biocidal agent.