Current trends in digital camera-based bioassays for point-of-care tests

Point-of-care and bedside tests are analytical devices suitable for a growing role in the current healthcare system and provide the opportunity to achieve an exact diagnosis by an untrained person and in various conditions and sites where it is necessary. Using a digital camera integrated into a well-accessible device like a smartphone brings a new way in which a colorimetric point-of-care diagnostic test can provide unbiased data. This review summarizes basic facts about the colorimetric point-of-care tests, principles of how to use a portable device with a camera in the assay, applications of digital cameras for the current tests, and new devices described in the recent papers. An overview of the recent literature and a discussion of recent developments and future trends are provided.

Teaching old presumptive tests new digital tricks with computer vision for forensic applications

Presumptive (or 'spot') tests have served forensic scientists, law enforcement, and legal practitioners for over a hundred years. Yet, the intended design of such tests, enabling quick identification of drugs by-eye, also hides their full potential. Here, we report the development and application of time-resolved imaging methods of reactions attending spot tests for amphetamines, barbiturates, and benzodiazepines. Analysis of the reaction videos helps distinguish drugs within the same structural class that, by-eye, are judged to give the same qualitative spot test result. It is envisaged that application of these results will bridge the existing suite of field and lab-based confirmatory forensic tests, and support a broader range of colorimetric sensing technologies.

Sulfonamide drugs: Low-cost spectrofluorometric determination using a computer monitor calibrator for detection

A possibility of the use of a common monitor calibrator as a portable and inexpensive tool for the fluorometric determination of sulfonamide drugs after their reaction with fluorescamine was examined. The luminescence measurements with a calibrator are based on irradiation of a test sample by the device lamp with a broadband spectrum in the visible and near UV regions and simultaneous registration of the secondary radiation by the device detector. Two types of cuvettes with black light absorbing sides eliminating the reflected self-radiation were tested. The commercially available Eppendorf-type black plastic microtubes ("LightSafe") were suggested as a good option for such measurements. It was shown that a monitor calibrator can be applied for optimization of the determination conditions. By the example of sulfanilamide and sulfamethazine, it was shown that the procedure should be carried out at pH 4-6 and fluorescamine concentration of 200 μmol L^-1, and 40 min of the interaction. The limit of detection of sulfanilamide and sulfamethazine using a monitor calibrator is 0.9 μmol L^-1 and 0.8 μmol L^-1, respectively, which is comparable with their spectrophotometric determination.

3D-printed device for the kinetic determination of As(III) in groundwater samples by digital movie analysis

High concentrations of inorganic arsenic in groundwater for human consumption is a worldwide common problem. Particularly, the determination of As(III) becomes important, since this species is more toxic than organic, pentavalent and elemental arsenic forms. In this work, a 3D-printed device that included a 24-well microplate was developed to perform the colourimetric kinetic determination of arsenic (III) by digital movie analysis. A smartphone camera attached to the device was used to take the movie during the process where As(III) inhibited the decolourization of methyl orange. The movie images were subsequently transformed from RGB to YIQ space to obtain a new analytical parameter called "d", which was related to the chrominance of the image. Then, this parameter allowed the determination of the inhibition time of reaction (t_in), which was linearly correlated with the concentration of As(III). A linear calibration curve (R = 0.9995) in the range from 5 μg L^-1 to 200 μg L^-1 was obtained. The method was precise (RSD = 1.2%), and the limits of detection (LOD) and quantification (LOQ) were 1.47 μg L^-1 and 4.44 μg L^-1, respectively. These values were lower than the limit established by the World Health Organization for total arsenic in drinking water (10 μg L^-1). The accuracy of the method was assessed by a recovery study with optimal results (94.3%-104.0%). Additionally, the Analytical GREEnness metric approach was applied, obtaining a score 1.7 times higher than previously published works. The method is simple, portable and low-cost, being in compliance with various principles of green analytical chemistry.

A highly sensitive colorimetric assessment of hexavalent chromium using a digital camera

Simple, low-cost, and sensitive methods for the assessment of hexavalent chromium as an important environmental pollutant are highly desirable, especially under resource-limited settings. Therefore, herein we propose an original approach for the simple, low-cost, selective, and extremely sensitive assessment of Cr(VI) utilizing its catalysis of the micellar sensitized o-dianisidine (DA)-hydrogen peroxide reaction. The initial rate of the amended reaction is monitored by tracing the oxidation product, either by a digital camera video recording or spectrophotometrically at 440 nm, for 120 s from mixing the reactants. The optimized reaction conditions were 5 mmol L^-1 DA, 0.6 mol L^-1 H₂O₂, 2.0 v/v% Tween 20, and 10 mmol L^-1 chloroacetate buffer (pH 4.5 ± 0.1), at 30 °C. The linear calibration graph extends to 90.0 ng mL^-1 Cr(VI) with detection limits (3S_b) of 0.8 and 1.0 ng mL^-1, for the video recording and spectrophotometric procedures, respectively. The amended method was successfully applied to the assessment of Cr(IV) in natural and polluted industrial wastewaters. The analytical data were in excellent statistical harmony with those of the standard ETAAS method. The proposed method is two orders of magnitude more sensitive than the diphenylcarbazide standard spectrophotometric method.Graphical abstract.

A simple and rapid technique for the determination of copper based on air-assisted liquid-liquid microextraction and image colorimetric analysis

In this study, a new, cheap, simple and rapid method for the determination of copper in water and food samples using air-assisted liquid-liquid microextraction and digital image decomposition into the primary colors Red (R), Green (G) and Blue (B) is introduced. In the proposed method, sodium diethyl-dithiocarbamate (Na-DDTC) and carbon tetrachloride (CCl4) were used as the chelating agent and extraction solvent, respectively. The digital images of the extraction phase were obtained using an Android mobile phone and analyzed using a free app (Color Grab). Then the value of the B channel was taken as the analytical signal. The effects of different parameters influencing the extraction efficiency were investigated and optimized. Under the optimal conditions, the limit of detection (LOD) and quantitation (LOQ) were 1.5 and 5 μg L-1, respectively. The repeatability of the proposed method, expressed as the relative standard deviation (RSD), was 4.53% for intra-day (n = 8, C = 100 μg L-1) and 5.66% for inter-day (n = 5) precision. The proposed method was applied for the determination of trace amounts of copper in rice, lettuce and water samples with satisfactory results validated by the Graphite Furnace Atomic Absorption Spectrometry technique.

A New Portable Colorimetric Sensor Based on RGB Chromaticity for Quantitative Determination of Sarin in Water

Background:

Sarin is a nerve agent which is lethal to people due to its high toxicity. According to its extreme toxicity, sarin, relatively lack of color, highly toxic, miscible in water, poses viable threats to potable water sources. Therefore, there is an urgent need for portable, rapid and yet reliable methods to monitor for adulteration of potable water sources by sarin on spot.

Methods:

A stock solution of 30 mg/L sarin was prepared daily by dissolving 300 μg of sarin in 10 mL isopropanol. A certain amount of sarin was added to the glass tube, and then o-dianisidine and hydrogen peroxide were added. The pH value of the solution was adjusted to 9.8. The solution was transferred to the test tube after 10 minutes. A test tube of 2 mL was placed between the light source and the RGB color sensor. The LED light source illuminates directly over the test tube while the RGB sensor obtained the generated spectral response. This RGB voltage output is connected to the ADC and microcontroller to convert these analog voltages to three digital data. This RGB digital data is linked to the microcomputer through the serial port that is interfaced with the user interface. The data thus obtained in the sensor can be processed to display the sarin concentration.

Results:

Under the optimum conditions as described above, the calibration curve of chromaticity value versus sarin concentration was linear in the range of 0.15 mg/L to 7.8 mg/L. According to the IUPAC definition, theoretical detection limits of this method were 0.147 mg/L and 0.140 mg/L for R and B values, respectively. The practical detection limit was 0.15 mg/L. The sensor was successfully applied to the determination of sarin in artificial water samples and the recoveries were between 86.0% to 95.9%.

Conclusion:

The results in the present work have demonstrated the feasibility to design a new portable colorimetric sensor based on the RGB chromaticity method for quantitative determination of sarin in water. The influences of chromogenic reagent, oxidant, reaction time, o-dianisidine concentration, hydrogen peroxide concentration, reaction temperature, pH on the chromaticity values were investigated. The results showed that the sensor possessed high selectivity, sensitivity and good repeatability. The method would be potentially applied to the analysis of other toxic compounds in environment, such as other chemical warfare agents.

The Yxy colour space parameters as novel signalling tools for digital imaging sensors in the analytical laboratory

Digital imaging devices can be promising, sensitive, and cost-effective chemical sensors for resource-limited settings and locally deprived communities.