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The present work describes a simple hands-on experiment kit for colorimetric quantification of ferric (III) ion (Fe[superscript 3+]) in an aqueous medium using anthocyanin extracted from "Ruellia tuberosa" L. as a green indicator. The extraction of a high amount of anthocyanin was easily accomplished by using only hot water instead of an organic solvent. The formation of the colored Fe[superscript 3+]-anthocyanin complex occurred on a homemade 24-well plate and the generated color was captured by a smartphone. The increase in color intensity was measured in the red, green, blue (RGB) system by the ImageJ software under the optimum conditions. The developed method enabled quantification of Fe[superscript 3+] at low concentrations with the detection limit of 0.03 mg L[superscript -1] and provided the linear range (0.05-2.0 mg L[superscript -1]) with good linearity (R[superscript 2] = 0.9985) with Fe[superscript 3+] concentration. The concentrations of Fe[superscript 3+] in water samples determined by the developed method were not significantly different from those measured with UV-visible spectrophotometry at a 95% confidence level. In addition, the extracted anthocyanin stored at 4 °C was stable for two months. This hands-on experiment was implemented as a 2 h activity for 30 grade-12 students in which they were asked to determine the concentration of Fe[superscript 3+] in a water sample using the smartphone-assisted colorimetric method. The students' understanding of the related concepts of oxidation-reduction and determination of iron was collected by a diagnostic conceptual test. Having participated in the experiment, the students were found to have significantly improved understanding of both concepts.

Low-density lipoprotein cholesterol (LDL-C), commonly called "bad cholesterol", is crucial to cardiovascular health. Increased LDL-C levels pose a substantial risk to human health. As a result, there is a demand for reliable, affordable, and highly sensitive analytical methods for LDL-C detection. Herein, a facile fluorometric aptasensor for LDL-C detection based on the aptamer-enhanced peroxidase-mimicking activity of gold nanoparticles (AuNPs) has been developed. AuNPs were functionalized with LDL-C-specific thiolated aptamer to enhance their intrinsic peroxidase-like activity, which could effectively catalyze the oxidation of o-phenylenediamine dihydrochloride (OPD) by H2O2 into the yellow-fluorescent product 2,3-diamino phenazine (DAP). The characterization studies confirmed that the presence of the aptamer enhances the affinity of AuNPs toward the OPD substrate, thereby leading to a marked increase in the peroxidase-mimicking activity. Moreover, after being functionalized with an aptamer, increased dispersibility and substrate affinity of AuNPs were achieved. Using LDL-C as a target analyte, under optimum conditions, a linear relationship between smartphone-recorded signal intensity and the logarithm of the analyte concentration was observed in the range of 0.05–1 mg dL–1 and the limit of detection was 0.0230 mg dL–1. The results agree with those obtained by a clinical laboratory method. This proposed method is readily deployable and a promising prototype for diverse diagnostic applications, particularly in biomarker detection within serum or plasma samples. It holds the potential to yield substantial advantages in point-of-care testing. [ABSTRACT FROM AUTHOR]

This work reports the first use of rubber latex waste as the hydrophobic reagent for a low-cost, simple, and rapid fabrication of a paper towel-based experimental device (PTED) with a circular design of 5 mm to demonstrate the factors affecting chemical equilibrium; this serves as a user-friendly means for a laboratory experiment. The illustration of the factors affecting chemical equilibrium is implemented in the PTED. In this approach, the color change of a cobalt(II) complex reaction from pink to blue was observed by the naked eye on the PTED when a tiny drop of hydrochloric acid solution and the treatment of heat by using a hot air dryer (1200 W, 2 min) were applied to the PTED with the precoated cobalt solution (pink color), separately or together. The return of the color of the reactions from blue to pink was carried out by using a tiny drop of water and the treatment of cooling by using an ice bath for 10 min. In addition, the chemical equilibrium constant ("K"[subscript c]) can be easily quantified by processing digital images of the detection zones of PTED captured with a smartphone camera under a control light box at room temperature (˜25 °C), while image analysis was performed using ImageJ software. This PTED laboratory is a new approach not only to enhance students' learning of the factors affecting chemical equilibrium based on Le Châtelier's principle, but also to present potential applications of PTED into all levels of chemistry from middle school through college classes.

In this article, a low-cost, simple, and rapid fabrication of paper-based analytical devices (PADs) using a wax screen-printing method is reported here. The acid-base reaction is implemented in the simple PADs to demonstrate to students the chemistry concept of a limiting reagent. When a fixed concentration of base reacts with a gradually increasing concentration of acid, a dramatic demonstration allows students to discover the limiting reagent by naked eyes observing the color change from phenolphthalein as an indicator. This demonstration is not only a new approach to enhancing students' learning of the chemistry concept of the limiting reagent, but also presents potential applications of PADs into all levels of chemistry from middle school through college classes.