The determination of pH values is essential in many chemical, medical, and environmental monitoring processes, which has been relying on conventional pH meters (glass electrodes) for quantitation and pH test strips for qualitative (or semi-quantitative) assessment. In this work, we demonstrate a smartphone-based pH determination technique, which performs digital image analysis of commercial test strips, particularly the determination of either the dominant wavelength (λd) or complementary wavelength (λc) of the color image. In conjunction with a 3D-printed optical accessory (with a surface light source and a macro lens), the quality of captured images have been warranted, and the quantitation accuracy of 0.05 pH units has been achieved. More importantly, the performance of this smartphone-based pH reading system (namely “Smart-pH-Reader”) was validated using multiple real-world samples, as the results are consistent with those determined with a standard pH meter. The Smart-pH-Reader is envisioned to be a simple, portable, and accurate tool for pH determination in the fields of environmental monitoring, medical diagnosis, and beyond.
Recently, fluorescent pH test paper has been extensively explored for visual assays due to its easy preparation, low-cost, and portable feature. In addition, intracellular pH also plays important roles in different pathological and physiological processes for understanding cellular functions and providing critical assistance for early disease diagnosis. Herein, the tricolor emission [email protected] carbon dots (CDs) were synthesized via one-pot hydrothermal method using 5-amino-1,10-phenanthroline (Aphen) and citric acid (CA) as the carbon sources. The fluorescence emission of CDs showed an interesting pH dependence due to the special structure and properties, which can make the CDs to be used as the pH test paper to qualitatively and quantitatively detect pH value in a wide pH range. At the same time, because of good cell compatibility and low toxicity, CDs can be used as a new type of cell imaging marker to detect intracellular pH. The unique tricolor emission property of CDs can well avoid the fluorescent dyes and protein fluorescence interference.
Even a small amount of harmful liquid/gas leakage is hazardous and probably leads to extraordinarily dangerous situations. To effectively control the storage of harmful liquids/gases, the monitoring of leakage is thus highly important. Herein, we develop an indicator film that can easily respond to harmful hydrophilic liquids and gases and allow for the visual recognition of a transparency transformation involving hydrated poly(N-isopropylacrylamide). The normalized transparency of the indicator film is 100% when it is wet and below 10% when it is triggered by hydrophilic liquids and gases. The pH paper-like indicator film responds to some harmful hydrophilic liquids and gases in the chemical laboratory, including alcohols, ketones, aldehydes, acid solutions, their corresponding vapors, and some gases. The response to hydrophilic liquids and gases by the indicator film is attributed to competition between hydrophilic molecules and poly(N-isopropylacrylamide) in absorbing water. This work not only provides an understanding of the adsorption and diffusion of gases and liquids on surfaces but also affords promising applications for monitoring chemical industry and chemical laboratory environments, general pollution levels, and indoor air quality.
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