Recent reports on using bio-active paper and bio-active thread to determine human blood type have shown a tremendous potential of using these low-cost materials to build bio-sensors for blood diagnosis. In this work we focus on understanding the mechanisms of red blood cell agglutination in the antibody-loaded paper. We semi-quantitatively evaluate the percentage of antibody molecules that are adsorbed on cellulose fibres and can potentially immobilize red blood cells on the fibre surface, and the percentage of the molecules that can desorb from the cellulose fibre surface into the blood sample and cause haemagglutination reaction in the bulk of a blood sample. Our results show that 34 to 42% of antibody molecules in the papers treated with commercial blood grouping antibodies can desorb from the fibre surface. When specific antibody molecules are released into the blood sample via desorption, haemagglutination reaction occurs in the blood sample. The reaction bridges the red cells in the blood sample bulk to the layer of red cells immobilized on the fibre surface by the adsorbed antibody molecules. The desorbed antibody also causes agglutinated lumps of red blood cells to form. These lumps cannot pass through the pores of the filter paper. The immobilization and filtration of agglutinated red cells give reproducible identification of positive haemagglutination reaction. Results from this study provide information for designing new bio-active paper-based devices for human blood typing with improved sensitivity and specificity.
This work presents a simple hydrothermal synthesis of nitrogen-doped carbon dots (N-CDs), fabrication of microfluidic paper-based analytical device (μPAD), and their joint application for colorimetric determination of total cholesterol (TC) in human blood. The N-CDs were characterized by various techniques including transmission electron microscopy (TEM), Xray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD), and the optical and electronic properties of computational models were studied using the time-dependent density functional theory (TD-DFT). The characterization results confirmed the successful doping of nitrogen on the surface of carbon dots. The N-CDs exhibited high affinity toward 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)-diammonium salt (ABTS) with the Michaelis−Menten constant (K M ) of 0.018 mM in a test for their peroxidase-like activity. Particularly, since hydrogen peroxide (H 2 O 2 ) is the oxidative product of cholesterol in the presence of cholesterol oxidase, a sensitive and selective method of cholesterol detection was developed. Overall, the obtained results from TD-DFT confirm the strong adsorption of H 2 O 2 on the graphitic N positions of the N-CDs. The laminated three-dimensional (3D)-μPAD featuring a 6 mm circular detection zone was fabricated using a simple wax screen printing technique. Classification of TC according to the clinically relevant criteria (healthy, <5.2 mM; borderline, 5.2−6.2 mM; and high risk, >6.2 mM) could be determined by the naked eye within 10 min by simple comparison using a color chart. Overall, the proposed colorimetric device serves as a low-cost, rapid, simple, sensitive, and selective alternative for TC detection in whole blood samples that is friendly to unskilled end users.
The stated purpose of this article is to provide teachers an inexpensive model for laboratory activity and demonstration of galvanic cells using a paper-based device. Metal strips, metal solutions, and KNO 3 solution serve as electrodes, metal ions, and electrolyte, respectively. A paper-based device is not only a support for reactions, but also a salt bridge for electrolyte. This activity ought to be interesting to all levels of chemistry from middle school classes through potential applications in upper division college classes. Furthermore, teachers may design and fabricate a paper-based device for their classes in chemistry and also related fields.
The present work describes a simple hands-on experiment kit for colorimetric quantification of ferric (III) ion (Fe 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 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 3+ at low concentrations with the detection limit of 0.03 mg L −1 and provided the linear range (0.05−2.0 mg L −1 ) with good linearity (R 2 = 0.9985) with Fe 3+ concentration. The concentrations of Fe 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 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.
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.
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