Color-Multiplexing-Based Fluorescent Test Paper: Dosage-Sensitive Visualization of Arsenic(III) with Discernable Scale as Low as 5 ppb

Abstract

Fluorescent colorimetry test papers are promising for the assays of environments, medicines, and foods by the observation of the naked eye on the variations of fluorescence brightness and color. Unlike dye-absorption-based pH test paper, however, the fluorescent test papers with wide color-emissive variations with target dosages for accurate quantification remain unsuccessful even if the multicolorful fluorescent probes are used. Here, we report the dosage-sensitive fluorescent colorimetry test paper with a very wide/consecutive "from red to cyan" response to the presence and amount of arsenic ions, As(III). Red quantum dots (QDs) were modified with glutathione and dithiothreitol to obtain the supersensitivity to As(III) by the quenching of red fluorescence through the formation of dispersive QDs aggregates. A small amount of cyan carbon dots (CDs) with spectral blue-green components as the photostable internal standard were mixed into the QDs solution to produce a composited red fluorescence. Upon the addition of As(III) into the sensory solution, the fluorescence color could gradually be reversed from red to cyan with a detection limit of 1.7 ppb As(III). When the sensory solution was printed onto a piece of filter paper, surprisingly a serial of color evolution from peach to pink to orange to khaki to yellowish to yellow-green to final cyan with the addition of As(III) was displayed and clearly discerned the dosage scale as low as 5 ppb. The methodology reported here opens a novel pathway toward the real applications of fluorescent test papers.

Fluorescent Nanomaterials for Color‐Multiplexing Test Papers toward Qualitative/Quantitative Assays

“…C) Unequal mixing of dual‐colored nanoprobes, followed by quenching of one probe by an analyte, resulting in a wide range of color variation from red to cyan. A–C) Reproduced with permission . Copyright 2016, American Chemical Society.…”

“…In this process, one of the probes, as an internal standard, retains very stable fluorescence, while the other probe selectively reacts with an analyte to cause fluorescence quenching. Scheme B illustrates the three typical scenarios in mixing two different colored probes from three primary colors (red, green, and blue) . i) A mixture of red and blue probes with equal fluorescence intensity leads to a composite intermediate purple, and thus the theoretical range of color variations is either “from purple to red” or “from purple to blue,” rather than a wider range from “from red to blue” or “from blue to red.” ii) Alternatively, a mixture of red and green probes leads to a composite intermediate yellow, and the maximal range of color variations is either “from yellow to red” or “from yellow to green.” iii) Similarly, a mixture of green and blue leads to a composite intermediate cyan, and the maximal range of color variations is only “from cyan to green” or “from cyan to blue.” From these analyses, the formation of a composite intermediate color greatly compresses the space of color variations, and thus their quantification capability in colorimetric assays is limited in a smaller range.…”

Nanomaterial-functionalized Cellulose: Design, Characterization and Analytical Applications

“…84 In addition to sensors based on optical detection, there are a number of devices with fluorescence detection in which either the nanomaterial used produces a fluorescent signal or nanomaterials are used in junction with a fluorescent compound. Fluorescent signals can be visualized with a UV lamp by the naked eye 85 which provides convenience for site analysis. A commonly used fluorescent agent is rhodamine B 70 which can be used by itself or alongside AuNPs.…”

“…91 Both of these materials provide a measurable response directly from the intrinsic fluorescent properties of the material without the need of an exterior fluorescent agent. Quantum/carbon dot hybrids 85 or two color carbon dot hybrids 92 can also be combined or covalently attached to achieve a more sensitive fluorescent response. By quenching one dot with the target analyte, a broad range of fluorescent response is produced with increasing analyte concentration (Fig.…”

“…The cyan CDs used in the system remain unchanged however, contribute to the background fluorescent response which allows for a wider range of detection, down to 5 ppb. 85 Choudhary et al have demonstrated fluorescent detection of Pb(II) utilizing cube-shaped nitrogen-doped CD. The yellow emission of the CDs changed to red with the addition of Pb(II) ions.…”