Ratiometric Fluorescent Paper Research Articles

A smartphone-integrated portable platform based on polychromatic ratiometric fluorescent paper sensors for visual quantitative determination of norfloxacin

The emergence of “superbugs” due to antibiotics overuse poses a significant threat to human health and security. The development of sensitive and effective antibiotics detection is undoubtedly a prerequisite for addressing antibiotics overuse-associated issues. However, current techniques for monitoring antibiotics typically require costly equipment and well-trained professionals. Hence, we developed herein a rapid, instrument-free, and on-site detection method for antibiotic residues such as norfloxacin (NOR) based on a ratiometric sensing platform utilizing “on–off–on” response properties of polychromatic fluorescence for direct visual quantitative NOR analysis. Specifically, this platform integrated iron ions (Fe3+)-chelated blue carbon dots (BCDs) for signal sensing and red carbon dots (RCDs) as an internal reference. The sensor mechanism is selective quenching of BCDs' blue fluorescence by Fe3+ via an inner filter effect with unaffected RCDs' red fluorescence. Further NOR addition led to competitive binding with BCDs due to Fe3+ shedding from the BCDs’ surface for a recovered blue fluorescence signal. Notably, the ratiometric fluorescence sensor demonstrated rapid and highly sensitive NOR detection in a concentration range of 1–70 μM with an impressive detection limit of 6.84 nM. The ratiometric fluorescence sensing platform was constructed by integrating smartphone and paper-based strategies, which exhibited exceptional sensitivity, selectivity, and rapid response for portable, instrument-free, visual quantification of NOR in real samples.

A ratiometric fluorescent paper sensor based on dye-embedded MOF for high-sensitive detection of arginine

Ratiometric fluorescent sensors can suppress the interference of factors unrelated to analysis due to their built-in self-calibration characteristics, which exhibit higher sensitivity and more obvious visual detection in the process of qualitative and quantitative analysis. Herein, we constructed a ratiometric fluorescence probe based on fluorescent/colorimetric dual-mode method for the determination of arginine by encapsulating rhodamine B in-situ into UiO-66-NH2 MOFs (UiO-66-NH2@RhB). The as-prepared probe showed dual-emission characteristics under a single excitation wavelength. The fluorescence intensity of UiO-66-NH2 was increased significantly by arginine, while the emission peak intensity of rhodamine B remained stable, resulting in a single-signal response with fixed reference. Furthermore, the practicality of the presented sensor was successfully validated by quantitative detection of arginine in human serum. More significantly, paper-based sensors for arginine detection were devised by using carboxymethyl cellulose modified filter papers. Under the irradiation of ultraviolet light, the paper-based sensors would produce obvious color variation from lightpink to bluish violet. This work provided a convenient and efficient method for on-site detection of arginine.

A colorimetric and ratiometric fluorescent paper chip for biogenic amine monitoring based on a simple pH-sensitive AIEgen

Existing single-signal-response fluorescent materials for biogenic amine detection have unsatisfactory detection performance. Herein, we developed a simple pH-sensitive aggregation-induced emission-active fluorogen (AIEgen) and demonstrated its potential for ratiometric monitoring of biogenic amines. This AIEgen, namely 4-(dimethylamino)styryl)quinoxalin-2(1H)-one (ASQ), shows a typical donor (D)-acceptor (A) structure with nonmonotonic color and fluorescence responses to pH stimulation by its protonation/deprotonation on the D/A moieties. Subsequently, the H+ASQ-labeled paper chips were successfully prepared by physically depositing ASQ on qualitative filter paper, followed by the acidification by hydrochloric acid. Upon the exposure to ammonia vapour, the obtained H+ASQ-labeled paper chips exhibited obvious color and ratiometric fluorescence responses owing to the deprotonation of H+ASQ indicators, indicating that the proposed paper chips can be used for the detection of biological amines by bimodal colorimetry and ratiometric fluorescence. Under the optimal conditions, H+ASQ-labeled paper chip achieved the real-time, non-destructive, and visual monitoring of meat and seafood freshness by simultaneously quantify the biogenic amine index with high performance liquid chromatography (HPLC). The results of this work suggest that ratiometric AIEgen can serve as a promising alternative strategy to ensure accurate monitoring of biogenic amines and food freshness.

Auto-fluorescence of cellulose paper with spatial solid phrase dispersion-induced fluorescence enhancement behavior for three heavy metal ions detection

Auto-fluorescence of cellulose paper is often considered as an interfering fluorescence, which directly impedes the cellulose paper as a substrate material. This paper creatively explored the composition and properties of auto-fluorescence, and lignosulfonate was primarily speculated as the main source of auto-fluorescence. Surprisingly, its spatial solid phrase dispersion-induced fluorescence enhancement behavior was found. Then, cellulose paper was modified with Mn-doped ZnS quantum dots, and the prepared ratiometric fluorescent paper chip has good performances on morphology, stability, and fluorescence properties. Besides, the paper chip exhibited different fluorescence responses to three heavy metal ions in water sample. The limit of detection for Cd2+, Hg2+ and Pb2+ reached 1.61 nM, 0.01 nM, and 0.02 nM, respectively. In short, the molecular simulation results theoretically proved that heavy metal ions owned substitution affinity with lignosulfonate. Ultimately, this study was the first attempt to utilize paper-based auto-fluorescence, which could better accelerate the development of paper-based chips.

Fluorescent color analysis of ascorbic acid by ratiometric fluorescent paper utilizing hybrid carbon dots-silica coated quantum dots

Monitoring the concentration of ascorbic acid (AA) in biological samples is essential to food quality and healthcare. Various fluorescence methods widely reported for the detection of AA are usually based on “turn-on” or “turn-off” principle. However, few ratiometric fluorescent sensors were reported for AA determination. Additionally, the application of ratiometric fluorescence probe is usually limited by the narrow range of color changes and insensitivity color change of the AA concentration. Herein, a novel ratiometric fluorescent test paper to achieve the continuous color changes from red to blue was developed for the fluorometric qualitative and quantitative determination of AA. The nanoprobe consists of blue-emitting carbon dots (C-dots) and red-emitting silica coated quantum dots (QDs@SiO2) with certain ratiometric fluorescence intensity of blue to red. The fluorescence of blue-emitting CDs (peaking at 450 nm) is quenched by Fe3+, then the blue fluorescence is restored consecutively with the gradual increasing of AA concentration due to the reduction from Fe3+ to Fe2+ by using AA. While the fluorescence of red-emitting QD@SiO2 (peaking at 630 nm) works as a stable internal standard. Therefore, a distinguish color transition from red to blue can be observed by naked eyes intuitively with the increasing of AA concentration. By calculating the ratiometric fluorescent intensity at 450 nm and 630 nm or observing the color of the mixture solution by naked eyes, the concentration of AA can be detected easily and accurately. Under optimized conditions, the fluorescent intensity ratio (I450/I630) shows linear relationship with the concentration of AA from 0 to 70 μM with the detection limit as low as 3.17 μM. Finally, a ratiometric fluorescent sensor paper was further developed for AA detection with satisfactory results in fruit juice. The method proposed here gives the wide applications of fluorescent test paper in food and biological assays.

Fluorescence detection of 2,4-dichlorophenoxyacetic acid by ratiometric fluorescence imaging on paper-based microfluidic chips.

Fluorescence detection of pesticide contamination enables timely control of food safety. This study aims to construct novel and facile microfluidic paper-based analytical devices for the ratiometric fluorescence determination of pesticides. Through fluorescence resonance energy transfer (FRET) of nitrobenzoxadiazole (NBD) and CdTe quantum dots (QDs), the new microfluidic paper chips allowed the rapid and selective visual detection of 2,4-dichlorophenoxyacetic acid (2,4-D). The performance changes of the fluorescent material on solid matrix material were studied in detail. The sensor products exhibited visual observability and fluorescence characteristics. Under optimized conditions, the sensors showed satisfactory linearity in the range of 0.56-80 μM, and achieved detection limits as low as 90 nM. The sensors were successfully applied for soybean sprouts and lake water samples. Four levels of spiked-in 2,4-D concentrations were obtained with high recovery rates ranging from 86.2% to 109.5% and the RSD less than 4.19%. Thus, the present work described the integration of surface imprinted grafts on cellulose paper and ratiometric fluorescence techniques for highly sensitive separation and detection of pesticides in real food and environmental samples. Ultimately, this study paved the way for the development of novel ratiometric fluorescence detection to address food safety and environmental issues.

Highly Sensitive Ratiometric Fluorescent Paper Sensors for the Detection of Fluoride Ions.

Two sensitive and ratiometric fluorescent probes (probe I and probe II) were developed for the detection of fluoride ions. Probe I can detect fluoride ions quantitatively within a range of 0–6 μM and a detection limit of 73 nM, while probe II has a range of 0–40 μM and a detection limit of 138 nM. The test strips from probe I are quickly able to recognize F– (5 min) inside of the F– safety level in drinking water (1.0 mg/L, ∼5 μM) under 254 nm ultraviolet light, and the test strips from probe II quickly recognize F– (12 min) in dangerously high F– levels in water (4.0 mg/L, ∼21 μM) under 254 nm ultraviolet light. This combination of fluorescent paper sensors from probe I and probe II can be used as a simple and convenient tool to determine whether water is safe to drink or dangerous.

Graphene oxide based ratiometric fluorescent paper sensor for hypochlorous acid visual detection

In this paper, a simple and effective ratiometric fluorescent nanoprobe for visual detection of hypochlorous acid (HOCl) has been developed by loading silicon coated rhodamine B (RBDS) nanospheres on the surface of amino-modified graphene oxide (GO-NH2) nanosheets. The fabricated nanoprobe exhibits dual-emissions peaked at 427 and 585 nm, under a single excitation wavelength of 365 nm. The blue fluorescence of GO-NH2 can be selectively quenched by oxidation of HOCl, while the red fluorescence of RBDS remain unchanged, resulting in a distinguishable fluorescent color change from blue to pink under a UV lamp. Nanoprobes present high selective and sensitive for HOCl determination with a limit of detection (LOD) of 2.92 μM. Moreover, potable paper sensor has been prepared by coating the ratiometric fluorescent probe on filter paper, which provides a convenient and simple approach for HOCl visual detection.

Highly sensitive ratiometric fluorescent paper sensor for the urine assay of cancer

Telomerase, as a valuable biomarker, is an important target in cancer diagnosis. Here, we report a ratiometric fluorescent probe for telomerase activity assay in urine and bladder cancer diagnoses based on the color change of Rox-DNA functionalized quantum dots (QDs). The green fluorescence of the QDs was sensitive to H2O2, but the red fluorescence of Rox showed no change. An HRP-mimicking hemin/G-quadruplex, which was formed with the help of telomerase activity, catalyzed H2O2 into H2O and O2. This quadruplex effectively avoided H2O2 interference with green fluorescence. In the presence of H2O2, the detected color changed from red to yellow-green by increasing the telomerase concentration. The detection limit (LOD) was 10 cells, and response time was within 60 min. More importantly, a paper sensor was developed based on this probe and used for the assay of telomerase activity in urine samples. The results were highly sensitive and reproducible, and visual semi-quantitative detection was realized using the naked eye.

A ratiometric fluorescent paper sensor for consecutive color change-based visual determination of blood glucose in serum

The ratiometric fluorescent paper sensor with a dosage-sensitive allochromatic capability for the visual determination of blood glucose in human serum.