2024-03

Lab on a Chip

The regular and on-site monitoring of ions in drinking water is essential for safeguarding public health, ensuring high water quality, and preserving the ecological balance of aquatic ecosystems. Thus, developing a portable analytical device for the rapid, cost-effective, and visual on-site detection of multiple environmental pollutants is notably significant. In the present work, a novel ratiometric microfluidic paper-based analytical device (μPAD) was designed and developed for the simultaneous detection of Fe3+ and Cu2+ ions in water samples taking advantages from built-in masking zone. The μPAD was functionalized with a greenish-yellow fluorescent Zn-based metal–organic framework@tetracycline (FMOF-5@TC) nanocomposite, and the ratiometric design was based on the change in emission color from greenish yellow (FMOF-5@TC) to blue (FMOF-5). The μPAD consisted of one sample zone linked to two detection zones via two channels: the first channel was for the detection of both ions, while the second was intended for detecting only Cu2+ ions and comprised a built-in masking zone to remove Fe3+ ions prior to reaching the detection zone. The corresponding color changes were recorded with the aid of a smartphone and RGB calculations. The linear ranges were 0.1–80 μM for Cu2+ and 0.2–160 μM for Fe3+, with limits of detection of 0.027 and 0.019 μM, respectively. The simple μPAD design enabled the simultaneous detection of Cu2+ and Fe3+ ions in drinking water samples with excellent accuracy and precision, with spike recoveries of 81.28–96.36% and 83.01–102.33% for Cu2+ and Fe3+, respectively.

2024-03

Food Chemistry

Current nanozyme applications rely heavily on peroxidase-like nanozymes and are limited to a specific temperature range, despite notable advancements in nanozyme development. In this work, we designed novel Mn-based metal organic frameworks (UoZ-4), with excellent oxidase mimic activity towards common substrates. UoZ-4 showed excellent oxidase-like activity (with Km 0.072 mM) in a wide range of temperature, from 10 °C to 100 °C with almost no activity loss, making it a very strong candidate for psychrophilic and thermophilic applications. Ascorbic acid, cysteine, and glutathione could quench the appearance of the blue color of oxTMB, led us to design a visual-based sensing platform for detection of total antioxidant capacity (TAC) in cold, mild and hot conditions. The visual mode successfully assessed TAC in citrus fruits with satisfactory recovery and precisions. Cold/hot adapted and magnetic property will broaden the horizon of nanozyme applications and breaks the notion of the temperature limitation of enzymes.

2023-12

Microchimica Acta (Volume : 191)

Synthesis of dual-state dual emitting metal–organic frameworks (DSDE-MOFs) is uncommon and challenging. Additionally, DSDE-MOFs can fulfil the expanding need for on-site detection due to their stability and self-reference for a variety of non-analyte variables. In the present work, a novel intrinsic DSDE of chemically engineered bi-ligand Eu-based MOF (UoZ-1) was designed. The prepared UoZ-1 spherical particles were small-sized around 10–12 nm and displayed blue (425 nm) and red fluorescence (620 nm) at both states, dispersed in liquid and in solid state, when excited at 250 nm. A ratiometry platform was developed since the red emission was quenched by the addition of folic acid and the blue emission was almost remained unaffected. In the fluorometric ratiometric-mode, a dynamic linear range was recorded from 10 to 200 µM with LOD about 0.4 µM. Visual-based detection with assistance of smartphone was developed for quantification based on RGB analysis using Color Grab App. In the visual-mode, LOD as small as 2.3 µM was recorded. By utilizing the intrinsic dual-emitting UoZ-1, highly stable, recyclable, sensitive, and selective on-site visual detection of folic acid can be achieved. UoZ-1, a DSDE-MOF with no encapsulation or functionalization requirements, exhibits great potential for diverse applications.

2023-09

ACS applied materials and Interfaces

Dual-state emitters (DSEs) are entities that exhibit fluorescence in both the solution and solid state, which open up a wide range of possibilities for their utilization in various fields. The development of detection platforms using intrinsic luminescent metal–organic frameworks (LMOFs) is highly desirable for a variety of applications. DSE MOFs as a subclass of intrinsic LMOFs are highly attractive due to no need for encapsulation/functionalization by fluorophores and/or using luminescent linkers. Herein, a highly stable intrinsic dual-state blue emission (λem = 425 nm) zinc-based MOF with rodlike nanostructures (denoted as UoZ-2) was synthesized and characterized. To the best of our knowledge, intrinsic DSE of Zn-MOFs with blue emission in the dispersed form in solution and solid-state fluorescence have not been reported yet. When tetracycline (TC) was added, a continuous color evolution from blue to greenish-yellow with dramatic enhancement was observed due to aggregation induced emission (AIE). Thus, a sensitive ratiometry-based visual detection platform, in solution and on paper independently, was designed for detection of TC exploiting the DSE and AIE properties of UoZ-2 alone and UoZ-2:TC. The detection limit was estimated to be 4.5 nM, which is considered to be one of the most sensitive ratiometric fluorescent probes for TC sensing. The ratiometry paper-based UoZ-2 sensor displays a reliable TC quantitative analysis by recognizing RGB values in the on-site TC detection with satisfactory recoveries.

2022-12

Talanta (Volume : 254)

Color tonality by intrinsic fluorescent metal-organic frameworks (MOFs) is highly desirable in bioanalytical applications due to its stability, low-cost and robustness with no need for functionalization and/or encapsulation of fluorophores. In the present work, ultra-small and higly fluorescent zinc-based MOFs (FMOF-5) were synthesized. The prepared FMOFs were around 5 nm in size, and gave strong blue emission at 440 nm when excited at 350 nm. Interestingly, tetracycline (TC) selectively tuned the blue emission of FMOF-5 to greenish-yellow emission (520 nm) with dramatic enhancement through aggregation induced emission (AIE). The fluorimetric analysis of TC was carried out through the ratiometric peak intensities of F520/F440, with detection limit (LOD) of 5 nM. To realize quantitative point-of-care based on color tonality, a smartphone integrated with the ratiometric visual platform was thereby design. Hence, TC was visually detected with LOD of 10 nM. The prepared FMOF-5-based probe showed high stability (3 months) and reusability (∼10 times). The developed visual-based platform presents great promise for practical point of care testing due to its low-cost, robustness, ruggedness, simple operation, and excellent selectivity and repeatability.

2022-06

Microchemical Journal (Issue : 107721) (Volume : 181)

Multicolor visual sensing approach significantly improves accuracy, reproducibility and detection rate of targets. Herein, a novel red emitter bi-ligand Eu-based metal organic framework (BiL-Eu-MOF) was successfully synthesized using a one step solvothermal method and was evaluated as a reference signal for multicolor visual-based ratiometry detection. The synergistic effects offered by the double ligand and Eu significantly showed red shift excitation towards many cations and anions and fluorescence stability at least for 6 months. As a fluorescent multicolor-visual probe, selective blue emitter carbon dots to Ag+ ions were encapsulated into the pores of the red emissive of BiL-Eu-MOF to form blue-purple color. Addition of Ag+ ions changed emission color from blue-purple to red, while addition of cysteine (Cys) restored the original blue-purple color. Employing RGB analysis using smartphone, the detection mode showed good linearity of Ag+ and Cys in the range of 0–660 and 0–405 μM with limit of detection of 2.1 and 0.15 μM, respectively. Ultimately, our probe was applied for the quantification of silver ions in water samples and Cys in human serum samples showing excellent accuracy and precision.