Portable smartphone-assisted ratiometric fluorescence sensor for visual detection of glucose

One-step cascade method via glucose oxidase-copper ion complex for detecting glucose using a portable device

In this study, a one-step cascade fluorescence method was developed for the detection of glucose in honey, based on the glucose oxidase-copper ion complexes (GOx@Cu2+). These complexes exhibit dual enzymatic activities-glucose oxidase and peroxidase-like activities-which enable them to catalyze a cascade reaction. This reaction involves the oxidation of glucose and o-phenylenediamine (OPD), leading to the formation of 2,3-diaminophenazine (oxOPD), a compound with fluorescent properties. The proposed method overcomes the challenges of pH mismatch between enzymes and streamlines the testing process, eliminating the need for nanomaterial preparation and reducing the detection time to just 20 min. The feasibility of the method was validated by analyzing three honey samples, achieving recoveries between 96.4 % and 106 %, with relative standard deviations of less than 1.9 %. The selectivity and accuracy of the method were verified by capillary electrophoresis in three honey samples. Moreover, a self-designed portable device was introduced to enable on-site glucose detection.

Colorimetry/fluorescence dual-mode detection of gentamicin based on curcumin nanoparticles and manganese dioxide nanosheets

This study used curcumin nanoparticles (CNPs) in phosphate buffer solution (pH 9) [CNPs (pH 9)] as a new oxidative substrate to detect gentamicin (GEN). Manganese dioxide nanosheets (MnO2-BSA NS) with excellent oxidizing properties were applied to catalytic oxidize CNPs (pH 9), which resulted in visual color changed from red to orange-yellow under sunlight. Moreover, the fluorescence of CNPs (pH 9) changed from orange to yellow. And we introduced carbon dots (CDs) as a reference signal, the fluorescence of CNPs quenched the fluorescence of CDs to generate a ratiometric fluorescence response. Therefore, we semi-qualitatively determined GEN with the naked eye and quantitatively evaluated by ratiometric colorimetry (I510 nm/I436 nm) and ratiometric fluorescence (F560 nm/F436 nm). The dual-mode immunoassay linearly correlated with GEN ranged from 10-4 μg/mL to 100 μg/mL with a detection limit (LOD) of 4.44 × 10-5 μg/mL and 3.16 × 10-5 μg/mL. Meanwhile, a smartphone-assisted system was designed for sensing of GEN by the distinct color change, providing a dependable, convenient and on-site assay of detecting GEN.

The FRET-Based APTA Sensor/Cy3 Complex for Glucose Determination

This study developed a sensitive and cost-effective fluorescent probe based on the Förster Resonance Energy Transfer (FRET) method to monitor blood glucose levels. The APTA sensor/Cy3 probe consisted of cadmium telluride quantum dots modified with thioglycolic acid (CdTe-TGA QDs), a thiol-glucose-aptamer, and a Cy3-labeled aptamer. Due to the well-matched emission spectrum of the CdTe QDs and the absorption spectrum of Cy3, the FRET system decreased fluorescence intensity. However, glucose molecules quenched it when introduced to the system. The linear relationship between fluorescence intensity and glucose concentration was established with a detection limit of 7.72 × 10-9 M. The APTA sensor/Cy3 complex demonstrated excellent selectivity and specificity toward glucose and a high recovery rate of 96.00-101.11% in human serum and urine using the spiking method. The structural and morphological characteristics of the APTA sensor/Cy3 complex were confirmed by UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS) analyses. The results suggest that the FRET-based APTA sensor/Cy3 complex would lead to the development of fluorescent probes for screening biological metabolites in clinical diagnostics and research.

Recent progress on nanomaterial-based electrochemical sensors for glucose detection in human body fluids

In the modern age, half of the population is facing various chronic illnesses due to glucose maintenance in the body, major causes of fatality and inefficiency. The early identification of glucose plays a crucial role in medical treatment and the food industry, particularly in diabetes diagnosis. In the past few years, non-enzymatic electrochemical glucose sensors have received a lot of interest for their ability to identify glucose levels accurately. Electrochemical biosensors are developing as a propitious solution for personalized health monitoring due to their accuracy, specificity, and affordability. This review article provides an observation of a variety of non-enzymatic glucose sensor resources, such as carbon nanomaterials, noble metals gold and silver, transition metal and their oxides, and porous material composites. Moreover, basic knowledge of the reaction mechanism of enzymatic and nonenzymatic glucose sensors are outlined and recent advancements in glucose sensors applications to various human body biofluids such as sweat, tears, urine, saliva, and blood are presented. Finally, this review summarizes electrochemical sensors for glucose detection in human body fluids, the challenges they faced, and their solutions.

Dual-State Red-Emitting Zinc-Based MOF Accompanied by Dual-Mode and Dual-State Detection: Color Tonality Visual Mode for the Detection of Tetracycline

Red-emitting metal-organic frameworks (MOFs) are still mostly based on the use of lanthanides or functionalization with red fluorophores. However, production of transition-metal-based MOFs with red-emitting is scarce. This work reports on the synthesis of a novel dual-state red-emitting Zn-based MOF (denoted as UoZ-7) with the capability to detect target molecules in dual state, in solution, and as solid on paper. UoZ-7 gives strong red emission when excited in the solution and in the solid state with 365 nm ultraviolet (UV) lamp irradiation. Coordination-induced emission is the mechanism for the red emission enhancement in the MOF as a restriction of intramolecular rotation occurred to the ligand within the framework structure. UoZ-7 was successfully used for tetracycline (TC) using dual-mode detection, fluorescence-based ratiometry, and color tonality, in the dual state, in solution, and on the paper. TC molecules adsorb on the red-emitting UoZ-7 surface, and a yellow-greenish color emerges due to aggregation-induced emission between TC and UoZ-7. Concurrently, the inner filter effect diminishes the red emission of UoZ-7. The dual-mode or dual-state detection platform provides a simple and reliable fast method for the detection of TC on-site in various environmental and biomedical applications. Moreover, red-emitting UoZ-7 will have further luminescence-based biomedical applications.

Dual-mode detection of glucose based on pistol-like DNAzyme-mediated exonuclease-assisted signal cycle

Detecting glucose accurately and sensitively from clinical samples like tears and saliva is still difficult. We have created a sensor that can detect glucose with high sensitivity and accuracy by combining the use of glucose oxidase (GOx) to catalyze glucose, a pistol-like DNAzyme (PLDz) to transform the signal, gold nanoparticles (AuNPs) to enhance the optical properties and the exonuclease-III (Exo-III) to amplify the signal. As a result, the proposed method exhibits a low detection limit of 7.5 pM and a wide detection range covering seven orders of magnitude. The suggested dual-mode strategy provides a sensitive, precise and specific detection method for glucose. Another advantage is that the dual-mode technique significantly improves the precision and consistency of the measurements, demonstrating its immense potential for use in biomedical research and clinical diagnostics.

Colorimetric detection of Fe2+ and Cr2O72- in environmental water samples based on dual-emitting RhB-embedded Zr-MOFs

Three dye-loaded tunable dual-emission colorimetric fluorescent probes RhB@UiO-66-Ph (R@U-P) were prepared by in-situ encapsulation method under solvothermal conditions. The resonance energy transfer between UiO-66-Ph and RhB made the dual emission of R@U-P easily tunable with the embedded dye content changing. The R@U-P composites achieved emission from purple light to red light, and served as probes to realize comparative detection of Fe3+, Fe2+ and Cr2O72- in water through colorimetric or quenching detection mode. Mechanism study indicates that the resonance energy transfer or electron transfer interactions between R@U-P composites and inorganic ions resulted in the relative changes of the two emission peaks and realized the selective detection of analytes. The preparation and application of R@U-P probes provide a promising strategy for the in-situ encapsulation dye to obtain two dual-emission composites for the comparative detection of Fe3+, Fe2+ and Cr2O72- in water samples.

The Fluorescent Detection of Glucose and Lactic Acid Based on Fluorescent Iron Nanoclusters

In this paper, a novel fluorescent detection method for glucose and lactic acid was developed based on fluorescent iron nanoclusters (Fe NCs). The Fe NCs prepared using hemin as the main raw material exhibited excellent water solubility, bright red fluorescence, and super sensitive response to hydrogen peroxide (H2O2). This paper demonstrates that Fe NCs exhibit excellent peroxide-like activity, catalyzing H2O2 to produce hydroxyl radicals (•OH) that can quench the red fluorescence of Fe NCs. In this paper, a new type of glucose sensor was established by combining Fe NCs with glucose oxidase (GluOx). With the increase in glucose content, the fluorescence of Fe NCs decreases correspondingly, and the glucose content can be detected in the scope of 0-200 μmol·L-1 (μM). Similarly, the lactic acid sensor can also be established by combining Fe NCs with lactate oxidase (LacOx). With the increase in lactic acid concentration, the fluorescence of Fe NCs decreases correspondingly, and the lactic acid content can be detected in the range of 0-100 μM. Furthermore, Fe NCs were used in the preparation of gel test strip, which can be used to detect H2O2, glucose and lactic acid successfully by the changes of fluorescent intensity.

Three-dimensional DNA biomimetic networks (B-3D Net)-based ratiometric fluorescence platform for cancer-related gene biosensing

Efficient detection of cancer-related nucleic acids is pivotal for early cancer diagnosis. This study introduces a target induced three-dimensional DNA biomimetic networks (B-3D Net)-based ratiometric fluorescence platform using manganese dioxide nanosheets (MnO2 NS)/o-phenylenediamine in combination with hybridization chain reaction to detect cancer-related genes (p53 gene). The incorporation of multiple signals within the B-3D networks can significantly enhance catalytic activity and amplify the output signals, enabling a high sensitivity. Compared with traditional ratio fluorescence platforms, there is no demand to synthesize fluorescent nanoprobes due to the in-situ formation of fluorescence species, which is simple and cost-effective. The corresponding assay demonstrated exceptional sensitivity (with a detection limit as low as 2 fM), selectivity, reproducibility, and accuracy, which mitigates disturbances caused by instrument errors, an inaccurate probe count, and the microenvironment. Furthermore, the ease and straightforwardness of discerning changes in fluorescent brightness and colour by the naked eye are evident. Using the relevant software, a linear relationship between fluorescent images using a smartphone and target concentration was obtained. Hence, the novel ratiometric sensing system will demonstrate new opportunities on determination of target DNA samples in complex biological environments.

Portable smartphone-assisted ratiometric fluorescent test paper based on one-pot synthesized dual emissive carbon dots for visualization and quantification of mercury ions

Dual-emissive fluorescent carbon dots (CDs) were prepared through the solvothermal method with citric acid and urea as raw materials and dimethylformamide as the solvent. Two emission peaks were observed at 465 nm and 630 nm. Hg2+ could selectively quench the fluorescence at 630 nm, but the fluorescence intensity at 465 nm was less affected. Accordingly, a ratiometric fluorescence sensor for Hg2+ detection was developed, with a linear detection range of 0.5-40 μM and a limit of detection (LOD) of 37 nM. The dual-emissive CDs were loaded on the surface of the filter paper to fabricate Hg2+ detection test paper. The color of the test paper could be changed from pink purple to blue by the addition of Hg2+, and thus the qualitative and quantitative detection of Hg2+ could be realized. The concentration distinguishable by the naked eye reached 50 μM, and the quantitative detection range was 5-10,000 μM. This method shows excellent selectivity for Hg2+ and can be used to detect Hg2+ in real water samples, providing a highly potential sensing platform for rapid on-site detection of mercury ions.