A dual-mode ratiometric fluorescence and smartphone-assisted colorimetric sensing platform based on bifunctional Fe,Co-CQD for glucose analysis at physiological pH

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.

Iron/cobalt co-doped boron quantum dots as nanozymes with peroxidase-like activities and the nanozyme-involved cascade catalysis system for ratiometric fluorescence and dual-mode visual detection of glutamate

To further explore the boron-involved nanomaterials toward efficient applications in chemo/bio sensing and detection fields, this work reports facile preparation of the emerging iron/cobalt co-doped boron quantum dots (Fe/Co@BQDs) that were explored as new artificial nanozymes for ratiometric fluorescence (FL) and visual detection of glutamate (Glu). In the presence of glutamate oxidase (GLOD), Glu was oxidized to produce H2O2, and then the H2O2 was catalyzed by Fe/Co@ BQDs nanozymes to produce hydroxyl radical (•OH). Afterwards, the •OH induced FL quenching responses of rhodamine B (RhB) and Fe/Co@BQDs. Therefore, a new nanozyme-assisted cascade catalysis platform was explored, consisting of Fe/Co@BQDs, GLOD, and RhB. The platform was successfully used for ratiometric FL sensing of Glu and liquid/solid dual-channel FL visual semi-quantitative detection of Glu. The platform exhibits a board linear detection range of 1-500 µM, a low limit of detection of 0.3 µM, highly selective ratiometric FL responses on Glu over potential interferents, and high-performance practical detection of Glu in biological samples. Experimental results verify high peroxidase-like activities of Fe/Co@BQDs that enable efficient applications for unique enzymatic reactions and nanozyme-involved cascade catalysis reactions. The platform can facilitate further development of other types of metal-doped nanomaterials with natural biological enzyme-like activities and their promising applications, especially chemo/bio sensing, bioimaging and therapeutics at the levels of living cells and small animals.

Carbon Dots with Antioxidant Capacity for Detecting Glucose by Fluorescence and Repairing High-Glucose Damaged Glial Cells

Diabetic mellitus management extends beyond blood glucose monitoring to the essential task of mitigating the overexpression of reactive oxygen species (ROS), particularly vital for cellular repair, especially within the nervous system. Herein, antioxidant carbon dots (Arg-CDs) were designed and prepared using anhydrous citric acid, L-arginine, and ethylenediamine as sources through a hydrothermal method. Arg-CDs exhibited excellent scavenging ability to 2,2-Diphenyl-1-picrylhydrazyl (DPPH∙), and fluorescence response to hydroxyl radicals (∙OH), a characteristic representative of reactive oxygen species (ROS). Assisted by glucose oxidase and Fe2+, Arg-CDs showed a sensitive and selective response to glucose. The quenching mechanism of Arg-CDs by formed ∙OH was based on the static quenching effect (SQE). The analytical performance of this method for glucose detection encompassed a wide linear range (0.3-15 μM), a low practical limit of detection (0.1 μM) and practical applicability for blood glucose monitoring. In an in vitro model employing glial cells (BV2 cells), it was observed that high glucose medium led to notable cellular damage ascribed to the excessive ROS production from hyperglycemia. The diminished and apoptotic glial cells were gradually recovered by adding increased contents of Arg-CDs. This work illustrates a promising area that designs effective carbon dots with antioxidant capacity for the dual applications of detection and cell repairing based on the utilization of antioxidant activity.

Detection of Hg2+ Using a Dual-Mode Biosensing Probe Constructed Using Ratiometric Fluorescent Copper Nanoclusters@Zirconia Metal-Organic Framework/N-Methyl Mesoporphyrin IX and Colorimetry G-Quadruplex/Hemin Peroxidase-Mimicking G-Quadruplex DNAzyme

Mercury (Hg2+) has been recognized as a global pollutant with a toxic, mobile, and persistent nature. It adversely affects the ecosystem and human health. Already developed biosensors for Hg2+ detection majorly suffer from poor sensitivity and specificity. Herein, a colorimetric/fluorimetric dual-mode sensing approach is designed for the quantitative detection of Hg2+. This novel sensing approach utilizes nanofluorophores, i.e., fluorescent copper nanoclusters-doped zirconia metal-organic framework (CuNCs@Zr-MOF) nanoconjugate (blue color) and N-methyl mesoporphyrin IX (NMM) (red color) in combination with peroxidase-mimicking G-quadruplex DNAzyme (PMDNAzyme). In the presence of Hg2+, dabcyl conjugated complementary DNA with T-T mismatches form the stable duplex with the CuNCs@Zr-MOF@G-quadruplex structure through T-Hg2+-T base pairing. It causes the quenching of fluorescence of CuNCs@Zr-MOF (463 nm) due to the Förster resonance energy transfer (FRET) system. Moreover, the G-quadruplex (G4) structure of the aptamer enhances the fluorescence emission of NMM (610 nm). Besides this, the peroxidase-like activity of G4/hemin DNAzyme offers the colorimetric detection of Hg2+. The formation of duplex with PMDNAzyme increases the catalytic activity. This novel biosensing probe quantitatively detected Hg2+ using both fluorimetry and colorimetry approaches with a low detection limit of 0.59 and 36.3 nM, respectively. It was also observed that the presence of interfering metal ions in case of real aqueous samples does not affect the performance of this novel biosensing probe. These findings confirm the considerable potential of the proposed biosensing probe to screen the concentration of Hg2+ in aquatic products.

Ultra-trace Ag doped carbon quantum dots with peroxidase-like activity for the colorimetric detection of glucose

Carbon quantum dots (CQDs) have significant applications in nanozymes. However, previous studies have not elucidated the structure-activity relationship and enzyme mechanism. In this study, we employed a one-step microwave method to synthesize ultra-trace Ag-doped carbon quantum dots (Ag-CQDs). In the presence of hydrogen peroxide (H2O2), we used the oxidative coupling reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to evaluate the intrinsic peroxidase-like activity, kinetics, and mechanism of Ag-CQDs. The trace amount of doped Ag (1.64 %) facilitated electron transfer from the CQDs interior to the surface. The electron transfer triggered the peroxide activity of CQDs, producing hydroxyl radical (·OH), which oxidized the colorless TMB to blue-colored TMB (oxTMB). By coupling with glucose oxidase (GOx), the Ag-CQDs/H2O2/TMB system has been used for colorimetric glucose determination. The system demonstrated a low detection limit (0.17 µM), wide linear range (0.5-5.5 µM), and satisfactory results when fruit juice was analyzed. This study reports a feasible method for the colorimetric detection of glucose by synthesizing ultra-trace Ag-doped carbon quantum dots with peroxidase-mimicking activity.

Carbon dot-based fluorescent probe for early diagnosis of pheochromocytoma through identification of circulating tumor cells

Pheochromocytoma (PCC), as a rare neuroendocrine tumor, is often missed or misdiagnosed because of its atypical clinical manifestations. To realize the early accurate diagnosis of PCC, we have selected circulating tumor cells (CTCs) with more complete biological information as biomarkers and developed a simple and novel fluorescence cytosensor. Octreotide-2,2',2'',2'''- (1,4,7,10 -tetraazacyclododecane-1,4,7,10-tetrayl) tetraacetic acid (DOTA) modified magnetic Fe3O4 and signal amplification CDs@SiO2 nanospheres are prepared to capture and detect PCC-CTCs from peripheral blood via binding to the somatostatin receptor SSTR2 overexpressed on the surface of PCC cells. During the detection process, the target cells were separated and enriched by magnetic capture probes (Fe3O4-DOTA), and then signal probes (CDs@SiO2-DOTA) could also specifically bound to target cells to form the sandwich-like structure for fluorescence signal output. The proposed fluorescence cytosensor has revealed good sensitivity and selectivity for quantitative analysis of PCC-CTCs in the concentration of 5-1000 cells mL-1 with a LOD of 2 cells mL-1. More importantly, designed fluorescence cytosensor has shown good reliability and stability in complex serum samples. This strategy provides a new way for detection of PCC-CTCs.

Glucose oxidase and metal catalysts combined tumor synergistic therapy: mechanism, advance and nanodelivery system

Cancer has always posed a significant threat to human health, prompting extensive research into new treatment strategies due to the limitations of traditional therapies. Starvation therapy (ST) has garnered considerable attention by targeting the primary energy source, glucose, utilized by cancer cells for proliferation. Glucose oxidase (GOx), a catalyst facilitating glucose consumption, has emerged as a critical therapeutic agent for ST. However, mono ST alone struggles to completely suppress tumor growth, necessitating the development of synergistic therapy approaches. Metal catalysts possess enzyme-like functions and can serve as carriers, capable of combining with GOx to achieve diverse tumor treatments. However, ensuring enzyme activity preservation in normal tissue and activation specifically within tumors presents a crucial challenge. Nanodelivery systems offer the potential to enhance therapy effectiveness by improving the stability of therapeutic agents and enabling controlled release. This review primarily focuses on recent advances in the mechanism of GOx combined with metal catalysts for synergistic tumor therapy. Furthermore, it discusses various nanoparticles (NPs) constructs designed for synergistic therapy in different carrier categories. Finally, this review provides a summary of GOx-metal catalyst-based NPs (G-M) and offers insights into the challenges associated with G-M therapy, delivery design, and oxygen (O2) supply.

Proximity hybridization regulated dual-mode ratiometric biosensor for estriol detection in pregnancy serum

Sensitive and accurate determination of estriol level is vastly significant for the fetal growth and development. Herein, we constructed a dual-mode ratiometric biosensor for estriol assay combining the competitive immunoreaction, proximity hybridization with a two-step resonance energy transfer (RET) strategy. Estriol antibody and goat anti-rabbit antibody labeled DNA probes (Ab1-DNA1-Pt NPs and Ab2-DNA2) both hybridized with silver nanoclusters labeled DNA strands (H1-Ag NCs). Thus, the formed proximity hybridization enabled the occurrence of fluorescence RET (FL-RET, as the primary RET) between Ag NCs (donor) and Pt NPs (acceptor), quenching FL intensity of Ag NCs (FL off). When target estriol existed, the competitive reaction of Ab1-DNA1-Pt NPs with estriol and Ab2-DNA2 avoided the proximity hybridization. Then, the estriol-dependent H1-Ag NCs quenched electrochemiluminescence (ECL) emission of CdS quantum dots (CdS QDs, ECL off), generating ECL-RET (as the second RET). Consequently, according to the reverse changes of FL and ECL responses, this sensor realized the quantification of estriol from 1 to 100 ng/mL. Moreover, satisfactory results were achieved while testing estriol in pregnancy serum specimens, suggesting that the system is promising for potential application in samples analysis.

Recent Advances in the DNA-Mediated Multi-Mode Analytical Methods for Biological Samples

DNA-mediated nanotechnology has become a research hot spot in recent decades and is widely used in the field of biosensing analysis due to its distinctive properties of precise programmability, easy synthesis and high stability. Multi-mode analytical methods can provide sensitive, accurate and complementary analytical information by merging two or more detection techniques with higher analytical throughput and efficiency. Currently, the development of DNA-mediated multi-mode analytical methods by integrating DNA-mediated nanotechnology with multi-mode analytical methods has been proved to be an effective assay for greatly enhancing the selectivity, sensitivity and accuracy, as well as detection throughput, for complex biological analysis. In this paper, the recent progress in the preparation of typical DNA-mediated multi-mode probes is reviewed from the aspect of deoxyribozyme, aptamer, templated-DNA and G-quadruplex-mediated strategies. Then, the advances in DNA-mediated multi-mode analytical methods for biological samples are summarized in detail. Moreover, the corresponding current applications for biomarker analysis, bioimaging analysis and biological monitoring are introduced. Finally, a proper summary is given and future prospective trends are discussed, hopefully providing useful information to the readers in this research field.