Fluorometric determination of glucose based on a redox reaction between glucose and aminopropyltriethoxysilane and in-situ formation of blue-green emitting silicon nanodots

Triple Sensing Modes for Triggered β-Galactosidase Activity Assays Based on Kaempferol-Deduced Silicon Nanoparticles and Biological Imaging of MCF-7 Breast Cancer Cells

β-Galactosidase (β-Gala) is an essential biomarker enzyme for early detection of breast tumors and cellular senescence. Creating an accurate way to monitor β-Gala activity is critical for biological research and early cancer detection. This work used fluorometric, colorimetric, and paper-based color sensing approaches to determine β-Gala activity effectively. Via the sensing performance, the catalytic activity of β-Gala resulted in silicon nanoparticles (SiNPs), fluorescent indicators obtained via a one-pot hydrothermal process. As a standard enzymatic hydrolysis product of the substrate, kaempferol 3-O-β-d-galactopyranoside (KOβDG) caused the fluorometric signal to be attenuated on kaempferol-silicon nanoparticles (K-SiNPs). The sensing methods demonstrated a satisfactory linear response in sensing β-Gala and a low detection limit. The findings showed the low limit of detection (LOD) as 0.00057 and 0.098 U/mL for fluorometric and colorimetric, respectively. The designed probe was then used to evaluate the catalytic activity of β-Gala in yogurt and human serum, with recoveries ranging from 98.33 to 107.9%. The designed sensing approach was also applied to biological sample analysis. In contrast, breast cancer cells (MCF-7) were used as a model to test the in vitro toxicity and molecular fluorescence imaging potential of K-SiNPs. Hence, our fluorescent K-SiNPs can be used in the clinic to diagnose breast cellular carcinoma, since they can accurately measure the presence of invasive ductal carcinoma in serologic tests.

Visual detection of H2O2 and glucose by HBcAb-HRP fluorescence-enhanced CdTe QDs/CDs ratiometric fluorescence sensing platform

This study presents the development of a sensitive and simple enhanced ratiometric fluorescence sensing platform in the consist of CdTe quantum dots (QDs), carbon dots (CDs), and hepatitis B core antibody labeled with horseradish peroxidase (HBcAb-HRP) for the visual analysis of H2O2 and glucose. The sulfur atoms in HBcAb-HRP have a strong affinity for Cd(II), which effectively enhances the fluorescence intensity of the CdTe QDs due to the generation of more radiative centers at the CdTe/Cd-SR complex. In the presence of H2O2, the Cd-S bonds are oxidized to form disulfide products and results in linear fluorescence quenching, while CDs maintain stable. Becasue glucose can be converted into H2O2 with the aid of glucose oxidase, this sensing platform can also be used for analyzing glucose. The detection limits for H2O2 and glucose are 2.9 μmol L-1 with RSD of 2.6% and 1.6 μmol L-1 with RSD of 2.4% respectively. In addition, under UV lamp irradiation, the orange-yellow CdTe QDs gradually quench with increasing H2O2 and glucose, while the blue CDs remain unchanged. A color change from orange-yellow to blue enables a visual semi-quantitative determination of H2O2 in commercial contact lens solution and glucose in human serum without any pretreatment. Thus, this CdTe QDs/CDs ratiometric sensing platform has significant potential for the rapid analysis of H2O2 and glucose in actual application.

Modular coupling MOF nanozyme with natural enzyme on hollow fiber membrane for rapid and reusable detection of H2O2 and glucose

A novel strategy based on gradient porous hollow fiber membrane (GPF) is proposed for the modular assembly of enzyme-nanozyme cascade systems. The porous structure of GPF provided sufficient specific surface area, while the gradient structure effectively minimized the leaching of enzymes and nanozymes. To enhance stability, we prepared and immobilized metal-organic framework (MOF) nanozymes, resulting in the fabrication of GPF-MOF with excellent stability and reusability for colorimetric H2O2 detection. To improve specificity and expand the detection range, micro-crosslinked natural enzymes were modularly assembled, using glucose oxidase as the model enzyme. The assembled system, GPF-mGOx@MOF, achieved a low detection limit of 0.009 mM and a linear range of 0.2 to 11 mM. The sensor retained 87.2% and 80.7% of initial activity after being stored for 49 days and 9 recycles, respectively. Additionally, the reliability of the biosensor was validated through glucose determination of human blood and urine samples, yielding comparable results to a commercial glucose meter.

Dual-functionalization of fluorescent carbon dots via cyclodextrin and aminosilane for visual detection of β-glucuronidase and bioimaging

A sensitive method for the detection of β-glucuronidase was established using functionalized carbon dots (β-CD-SiCDs) as fluorescent probes. The β-CD-SiCDs were found to be obtained through in situ autopolymerization by mixing the solutions of methyldopa, mono-6-ethylenediamine-β-cyclodextrin and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane at room temperature. The method has the characteristics of low energy consumption, simple and rapid. β-CD-SiCDs exhibited green fluorescence at 515 nm emission with a quantum yield of 7.9 %. 4-nitrophenyl-β-D-glucuronide was introduced as a substrate for β-glucuronidase to generate p-nitrophenol. Subsequently, p-nitrophenol self-assembled with β-CD-SiCDs through host-guest recognition to form a stable inclusion complex, resulting in the fluorescence quenching of β-CD-SiCDs. The linear range of β-CD-SiCDs for detecting β-glucuronidase activity was 0.5-60 U L-1 with a detection limit of 0.14 U L-1. For on-site detection, gel reagents were prepared by a simple method and the images were visualized and quantified by taking advantage of smartphones, avoiding the use of large instrumentation. The constructed fluorescence sensing platform has the benefits of easy operation and time saving, and has been successfully used for the detection of β-glucuronidase activity in serum and cell imaging.

A sensitive fluorescence detection strategy for H2O2 and glucose by using aminated Fe-Ni bimetallic MOF as fluorescent nanozyme

An aminated Fe-Ni bimetallic metal-organic framework (Fe₃Ni-MOF-NH₂) with both peroxidase-like activity and fluorescence properties was developed. Fe₃Ni-MOF-NH₂ possessed the enhanced peroxidase-like activity through the enhanced electron transfer process and hydroxyl radical (·OH) generation. It was found that the amino group endowed the material with fluorescent property and the metal site Ni in Fe₃Ni-MOF-NH₂ could also enhance the fluorescence emission intensity (Ex = 345 nm, Em = 452 nm). Based on the dual excellent performance of Fe₃Ni-MOF-NH₂, a novel sensitive fluorescence detection strategy for H₂O₂ and glucose was designed and achieved. First, Fe₃Ni-MOF-NH₂ converted H₂O₂ to ·OH by exerting peroxidase-like activity, and ·OH converts catechol to o-benzoquinone. Then, the amino group in Fe₃Ni-MOF-NH₂ connected to o-benzoquinone, which resulted in its fluorescence quenching. The detection limit of H₂O₂ was as low as 5 nM. Combined with glucose oxidase which can oxidize glucose and produce H₂O₂ the glucose could be indirectly determined with a detection limit of 40 nM. The method was applied to the detection of low-level glucose in human urine samples with good recoveries and reproducibilities.

Facile preparation of Fe3O4@Pt nanoparticles as peroxidase mimics for sensitive glucose detection by a paper-based colorimetric assay

A simple strategy to rapidly detect glucose was developed by utilizing core (Fe₃O₄)-shell (Pt) magnetic nanoparticles (Fe₃O₄@Pt NPs) as a nanoenzyme and a paper-based colorimetric sensor. In the presence of H₂O₂, Fe₃O₄@Pt NPs catalyze the redox reaction of 3,3',5,5'-tetramethylbenzidine (TMB) and generate a colour change from colourless to blue. On this basis, a colorimetric glucose sensing method assisted by glucose oxidase (GOx) was developed. Under the optimal conditions, the detection limits of the proposed assay for H₂O₂ and glucose were 0.36 µM and 1.27 µM, respectively. Furthermore, the fabricated colorimetric method was successfully applied to analyze glucose concentrations by using a paper device as a measuring platform without a spectrometer. In addition, this method exhibited satisfactory recovery for glucose detection in human serum samples and urine samples, which satisfied the requirements for normal detection of real samples. This study provides a good candidate for health monitoring of glucose and also expands the applications of nanoenzymes and paper-based colorimetric assays in point-of-care testing.

Structure engineering of silicon nanoparticles with dual signals for hydrogen peroxide detection

Fluorescent silicon nanoparticles (SiNPs) were synthesized by a one-step, simple, and green method with 3-Aminopropyltriethoxysilane (APTES) and ascorbic acid (AA) as reaction agents. Subsequently, the SiNPs and AgNPs nanocomplex (SiNPs@AgNPs) was constructed as the probe for hydrogen peroxide (H₂O₂) detection. The fluorescence of SiNPs was quenched due to the surface plasmonic-enhanced energy transfer between SiNPs and AgNPs. Meanwhile, the color tends to be yellow due to the existence of AgNPs. As the AgNPs were etched by H₂O₂, the fluorescence recovers and color fadings. Based on the well-designed structure, the "off-on" fluorescence sensing and "on-off" color sensing platforms for H₂O₂ were fabricated. The as-synthesized materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Fluorescence and UV-vis absorption spectra were used to evaluate the optical performance. The fabricated sensor exhibited a linear range of 1.0-100.0 μM, with a limit of detection of 0.36 μM for the fluorescence sensing of H₂O₂. Additionally, a linear range of 1.0-50.0 μM and a limit of detection of 0.45 μM were displayed for the detection of H₂O₂ by colorimetric assay. The feasibility in complex medium of the fabricated fluorescent and colorimetric dual-signal sensor was evaluated by the detection of H₂O₂ in phosphate buffer saline (PBS) and lake water samples.

A pH-responsive fluorometric and colorimetric system based on silicon quantum dots and 4-nitrophenol for urease activity detection

In this paper, we proposed a dual-signal fluorometric and colorimetric system based on silicon quantum dots (SiQDs) and 4-nitrophenol (4-NP) for pH and urease sensing. SiQDs with fluorescence emission of 460 nm were prepared via aqueous-phase synthesis. As the pH of the system gradually increased, the absorption band of 4-NP at 400 nm increased and a color reaction from colorless to yellow occurred. The absorption of 4-NP overlapped quiet well with the fluorescence excitation spectrum of SiQDs, which can effectively quench the fluorescence of SiQDs. Therefore, the change of fluorescence and absorption intensities could be used to quantify pH value. The fluorometric and colorimetric pH-sensing systems both exhibited a linear respond to pH ranging from 6.0 to 7.8 with an interval of 0.2 pH unit. Urease could specifically hydrolyze urea to generate carbon dioxide and ammonia, causing an obvious increase of the pH value. Thus, urease could also be detected quantitatively by the above dual-signal pH sensing system. The linear ranges of the fluorometric and colorimetric methods for urease detection were both 2-40 U L-1. The limits of detection were 1.67 and 1.07 U L-1, respectively. More importantly, this established dual-signal system has been successfully exploited in the detection of urease in real samples with satisfactory recoveries. Compared with other traditional single-signal assay strategies, the results obtained by dual-signal methods are more accurate and reliable.

Turn-on fluorescent probe for dopamine detection in solutions and live cells based on in situ formation of aminosilane-functionalized carbon dots

Dopamine (DA) is a critical biomarker for a variety of neurological diseases. Methods for simple and rapid DA detection are crucial for clinical diagnosis and treatments for those diseases. In this work, we developed a novel pretreatment-free method for dopamine detection using carbon dots as a turn-on fluorescent probe synthesized in situ. The aminosilane-functionalized carbon dots (SiCDs) were produced in a mild condensation reaction between N-[3-(Trimethoxysilyl)propyl]ethylenediamine (AEATMS) and dopamine, which were directly used for probing of dopamine. The prepared SiCDs exhibited green fluorescence with excitation/emission maximum at 380/495 nm, the intensity of which can be measured to quantify the DA present in the reaction mixture. The linear range of the assay was between 0.1 and 100 μM with a limit of detection (LOD) of 56.2 nM. The probe is of good selectivity and the recoveries of the developed method were in the range of 101.77-119.91% with RSDs within 3.67% in human serum sample tests. The SiCDs were also synthesized within MN9D cells under 37 °C and generated bright fluorescence, which can probe the DA's distribution in the cells. The described method exhibit potential in DA detection and live-cell imaging for its feature of facility, inexpensiveness, and sensitivity.

Non-enzymatic detection of serum glucose using a fluorescent nanopolymer probe

A fluorescent probe is described for the determination of serum glucose after hepatotoxin-induced liver injury. The probe is based on the use of a water-soluble polymer and has been prepared from a multi-functional azlactone polymer as the linker, amino boronic acid, and Alizarin Red as the signalling moiety. The excitation/emission peaks of the polymeric fluorescent probe are at 468/567 nm. Fluorescence is reduced on addition of glucose. Intensity drops linearly in the 0.1 mM to 14 mM glucose concentration range. The probe was applied to non-enzymatic detection of glucose in rat serum after CCl₄-induced liver damage. Graphical abstract A polymer based fluorescent probe has been constructed and applied for non-enzymatic monitoring of serum glucose following hepatotoxin induced liver injury.