Conjugation of Glucose Oxidase onto Mn-Doped ZnS Quantum Dots for Phosphorescent Sensing of Glucose in Biological Fluids

Phosphorescent immunosensor for simple and sensitive detection of microcystin-LR in water

A simple and sensitive Mn–ZnS quantum dot room-temperature phosphorescent immunosensor for detecting microcystin-LR was developed. This sensor adopted antigens and antibodies as recognition units and used Mn–ZnS RTP QDs as sensing materials to specifically bind with MC-LR. The structurally specific binding between the microcystin-LR antibody and MC-LR led to the aggregation of antibody-crosslinked QDs, and then the electrons of QDs would be transferred to the complex, leading to the phosphorescence quenching of QDs. The microcystin-LR antigen–antibody specific binding site was first analyzed. This phosphorescent immunosensor rapidly and sensitively detected microcystin-LR, with linear ranges of 0.2–1.5 μg L⁻¹ and 1.5–20 μg L⁻¹ and a detection limit of up to 0.024 μg L⁻¹. Meanwhile, coexisting pollutants of microcystin-LR in water did not significantly interfere with microcystin-LR detection. The new sensor was applied to detect real water samples and showed high sensitivity and selectivity.

A simple and sensitive Mn–ZnS quantum dot room-temperature phosphorescent immunosensor for detecting microcystin-LR was developed.

Nitrogen-containing three-dimensional biomass porous carbon materials as an efficient enzymatic biosensing platform for glucose sensing

Schematic illustration of the fabrication and structure of the 3D-CVS/GOD electrode.

Facile detection of glucose in human serum employing silver-ion-guided surface-enhanced Raman spectroscopy signal amplification

A facile surface-enhanced Raman scattering (SERS) sensor based on a silver-ion-mediated amplification effect was designed for the determination of glucose concentration. In this approach, 4-aminothiophenol (4-ATP) molecules assembled on the surface of a gold wafer (Au wafer@4-ATP) act not only as Raman tags but also as linkage agents. Silver nanoparticles marked with cysteamine (AgNP@cys) were used as the SERS enhancement components because they could be bound to the Au wafer@4-ATP in the presence of silver ions through the formation of N → Ag⁺ ← N coordination compounds. Here, the Ag⁺ ions were obtained by using glucose oxidase to catalyze the oxidation of glucose, producing hydrogen peroxide (H₂O₂) to etch the AgNPs. Therefore, we recorded the SERS intensity of 4-ATP to determine the concentration of glucose in a phosphate buffer as low as 0.1 mM and further achieved a lowest detection of 0.5 mM glucose in human serum. These results show that the proposed approach has strong potential for practical applications.

Human serum albumin templated MnO2 nanosheets are oxidase mimics for colorimetric determination of hydrogen peroxide and for enzymatic determination of glucose

This paper reports on a colorimetric assay for H₂O₂ and glucose. It is based on the use of human serum albumin-templated MnO₂ nanosheets that possess oxidase-like activity. They are capable of oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with oxygen to give a blue product (oxTMB) with an absorbance maximum at 652 nm. When H₂O₂ is introduced, the MnO₂ nanosheets are reduced to Mn(II) ions, and this inhibits the formation of oxTMB. Based on these findings, a colorimetric assay was established for H₂O₂ that has a 0.56 μM detection limit. If glucose is oxidized by glucose oxidase under formation of H₂O₂, the nanosheets can be used to quantify H₂O₂ and thereby to sense glucose. Response is linear in the 0.5 μM to 50 μM glucose concentration range, and the detection limit is 0.32 μM. The method was applied to the determination of glucose in spiked serum samples and gave satisficatory results. Graphical abstract Human serum albumin (HSA) is used as a template for the synthesis of MnO₂ nanosheet. These possess oxidase mimicking activity. H₂O₂ can reduce the nanosheets. The effect is exploited in colorimetric assays for H₂O₂ and glucose using tetramethylbenzidine (TMB) as a chromogenic substrate.

Precise mono-Cu+ ion doping enhanced electrogenerated chemiluminescence from Cd-In-S supertetrahedral chalcogenide nanoclusters for dopamine detection

Herein, the ECL behaviors of precise mono-Cu+ ion doped Cd-In-S supertetrahedral chalcogenide nanoclusters (Cu@CdInS NCs) were investigated, and the effect of mono-Cu+ ions at the vacancy site of NCs on ECL emission performance was also elucidated. Precise mono-Cu+ ion doping not only induced new ECL emission at 596 nm with enhanced efficiency as high as 21.72% relative to [Ru(bpy)3]2+, but also improved acid tolerance of the ECL performances of NCs. In addition, a simple, fast and label-free dopamine ECL sensor with excellent selectivity was achieved.

An ''off-on'' phosphorescent aptasensor switch for the detection of ATP

An "off-on" phosphorescent aptasensor based on the 3-mercaptopropionic acid (MPA) capped Mn-doped ZnS quantum dots (MPA-Mn:ZnS QDs)/aptamer hybrid system was developed to detect adenosine triphosphate (ATP) in biological fluids. The phosphorescence of MPA-Mn:ZnS QDs was obviously quenched when ATP aptamer was added due to the aggregation induced effect. ATP aptamer, adsorbed on the surface of the phosphorescent MPA-Mn:ZnS QDs, has a high affinity for ATP. And then, with the addition of ATP, phosphorescence was gradually recovered because of the stronger special binding interaction between ATP and ATP aptamer than that between QDs and ATP aptamer. In this case, a high sensitivity and selectivity of phosphorescent aptasensor for the detection of ATP has constructed with a low detection limit of 0.9 nM and a wide linear range from 2 nM to 9 µM. What's more, the phosphorescent aptasensor does not require complex pretreatments and can effectively eliminate the interference from auto fluorescence and scattering light.

Detection of resveratrol by phosphorescence quantum dots without conjunction and mutual impact exploration

In this study, a convenient and sensitive method for the detection of resveratrol was established based on phosphorescence quenching of resveratrol for MPA-capped Mn:ZnS QDs. The quenching intensity was in proportion to the concentration of resveratrol within a certain range. Under optimal conditions, the present assay was valid for detecting resveratrol in the range from 0.03 μM to 14 μM with a detection limit of 0.01 μM. The mechanism of action was also explored, and its application in actual samples was also demonstrated with satisfactory results. This study aims to provide a convenient method for the detection of resveratrol.

Functional Bioinorganic Hybrids from Enzymes and Luminescent Silicon-Based Nanoparticles

This study reports the preparation of functional bioinorganic hybrid materials exhibiting catalytic activity and photoluminescent properties arising from the combination of enzymes and freestanding silicon-based nanoparticles. The hybrid materials reported herein have potential applications in biological sensing/imaging and theranostics, as they combine long-lived silicon-based nanoparticle photoluminescence with substrate-specific enzymatic activity. Thermal hydrosilylation of undecenoic acid and alkene-terminated poly(ethylene oxide) with hydride-terminated silicon nanocrystals afforded nanoparticles functionalized with a mixed surface made up of carboxylic acid and poly(ethylene oxide) moieties. These silicon-based nanoparticles were subsequently conjugated with prototypical enzymes through the carbodiimide-mediated amide coupling reaction in order to form bioinorganic hybrids that display solubility and photostability in phosphate buffer, photoluminescence (λ_max = 630 nm), and enzymatic activity. They were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), dynamic light scattering analysis (DLS), photoluminescence spectroscopy, and pertinent enzyme activity assays.

Aggregation-induced phosphorescence enhancement of Mn-doped ZnS quantum dots: the role of dot-to-dot distance

Assembled nanoparticles promote many applications in optics due to their instinct properties. The aggregation-induced phosphorescence enhancement (AIPE) of Mn-doped ZnS quantum dots (QDs) is widely used in biosensing, but the mechanism of such an enhancement is still unproven. This study explores the mechanism of the interesting finding of AIPE of Mn-doped ZnS QDs. To induce the aggregation of QDs, the method of electrostatic assembly was explored herein: negatively charged QDs were aggregated with protamine and positively charged QDs were aggregated with heparin. Using several ligands with hierarchical molecular weights for capping Mn-doped ZnS QDs, it was found that the AIPE of Mn-doped ZnS QDs was exponentially dependent on the dot-to-dot distance in aggregates. Together with detailed analysis of both the steady- and transient-state luminescence behaviors of Mn-doped ZnS QDs before and after aggregation, charge transfer from one dot (surface traps) to another (dopant bands) was identified as the driving factor for AIPE. Moreover, the d-band of the Mn2+ dopants was essential for the AIPE since it acts as the acceptor for the transferred charge from neighboring QDs. These conclusions can significantly contribute for better understanding of this interesting luminescence mechanism and future designing of the most suitable sensing systems.

Use of Water Soluble and Phosphorescent MPA-capped CdTe Quantum Dots for the Detection of Urea

Objectives

To describe a method for the determination of urea in blood serum using urease enzyme and 3-MPA-capped CdTe quantum dots.

Materials and Methods

The method is based on the increase in pH of the solution as a result of the reaction between urea and urease, which causes an increase in the phosphorescence signal of MPA-CdTe quantum dots in the pH range of 2.5-5.0. Under the optimum conditions, the linear range of urea was 0.016-0.16 mM (1-10 mg/L) and the limit of detection based on 3 s/b was calculated as 0.003 mM (0.17 mg/L). The relative standard deviation was calculated as 3.4% at 4 mg/L urea concentration (n=7).

Results

The method was applied to human serum samples. The same samples were analyzed by an independent laboratory and the results were not statistically different, at 95% confidence level (F test).

Conclusion

The proposed method does not need sample pretreatment, is simple, selective, and cost-effective for the determination of urea in serum samples.

Molecular imprinting based on phosphorescent resonance energy transfer for malachite green detection in fishes and water

Room temperature phosphorescent quantum dots combined with molecular imprinting technology for the highly selective detection of malachite green (MG) in fish and water.

Ternary nanocomposites of Au/CuS/TiO2 for an ultrasensitive photoelectrochemical non-enzymatic glucose sensor

Ternary nanocomposites of Au/CuS/TiO₂ hybrid arrays were prepared for the fabrication of an ultrasensitive photoelectrochemical non-enzymatic glucose sensor.

“Turn on” room-temperature phosphorescent biosensors for detection of hyaluronic acid based on manganese-doped ZnS quantum dots

Biosensors based on excellent optical properties of quantum dots (QDs) nanohybrids are efficient for biological detection. In this work, a room-temperature phosphorescent (RTP) PDAD–Mn–ZnS QDs biosensor was constructed with poly(diallyldimethylammonium chloride) (PDAD) as the modifier of MPA-capped Mn–ZnS QDs, and used to detect hyaluronic acid (HA). The newly-added HA induced severe electrostatic interaction with PDAD–Mn–ZnS QDs, leading to the aggregation between PDAD–Mn–ZnS QDs and HA and thereby enhancing RTP. The enhancement of RTP was proportional to the HA concentrations within certain ranges. On this basis, a high-performance HA sensor was built and this sensor had a detection limit of 0.03 μg mL⁻¹ and a detection range of 0.08–2.8 μg mL⁻¹. This proposed RTP sensor can avoid interferences from the background fluorescence or scattering light of the matrix that are encountered in spectrofluorometry. Thus, this biosensor is potentially suitable for detection of HA in real samples without complicated pretreatment.

Fabricating PDAD–Mn–ZnS QDs nanohybrids as a facile room-temperature phosphorescent biosensor for detection of hyaluronic acid.

Noninvasive and Highly Selective Monitoring of Intracellular Glucose via a Two-Step Recognition-Based Nanokit

Accurate determination of intracellular glucose is very important for exploring its chemical and biological functions in metabolism events of living cells. In this paper, we developed a new noninvasive and highly selective nanokit for intracellular glucose monitoring via two-step recognition. The liposome-based nanokit coencapsulated the aptamer-functionalized gold nanoparticles (AuNPs) and the Shinkai's receptor together. When the proposed nanokit was transfected into living cells, the Shinkai's receptor could recognize glucose first and then changed its conformation to endow aptamers with binding and sensing properties which were not readily accessible otherwise. Then, the binary complexes formed by the intracellular glucose and the Shinkai's receptor can in situ displace the complementary oligonucleotide of the aptamer on the surface of AuNPs. The fluorophore-labeled aptamer was away from the AuNPs, and the fluorescent state switched from "off" to "on". Through the secondary identification of aptamer, the selectivity of the Shinkai's receptor could be greatly improved while the intracellular glucose level was assessed by fluorescence signal recovery of aptamer. In the follow-up application, the approach exhibits excellent selectivity and is noninvasive for intracellular glucose monitoring under normoxia and hypoxia. To the best of our knowledge, this is the first time that the advantages of organic receptors and nucleic acids have been combined and highly selective monitoring of intracellular glucose has been realized via two-step recognition. We expect it to open up new possibilities to integrate devices for diagnosis of various metabolic diseases and insulin delivery.

Thiolate-Capped CdSe/ZnS Core-Shell Quantum Dots for the Sensitive Detection of Glucose

A semiconducting water-soluble core-shell quantum dots (QDs) system capped with thiolated ligand was used in this study for the sensitive detection of glucose in aqueous samples. The QDs selected are of CdSe-coated ZnS and were prepared in house based on a hot injection technique. The formation of ZnS shell at the outer surface of CdSe core was made via a specific process namely, SILAR (successive ionic layer adsorption and reaction). The distribution, morphology, and optical characteristics of the prepared core-shell QDs were assessed by transmission electron microscopy (TEM) and spectrofluorescence, respectively. From the analysis, the results show that the mean particle size of prepared QDs is in the range of 10–12 nm and that the optimum emission condition was displayed at 620 nm. Further, the prepared CdSe/ZnS core shell QDs were modified by means of a room temperature ligand-exchange method that involves six organic ligands, L-cysteine, L-histidine, thio-glycolic acid (TGA or mercapto-acetic acid, MAA), mercapto-propionic acid (MPA), mercapto-succinic acid (MSA), and mercapto-undecanoic acid (MUA). This process was chosen in order to maintain a very dense water solubilizing environment around the QDs surface. From the analysis, the results show that the CdSe/ZnS capped with TGA (CdSe/ZnS-TGA) exhibited the strongest fluorescence emission as compared to others; hence, it was tested further for the glucose detection after their treatment with glucose oxidase (GOx) and horseradish peroxidase (HRP) enzymes. Here in this study, the glucose detection is based on the fluorescence quenching effect of the QDs, which is correlated to the oxidative reactions occurred between the conjugated enzymes and glucose. From the analysis of results, it can be inferred that the resultant GOx:HRP/CdSe/ZnS-TGA QDs system can be a suitable platform for the fluorescence-based determination of glucose in the real samples.

Gram-Scale Synthesis of Hydrophilic PEI-Coated AgInS2 Quantum Dots and Its Application in Hydrogen Peroxide/Glucose Detection and Cell Imaging

Assisted with polyethylenimine, 4.0 L of water-soluble AgInS₂ quantum dots (AIS QDs) were successfully synthesized in an electric pressure cooker. As-prepared QDs exhibit yellow emission with a photoluminescence (PL) quantum yield up to 32%. The QDs also show excellent water/buffer stability. The highly luminescent AIS QDs are used to explore their dual-functional behavior: detection of hydrogen peroxide (H₂O₂)/glucose and cell imaging. The amino-functionalized AIS QDs show high sensitivity and specificity for H₂O₂ and glucose with detection limits of 0.42 and 0.90 μM, respectively. A linear correlation was established between PL intensity and concentration of H₂O₂ in the ranges of 0.5-10 μM and 10-300 μM, while the linear ranges were 1-10 μM and 10-1000 μM for detection of glucose. The AIS QDs reveal negligible cytotoxicity on HeLa cells. Furthermore, the luminescence of AIS QDs gives the function of optical imaging.

Phosphorescence detection of manganese(VII) based on Mn-doped ZnS quantum dots

The phosphorescent l-cysteine modified manganese-doped zinc sulfide quantum dots (l-cys-MnZnS QDs) was developed for a highly sensitive detection of permanganate anions (MnO₄^-). l-cys-MnZnS QDs, which were easily synthesized in aqueous media using safe and low-cost materials, can emit intense phosphorescence even though the solution was not deoxygenated. However, the phosphorescence of l-cys-Mn-ZnS QDs was strongly quenched by MnO₄^- ascribed to the oxidation of l-cys and the increase of surface defects on l-cys-MnZnS QDs. Under the optimal conditions, l-cys-MnZnS QDs offer high selectivity over other anions for MnO₄^- determination, and good linear Stern-Volmer equation was obtained for MnO₄^- in the range of 0.5-100μM with a detection limit down to 0.24μM. The developed method was finally applied to the detection of MnO₄^- in water samples, and the spike-recoveries fell in the range of 95-106%.

A glucose-activatable trimodal glucometer self-assembled from glucose oxidase and MnO2nanosheets for diabetes monitoring

For the first time a glucose-activatable trimodal glucometer with an exceptional enhanced enzymatic activity, self-assembled from glucose oxidase and MnO₂nanosheets for diabetes monitoringin vitro, has been presented.

Ag@Au nanoprism-metal organic framework-based paper for extending the glucose sensing range in human serum and urine

Ag@Au nanoprism-MOFs-based paper for enhancing the glucose sensing range in human serum and in urine.

Detection of tumor marker miRNA21 based on phosphorescent resonance energy transfer of Mn–ZnS QDs

Since miRNA21 is a marker of many human tumors, trace detection of miRNA21 contributes to early tumor diagnosis.

Detection of phosphate based on phosphorescence of Mn doped ZnS quantum dots combined with cerium(iii)

A simple and rapid room-temperature phosphorescence (RTP) sensor for phosphate detection was developed on the basis of Ce³⁺ modulated mercaptopropionic acid (MPA)-capped Mn-doped ZnS quantum dots (QDs).

Phosphorescence detection of 2-mercaptobenzothiazole in environmental water samples by Mn-doped ZnS quantum dots

A room-temperature phosphorescence sensor was constructed based on MPA-capped Mn-doped ZnS QDs for the detection of MBT in water samples.

CdS nanocrystals as fluorescent probe for detection of dolasetron mesylate in aqueous solution: Application to biomedical analysis

A simple and straightforward method for the determination of dolasetron mesylate (DM) in aqueous solution was developed based on the fluorescence quenching of 3-Mercaptopropionic acid (MPA) capped CdS quantum dots (QDs). The structure, morphology, and optical properties of synthesized QDs were characterized by using UV-Vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. Under the optimum conditions, the MPA-CdS QDs fluorescence probe offered good sensitivity and selectivity for detecting DM. The probe provided a highly specific selectivity and a linear detection of DM in the range of 2-40 µg/mL with detection limit (LOD) 1.512 µg/mL. The common excipients did not interfere in the proposed method. The fluorescence quenching mechanism of CdS QDs is also discussed. The developed sensor was applied to the quantification of DM in urine and human serum sample with satisfactory results.

Sensitive fluorescent detection of H2O2 and glucose in human serum based on inner filter effect of squaric acid-iron(III) on the fluorescence of upconversion nanoparticle

Diabetes mellitus is an epidemic disease that it has became a worldwide public health problem. Thus, blood glucose monitoring has attracted extensive attention. Here, we report a nanosensor based on inner filter effect (IFE) between upconversion nanoparticles (UCNPs) and squaric acid (SQA)-iron(III) for the highly sensitive and selective detection of glucose levels in human serum. In this assay, GOx-catalyzed oxidization of glucose produces gluconic acid and hydrogen peroxide (H₂O₂). The latter can catalytically oxidize iron(II) to iron(III) which can rapidly (<1min) coordinate with the SQA to produce (SQA)-iron(III). The absorption band of (SQA)-iron(III) largely covered the emission band of UCNPs, resulting the fluorescence emission of UCNPs was effectively quenched. Therefore, the glucose can be monitored based on the formation of SQA-iron(III). Under the optimal condition, the fluorescence quenching efficiency shows a good linear response to glucose concentration in the ranges of 7-340μmol/L with a detection limit of 2.3μmol/L. The developed method has been further applied to monitor glucose levels in human serum with satisfactory results. Compared with other fluorescence methods, current method displayed high sensitivity and signal-to-noise ratio. Meanwhile, this nanosystem is also generalizable and can be easily expanded to the detection of various H₂O₂-involved analytes.

Sensing Glucose in Urine and Serum and Hydrogen Peroxide in Living Cells by Use of a Novel Boronate Nanoprobe Based on Surface-Enhanced Raman Spectroscopy

Hydrogen peroxide (H2O2) is known as a key molecule in a variety of biological processes, as well as a crucial byproduct in many enzymatic reactions. Therefore, being able to selectively and sensitively detect H2O2 is not only important in monitoring, estimating, and decoding H2O2 relevant physiological pathways but also very helpful in developing enzymatic-based biosensors for other analytes of interest. Herein, we report a plasmonic probe for H2O2 based on 3-mercaptophenylboronic acid (3-MPBA) modified gold nanoparticles (AuNPs) which is coupled with surface-enhanced Raman scattering (SERS) to yield a limit of detection (LOD) of 70 nM. Our probe quantifies both exogenous and endogenous H2O2 levels in living cells and can further be coupled with glucose oxidase (GOx) to achieve quantitative and selective detection of glucose in artificial urine and human serum.

Glutathione-capped Mn-doped ZnS quantum dots as a room-temperature phosphorescence sensor for the detection of Pb(2+) ions

The room-temperature phosphorescence (RTP) of glutathione-capped Mn-doped ZnS quantum dots (GSH-Mn-ZnS QDs) was effectively quenched by the addition of Pb(2+). A simple and sensitive RTP sensor for Pb(2+) detection based on the quenching effect was developed. Under the optimal conditions, good linear correlations were obtained for Pb(2+) over a concentration range from 1.0 to 100μg·L(-1), and the detection limit was 0.45μg·L(-1). The established method has been successfully applied for the determination of Pb(2+) in real water samples without complicated sample pretreatment with the recoveries in the range of 95.4%-104.0%.

Multi-doped carbon dots with ratiometric pH sensing properties for monitoring enzyme catalytic reactions

Multi-doped carbon dots (C-dots) were synthesized using a facile one-pot solvothermal method, and the C-dots can be used as a ratiometric pH probe directly without integrating with other dyes, which was demonstrated by monitoring the proton-producing enzyme catalytic reactions.