Determination of free cholesterol based on a novel flow-injection chemiluminescence method by immobilizing enzyme

Recent Advancements in Metal and Non-Metal Mixed-Doped Carbon Quantum Dots: Synthesis and Emerging Potential Applications

In nanotechnology, the synthesis of carbon quantum dots (CQDs) by mixed doping with metals and non-metals has emerged as an appealing path of investigation. This review offers comprehensive insights into the synthesis, properties, and emerging applications of mixed-doped CQDs, underlining their potential for revolutionary advancements in chemical sensing, biosensing, bioimaging, and, thereby, contributing to advancements in diagnostics, therapeutics, and the under standing of complex biological processes. This synergistic combination enhances their sensitivity and selectivity towards specific chemical analytes. The resulting CQDs exhibit remarkable fluorescence properties that can be involved in precise chemical sensing applications. These metal-modified CQDs show their ability in the selective and sensitive detection from Hg to Fe and Mn ions. By influencing their exceptional fluorescence properties, they enable precise detection and monitoring of biomolecules, such as uric acid, cholesterol, and many antibiotics. Moreover, when it comes to bioimaging, these doped CQDs show unique behavior towards detecting cell lines. Their ability to emit light across a wide spectrum enables high-resolution imaging with minimal background noise. We uncover their potential in visualizing different cancer cell lines, offering valuable insights into cancer research and diagnostics. In conclusion, the synthesis of mixed-doped CQDs opens the way for revolutionary advancements in chemical sensing, biosensing, and bioimaging. As we investigate deeper into this field, we unlock new possibilities for diagnostics, therapeutics, and understanding complex biological processes.

Nitrogen, Cobalt Co-doped Fluorescent Magnetic Carbon Dots as Ratiometric Fluorescent Probes for Cholesterol and Uric Acid in Human Blood Serum

Detection of cholesterol and uric acid biomarkers is of great importance for clinical diagnosis of several serious diseases correlated with their variations in human blood serum. In this study, a new kind of well selective and highly sensitive ratiometric fluorescent probe for cholesterol and uric acid determination in human blood serum was innovatively developed on the basis of the inner filter effect (IFE) process of nitrogen, cobalt co-doped carbon dots (N,Co-CDs) with 2,3-diaminophenazine (DAP). DAP was the oxidative product during the oxidation reaction between o-phenylenediamine and H2O2. Fluorescent magnetic N,Co-CDs possessing blue emission and magnetic property were prepared through a facile one-pot hydrothermal strategy by using citric acid, diethylenetriamine, and cobalt(II) chloride hexahydrate as precursors. N,Co-CDs exhibited good ferromagnetic property and excellent optical properties even in extremely harsh environmental conditions, implying the huge potential applications of such N,Co-CDs in biological areas. On the basis of the IFE process between N,Co-CDs and DAP, N,Co-CDs were applied to establish ratiometric fluorescent probes for the indirect detection of cholesterol and uric acid that participated in enzyme-catalyzed H2O2-generation reactions. The established IFE-based fluorescent probes exhibited relatively low detection limits of 3.6 nM for cholesterol and 3.4 nM for uric acid, respectively. The fluorescent probe was successfully utilized for the determination of cholesterol and uric acid in human blood serum with satisfying results, which provided an informed perspective on the applications of such doped CDs to explore the specific and sensitive nanoprobe in disease diagnoses and clinical therapy.

A Ratiometric Fluorescence Universal Platform Based on N, Cu Codoped Carbon Dots to Detect Metabolites Participating in H2O2-Generation Reactions

In this work, a new kind of N, Cu codoped carbon dots (N/Cu-CDs) was prepared via a facile one-pot hydrothermal method by using citric acid monohydrate, copper acetate monohydrate and diethylenetriamine. The prepared N/Cu-CDs with a high quantum yield (50.1%) showed excitation-independent emission at 460 nm. The structure and fluorescence properties of N/Cu-CDs were characterized by high-resolution transmission electron microscopy, fluorescence spectrofluorometer, FT-IR spectrometer, UV-visible spectrophotometer and X-ray photoelectron spectroscopy. N/Cu-CDs were applied to establishing a ratiometric fluorescence probe toward H₂O₂ based on the inner filter effect (IFE) between N/Cu-CDs and DAP (2,3-diaminophenazine, the oxidative product of o-phenylenediamine (OPD)), and provided a ratiometric fluorescence universal platform for detection of the metabolites participating in H₂O₂-generation reactions (cholesterol and xanthine). The proposed method was demonstrated to be ultrasensitive and highly selective for cholesterol and xanthine assay with detection limits of 0.03 and 0.10 μM, respectively. The fluorescence probe built was applied to the determination of cholesterol and xanthine in human serum with satisfactory results.

A novel chemiluminescence sensor for sensitive detection of cholesterol based on the peroxidase-like activity of copper nanoclusters

A sensitive and selective chemiluminescence (CL) sensor based on the peroxidase-like activity of copper nanoclusters was established for the detection of cholesterol. Copper nanoclusters catalyse the CL reaction between luminol and H₂O₂. Because H₂O₂ is the oxidative product of cholesterol in the presence of cholesterol oxidase, the oxidation of cholesterol can be quantitatively converted to a CL response by combining the two reactions. The proposed method is simple and can be completed in a few minutes with high sensitivity. Under the optimal conditions, the CL intensity was proportional to the concentration of cholesterol over a wide range of 0.05-10 mM, with a detection limit of 1.5 μM. Furthermore, the method was successfully applied to determine cholesterol in milk powder and human serum with satisfactory accuracy and precision. This method expands the applications of nano-mimic enzymes in the field of CL-based sensors.

Ultrasensitive detection of proteins and sugars at single-cell level

Each cell produces its own responses even if it appears identical to other cells. To analyze these individual cell characteristics, we need to measure trace amounts of molecules in a single cell. Nucleic acids in a single cell can be easily amplified by polymerase chain reaction, but single-cell measurement of proteins and sugars will require de novo techniques. In the present study, we outline the techniques we have developed toward this end. For proteins, our ultrasensitive enzyme-linked immunosorbent assay (ELISA) coupled with thionicotinamide-adenine dinucleotide cycling can detect proteins at subattomoles per assay. For sugars, fluorescence correlation spectroscopy coupled with glucose oxidase-catalyzed reaction allows us to measure glucose at tens of nM. Our methods thus offer versatile techniques for single-cell-level analyses, and they are hoped to strongly promote single-cell biology as well as to develop noninvasive tests in clinical medicine.

Electrochemiluminescent disposable cholesterol biosensor based on avidin-biotin assembling with the electroformed luminescent conducting polymer poly(luminol-biotinylated pyrrole)

An electrochemiluminescent cholesterol disposable biosensor has been prepared by the formation of assembled layers on gold screen-printed cells. The detection layer is based on the electro-formation of new luminol copolymers with different synthesized biotinylated pyrroles prepared by click-chemistry, offering a new transduction layer with new electroluminescent properties on biosensors. The electrochemiluminescence (ECL) luminol copolymers are electroformed by cyclic voltammetry (five cycles) at pH 7.0 uses a10(-3)M biotinylated pyrrole-luminol ratio of 1:10 in PBS buffer. With respect to the recognition layer, cholesterol oxidase was biotinylated by incubation with biotin vinyl sulfone, and immobilized on the copolymer by avidin-biotin interaction. The analytical signal of the biosensor is the ECL enzymatic initial rate working in chronoamperometric mode at 0.5V excitation potential with 10s between pulses at pH 9.5. The disposable device offers a cholesterol linear range from 1.5×10(-5)M to 8.0×10(-4)M with a limit of detection of 1.47×10(-5)M and accuracy of 7.9% for 9.0×10(-5)M and 14.1% for 2.0×10(-4)M, (n=5). Satisfactory results were obtained for cholesterol determination in serum samples compared to a reference procedure.

Highly sensitive determination of hydrogen peroxide and glucose by fluorescence correlation spectroscopy

Background

Because H₂O₂ is generated by various oxidase-catalyzed reactions, a highly sensitive determination method of H₂O₂ is applicable to measurements of low levels of various oxidases and their substrates such as glucose, lactate, glutamate, urate, xanthine, choline, cholesterol and NADPH. We propose herein a new, highly sensitive method for the measurement of H₂O₂ and glucose using fluorescence correlation spectroscopy (FCS).

Methodology/Principal Findings

FCS has the advantage of allowing us to determine the number of fluorescent molecules. FCS measures the fluctuations in fluorescence intensity caused by fluorescent probe movement in a small light cavity with a defined volume generated by confocal illumination. We thus developed a highly sensitive determination system of H₂O₂ by FCS, where horseradish peroxidase (HRP) catalyzes the formation of a covalent bond between fluorescent molecules and proteins in the presence of H₂O₂. Our developed system gave a linear calibration curve for H₂O₂ in the range of 28 to 300 nM with the detection limit of 8 nM. In addition, by coupling with glucose oxidase (GOD)-catalyzed reaction, the method allows to measure glucose in the range of 80 nM to 1.5 µM with detection limit of 24 nM. The method was applicable to the assay of glucose in blood plasma. The mean concentration of glucose in normal human blood plasma was determined to be 4.9 mM.

Conclusions/Significance

In comparison with commercial available methods, the detection limit and the minimum value of determination for glucose are at least 2 orders of magnitude more sensitive in our system. Such a highly sensitive method leads the fact that only a very small amount of plasma (20 nL) is needed for the determination of glucose concentration in blood plasma.