A novel electrochemiluminescent immunosensor based on the quenching effect of aminated graphene on nitrogen-doped carbon quantum dots

Nitrogen-doped carbon quantum dots (N-CQDs) with an average diameter of 2 nm were synthesized by carbonization of diethylene triamine pentacetate acid (DTPA). The simple prepared N-CQDs showed excellent electrochemiluminescence (ECL) property and were used as luminophors to fabricate a sandwich-type ECL immunosensor. Aminated graphene (NH₂-G) was also synthesized and used as a label of secondary antibody. The labeled NH₂-G could effectively quench the ECL of N-CQDs modified on electrodes due to ECL resonance energy transfer (ERET). Immunological recognition which induced ECL quenching enabled the quantitative determination of biomarkers. Alpha fetoprotein (AFP) was selected as a model analyte to investigate the analytical performance of the proposed immunosensor. Under optimal conditions, a good linear relationship between ECL intensity and the logarithm of AFP concentration was obtained in the range of 0.01–100 ng mL⁻¹ with the detection limit of 3.3 pg mL⁻¹. The proposed ECL immunosensor showed good stability, acceptable selectivity and reproducibility.     

ZnO-离子液体功能化的石墨烯量子点的制备及荧光性能

利用水热法制备了ZnO-1-丙胺基-3-甲基咪唑氯离子液体功能化的石墨烯量子点溶液,通过紫外-可见吸收光谱、红外吸收光谱和透射电镜对其进行了表征.通过研究各种因素对ZnO-离子液体功能化的石墨烯量子点的荧光发射光谱的影响,发现Cr₂O₇^2-对ZnO-离子液体功能化的石墨烯量子点有荧光猝灭现象.实验结果表明,在优化的实验条件下,pH=5.0,Cr(Ⅵ)浓度为1.0×10^-7～1.6×10^-6 mol·L^-1时,Cr(Ⅵ)对ZnO-离子液体功能化的石墨烯量子点的荧光猝灭呈线性,其线性方程为F/F₀=0.969 5-0.008 4c,R=0.998 8,检出限为7.6×10^-2μmol·L^-1.     

栀子甙对碲化镉量子点的荧光淬灭作用

以3-巯基丙酸作为稳定剂,在水溶液中合成了CdTe量子点;采用荧光光谱法初步研究了栀子甙对巯基丙酸稳定的CdTe量子点的荧光淬灭作用,考察了量子点浓度、pH、反应时间等多种因素对量子点-栀子甙体系荧光强度的影响,确定了测定栀子甙的最佳实验条件;并初步探讨了栀子甙与该量子点相互作用的可能反应机理.结果表明,在最佳实验条件下,巯基丙酸稳定的CdTe量子点对栀子甙检测的线性范围为2×10-7~4×10-6 mol/L,检出限为1.4×10-7 mol/L,相对标准偏差为0.355%;且常见的金属阳离子、糖类和氨基酸对栀子甙的测定无显著影响.总体而言,该方法可用于人体体液中栀子甙的检测,且两者的作用过程可初步推断为动态淬灭过程.     

Determination of abscisic acid based on the fluorescent quenching of quantum dots

The quenching mechanism of the fluorescence of quantum dots by abscisic acid has been systematically investigated.The quenching constant KSV = 5.1 × 1011 / M was obtained under the optimized condition.On the basis of that,a very sensitive method for the determination of abscisic acid has been developed.The linear equation was F0/F = 0.9309 + 0.5072 C(pmol/L) and its linear range was 0.2-3.0 pmol/L with a correlation coefficient of 0.9939.The limit of detection was 0.09 pmol/L.     

Mn掺杂ZnS量子点荧光猝灭法测定对乙酰氨基酚

利用水热合成法合成了L-谷胱甘肽(GSH)修饰的Mn掺杂ZnS量子点(QDs),基于对乙酰氨基酚对该量子点的荧光猝灭作用,建立了一种快速高效检测对乙酰氨基酚的方法.在最优实验条件下,量子点荧光强度的变化与对乙酰氨基酚浓度在0.25~10μmol·L-1范围内呈良好的线性关系(R=0.999 5),检出限为4.1×10-8mol·L-1,相对标准偏差为0.35%.该方法成功地应用于人尿液中对乙酰氨基酚的测定,样品加标回收率为95%~100%.     

Fluorescent blood glucose monitor by hemin-functionalized graphene quantum dots based sensing system

In the present work, a highly sensitive and specific fluorescent biosensor for blood glucose monitoring is developed based on hemin-functionalized graphene quantum dots (GQDs) and glucose oxidase (GOx) system. The GQDs which are simply prepared by pyrolyzing citric acid exhibit strong fluorescence and good water-solubility. Due to the noncovalent assembly between hemin and GQDs, the addition of hemin can make hydrogen peroxide (H₂O₂) to destroy the passivated surface of GQDs, leading to significant fluorescence quenching of GQDs. Based on this effect, a novel fluorescent platform is proposed for the sensing of glucose. Under the optimized conditions, the linear range of glucose is from 9 to 300 μM, and the limit of detection is 0.1 μM. As unique properties of GQDs, the proposed biosensor is green, simple, cost-efficient, and it is successfully applied to the determination of glucose in human serum. In addition, the proposed method provides a new pathway to further design the biosensors based on the assembly of GQDs with hemin for detection of biomolecules.     

水溶性CdTe量子点的合成及其用于荧光猝灭法测定肌红蛋白

以3-巯基丙酸为稳定剂,合成了具有特殊光学性质的水溶性CdTe量子点,其最大发射波长位于544 nm.利用荧光光谱、紫外可见光谱及圆二色光谱法系统的研究了CdTe量子点与肌红蛋白(Mb)二者结合前后体系光谱的变化,从而证实了CdTe量子点与Mb之间静电结合反应的特征.在pH 7.0的PBS缓冲液中,用CdTe量子点作为荧光探针研究了肌红蛋白与量子点的相互作用,并基于肌红蛋白对CdTe量子点有显著的荧光猝灭作用,建立了肌红蛋白的快速检测方法.在最佳实验条件下,该体系荧光强度的猝灭程度(△F)与肌红蛋白质量浓度呈良好的线性关系,线性范围为0.3～24 μg/mL,检出限为0.13 μg/mL.该方法已对合成样品中肌红蛋白进行检测,并用于人体尿样中肌红蛋白的测定.     

A new hydrogen cyanide chemiresistor gas sensor based on graphene quantum dots

Graphene quantum dots (GQDs), synthesised via controlled carbonisation of citric acid, were reduced by hydrazine hydrate and then used as hydrogen cyanide (HCN) gas sensors. Checking of the reduction step by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) techniques revealed that most of the oxygen-containing functional groups were removed from the GQDs. It was observed the reduction process is necessary for sensitising of GQDs for HCN gas. The electrical resistance of the reduced GQDs was increased as a result of their exposure to HCN gas. Accepting a p-type semiconducting characteristic for GQD material, the above-mentioned behaviour suggested electron donation from HCN to GQD. The sensor response to HCN gas was reversible, suggesting a reversible adsorption/desorption phenomenon of HCN to the GQDs. The response as well as the recovery time of the sensor was different depending on the HCN concentration tested. The developed sensor showed linear HCN response from 1 to 100 ppm. The detection limit of the sensor was estimated to be 0.6 ppm (S/N). Relative standard deviation f HCN determination by the developed sensor was calculated to be 5.7% (n = 4, [HCN] = 50 ppm). The sensor response was did not vary significantly within 6 months.     

Sensitive detection of trace hemoglobin using fluorescence method based on functionalized quantum dots

The fluorescence quenching of quantum dots by hemoglobin has been demonstrated to depend on surface functionalization, and this property has been utilized to construct a novel fluorescent method for rapid, sensitive, and selective detection of trace hemoglobin in urine at microgram level. This method shows low interference and high selectivity for hemoglobin with a limit of detection of 4.3 μg L^?1 in water and 66.1 μg L^?1 in urine, which are lower than those of currently used methods in labs and clinics. Spike and recovery tests in raw, acidified, and alkalized urine samples exhibit good recovery rates for the spiked concentrations close to the limit of detection.

Determination of nitrite based on its quenching effect on anodic electrochemiluminescence of CdSe quantum dots

A novel method for electrochemiluminescent (ECL) detection of nitrite was proposed based on its quenching effect on anodic ECL emission of CdSe quantum dots (QDs). The ECL emission could be greatly enhanced by sulfite and dissolved oxygen in a neutral system and occurred at a relatively low potential in comparison with traditional anodic ECL emitter, leading to high sensitivity and good selectivity. The quenching mechanism followed an “electrochemical oxidation inhibition” process, which was completely different from those of some analytes on the ECL emission of QDs. The coincidence of photoluminescence and ECL spectra of the QDs indicated that the ECL emission resulted from the redox process of QDs core and the sulfite acted as a coreactant. The nitrite quenched ECL emission could be analyzed according to the treatment of Stern-Volmer equation with a linear range from 1 μM to 0.5 mM for detection of nitrite. This work presented a new efficient ECL methodology for quencher-related detection.     

Dopamine detection based on its quenching effect on the anodic electrochemiluminescence of CdSe quantum dots

Anodic electrochemiluminescence (ECL) of CdSe quantum dots (QDs) in a neutral system was for the first time observed at a relatively low potential by using sulfite as a co-reactant to produce the ECL emission at an indium tin oxide (ITO) electrode, which could be used for the sensitive detection of ECL quenchers using dopamine (DA) as a model molecule.     

量子点标记链霉亲和素荧光免疫分析测定雌三醇

以生物素化羊抗兔免疫球蛋白和量子点标记链霉亲和素为荧光探针,采用竞争免疫分析模式,建立了一种灵敏度高、选择性好的检测雌三醇的荧光免疫分析方法.对几种测量参数如温育时间和温度、缓冲溶液pH、试剂浓度等进行了优化;方法的线性范围为0.01～1000ng/mL,检出限0.0029 ng/mL,血清样品加标回收率在91%～117%之间.     

CdSe/ZnS quantum dots based fluorescence quenching method for determination of paeonol

Aqueous polymethylmethacrylate (PMMA)-capped CdSe/ZnS quantum dots were used as fluorescence probes for paeonol determination. Based on the fluorescence quenching of aqueous CdSe/ZnS quantum dots caused by paeonol, a simple, sensitive and rapid method was developed. Under the optimal conditions, with excitation and emission wavelengths at 350 nm and 620 nm, respectively, the calibration plot of F0-F with concentration of paeonol was linear in the range of 25.04-175.2 mg L(-1) with correlation coefficient of 0.9986. The limit of detection was 0.017 mg L(-1). The concentration of paeonol in paeonol ointment was determined by the proposed method and the result agreed with the claimed value. Furthermore, the possible fluorescence quenching mechanism was discussed.     

Sensing of ozone based on its quenching effect on the photoluminescence of CdSe-based core-shell quantum dots

Microchimica Acta - Thin films of CdSe-based core-shell type quantum dots (CdSe/CdZnS, CdSe/ZnS and CdSeTe/ZnS) deposited on glass substrate were found to undergo a reversible change in...     

The quenching of CdSe quantum dots photoluminescence by gold nanoparticles in solution

The photoluminescence (PL) of CdSe quantum dots (QD) in aqueous media has been studied in the presence of gold nanoparticles (NP) with different shapes. The steady state PL intensity of CdSe QD (1.5-2 nm in size) is quenched in the presence of gold NP. Picosecond bleach recovery and nanosecond time-resolved luminescence measurements show a faster bleach recovery and decrease in the lifetime of the emitting states of CdSe QD in the presence of quenchers. Surfactant-capped gold nanorods (NR) with aspect ratio of 3 and surfactant-capped and citrate-capped nanospheres (NS) of 12 nm diameter were used as quenchers in order to study the effect of shape and surface charge on the quenching rates. The Stern-Volmer kinetics model is used to examine the observed quenching behavior as a function of the quencher concentration. It was found that the quenching rate of NR is more than 1000 times stronger than that of NS with the same capping material. We also found that the quenching rate decreases as the length of the NR decreases, although the overlap between the CdSe emission and the NR absorption increases. This suggests that the quenching is a result of electron transfer rather than long-range (Forster-type) energy transfer processes. The quenching was attributed to the transfer of electron with energies below the Fermi level of gold to the trap holes of CdSe QD. The observed large difference between NR and NS quenching efficiencies was attributed to the presence of the [110] facets only in the NR, which have higher surface energy.     

Unusual emission transformation of graphene quantum dots induced by self-assembled aggregation

Graphene quantum dots prepared by a one-step hydrothermal procedure in a microwave exhibit an unusual emission transformation in strong acidic media and at high concentration, induced by self-assembled J-type aggregation under restrained π-π interactions.     

Determination of uranium in environmental sample by nanosensor graphene quantum dots

Journal of Radioanalytical and Nuclear Chemistry - The unique properties of graphene quantum dots (GQDs) i.e. low toxicity, excellent water solubility, low cost, high photostability,...     

Phenol-like group functionalized graphene quantum dots structurally mimicking natural antioxidants for highly efficient acute kidney injury treatment

Acute kidney injury (AKI) is a syndrome characterized by rapid loss of renal excretory function with high in-hospital mortality. The excess generation of reactive oxygen species (ROS) in the kidneys during AKI has been considered a major cause of renal failure. Currently available antioxidants for AKI treatment often lack the required antioxidative efficacy or renal accumulation rate. Herein, inspired by the structure of natural phenolic antioxidants, phenol-like group functionalized graphene quantum dots (h-GQDs) with both high ROS scavenging efficacy and renal specificity are constructed for AKI antioxidative therapy. Similar to natural polyphenols, the abundant phenol-like groups on h-GQDs are demonstrated to be the active components exerting antioxidative effects. Further exhaustive mechanistic investigations indicate that the ultrahigh antioxidative activity of h-GQDs originates not solely from the phenol-like groups, but also from the synergy between adjacent phenol-like groups, as well as the removal of unfavorable carbonyl groups on h-GQDs. In AKI mice, h-GQDs can effectively protect the kidneys from oxidative injury with only a one-sixteenth dose of the clinical antioxidant N-acetylcysteine (NAC) and show no evidence of toxicity. The findings of this study will facilitate development of high-performance carbon-based antioxidative platforms via structure–activity relationships for treating AKI and other ROS-related diseases.

Phenol-like group functionalized graphene quantum dots that structurally mimic natural antioxidants are constructed as high-efficacy reactive oxygen species scavengers for acute kidney injury antioxidative therapy.     

Nitrogen-doped graphene quantum dots doped silica nanoparticles as enhancers for electrochemiluminescence thrombin aptasensors based on 3D graphene

Journal of Solid State Electrochemistry - A sensitive electrochemiluminescence (ECL) aptasensor based on 3D graphene is described for thrombin detection utilizing nitrogen-doped graphene quantum...     

Nitrogen-doped graphene quantum dots with oxygen-rich functional groups

Graphene quantum dots (GQDs) represent a new class of quantum dots with unique properties. Doping GQDs with heteroatoms provides an attractive means of effectively tuning their intrinsic properties and exploiting new phenomena for advanced device applications. Herein we report a simple electrochemical approach to luminescent and electrocatalytically active nitrogen-doped GQDs (N-GQDs) with oxygen-rich functional groups. Unlike their N-free counterparts, the newly produced N-GQDs with a N/C atomic ratio of ca. 4.3% emit blue luminescence and possess an electrocatalytic activity comparable to that of a commercially available Pt/C catalyst for the oxygen reduction reaction (ORR) in an alkaline medium. In addition to their use as metal-free ORR catalysts in fuel cells, the superior luminescence characteristic of N-GQDs allows them to be used for biomedical imaging and other optoelectronic applications.