A potential-resolved electrochemiluminescence resonance energy transfer strategy for the simultaneous detection of neuron-specific enolase and the cytokeratin 19 fragment.

An electrochemiluminescence resonance energy transfer (ECL-RET) immunosensor was developed based on the potential-resolved technology for the simultaneous detection of neuron-specific enolase (NSE) and the cytokeratin 19 fragment (CYFRA21-1). The absorption spectrum of gold nanorods (AuNRs) perfectly overlapped with the ECL spectra of SnS2@Pt and Ru(bpy)32+/Zn-MOF, so they exhibited an excellent ECL-RET effect with high efficiency. Zn-MOF possesses a large surface area, which allows for the loading of Ru(bpy)32+. This results in a signal probe of Ru(bpy)32+/Zn-MOF/Ab1 showing a strong ECL emission. Simultaneously, owing to the excellent electronic conductivity of PtNPs, they can increase the electron transfer rate between S2O82- and tin disulfide nanoflowers (SnS2NFs). Hence, the ECL signal of SnS2NFs can be enhanced. Under the optimal conditions, the linear range for NSE is 0.2 pg mL-1-20 ng mL-1 with a detection limit of 79 fg mL-1. The linear range for CYFRA21-1 is 1.25 pg mL-1-12.5 ng mL-1 with a detection limit of 0.43 pg mL-1. The proposed immunosensor can be used for the sensitive simultaneous detection of NSE and CYFRA21-1 in human serum and has promise for clinical diagnostics.

N-doped carbon quantum dots from osmanthus fragrans as a novel off-on fluorescent nanosensor for highly sensitive detection of quercetin and aluminium ion, and cell imaging.

In this work, fluorescent N-doped carbon quantum dots (N-CQDs) have been synthesized by simple hydrothermal heating of natural osmanthus fragrans, without any toxic ingredients or surface chemical modifications. The N-CQDs possess a high quantum yield of 21.9 %, outstanding blue fluorescence, good water dispersity, and excellent optical stability. Because the favorable inner filter effect (IFE) between N-CQDs and quercetin (QT) occurs, the addition of QT to N-CQDs can cause their fluorescence quenching. When Al3+ was added to the N-CQDs/QT system solution, it was found that the inhibition of IFE leads to the fluorescence intensity of N-CQDs/QT system enhancement by virtue of a specific binding of QT to aluminum ion (Al3+). Therefore, we used the N-CQDs as a novel off-on fluorescent nanosensor to detect QT and Al3+. Under optimal conditions, the fluorescent nanosensor can detect QT within the wide linear response in the range of 0.003-80 µmol/L with as low as 1 nmol/L detection limit. For the detection of Al3+, the N-CQDs/QT system showed linearity response toward Al3+ in a range of 0.1∼100 µmol/L and the limit of detection was found at 26 nmol/L. In addition, N-CQDs have been successfully used to efficient quantification QT in human plasma and monitor Al3+ in serum samples. Noteworthy, the N-CQDs demonstrated low toxicity toward T24 cells, which realized sensing QT and Al3+ in the living cells.

Electrochemiluminescence immunoassay of human chorionic gonadotropin using silver carbon quantum dots and functionalized polymer nanospheres.

A composite, reduced graphene oxide (rGO) doped with silver nanoparticles (Ag NPs), was prepared by using binary reductants of sodium citrate and hydrazine hydrate. Carbon quantum dots (CQDs) synthesized by papaya peel combined with silver ions to form a CQDs-loaded silver nanoparticle (AgCQDs) nanocomposite. Polymer nanospheres (PNS) were generated via the infinite coordination polymer of ferrocene dicarboxylic acid and employed as carriers to load AgCQDs. The prepared AgCQDs@PNS-PEI has good biocompatibility and electrical conductivity and can be used as a matrix for the immobilization of a secondary antibody (Ab2). A sandwich-type electrochemiluminescence (ECL) immunosensor using AgCQDs@PNS-PEI nanocomposite as probe has been developed for the detection of human chorionic gonadotropin (HCG). The proposed immunosensor exhibits a linear range from 0.00100 to 500 mIU mL-1 and the detection limit is 0.33 µIU mL-1 (S/N = 3) under optimal conditions. The sensor exhibits excellent selectivity, good reproducibility, and high stability. These features demonstrate that the proposed method has promising potential for clinical protein detection and displays a new strategy to fabricate an immunosensor. Graphical abstract.

Electrochemiluminescent immunoassay for neuron specific enolase by using amino-modified reduced graphene oxide loaded with N-doped carbon quantum dots.

An ultrasensitive electrochemiluminescence based sandwich immunoassay is presented for determination of neuron specific enolase. The method uses silver-cysteine nanowires as the capture probe and a composite made of amino-modified reduced graphene oxide and nitrogen-doped carbon quantum dots as the signal probe. It was synthesized by covalent coupling of amino-modified reduced graphene oxide to the carboxy groups of nitrogen-doped carbon quantum dots. The nanowires possess a large specific surface and abundant functional groups which facilitate immobilizing the primary antibody (Ab1). The amino-modified reduced graphene oxide is employed as a carrier for loading a large number of the quantum dots and secondary antibody (Ab2). This increases the electrochemiluminescence intensity of quantum dots. Response to neuron specific enolase is linear in the 0.55 fg·mL-1 to 5.5 ng·mL-1 concentration range. It has a detection limit of 0.18 fg·mL-1 (at S/N = 3). The relative standard deviation (for n = 6) is less than 2.9%. The assay is highly sensitive, reproducible, selective and stable. Graphical abstractA novel electrochemiluminescence immunosensor is described that uses amino-modified reduced graphene oxide (amino-rGO), nitrogen-doped carbon quantum dots (N-CQDs) and silver-cysteine nanowires (SCNWs). It was applied to the determination of neuron specific enolase (NSE). Bovine serum albumin: BSA;1-ethyl-3-(3-dimethylaminopropyl)carbodiimide: (EDC;, N-hydroxysuccinimide: NHS.

Facile Preparation of Boron and Nitrogen Codoped Green Emission Carbon Quantum Dots for Detection of Permanganate and Captopril.

A hydrothermal strategy for preparing boron and nitrogen codoped carbon quantum dots was studied using the precursors of p-amino salicylic acid, boric acid and ethylene glycol dimethacrylate. The boron and nitrogen codoped carbon quantum dots have high fluorescence intensity, good monodispersity, high stability, superior water solubility, and a fluorescence quantum yield of 19.6%. Their average size is 5 nm. Their maximum excitation and emission wavelengths are 380 and 520 nm, respectively. Permanganate (MnO4-) quenched boron and nitrogen codoped carbon quantum dots fluorescence through inner filter effect and static quenching effects. The linear relation between quenching efficiency and MnO4- concentration ranged from 0.05 to 60 µmol/L with a detection limit of 13 nmol/L. In the presence of captopril, MnO4- was reduced to Mn2+ and the fluorescence of boron and nitrogen codoped carbon quantum dots was recovered. The linear range between recovery and captopril concentration was from 0.1 to 60 µmol/L. The limit of detection was 0.03 µmol/L. The developed method can be employed as a sensitive fluorescence sensing platform for MnO4-. It has been successfully used for captopril detection in mouse plasma.