Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluores...

Review of Carbon and Graphene Quantum Dots for Sensing

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence.

Carbon quantum dots (CQDs) as an emerging class of quantum dots (QDs) with advantages such as good photoluminescence (PL) properties, easy synthesis routes, economical synthesis, cheap starting materials, water-solubility, low levels of toxicity, chemical stability, and easy functionalization have received great attention during recent years. CQDs have been used in versatile sensor applications. CQD sensors could be ultimately sensitive, and the limit of detection (LOD) for these sensors can reach the nanomolar, picomolar or even femtomolar ranges. CQD-based sensors and biosensors work with different mechanisms including fluorescence quenching, static quenching, dynamic quenching, energy transfer, inner filter effect (IFE), photo-induced electron transfer (PET), and fluorescence resonance energy transfer (FRET). CQD-based sensors and biosensors have been applied for the detection of different species such as metal ions, acids, proteins, biothiols, polypeptides, DNA and miRNA, water pollutants, hematin, drugs, vitamins, and other chemicals. It seems that CQD-based sensors and biosensors are promising candidates for high performance and yet accurate sensors in different areas. In this review, CQDs are introduced, and the synthesis methods and optical properties of CQDs are discussed. Different types of CQD-based sensors and biosensors and their working mechanisms are clarified.

Principles, mechanisms, and application of carbon quantum dots in sensors: a review

Exosomes are nanoscale extracellular vesicles and have proven to be an effective biomarker for early cancer diagnosis. In this work, an ECL and photothermal dual-mode biosensor was fabricated for exosomes detection by utilizing emerging materials black phosphorous quantum dots (BPQDs) and MXenes as signal amplifier. To be specific, BPQDs can catalyze the oxidization of Ru(dcbpy)32+ and was for the first time used as coreactant, the prepared self-enhanced Ru(dcbpy)32+@BPQDs ECL system can produce a strong ECL signal by reducing energy loss and shortening electron transfer distance. MXenes possess large specific surface area and outstanding conductivity, which was employed as supporter to increase the immobilization amount of Ru(dcbpy)32+ and BPQDs, further enhanced ECL signal. Furthermore, BPQDs and MXenes both have excellent photothermal effect, which were dexterously used as thermal convertor device to develop photothermal biosensor for exosomes analysis. This work innovatively employed a dual-modality probe of MXenes-BPQDs to establish biosensor, which not only enriched the application of MXenes and BPQDs in biodetection but also provided an effective and reliable method for exosomes detection.

Black phosphorus quantum dots functionalized MXenes as the enhanced dual-mode probe for exosomes sensing

Carbon materials based quantum dots, mainly including carbon and graphene dots, with wonderful optical, electrical and chemical properties have greatly boosted the development of advanced sensors and analytical chemistry. Electrochemiluminescence (ECL) sensors based on carbon and graphene dots have shown promising potential and rapid developments in recent decades and have also attained great achievements. Deep insight into the applications of carbon and graphene dots in ECL sensing platforms will benefit the design of advanced sensors in the future. In this review, we aim to give a brief overview of carbon and graphene dots with versatile roles in the fabrication of ECL sensors. A general description of the basic ECL mechanisms, main synthesis routes of carbon and graphene dots, and a series of sensing approaches for the detection of targets including metal ions, small molecules, proteins, DNA and cells will be presented. In addition, recent developments of ECL sensors made of carbon-based dots, relevant signal amplification methodologies and an outlook for the construction of highly sensitive ECL sensors based on various carbon-based dots are also discussed.

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Carbon-based dots for electrochemiluminescence sensing

Electrogenerated chemiluminescence (ECL) of semiconductor quantum dots (QDs) is considered as a powerful technique in the fabrication of biosensor, however, the inherent toxicity of the heavy metal ion containing in QDs limits their further applications. Thus, searching for environment-friendly luminescent nanomaterials with high electrochemiluminescence (ECL) efficiency is an urgent goal. In this work, a solid-state method under low temperature was adopted to prepare graphitic carbon nitride quantum dots (g-CNQDs). By using coreactant K2S2O8, a strong cathodic ECL signal of g-CNQDs could be observed in phosphate buffer. A novel ECL resonance energy transfer procedure was constructed between g-CNQDs (emitter) and gold nanoparticles (acceptor). A signal probe was formed by connecting gold nanoparticles at the hairpin DNA (Hai-DNA) terminal. When the signal probe was anchored on g-CNQDs, ECL resonance energy transfer occurred due to the ECL quenching of gold nanoparticles to g-CNQDs. This phenomenon decreased the ECL signal. In the presence of target DNA (T-DNA), the looped structure of Hai-DNA could be destroyed by T-DNA, and gold nanoparticles were separated from g-CNQDs. Accordingly, the ECL resonance energy transfer procedure was hindered, and the ECL signal was recovered again. The ECL intensities exhibited linear correlation with the logarithm of T-DNA concentration from 0.02 fM to 0.1 pM, and the limit of detection was 0.01 fM (3σ). With the developed ECL resonance energy transfer system, good selectivity and high sensitivity were achieved in T-DNA detection.

Electrochemiluminescence sensing platform for ultrasensitive DNA analysis based on resonance energy transfer between graphitic carbon nitride quantum dots and gold nanoparticles

A facile electrochemiluminescence (ECL) sensing platform for the sensitive analysis of sophoridine was constructed using Ru(bpy) 3 2+ /carbon quantum dots – polyvinyl alcohol composite film as modifier. The carbon quantum dots (CQDs) which have the ability to enhance the ECL intensity were synthesized through a simple hydrothermal method. As Ru(bpy) 3 2+ was entrapped in the polyvinyl alcohol (PVA), it was beneficial to immobilize Ru(bpy) 3 2+ efficiently on the GCE surface, and therefore a stable ECL signal could be obtained. In addition, the ECL response on the Ru(bpy) 3 2+ /CQDs/PVA composite system was greatly enhanced by sophoridine. Single-factor was applied to optimize the measurement conditions. The fabricated sophoridine sensor exhibited a well-proportional correlation between ECL intensity and the logarithm of sophoridine concentration in the range of 1.0 × 10 −10 –1.0 × 10 −5  M, and the detection limit was 5.0 × 10 −11  M (S/N = 3). Moreover, the detection of sophoridine in blood serum was successfully accomplished and a desirable result by using the ECL sensing system was achieved, which indicated that the fabricated ECL sensor has potential value in sophoridine monitoring in practical samples.

Development of a highly sensitive electrochemiluminescence sophoridine sensor using Ru(bpy)32+ integrated carbon quantum dots – polyvinyl alcohol composite film

Xing Zhang

Papers

Electrochemiluminescence sensing platform for ultrasensitive DNA analysis based on resonance energy transfer between graphitic carbon nitride quantum dots and gold nanoparticles

Development of a highly sensitive electrochemiluminescence sophoridine sensor using Ru(bpy)32+ integrated carbon quantum dots – polyvinyl alcohol composite film

Novel Z-scheme Sr2MgSi2O7:Eu2+,Dy3+/Ag3PO4 photocatalyst for round-the-clock efficient degradation of organic pollutants and hydrogen production