One-step synthesis of nitrogen-doped carbon quantum dots for paper-based electrochemiluminescence detection of Cu2+ ions

Synthesis and Application of Carbon Quantum Dots Derived from Carbon Black in Bioimaging

Carbon quantum dots (CQDs) are a new type of fluorescent QDs that consists mainly of carbon atoms. In this research, CQDs were synthesized through harsh oxidizing conditions applied on carbon black and subsequent N-doping using hexamethylenetetramine (Hexamine) and polyethyleneimine (PEI). The synthesized CQDs were characterized using FTIR, AFM, UV-Visible spectroscopy, photoluminescence (PL) spectroscopy, and fluorescence imaging respectively. The AFM images showed that the dots are in the range of 2-8 nm. N-doping of the CQDs increased the PL intensity. The PL enhancement for the CQDs that were N-doped with PEI was higher compared to those N-doped with hexamine. The shift in PL by changing the excitation wavelength has been attributed to the nano-size of the CQDs, functional groups, defect traps, and quantum confinement effect. The in vitro fluorescence imaging revealed that N-doped CQDs can internalize into the cells and be used for fluorescent cell imaging.

Bipotential-resolved electrochemiluminescence biosensor based on Bi2S3@Au nanoflowers for simultaneous detection of Cd(II) and ampicillin in aquatic products

In this paper, an electrochemiluminescence (ECL) biosensor was constructed using Bi₂S₃@Au nanoflowers as the based nanomaterial and Au@luminol and CdS QDs as independent ECL emission signal respectively. As the substrate of the working electrode, Bi₂S₃@Au nanoflowers improved the effective area of electrode and accelerated electron transfer rate between gold nanoparticles and aptamer, provided a good interface environment for the loading of luminescent materials. Then, the Au@luminol functionalized DNA2 probe was used as an independent ECL signal source under positive potential and recognized Cd(II), while the CdS QDs functionalized DNA3 probe was used as an independent ECL signal source under negative potential and recognized ampicillin. The simultaneous detection of Cd(II) and ampicillin in different concentrations are realized. This sensor not only has good selectivity and high sensitivity in real sample detection, but also open up a novel way to construct multi-target ECL biosensor for simultaneous detection.

ECL sensor for selective determination of citrate ions as a prostate cancer biomarker using polymer of intrinsic microporosity-1 nanoparticles/nitrogen-doped carbon quantum dots

Urine citrate analysis is relevant in the screening and monitoring of patients with prostate cancer and calcium nephrolithiasis. A sensitive, fast, easy, and low-maintenance electrochemiluminescence (ECL) method with conductivity detection for the analysis of citrate in urine is developed and validated by employing polymer of intrinsic microporosity-1 nanoparticles/nitrogen-doped carbon quantum dots (nano-PIM-1/N-CQDs). Using optimum conditions, the sensor was applied in ECL experiments in the presence of different concentrations of citrate ions. The ECL signals were quenched gradually by the increasing citrate concentration. The linear range of the relationship between the logarithm of the citrate concentration and ΔECL (ECL of blank - ECL of sample) was obtained between 1.0 × 10^-7 M and 5.0 × 10^-4 M. The limit of detection (LOD) was calculated to be 2.2 × 10^-8 M (S/N = 3). The sensor was successfully applied in real samples such as human serum and patient urine.

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Fabrication of Carbon-Based Quantum Dots via a "Bottom-Up" Approach: Topology, Chirality, and Free Radical Processes in "Building Blocks"

The discovery of carbon-based quantum dots (CQDs) has allowed opportunities for fluorescence bioimaging, tumor diagnosis and treatment, and photo-/electro-catalysis. Nevertheless, in the existing reviews related to the "bottom-up" approaches, attention is mainly paid to the applications of CQDs but not the formation mechanism of CQDs, which mainly derived from the high complexities during the synthesis of CQDs. Among the various synthetic methods, using small molecules as "building blocks", the development of a "bottom-up" approach has promoted the structural design, modulation of the photoluminescence properties, and control of the interfacial properties of CQDs. On the other hand, many works have demonstrated the "building blocks"-dependent properties of CQDs. In this review, from one of the most important variables, the relationships among intrinsic properties of "building blocks" and photoluminescence properties of CQDs are summarized. The topology, chirality, and free radical process are selected as descriptors for the intrinsic properties of "building blocks". This review focuses on the induction and summary of recent research results from the "bottom-up" process. Moreover, several empirical rules pertaining thereto are also proposed.

Hydrophobic plasmonic silver membrane as SERS-active catcher for rapid and ultrasensitive Cu(II) detection

The rapid and selective identification of heavy metal ions is crucial for environmental water safety. In this study, a novel surface-enhanced Raman scattering (SERS)-active catcher was designed for Cu(II) detection using a hydrophobic hydroxyoxime-mediated plasmonic silver membrane (HOX@Ag-PVDF). Uniformly dispersed Ag nanoparticles (ca. 80 nm) and hydroxyoxime molecules were synchronously decorated on the skeleton of the polyvinylidene fluoride membrane via an in situ interfacial assembly strategy. HOX@Ag-PVDF shows excellent SERS activity (EF = 2.5 × 10⁷), high reproducibility (~8% RSD), and long-term stability (50 days) for detecting 4-nitrothiophenol (4-NTP). Moreover, HOX@Ag-PVDF can serve as a new platform for rapid and dry-free SERS detection of Cu(II) owing to its strong affinity and surface hydrophobicity. Cu(II) ions can be rapidly captured in 5 s and selectively recognized by SERS signals without interference from other metal ions. HOX@Ag-PVDF exhibits linear SERS response signals at low concentrations ranging from 10^-6 to 10^-10 mol/L Cu(II) (R² = 0.9893) with a low detection limit (LOD) of 52.0 pmol/L. This hydrophobic plasmonic membrane, with its simple sampling and rapid SERS response characteristics, provides ultrasensitive recognition and heavy metal detection for practical applications.

Study on the Performance of Composite Adsorption of Cu2+ by Chitosan/β-Cyclodextrin Cross-Linked Zeolite

In order to remove Cu2+ from wastewater, a kind of microsphere adsorbent (SCDO) with high efficiency for Cu2+ adsorption was prepared by the microdrop condensation method, where chitosan (CTS) and sodium alginate (SA) were used as the matrix to crosslink β-cyclodextrin (β-CD) and zeolite (Zeo). The structure and properties of SCDO were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Upon that, the adsorption performance of SCDO for Cu2+ was studied, in which the effects of pH, initial concentration, dosage, adsorption time and temperature were investigated. The results showed that the removal rate of Cu2+ reached 97.08%, and the maximum adsorption capacity was 24.32 mg/g with the temperature at 30 °C, the dosage of SCDO at 12 g/L, the initial concentration of Cu2+ at 100 mg/L, the pH of the solution at 6.0 and the adsorption time at 120 min, respectively. The adsorption process of Cu2+ by SCDO occurred in accordance with quasi-second-order kinetics model and Langmuir adsorption isotherm. After four repeats of continuous adsorption and desorption, the regenerative removal rate of Cu2+ could still reach 84.28%, which indicated that SCDO had outstanding reusability.