DNA supported graphene quantum dots for Ag ion sensing

Role of Förster Resonance Energy Transfer in Graphene-Based Nanomaterials for Sensing

Förster resonance energy transfer (FRET)-based fluorescence sensing of various target analytes has been of growing interest in the environmental, bioimaging, and diagnosis fields. Graphene-based zero- (0D) to two-dimensional (2D) nanomaterials, such as graphene quantum dots (GQDs), graphene oxide (GO), reduced graphene oxide (rGO), and graphdiyne (GD), can potentially be employed as donors/acceptors in FRET-based sensing approaches because of their unique electronic and photoluminescent properties. In this review, we discuss the basics of FRET, as well as the role of graphene-based nanomaterials (GQDs, GO, rGO, and GD) for sensing various analytes, including cations, amino acids, explosives, pesticides, biomolecules, bacteria, and viruses. In addition, the graphene-based nanomaterial sensing strategy could be applied in environmental sample analyses, and the reason for the lower detection ranges (micro- to pico-molar concentration) could also be explained in detail. Challenges and future directions for designing nanomaterials with a new sensing approach and better sensing performance will also be highlighted.

Metal ion sensing with graphene quantum dots: detection of harmful contaminants and biorelevant species

Graphene quantum dots (GQDs) are attractive materials for use as highly selective and sensitive chemical sensors, owing to their simple preparation and affordability. GQDs have been successfully deployed as sensors for toxic metal ions, which is a significant issue due to the ever-increasing environmental contamination from agricultural and industrial activities. Despite the success of GQDs in this area, the mechanisms which underpin GQD-metal ion specificity are rarely explored. This lack of information can result in difficulties when attempting to replicate published procedures and can limit the judicious design of new highly selective GQD sensors. Furthermore, there is a dearth of GQD examples which selectively detect biologically relevant alkali and alkaline earth metals. This review will present the current state of GQDs as metal ion sensors for harmful contaminants, highlighting and discussing the discrepancies that exist in the proposed mechanisms regarding metal ion selectivity. The emerging field of GQD sensors for biorelevant metal ion species will also be reviewed, with a perspective to the future of this highly versatile material.

High-Performance, Nitrogen-Doped, Carbon-Nanotube-Based Electrochemical Sensor For Vitamin D3 Detection

With the fast changing lifestyle, vitamin D deficiency is becoming extremely common. Therefore, development of economical, efficient, and fast sensors for vitamin D is the need of the hour. Carbon-based nanomaterials are extensively explored in sensing of variety of biomolecules. In the present study, an antibody-free, highly sensitive, carbon-nanotube-based, highly responsive vitamin D3 sensor is reported. Nitrogen-doped carbon nanotubes are utilized to overcome the limiting factor of hydrophobic character of pure carbon. The synthesized N-doped CNTs showed a specific surface area of 24 m²/g. The surface charges of vitamin D3 and the vitamin D3/NCNT complex are found to be -20 and -6.4 mV, respectively, by zeta potential measurements. The sensor is able to deliver high performance in the concentration range of 0-10 nM, with a limit of detection of 16 pM. The response study indicated the sensitivity value as 0.000495 mA/cm² nM. The sensor is also able to show a higher selectivity toward vitamin D3 in comparison to other biomolecules. The long-term stability, reproducibility, good linear range, and ultralow detection capability of the sensor are also reported.

Hierarchical cage-frame type nanostructure of CeO2 for bio sensing applications: from glucose to protein detection

Self-assembled hierarchical nanostructures are slowly superseding their conventional counterparts for use in biosensors. These morphologies show high surface area with tunable porosity and packing density. Modulating the interfacial interactions and subsequent particle assembly occurring at the water-and-oil interface in inverse miniemulsions, are amongst the best strategies to stabilize various type of hollow nanostructures. The paper presents a successful protocol to obtain CeO₂ hollow structures based biosensors that are useful for glucose to protein sensing. The fabricated glucose sensor is able to deliver high sensitivity (0.495 μA cm^-2 nM^-1), low detection limit (6.46 nM) and wide linear range (0 nM to 600 nM). CeO₂ based bioelectrode can also be considered as a suitable candidate for protein sensors. It can detect protein concentrations varying from 0 to 30 µM, which is similar or higher than most reports in the literature. The limit of detection (LOD) for protein was ∼0.04 µM. Therefore, the hollow CeO₂ electrodes, with excellent reproducibility, stability and repeatability, open a new area of application for cage-frame type particles.

Solution plasma: new synthesis method of N-doped carbon dots as ultra-sensitive fluorescence detector for 2,4,6-trinitrophenol

Herein, we report the synthesis of nitrogen-doped carbon dots (NCDs) through solution plasma (SP) for the first time. The SP method occurs a rapid dissociation of molecules, such as organic compounds, caused by an electrical discharge between electrodes immersed in a solution. The dissociation can result in the creation of various radicals such as ·C2, ·CN, and ·H which enable the rapid synthesis of carbon dots (CDs). The unique reaction of radicals allowed the formation of CDs with high N concentration and functionalization of the surface in a short time. In this study, by using the SP method, a very fine NCDs with size of 6 nm were synthesized from a pyridine/water mixture in just 10 min. Bright blue fluorescence (410 nm) with a high quantum yield (61%) was observed due to the high N concentration and the surface passivation. From the potential application point of view, the synthesized NCDs showed an excellent detection property for 2,4,6-trinitrophenol (TNP) by fluorescence quenching effect. It was due to rich amino-functional groups which act as a reaction pathway to TNP. This phenomenon was caused by the synergetic effect of a photo-induced electron transfer with the assistance of proton transfer-assisted electron transfer.

New water-soluble colorimetric pH and metal ione sensor based on graphene quantum dot modified with alizarine red S

A new colorimetric sensor was designed for the screening pH changes in solutions, as well as, detection of some cations. The sensor preparation includes the chemical binding of alizarine red S (ARS) as a sensor of pH and cation to graphene quantum dots (GQD). Loading ARS on GQD led to the formation of water soluble sensor which finally responded to the colorimetric detection of some cations in water. Solubility and stability of the sensor in water indicate that the sensor is an ideal system for the biological and environmental applications. To demonstrate the applicability of the new sensor, the colorimetric responds of sensor were examined for some cations including Fe³⁺, Co²⁺, Ca²⁺, As³⁺, Cd²⁺, Hg²⁺, Pb²⁺, Sn²⁺, Al³⁺, and Cr³⁺. The colorimetric detections of all the ions were performable individually in a solution. In addition, GQD-ARS as a colorimetric sensor detected Co²⁺ at pH < 0.6 with limit of quantification 0.08 mM and Fe³⁺ at 0.6 < pH < 4.0 with limit of quantification 0.03 mM in the mixture of cations.

Hollow nanostructures of metal oxides as emerging electrode materials for high performance supercapacitors

Comparative study of TMO based hollow and solid nanostructures for supercapacitor applications.

DNA-templated quantum dots and their applications in biosensors, bioimaging, and therapy

Over the past 10 years, DNA functionalized quantum dots (QDs) have attracted considerable attention in sensing and imaging of disease-relevant biological targets, as well as cancer therapy. Considerable efforts have been devoted to obtaining DNA functionalized QDs with enhanced stability and quantum yield. Here, we focus on a one-pot method, in which phosphorothioate-modified DNA is used as the co-ligand on the basis of the strong binding of sulfur and Cd²⁺. After a short summary of the preparation of DNA-templated QDs, versatile bioapplications based on the constructed ratiometric fluorescent probes, nanobeacons and multiple bottom-up assemblies will be discussed. A substantial part of the review will focus on these applications, ranging from small molecule, biological macromolecule, cancer cell and pathogen sensing to in vitro and in vivo imaging. Besides, drug or siRNA delivery based on DNA-templated QD assemblies will also be briefly discussed here.