Nanomolar level electrochemical detection of glycine on a miniaturized modified screen-printed carbon-based electrode: a comparison of performance with glassy carbon electrode system

In this work, we demonstrate the electrochemical (EC) sensing of glycine (GLY) on a gold-copper nanocluster on nitrogen-doped graphene quantum dot-modified (indigenously fabricated) screen-printed electrode (AuCuNC@N-GQD/SPE). SPE was fabricated by step-by-step printing of reference, working, and counter electrodes to develop an all-printed SPE. A comparison strategy between SPE and the glassy carbon electrode (GCE) towards the EC sensing of GLY was carried out. The sensing performance was enhanced while replacing GCE with SPE. The limit of detection (LOD) for GLY obtained by EC sensing with AuCuNC@N-GQD/GCE was 10 nM and that with AuCuNC@N-GQD/SPE was 10 times lower, 1 nM, and is the lowest LOD value reported hitherto. Compared with AuCuNC@N-GQD/GCE, the current response of AuCuNC@N-GQD/SPE exhibited a ∼2.6-times enhancement with a sensitivity of 0.206 μA μM-1 cm-2. Thus, the successful shift from GCE to SPE not only miniaturizes the sensor device but also enhances the electrochemical detection performance.

Ca@Cu-CD nanoprobe for dual detection of glycine and ex vivo glycine imaging

Hydrothermally prepared copper-doped carbon dots (Cu-CDs) were modified with Ca2+, which serve as an excellent platform for the recognition of glycine. The feeble emission of Ca@Cu-CD increases substantially in the presence of glycine due to aggregation-induced emission. At the same time, there was a 5-fold increase in the current response of the Ca@Cu-CD modified electrode as compared to the control. The exceptional combination of fluorescence and conducting properties, along with Ca-glycine interaction, establishes our probe as a dual sensor for the detection of glycine in real serum samples. The limit of detection for this nonenzymatic fluorescence and electrochemical sensing are 17.2 and 4.1 nM, respectively. Furthermore, an extensive evaluation of the toxicity and bioimaging properties in fruit fly Drosophila melanogaster shows that the Ca@Cu-CD probe is not cytotoxic and can be applied for ex vivo imaging of glycine.

Stability and Electronic Structure of Nitrogen-Doped Graphene-Supported Cun (n = 1-5) Clusters in Vacuum and under Electrochemical Conditions: Toward Sensor and Catalyst Design

Here, we present a detailed computational study of the stability and the electronic structure of nitrogen-doped graphene (N4V2) supported Cun (n = 1-5) clusters, which are promising carbon-dioxide electroreduction catalysts. The binding of the clusters to the nitrogen-doped graphene and the electronic structure of these systems were investigated under vacuum and electrochemical conditions. The stability analysis showed that among the systems, the nitrogen-doped graphene bound Cu4 is the most stable in vacuum, while in an electrolyte, and at a negative potential, the N4V2-Cu3 is energetically more favorable. The ground state electronic structure of the nitrogen-doped graphene substrate undergoes topological phase transition, from a semimetallic state, and we observed a metallic and topologically trivial state after the clusters are deposited. The electrode potential adjusts the type and density of the charge carriers in the semimetallic models, while the structures containing copper exhibit bands which are deformed and relaxed by the modified number of electrons.

Ratiometric fluorescence detection of dopamine based on copper nanoclusters and carbon dots

Nanoclusters for fluorescence detection are generally comprised of rare and expensive noble metals, and the nanoclusters based on more affordable transition metal have attracted increasing attention. This study designed a ratiometric fluorescent probe to detect dopamine (DA), an important neurotransmitter. With carbon dots encapsulated within silica (CDs@SiO2) as the reference, the emitted reference signal was almost unchanged due to the protection of inert silicon shell. Meanwhile, copper nanoclusters modified with 3-aminophenyl boronic acid (APBA-GSH-CuNCs) provided the sensing signal, in which the phenylboric acid could specifically recognize the cis-diol structure of DA, and caused the fluorescence quenching by photoinduced electron transfer. This dual emission ratiometric fluorescent probe exhibited high sensitivity and anti-interference, and was able to selectively responded to DA with a linear range of 0-1.4 mM, the detection limit of 5.6 nM, and the sensitivity of 815 mM-1. Furthermore, the probe successfully detected DA in human serum samples, yielding recoveries ranging from 92.5% to 102.7%. Overall, this study highlights the promising potential of this ratiometric probe for detecting DA.

Designing and preparing supramolecular encapsulation systems based on fraxetin and cyclodextrins for highly selective detection of nicotine

Herein, a series of water-soluble supramolecular inclusion complexes (ICs) probes were prepared using cyclodextrins (CDs) and fraxetin (FRA) to detect nicotine (NT) with high selectivity in vitro and in vivo. The FRA/CD ICs prepared through the saturated solution method exhibited excellent water solubility, stability, and biocompatibility. A clear host-guest inclusion model was provided by the theoretical calculations. The investigation revealed that NT was able to enter into the cavities of FRA/β-CD IC and FRA/γ-CD IC, and further formed charge transfer complexes with FRA in the CD cavities, resulting in a rapid and highly selective fluorescence-enhanced response with the lowest detection limits of 1.9 × 10-6 M and 9.7 × 10-7 M, and the linear response ranged from 0.02 to 0.3 mM and 0.01-0.05 mM, respectively. The IC probes showed good anti-interference performance to common interferents or different pH environments, with satisfactory reproducibility and repeatability of response to NT. Furthermore, the potentiality of the probes was confirmed through fluorescence imaging experiments using human lung cancer cells and the lung tissue of mice. This study offers a fresh perspective for detecting NT in environmental and biomedical analysis.

Doped Graphene Quantum Dots as Biocompatible Radical Scavenging Agents

Oxidative stress is proven to be a leading factor in a multitude of adverse conditions, from Alzheimer's disease to cancer. Thus, developing effective radical scavenging agents to eliminate reactive oxygen species (ROS) driving many oxidative processes has become critical. In addition to conventional antioxidants, nanoscale structures and metal-organic complexes have recently shown promising potential for radical scavenging. To design an optimal nanoscale ROS scavenging agent, we have synthesized ten types of biocompatible graphene quantum dots (GQDs) augmented with various metal dopants. The radical scavenging abilities of these novel metal-doped GQD structures were, for the first time, assessed via the DPPH, KMnO4, and RHB (Rhodamine B protectant) assays. While all metal-doped GQDs consistently demonstrate antioxidant properties higher than the undoped cores, aluminum-doped GQDs exhibit 60-95% radical scavenging ability of ascorbic acid positive control. Tm-doped GQDs match the radical scavenging properties of ascorbic acid in the KMnO4 assay. All doped GQD structures possess fluorescence imaging capabilities that enable their tracking in vitro, ensuring their successful cellular internalization. Given such multifunctionality, biocompatible doped GQD antioxidants can become prospective candidates for multimodal therapeutics, including the reduction of ROS with concomitant imaging and therapeutic delivery to cancer tumors.