Excitation-independent and fluorescence-reversible N-GQD for picomolar detection of inhibitory neurotransmitter in milk samples ‒ an alleyway for possible neuromorphic computing application

Tailor-designed carbon-based novel fluorescent architecture for nanomolar detection of radioactive elements U(VI) and Th(IV) in pH ± 5.0

Highly stable nitrogen-doped Graphene Quantum Dots (N-GQD) functionalized with Pamoic Acid (PA@N-GQD) are utilized for nanomolar detection of radioactive elements, Uranium (VI) and Thorium (IV), in pH ± 5.0. The absorption, fluorescence, crystalline nature, elemental composition, functional groups, and morphological state of as-prepared PA@N-GQD are evaluated by UV-visible absorption, photoluminescence, XRD, XPS, FTIR, HRTEM, FESEM, and AFM characterizations. The aqueous solution of PA@N-GQD is characterized by its spherical morphology, averaging 6.5 nm in size. PA@N-GQD exhibits a gradual decrease in fluorescence intensity at 438 nm (λex 344 nm) upon the addition of Uranium (VI) and Thorium (IV) ions. The selectivity, sensitivity, competitivity, pH, time effect, and reversibility studies of PA@N-GQDs have been carried out using the photoluminescence technique. The attained fluorescence Limit of Detection (LoD) of PA@N-GQD for Uranium (VI) and Thorium (IV) ions are 2.009 × 10-9 and 1.351 × 10-9 M, respectively. From the fluorescence titration studies of U(VI) and Th(IV), the binding constant, Stern-Volmer constant, Modified Stern-Volmer constant, association constant, and dissociation constants have been calculated separately. These aforementioned results indicate that the PA@N-GQD has a higher binding affinity towards Th(IV) than U(VI) in aqueous medium. This current research represents the development of advanced materials for environmental and analytical applications, specifically focusing on the precise detection and quantification of radioactive elements.

A Fluorescence Turn On-off-on Method for Sensitive Detection of Sn2+ and Glycine Using Waste Eggshell Membrane Derived Carbon Nanodots as Probe

Changes in Sn2+ and glycine levels are relevant to many important physiological procedures in human health. However, investigation of their physiological functions is limited because few versatile methods towards Sn2+ and glycine detection have been developed. In this work, a fluorescence turn on-off-on strategy was firstly constructed for rapid and sensitive detection of Sn2+ and glycine through the specific binding between Sn2+ and glycine. Carbon nanodots (CDs) with a quantum yield of 19.5% were synthesized by utilizing inner film of waste eggshell as carbon source and employed as fluorescent probe. In the presence of Sn2+, the fluorescence of CDs was quenched by Sn2+ via the primary inner filter effect (IFE). However, the binding between Sn2+ and glycine prevented the IFE between Sn2+ and CDs, resulting in fluorescence recovery of CDs. Under optimized conditions, the fluorescent response of CDs displayed good linear relationships with the concentrations of Sn2+ in the range of 10-200 µM and 200-5000 µM, and the limit of detection (LOD) was 2.4 µM. For glycine detection, a good linear relationship was obtained in the concentration range of 5-1000 µM with a low LOD down to 0.76 µM. Moreover, the practicability of the assay was also demonstrated by measuring glycine content in human serum samples. This work provides an economical, green and fast method for biological analysis of Sn2+ and glycine.

Alkaline n-gqds fluorescent probe for the ultrasensitive detection of creatinine

Creatinine (Crn) is an important excretory product of the human body. Medical laboratory technology has improved over years and brought many advancements in clinical diagnostics equipment, and testing techniques and made the tests more efficient. Yet, the quantitative analysis of Crn is still carried out by the classical Jaffe's reaction (using Picric acid (PA) with NaOH) method. Since PA is hazardous to human health, alternative solutions such as; nanoparticles and surface-modified nanoparticles can be used. Exploring the optoelectronic properties of carbon-based quantum dots for biomolecule sensing is of current interest among researchers. Nitrogen functionalized graphene quantum dots (Alk-NGQDs) measured featured Crn easier and reduced the time taken for the test carried out in laboratories. The synthesized Alk-NGQDs optical, structural, morphological properties, surface and compositions are studied through XPS, HRTEM, XRD, FTIR, and spectroscopic techniques. Alk-NGQDs at alkaline conditions (pH 9.5) form a stable complex with Crn through intermolecular charge transfer (ICT). The fluorescence titration method is used to sense Crn in commercial Crn samples and human blood serum. To understand the efficacy of sensing creatinine using Alk-NGQDs, working concentration, fluorescence quantum yield, the limit of detection, and quenching constant are calculated using the Stern-Volmer plot. The emission property of Alk-NGQDs is aimed to bring an alternative to the traditional colorimetric Jaffe's reaction.