Microwave-Assisted Synthesis of Functionalized Carbon Nanospheres Using Banana Peels: pH-Dependent Synthesis, Characterization, and Selective Sensing Applications

This work presents a microwave-based green synthesis method for producing carbon nanospheres (CNSs) and investigates the impact of presynthesis pH on their size and assembly. The resulting CNSs are monodispersed, averaging 35 nm in size, and exhibit notable characteristics including high water solubility, photostability, and a narrow size distribution, achieved within a synthesis time of 15 min. The synthesized CNS features functional groups such as -OH, -COOH, -NH, -C-O-C, =C-H, and -CH. This diversity empowers the CNS for various applications including sensing. The CNS exhibits a distinct UV peak at 282 nm and emits intense fluorescence at 430 nm upon excitation at 350 nm. These functionalized CNSs enable selective and specific sensing of Cu2+ ions and the amino acid tryptophan (Trp) in aqueous solutions. In the presence of Cu2+ ions, static-based quenching of CNS fluorescence was observed due to the chelation-enhanced quenching (CHEQ) effect. Notably, Cu2+ ions induce a substantial change in UV spectra alongside a red-shift in the peak position. The limits of detection and quantification for Cu2+ ions with CNS are determined as 0.73 and 2.45 μg/mL, respectively. Additionally, on interaction with tryptophan, the UV spectra of CNS display a marked increase in the peak at 282 nm, accompanied by a red-shift phenomenon. The limits of detection and quantification for l-tryptophan are 4.510 × 10-3 and 1.50 × 10-2 μg/mL, respectively, indicating its significant potential for biological applications. Furthermore, the practical applicability of CNSs is demonstrated by their successful implementation in analyzing real water samples and filter paper-based examination, showcasing their effectiveness for on-site sensing.

Influence of the Reaction Sequence on the Complexation of an NS4-Macrocycle with CdII and CuI Salts Leading to the Formation of Supramolecular Isomers and an Endo/Exocyclic CuI Complex

In the construction of metallosupramolecules, the reaction sequence in a three-reactant system (one ligand plus two metal ions) could be one of the controlling factors influencing the outcome of the reaction. In this work, the formation of supramolecular isomers (1 and 2) and an endo/exocyclic Cu⁺ complex (4) of the NS₄-macrocycle (L) via different sequential metal addition protocols (routes I-III) is reported. In one-pot reactions of L with Cu(CH₃CN)₄PF₆ in the absence (route I) and presence (route II) of CdI₂, a cyclic dimer Cu^I complex, [Cu₂(L)₂](PF₆)₂ (1), and a one-dimensional coordination polymer, [Cu₂(L)₂]_n·n[CdI₄] (2), were obtained, respectively. Interestingly, the complex cations in 1 and 2 are supramolecular isomers formed via cyclization and polymerization upon complexation, respectively, probably due to different geometric and electronic complementarities, via the C-H···X^- hydrogen bonds, between L and the counterion. In the two-step reaction (route III), an endocyclic Cd²⁺ complex, [Cd(L)I₂] (3), obtained in the first step was utilized in the following reaction with Cu(CH₃CN)₄PF₆, giving rise to an endo/exocyclic tetranuclear Cu⁺ complex, [Cu₄(L)₂(CH₃CN)₆](PF₆)₄ (4), via Cd²⁺ → 2Cu⁺ substitution, which is not accessible by conventional procedures. Solution studies by comparative NMR and electrospray ionization mass spectroscopy also support metal substitution by showing the stronger binding affinity of Cu⁺ over Cd²⁺. These results demonstrate that the metal substitution protocol could be useful for reaching novel metallosupramolecules difficult to obtain by other methods.

Rhodol-derived turn-on fluorescent probe for copper ions with high selectivity and sensitivity

A new rhodol-derived fluorescent probe 1 with picolinate as the recognition receptor was designed and simply synthesized using a one-step reaction. With the concentration of added Cu²⁺ increases, it gradually turns pink, so the effect of naked eye detection can be achieved. The detection limit of probe 1 for Cu²⁺ is 42 nM, and the linear detection range was 0-2 μM. The experimental results showed that 1 was a fluorescent probe with high selectivity, good water solubility, and high sensitivity to Cu²⁺ . Probe 1 was successfully applied in cell imaging experiments and can detect the concentration of Cu²⁺ in water samples. All these indicate that probe 1 has the potential to be applied to the detection of Cu²⁺ concentration in the real environment.

Argentivorous Molecules with Chromophores in Side Arms: Silver Ion-Induced Turn On and Turn Off of Fluorescence

The synthesis of argentivorous molecules (L¹ and L²) having two chromophores (4-(anthracen-9-yl)benzyl or 4-(pyren-1-yl)benzyl groups) and two benzyl groups and the fluorescence properties of their silver complexes in a solution and the solid state are reported. A crystallographic approach for the Ag⁺ complexes with L¹ and L² revealed that the observed fluorescence changes stem from the excimer formation and extinction of fluorescent. Furthermore, binding stabilities of L¹ and L² toward Ag⁺ ions were estimated by the Ag⁺-induced UV-vis and PL spectral changes.

Monodisperse functionalized GO for high-performance sensing and bioimaging of Cu2+ through synergistic enhancement effect

The metal ion fluorescence probes based on chemical reactions triggered by specific metal ions is characterized by high selectivity. However, they are also subject to inherent limitations, such as easy aggregation under water solution, poor optical stability, and long response time. In order to solve these problems, a simple and effective method was studied. The specific design is as follows. Fluorescence probe RACD is assembled onto a single layer graphene oxide (GO) via π-π interaction and hydrogen bonding to prepare RACD functionlized graphene oxide RACD/GO. The experimental results show that the resulting RACD/GO possesses very well monodispersion, hydrophilicity and photostability, particularly reduce the aggregation degree of RACD owing to π-π effect. Simultaneously, it was found that due to the strong synergy between GO and RACD, the response time, selectivity, anti-interference ability, detection sensitivity, detection limit and bioimaging ability of RACD/GO were significantly improved compared with RACD. The resulting RACD/GO not only possesses very well photostability, multiple repeated cycles, but also have been triumphantly put into the monitoring Cu²⁺ of environmental water, sewage, cells and zebrafish specimens in practice. The detection limit is as low as 1.76 nM, and the correlation coefficient is 0.9998.