Ratiometric fluorescence sensing of hazardous ciprofloxacin based on aggregation induced emission enhancement of thiolate-protected gold nanoclusters induced by La3+ ion

Developing a switch "OFF-ON" fluorescent probe for detection of melamine based on doubly-protected red emissive copper nanoclusters mediated by Hg2+ ions

Melamine, often used as an adulterant in infants' formula due to its high protein content, can be harmful when ingested in large amounts, leading to the formation of cyanurate-melamine co-crystals in infants and potentially causing kidney damage. In this study, we introduce a fluorescent method for the selective and reliable detection of melamine in milk and infants' formula. The fluorescent probe comprises copper nanoclusters (Cu NCs) functionalized with thiosalicylic acid (TSA) and polyvinylpyrrolidone (PVP) as double-protecting ligands. Upon the addition of Hg2+, the fluorescence emission of TSA-PVP@Cu NCs is diminished due to static quenching. Subsequently, the fluorescence emission of the TSA-PVP@Cu NCs + Hg2+ probe is restored upon the introduction of melamine, facilitated by the coordination interaction between melamine and Hg2+ and the formation of a stable chelate between them. Under optimized conditions, the fluorescence emission was recorded initially for the TSA-PVP@Cu NCs + Hg2+ probe (F°) and after melamine addition (F). The (F/F°) ratio increased with rising melamine concentrations within the range of 0.025-65 µM. The detection limit, calculated using a signal-to-noise ratio of 3, was determined to be 8.0 nM. The TSA-PVP@Cu NCs + Hg2+ probe was successfully employed to detect melamine in milk and infants' formula, yielding acceptable recovery percentages and relative standard deviations. These results underscore the reliability and efficacy of the proposed probe for the fluorometric detection of melamine in real-world samples.

A ratiometric fluorescence nanosensor for glutathione detection based on spatially confined dual-emission of α-lipoic acid-modified gold nanoclusters and silicon nanoparticles

The development of dual-emission ratiometric fluorescent probes with aggregation-induced emission enhancement (AIEE) overcomes the limitations of gold nanocluster (Au NC)-based probes, particularly their weak intrinsic fluorescence, in real-world applications. These AIEE probes also exhibit superior detection limits and enhanced sensitivity. A novel combination for the reliable fluorometric detection of glutathione (GSH) was proposed, utilizing aggregation-induced emission enhancement (AIEE) facilitated by electrostatic interaction and spatial confinement. The probe consists of a ratiometric combination of negatively charged α-lipoic acid-modified Au NCs (LA@Au NCs) and positively charged silicon nanoparticles (SiNPs). The addition of SiNPs causes aggregation of LA@Au NCs, enhancing the fluorescence of LA@Au NCs through the AIE effect under electrostatic interaction and spatial confinement. The addition of Cu2+ quenched the emission of LA@Au NCs as a result of charge transfer. The fluorescence emissions of LA@Au NCs were restored upon the addition of GSH due to the interaction between GSH and Cu2+. Simultaneously, the emission signal of SiNPs remains unchanged, serving as an internal reference signal during GSH measurement. It was found that the fluorescence ratio (F680/F465) is directly proportional to the concentration of GSH in the range of 0.05-100 μM, with a detection limit of 1.7 nM (S/N = 3). The proposed system was applied to detect GSH in real samples, including dietary supplements, human serum, and saliva samples. This work opens new avenues for constructing novel sensors based on AIEE for detecting biomolecules.

Functional structures assembled based on Au clusters with practical applications

The advancement of gold nanoclusters (Au NCs) has given rise to a new era in fabricating functional materials due to their controllable morphology, stable optical properties, and excellent biocompatibility. Assemblies based on Au NCs demonstrate significant potentiality in constructing multiple structures as acceptable agents in applications such as sensing, imaging technology, and drug delivery systems. In addition, the assembled strategies illustrate the integration mechanism between each component while facing material requirement. It is necessary to provide supplementary and comprehensive reviews on the assembled functional structures (based Au NCs), which hold promise for applications and could expand their functional range and potential applications. This review focuses on the assembled structures of Au NCs in combination with metals, metal oxides, and non-metal materials, which are intricately arranged through various interaction forces including covalent bonds and metal coordination, resulting in a diverse array of multifunctional Au NC assemblies. These assemblies have widespread applications in fields such as biological imaging, drug delivery, and optical devices. The review concludes by highlighting the challenges and future prospects of Au NC assemblies, emphasizing the importance of continued research to advance nanomaterial assembly innovation.

Enhanced fluorometric detection of histamine using red emissive amino acid-functionalized bimetallic nanoclusters

Lysine-capped gold nanoclusters doped with silver (LYS@Ag/Au NCs) have been developed for the sensitive and selective "turn-off" fluorescence detection of histamine. This fluorescent probe demonstrates excellent stability and a high quantum yield of 9.45%. Upon addition of histamine, a positively charged biogenic amine, to the LYS@Ag/Au NCs fluorescent probe, its fluorescence emission is quenched due to electrostatic interaction, aggregation, and hydrogen bond formation. The probe exhibits good sensitivity for the determination of histamine within the range of 0.003-350 μM, with a detection limit of 0.001 μM based on a signal-to-noise ratio of 3. Furthermore, the probe has been applied to detect biogenic amines in complicated matrices, highlighting its potential for practical applications. However, interference from the analogue histidine was observed during analysis, which can be mitigated by using a Supelclean™ LC-SAX solid-phase extraction column for removal.

Enhanced fluorescent detection of oxaliplatin via BSA@copper nanoclusters: a targeted approach for cancer drug monitoring

A new fluorescence sensing approach has been proposed for the precise determination of the anti-cancer drug oxaliplatin (Oxal-Pt). This method entails synthesizing blue-emitting copper nanoclusters (CuNCs) functionalized with bovine serum albumin (BSA) as the stabilizing agent. Upon excitation at 360 nm, the resultant probe exhibits emission at 460 nm. Notably, the fluorescence response of BSA@CuNCs substantially increases upon incubation with Oxal-Pt due to multiple binding interactions between the drug and the fluorescent probe. These interactions involve hydrogen bonding, hydrophobic interaction, and the high affinity between the SH groups (cysteine residues of BSA) and platinum (in Oxal-Pt). Consequently, this interaction induces aggregation-induced emission enhancement (AIEE) of BSA@CuNCs. The probe demonstrates a broad response range from 0.08 to 140.0 μM, along with a low detection limit of 20.0 nM, determined based on a signal-to-noise ratio of 3. Furthermore, the probe effectively detects Oxal-Pt in injections, human serum, and urine samples, yielding acceptable results. This study represents a significant advancement in the development of a straightforward and efficient sensor for monitoring platinum-containing anti-cancer drugs during chemotherapy.

A reliable and selective ratiometric sensing probe for fluorometric determination of P2O74- based on AIE of GSH@CuNCs-assisted by Al-N@CQDs

In this study, a novel composite material was developed for the ratiometric detection of pyrophosphate anion (P2O74-). This composite consisted of Al and nitrogen co-doped carbon dots (Al-N@CQDs) and glutathione-capped copper nanoclusters (GSH@CuNCs). The Al-N@CQDs component, with its high reserved coordination capacity of Al3+, induced the non-luminescent behavior of GSH@CuNCs, resulting in an aggregation-induced emission (AIE) effect. The hybrid material (Al-N@CQDs/GSH@CuNCs) exhibited dual-emission signals at 620 nm and 450 nm after integrating the two independent materials utilizing the AIE effect and the fluorescence resonance energy transfer (FRET) approach. This approach represents the first utilization of this composite for ratiometric detection. Nevertheless, upon the addition of P2O74-, the AIE and FRET processes were hindered due to the higher coordination interaction of Al3+ towards P2O74- compared to the amino/carboxyl groups on Al-N@CQDs. This successful interference of the AIE and FRET processes allowed for the effective estimation of P2O74-. The response ratio (F450/F620) increased with increasing the concentration of P2O74- in the range of 0.035-160 µM, with an impressive detection limit of 0.012 µM. This innovative approach of utilizing hybrid CQDs/thiolate-capped nanoclusters as a ratiometric fluorescent sensor for analytical applications introduces new possibilities in the field. The as-fabricated system was successfully applied to detect P2O74- in different real samples such as water, serum, and urine samples with acceptable results.

Ratiometric fluorometric determination of sulfide using graphene quantum dots and self-assembled thiolate-capped gold nanoclusters triggered by aluminum

A ratiometric-based fluorescence emission system was proposed for the determination of sulfide. It consists of blue emissive graphene quantum dots (GQDs) and self-assembled thiolate-protected gold nanoclusters driven by aluminum ion (Al3+@GSH-AuNCs). The two types of fluorophores are combined to form a ratiometric emission probe. The orange emission of Al3+ @GSH-AuNCs at 624 nm was quenched in the presence of sulfide ion owing to the strong affinity between sulfide and Au(I), while the blue GQDs fluorescence at 470 nm remained unaffected. Interestingly, the Al3+@GSH-AuNCs and GQDs were excited under the same excitation wavelength (335 nm). The response ratios (F470/F624) are linearly proportional to the sulfide concentration within the linear range of 0.02-200 µM under the optimal settings, with a limit of detection (S/N = 3) of 0.0064 µM. The proposed emission probe was applied to detect sulfide ions in tap water and wastewater specimens, with recoveries ranging from 95.3% to 103.3% and RSD% ranging from 2.3% to 3.4%, supporting the proposed method's accuracy.