Advances in Nanocomposite Luminescent Sensors

The substrate N¹, N³, N⁵-tris(2-hydroxyphenyl)benzene-1,3,5-tricarboxamide (Sensor A) was prepared in the reaction of 1,3,5-benzenetricarboxylic acid (trimesic acid) and o-aminophenol in ethanol. The prepared organic sensor fulfills the chemiluminescent requirements including a luminophore, spacer, and suitable binding receptor that distress the probe’s luminescent features, providing selective and sensitive detection of mercury and iron ions in aqueous solutions. The sensor selectively detects mercury and iron ions in a water matrix containing various metal ions, including sodium, calcium, magnesium, zinc, and nickel. Strong and immediate binding was observed between mercury ions and the substrate at pH 7.0 with a binding affinity toward Hg²⁺ 9-fold higher than that observed for iron sensor binding affinity, which makes the substrate a distinctive luminescence sensor for mercury detection at ambient conditions. The sensor shows a linear response toward Hg²⁺ in the concentration range from 50 ppb to 100 ppm (2.0 × 10⁻⁸ to 4.2 × 10⁻⁵ M) with a limit of detection of 2 ppb (1.0 × 10⁻⁸ M). Further, Sensor A provides linear detection for iron ions in the range from 10 ppb to 1000 ppm (1.5 × 10⁻⁸ to 1.5 × 10⁻³ M). The measured adsorption capacity of Sensor A toward mercury ions ranged from 1.25 to 1.97 mg/g, and the removal efficiency from water samples reached 98.8% at pH 7.0. The data demonstrate that Sensor A is an excellent probe for detecting and removing mercury ions from water bodies. Full article

Here, we report a novel, easy-to-implement scalable single-step procedure for the fabrication of a solid-state surface-enhanced photoluminescence (SEPL) sensor via the direct femtosecond (fs) laser patterning of monocrystalline Si wafers placed under the layer of functionalizing solution simultaneously containing a metal salt precursor (AgNO₃) and a photoluminescent probe (d114). Such laser processing creates periodically modulated micro- and nanostructures decorated with Ag nanoparticles on the Si surface, which effectively adsorbs and retains the photoluminescent sensor layer. The SEPL effect stimulated by the micro- and nanostructures formed on the Si surface localizing pump radiation within the near-surface layer and surface plasmons supported by the decorating Ag nanoparticles is responsible for the intense optical sensory response modulated by a small amount of analyte species. The produced SEPL sensor operating within a fluidic device was found to detect sub-nanomolar concentrations of Hg²⁺ in water which is two orders of magnitude lower compared to this molecular probe sensitivity in solution. The fabrication technique is upscalable, inexpensive, and flexible regarding the ability to the control surface nano-morphology, the amount and type of loading noble-metal nanoparticles, as well as the type of molecular probe. This opens up pathways for the on-demand development of various multi-functional chemosensing platforms with expanded functionality. Full article

A new europium-based complex, K[Eu(hfa)₄] with hfa = hexafluoroacetylacetonate is synthesized and its structure confirmed via X-ray crystallography. The structure unravels an anionic octa-coordinate complex, K[Eu(hfa)₄], as opposed to the neutral hexacoordinate complex Eu(hfa)₃ routinely/ubiquitously presumed to be the case in the literature. The complex displayed pH-dependent, “on–off” emission changes in solution and exhibited a pK_a of 6.13 ± 0.06 in ethylene glycol. In solution, the sensor complex exhibited drastic variation in emission intensity corresponding to changes in the concentration of CO₂ gas purged. Based on multiple purge cycles of N₂ and CO₂, the emission intensity changes can be correlated to the concentration of CO₂ in the solution. The sensor’s ability to quantify the CO₂ presence is based on emission variations of the ⁵D₀ → ⁷F₂ line in the Eu(III) complex at 618 nm. The sensor exhibits a linear response to CO₂ concentrations in the range of 0–25% (0–8.50 mM or 0–189.95 mmHg). Based on calibration data, the limit of detection (LOD) is determined to be 0.57% (0.19 mM or 4.33 mmHg) in solution. The I₁₀₀/I₀ ratio is determined to be 80.29 ± 3.79. The percent change in intensity from purging N₂ to 100% CO₂ is 7911.16%. Over the course of seven cycles of purging different concentrations of CO₂, there is essentially no deviation in the emission intensity of the sensor in solution, indicating stability and reversibility. In addition to the analytical characterization of the sensor, the mechanism of CO₂ sensing is investigated using cyclic voltammetry, IR, and Raman spectroscopy. These data indicate the reduction of europium(III) to europium(II) in an alkaline medium and suggest changes in the hfa ligand chemistry (association/dissociation and protonation) due to CO₂ purging. The potential use of the sensor complex for real-life applications is herein evaluated via a well-known fermentation reaction. The CO₂ generated during yeast’s anaerobic respiration in sucrose media is quantified using the sensor complex and a calibrated, commercial CO₂ probe; both exhibit similar CO₂ concentration values, validating the calibration curve and the viability of the complex as a bona fide sensor. Based on the data collected, a highly stable, brightly red-emissive Eu(III) complex with the ability to differentiate concentrations of CO₂ in solution is hereby developed and characterized with benefits for various CO₂ sensing applications. Full article

We investigated the easily synthesized ligand H₃L as a fluorescent chemosensor for the detection of CdSe nanoparticles (CdSe NPs) and L-cysteine-capped CdSe quantum dots (CdSe-Cys QDs) in ethanol–water samples. A drastic quenching of the fluorescence emission of H₃L at 510 nm occurred, as a result of the addition of CdSe NPs and CdSe-Cys QDs. A solution of H₃L (1.26 ppb) showed sensitive responses to both CdSe NPs and CdSe-Cys QDs, with limits of detection (LOD) as low as 40 and 62 ppb, respectively. Moreover, using a smartphone color recognizer application, the fluorescence intensity response of H₃L-modified cellulose paper to CdSe-Cys QDs was recorded on a red channel (R), which allowed us to detect CdSe-Cys QDs with LOD = 15 ppb. Interference of some common metal nanomaterials (NMs), as well as metal ions, in the determination of CdSe NMs in solution was studied. The affinity of H₃L to CdSe NPs and CdSe-Cys QDs was spectroscopically determined. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), micro-X-ray fluorescence (µ-XRF), ¹H-NMR, attenuated total reflection infrared spectroscopy (ATR-IR), and density functional theory (DFT) were also used to investigate the interaction of H₃L with CdSe NMs. Full article

Quantum dots nanomaterials have attracted extensive interest for fluorescence chemical sensors due their attributes, such as excellent optical characteristics, quantum size effects, interface effects, etc. Moreover, the fluorescence properties of quantum dots can be adjusted by changing their structure, size, morphology, composition, doping, and surface modification. In recent years, quantum dots nanomaterials have been considered the preferred sensing materials for the detection of heavy metal ions and pesticide residues by the interactions between quantum dots and various analytes, showing excellent sensitivity, selectivity, and interference, as well as reducing the cost of equipment compared with traditional measurement methods. In this review, the applications and sensing mechanisms of semiconductor quantum dots and carbon-based quantum dots are comprehensively discussed. The application of semiconductor quantum dots, carbon quantum dots, graphene quantum dots, and their nanocomposites that are utilized as fluorescence sensors are discussed in detailed, and the properties of various quantum dots for heavy metal ion and pesticide residue determination are also presented. The recent advances in and application perspectives regarding quantum dots and their composites are also summarized. Full article