Enhanced Turn-On Fluorescence Detection of Aqueous Lead Ions with Size-Shrinkable Hydrogels

Highly sensitive detection of lead ions in water is of importance. This paper reports a new method to enhance the sensitivity of fluorescence detection of aqueous lead ions by exploiting the large volume reduction of hydrogels upon dehydration. Rhodamine-derived prefluorescent probes with high selectivity to lead ions are grafted on a carboxylated agarose hydrogel. Upon binding low-concentration lead ions, fluorescence emission is turned on. The dehydration of the hydrogel leads to a size reduction of over 40 times and an enhancement of fluorescence of 10 times at a lead-ion concentration of 10-7 M, allowing fluorescence detection with naked eyes. Given its low cost, easy operation, and high sensitivity, the volume reduction hydrogel can be used to detect lead ions in drinking water.

A Review of Microfluidic Detection Strategies for Heavy Metals in Water

Heavy metal pollution of water has become a global issue and is especially problematic in some developing countries. Heavy metals are toxic to living organisms, even at very low concentrations. Therefore, effective and reliable heavy metal detection in environmental water is very important. Current laboratory-based methods used for analysis of heavy metals in water require sophisticated instrumentation and highly trained technicians, making them unsuitable for routine heavy metal monitoring in the environment. Consequently, there is a growing demand for autonomous detection systems that could perform in situ or point-of-use measurements. Microfluidic detection systems, which are defined by their small size, have many characteristics that make them suitable for environmental analysis. Some of these advantages include portability, high sample throughput, reduced reagent consumption and waste generation, and reduced production cost. This review focusses on developments in the application of microfluidic detection systems to heavy metal detection in water. Microfluidic detection strategies based on optical techniques, electrochemical techniques, and quartz crystal microbalance are discussed.

Sensor and Bioimaging Studies Based on Carbon Quantum Dots: The Green Chemistry Approach

Since carbon quantum dots have high photoluminescent efficiency, it has been a desired material in sensor and bioimaging applications. In recent years, the green chemistry approach has been preferred and the production of quantum dots has been reported in many studies using different precursors from natural, abundant, or waste sources. Hydrothermal, chemical oxidation, microwave supported, ultrasonic, solvothermal, pyrolysis, laser etching, solid-state, plasma, and electrochemical methods have been reported in the literature. In this review article, green chemistry strategies for carbon quantum dot synthesis is summarized and compared with conventional methods using methodologic and statistical data. Furthermore, a detailed discussion on sensor and bioimaging applications of carbon quantum dots produced with green synthesis approaches are presented with a special focus on the last decade.

Rhodamine-Appended Benzophenone Probe for Trace Quantity Detection of Pd2+ in Living Cells

Designing a fluorogenic probe for the determination of Pd²⁺ is a challenging analytical task. Pd²⁺ is a potentially toxic and harmful substance even at a very low level of contamination in the end product. Herein, a promising spirolactam-functionalized chemosensor, rhodamine-appended benzophenone (HBR), is designed and characterized by spectroscopic (¹H NMR, ¹³C NMR, ESI-MS, and FT-IR) data along with the single-crystal X-ray diffraction technique. It acts as a highly sensitive and selective fluorogenic chemosensor for Pd²⁺ ions over other environmentally relevant cations in aqueous ethanol (1:1, v/v) at pH 7.4. The limit of detection (LOD) is 34 nM that is far below the WHO recommended Pd uptake (47 μM). The plausible mechanism involves the specific binding of HBR with Pd²⁺ and the formation of 1:1 stoichiometry of the complex, which has been supported by ESI-MS, FT-IR data, Job plot, and association constant data (Benesi-Hildebrand plot). The computation study has been attempted to explain the ring cleavage fluorescence enhancement scheme of HBR upon binding with Pd²⁺. Furthermore, this "turn-on" probe has successfully applied to image the Pd²⁺ ion in cultured MDA-MB-231 cells.

A nanomolar detection of mercury(II) ion by a chemodosimetric rhodamine-based sensor in an aqueous medium: Potential applications in real water samples and as paper strips

A new promising rhodamine based colorimetric and fluorometric chemosensor, RDV has been designed and synthesized for specific detection of Hg²⁺ ion. It acts as highly selective "turn-on" fluorescent chemosensor for Hg²⁺ ion without interference from other competitive metal ions in aqueous acetonitrile medium. The drastic color change with addition of Hg²⁺, from colorless to pink, indicates RDV can acts as "naked-eye" indicator for Hg²⁺. The Hg²⁺ promoted selective hydrolysis of appended vinyl ether group in RDV followed by Hg²⁺ chelated complex formation with concomitant opening of spirolactam ring is the plausible sensing mechanism. The detailed absorption, fluorescence, ¹H NMR, ¹³C NMR and mass spectrometry confirms the proposed sensing mechanism. The limit of detection (LOD) of Hg²⁺ by RDV is 136 nM indicating the high sensitivity towards Hg²⁺. The RDV shows consistent spectroscopic response in biological pH range 4-10. In addition to explore practical applicability of RDV, its paper strips have been made and used to detect Hg²⁺ in pure water solution up to 10 ppm level. Furthermore, the potential application of RDV for the sensing of Hg²⁺ in real water samples (tap water and drinking waters from different sources) were also monitored and demonstrated.

Carbon-based quantum particles: an electroanalytical and biomedical perspective

Carbon-based quantum particles, especially spherical carbon quantum dots (CQDs) and nanosheets like graphene quantum dots (GQDs), are an emerging class of quantum dots with unique properties owing to their quantum confinement effect.

Exploring the Scope of Photo-Induced Electron Transfer-Chelation-Enhanced Fluorescence-Fluorescence Resonance Energy Transfer Processes for Recognition and Discrimination of Zn2+, Cd2+, Hg2+, and Al3+ in a Ratiometric Manner: Application to Sea Fish Analysis

A rhodamine-based smart probe (RHES) has been developed for trace-level detection and discrimination of multiple cations, viz. Al³⁺, Zn²⁺, Cd²⁺, and Hg²⁺ in a ratiometric manner involving photo-induced electron transfer-chelation-enhanced fluorescence-fluorescence resonance energy transfer processes. The method being very fast and highly selective allows their bare eye visualization at a physiological pH. The optimized geometry and spectral properties of RHES and its cation adducts have been analyzed by time-dependent density functional theory calculations. RHES detects as low as 1.5 × 10^-9 M Al³⁺, 1.2 × 10^-9 M Zn²⁺, 6.7 × 10^-9 M Cd²⁺, and 1.7 × 10^-10 M Hg²⁺, whereas the respective association constants are 1.33 × 10⁵ M^-1, 2.11 × 10⁴ M^-1, 1.35 × 10⁵ M^-1, and 4.09 × 10⁵ M^-1. The other common ions do not interfere. The probe is useful for intracellular imaging of Zn²⁺, Cd²⁺, and Hg²⁺ in squamous epithelial cells. RHES is useful for the determination of the ions in sea fish and real samples.

Robust polymer nanofilms with bioengineering and environmental applications via facile and highly efficient covalent layer-by-layer assembly

Novel robust and multifunctional polymer nanofilms were prepared through facile and highly efficient covalent layer-by-layer assembly.

Sustainable carbon-dots: recent advances in green carbon dots for sensing and bioimaging

This review article highlights recent progress in use of green precursors for synthesis of carbon-dots and their applications in fluorescence-based sensing and bioimaging.

Self-assembly of nitrogen-doped carbon nanoparticles: a new ratiometric UV-vis optical sensor for the highly sensitive and selective detection of Hg2+ in aqueous solution

A novel ratiometric UV-vis optical sensor for Hg²⁺ was developed based on the self-assembly of nitrogen-doped carbon nanoparticles.

Multifunctional optical sensing probes based on organic–inorganic hybrid composites

Several hybrid sensing materials, which are prepared by the covalent grafting of organic fluorescent molecules onto inorganic supports, have emerged as a novel and promising class of hybrid sensing probes and have attracted tremendous interest.

A metal-enhanced fluorescence sensing platform based on new mercapto rhodamine derivatives for reversible Hg(2+) detection

A new metal-enhanced fluorescence (MEF) chemosensor HMS-Ag-R-2SH for Hg(2+) has been prepared via a simple and effective method. The fluorescent chemosensor was based on a mercapto rhodamine derivatives linked with Ag nanoparticles, and the Ag nanoparticles were supported on hexagonal mesoporous silica material (HMS). Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), absorption spectroscopy and fluorescence spectroscopy techniques were employed to characterize morphology, mesostructure and spectral features of the chemosensor. This chemosensor works in a nearly pure aqueous solution with a broad pH range. The output signals include color change and fluorescence. Moreover, HMS-Ag-R-2SH presents excellent anti-disturbance ability when exposed to a series of competitive cations such as Ag(+), K(+), Li(+), Na(+), Ba(2+), Ca(2+), Cd(2+), Co(2+), Cu(2+), Mg(2+), Mn(2+), Ni(2+), Pb(2+), Zn(2+), Al(3+), Cr(3+) and Fe(3+). The selectivity of this chemosensor was significantly improved due to the introduction of the sulphydryl. The chemosensor showed a lower detection limit of 2.1ppb for Hg(2+). Importantly, HMS-Ag-R-2SH could be regenerated with sodium sulfide solution for several cycles and maintain a high sensitivity.

One-step click engineering considerably ameliorates the practicality of an unqualified rhodamine probe

This study describes the exploitation of click chemistry in the one-step molecular engineering of an unqualified rhodamine probe, leading to its considerable functional enhancement in terms of water solubility, ion selectivity, and usefulness in detecting biological and environmental samples. A dipropargyl rhodamine dye previously identified as an unselective and poorly water-soluble mercury(II) probe was used to couple with an azido polyethylene glycol (PEG) by the Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition click reaction in almost quantitative yield. The simple click-engineered rhodamine probe shows, remarkably, better water solubility and mercury(II) selectivity comparing to the raw counterpart, and can be used to sensitively image mercury ions internalized by live cells and to accurately quantify the ion spiked in river water specimens. This study provides insights into the simple functional improvement of unqualified molecular dye probes via the efficient "click engineering".

Rhodamine-based fluorescent off–on sensor for Fe3+ – in aqueous solution and in living cells: 8-aminoquinoline receptor and 2 : 1 binding

A rhodamine-based Fe³⁺ sensor of a rigid 8-aminoquinoline receptor shows a 2 : 1 binding according to 1D and 2D-¹HNMR experiments.

Click to bind: metal sensors

The copper-catalyzed azide-alkyne "click" cycloaddition reaction is an efficient coupling reaction that results in the formation of a triazole ring. The wide range of applicable substrates for this reaction allows the construction of a variety of conjugated systems. The additional function of triazoles as metal-ion ligands has led to the click reaction being used for the construction of optical sensors for metal ions. The triazoles are integral binding elements, which are formed in an efficient modular synthesis. Herein, we review recent examples of triazoles as a metal-binding element in conjugated metal-ion sensors.

Fluorescent film sensors based on SAMs of pyrene derivatives for detecting nitroaromatics in aqueous solutions

The detection of nitroaromatics in aqueous solutions by a novel pyrene-functionalized film has been investigated in the present study. The pyrene moieties were attached on the glass surface via a long flexible spacer based on self-assembled monolayer technique. Steady-state fluorescence measurements revealed that these surface-attached pyrene moieties exhibited both monomer and excimer emission. Nitroaromatics such as 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and 2,4,6-trinitrophenol (picric acid) were found to efficiently quench the fluorescence emission of this film. The quenching results demonstrated that the excimer emission of these surface-confined pyrene moieties is more sensitive to the presence of nitroaromatics than the monomer emission. The quenching mechanism was examined through fluorescence lifetime measurement and it revealed that the quenching is static in nature and may be caused by electron transfer from the polycyclic aromatics to the nitroaromatics. Furthermore, the response of the film to nitroaromatics is fast and reversible, and the obtained film shows promising potentials in detecting explosives in aqueous environment.