Dual-Responsive Hydrogels for Mercury Ion Detection and Removal from Wastewater

This study describes the development of a fast and cost-effective method for the detection and removal of Hg2+ ions from aqueous media, consisting of hydrogels incorporating chelating agents and a rhodamine derivative (to afford a qualitative evaluation of the heavy metal entrapment inside the 3D polymeric matrix). These hydrogels, designed for the simultaneous detection and entrapment of mercury, were obtained through the photopolymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and N-vinyl-2-pyrrolidone (NVP), utilizing N,N'-methylenebisacrylamide (MBA) as crosslinker, in the presence of polyvinyl alcohol (PVA), a rhodamine B derivative, and one of the following chelating agents: phytic acid, 1,3-diamino-2-hydroxypropane-tetraacetic acid, triethylenetetramine-hexaacetic acid, or ethylenediaminetetraacetic acid disodium salt. The rhodamine derivative had a dual purpose in this study: firstly, it was incorporated into the hydrogel to allow the qualitative evaluation of mercury entrapment through its fluorogenic switch-off abilities when sensing Hg2+ ions; secondly, it was used to quantitatively evaluate the level of residual mercury from the decontaminated aqueous solutions, via the UV-Vis technique. The ICP-MS analysis of the hydrogels also confirmed the successful entrapment of mercury inside the hydrogels and a good correlation with the UV-Vis method.

Anti-cancer potential of substituted "amino-alkyl-rhodamine" derivatives against MCF-7 human breast cancer cell line

Breast cancer is the most prevalent diagnosed cancer among women and the main cause of morbidity and mortality. As for breast cancer, MCF-7 cells are an important candidate since they are widely utilized in research for estrogen receptor (ER)-positive breast cancer cell assays, and various sub-clones have been identified to reflect different classes of ER-positive tumors with varied levels of nuclear receptor expression. Rhodamines and its derivatives have shown a great interest over the past two decades due to their excellent structural and spectroscopic properties. Rhodamine derivatives have been widely investigated for their mitochondrial targeting and chemotherapeutic properties. Rhodamine derivatives, in particular, have been widely investigated for their therapeutic properties. In this regard, several studies have shown that rhodamine dye derivatives have promising in vitro and in vivo therapeutic efficacy. The present study deals with potential anticancer activity of few synthesized rhodamine derivatives against MCF-7 cell lines.

Novel schiff base as Fe3+ sensor as well as an antioxidant and its theoretical studies

A novel Schiff base derivative L (N1-(thiophene-2-ylmethylene)benzene-1,2-diamine) was synthesized via condensation reaction of 3-thiophene carboxaldehyde and 1,2-diamino benzene. The synthesized compound was authenticated using 1 H NMR, 13 C NMR, HRMS, and IR spectroscopy. The compound L was found to be a Fe3+ sensor with the complexation ratio of 1 : 3 as revealed by Job’s plot with maximum absorption at 318 nm. The photophysical properties were studied using absorption and emission spectra. DFT and TD-DFT studies were carried out in order to support the photophysical outcomes of compound L. An antioxidant behaviour of compound L was studied using TAC, FRAP, and DPPH assays and it was found to be showing better TAC activity than the used standard i.e. gallic acid.

Chain length effect of spiro-ring N-alkylation on photophysical signalling parameters in Fe(III) selective rhodamine probes

Manifestation of photophysical signalling parameters in rhodamine derivatives exhibiting complexation induced spiro-ring opening is crucial for the realization of selective metal ion detection at trace levels. Substitution of various functional groups, such as alkylation to the core architecture, modulates the physico-chemical properties of such molecular probes. Despite a few studies, relationships between the extent of photophysical signal modulations and the chain lengths of n-alkyl substituents are still elusive. In this investigation, a few molecular probes based on the rhodamine B (1-5) and rhodamine 6G (6-10) platform were synthesized by their derivatization with n-alkyl substituents of varying chain lengths at the amino-donor of their spiro-ring end, which exhibited Fe(III)-selective absorption and fluorescence 'off-on' signal transduction along with colorization of solution. The Fe(III)-selectivity in these probes remained the same despite their structural distinctions through varied n-alkyl chain lengths of the substituents; however, the quantifiable signalling parameters such as spectroscopic enhancement factors, sensitivity, the kinetics of spiro-ring opening and effectiveness of probe-Fe(III) interactions were analyzed. These parameters were also correlated in terms of the influence of different chain lengths of n-alkyl substituents that efficiently contributed to their inter-componential interactive stereo-electronic environment.

Recent studies on cellulose-based fluorescent smart materials and their applications: A comprehensive review

The progress of bio-based fluorescent smart materials and their multifunctional applications have attained increasing interest in the recent decades. Cellulose is among the cheapest and widespread raw material on earth which can be modified into diverse useful materials. This review summarizes the chemical modification of cellulose into smart fluorescent materials. This further highlights on the fabrication of the prepared fluorescent materials into films, fibers, paper strips, carbon dots, hydrogels and solutions which are applied for the sensing of toxic metals and anions, pH, bioimaging, common organic solvents, aliphatic and aromatic amines, nitroaromatics, fluorescent printing, coating, and anti-counterfeiting applications. Finally, the discussion about the upcoming investigations, challenges, and options open for the cellulose-based luminescence sensors are communicated. We believe that this review will appeal more and more attention and curiosity for the chemists, biochemists, and chemical engineers working with the synthesis of cellulose-based fluorescent materials for widespread applications.

Dynamic cross-linking of an alginate-acrylamide tough hydrogel system: time-resolved in situ mapping of gel self-assembly

Hydrogels are a popular class of biomaterial that are used in a number of commercial applications (e.g.; contact lenses, drug delivery, and prophylactics). Alginate-based tough hydrogel systems, interpenetrated with acrylamide, reportedly form both ionic and covalent cross-links, giving rise to their remarkable mechanical properties. In this work, we explore the nature, onset and extent of such hybrid bonding interactions between the complementary networks in a model double-network alginate-acrylamide system, using a host of characterisation techniques (e.g.; FTIR, Raman, UV-vis, and fluorescence spectroscopies), in a time-resolved manner. Further, due to the similarity of bonding effects across many such complementary, interpenetrating hydrogel networks, the broad bonding interactions and mechanisms observed during gelation in this model system, are thought to be commonly replicated across alginate-based and broader double-network hydrogels, where both physical and chemical bonding effects are present. Analytical techniques followed real-time bond formation, environmental changes and re-organisational processes that occurred. Experiments broadly identified two phases of reaction; phase I where covalent interaction and physical entanglements predominate, and; phase II where ionic cross-linking effects are dominant. Contrary to past reports, ionic cross-linking occurred more favourably via mannuronate blocks of the alginate chain, initially. Evolution of such bonding interactions was also correlated with the developing tensile and compressive properties. These structure-property findings provide mechanistic insights and future synthetic intervention routes to manipulate the chemo-physico-mechanical properties of dynamically-forming tough hydrogel structures according to need (i.e.; durability, biocompatibility, adhesion, etc.), allowing expansion to a broader range of more physically and/or environmentally demanding biomaterials applications.

One-step synthesis of rhodamine-based Fe3+ fluorescent probes via Mannich reaction and its application in living cell imaging

Four rhodamine-based fluorescent probes M1-M4 were synthesized in one step using Mannich reaction. The Mannich reaction based approach has the advantages of simplicity, good yield and excellent atomic economy. The structures were determined by ¹H NMR, ¹³C NMR, IR and HRMS. The probe M3 as a representative compound was characterized by single-crystal X-ray analyses. The fluorescence and absorbance spectra research of the probes demonstrated that they could be used as Fe³⁺-selective fluorescent probes with good sensitivity, excellent linearity, and outstanding anti-interference in acetonitrile/Tris-HCl buffer solution (3:7, V/V; pH = 7.4). Moreover, confocal laser scanning microscopy experiments have proven that the probe M3 was successfully used for fluorescence imaging in MCF-7 cells.

Effect of n-alkyl substitution on Cu(ii)-selective chemosensing of rhodamine B derivatives

Rhodamine B hydrazide-based molecular probes (1-10) were synthesized by derivatization with n-alkyl chains of different lengths at the hydrazide amino end. These probes exhibited selective absorption (A∼557) and fluorescence (I∼580) 'off-on' signal transduction along with a colourless → magenta colour transition in the presence of Cu(ii) ions among all the competitive metal ions investigated. The effective coordination of these probes to Cu(ii) ions under the investigated environment forming [Cu·L]2+ (L = 1-5) and [Cu·L2]2+ (L = 6-10) complexes led to their spiro-ring opening, which in turn was expressed through signatory spectral peaks of ring-opened rhodamine. All these probes exhibited Cu(ii) selectivity in signalling despite structural modifications to the core receptor unit through variation of the nature of the alkyl substituents. However, the sensitivity of the signalling and kinetics of the spiro-ring opening varied and could be correlated with the number of carbon atoms present in the n-alkyl substituents. Structural elucidation with X-ray diffraction and X-ray photoemission spectroscopic analyses provided further insight into the structure-function correlation in their Cu(ii) complexes. These probes with Cu(ii) coordination showed selectivity in signalling, high complexation affinity (log Ka = 4.8-8.8), high sensitivity (LOD = 4.1-80 nM), fast response time (rate = 0.0017-0.0159 s-1) and reversibility with counter anions, which ascertained their potential utility as chemosensors for Cu(ii) ion detection.

Role of hydrophobicity in tuning the intracellular uptake of dendron-based fluorophores for in vitro metal ion sensing

Fluorophores are used for sensing biologically relevant ions, toxic metals or pathogenic markers. However, the mode of entry of such fluorophores into the cell greatly depends on their size, shape, surface charge, functional groups, and hydrophobicity. In particular, the influence of hydrophobicity on the intracellular uptake of fluorophores is poorly investigated. Self-assembly is a recent strategy to tune the intracellular uptake of fluorophores, facilitating increased intracellular sensing and fluorescence. Herein, self-assembly of three novel poly(aryl ether) dendron derivatives that contain rhodamine units was used to investigate the effect of hydrophobicity on the intracellular uptake of self-assembled fluorophores. The results suggest that monomer hydrophobicity plays an important role in the uptake. The dendron-based fluorophores, which upon self-assembly, formed stable spherical aggregates ranging from 300 to 500 nm. The rhodamine-based dendrons could selectively sense Hg²⁺ ions in the presence of other competing metal cations. Intracellular imaging of the dendron-based fluorophores displayed bright red fluorescence in human embryonic kidney cells. The rate of intracellular uptake of the three dendron-based fluorophores was analyzed by flow cytometry. The results establish the importance of the hydrophilic-lipophilic balance of the self-assembled amphiphiles for tuning the intracellular uptake.

A Dual Associated-Functional Fluorescent Switch: From Alternate Detection Cycle for Fe(III) and pH to Molecular Logic Operations

With the expansion and deepening of scientific research, dual-functional or multifunctional materials are urgently needed to replace those for single application. Herein, a fluorescence sensing system based on an In(III)-organic complex with in situ Lewis acid sites has been constructed, exhibiting high sensitivity for the detection of Fe(III) ions with a low detection limit of 3.95 μM and a short response time of within 10 s. It is noteworthy that the quenched fluorescence of the Fe(III)-incorporated sample could be reopened linearly with an increase of alkalinity, followed by the reactivation of its functionality to identify Fe(III) ions, forming an alternate detection cycle for Fe(III) and pH with off-on-off fluorescent switch characteristics. Considering its unique molecular recognition capability, an advanced three-input (Fe(III), EDTA, and OH^-) and two-output (B440 and G489) Boolean logic operation comprising BUFF, NOT, OR, and AND logic gates was integrated, possessing potential applications in intelligent multianalyte sensing systems.

Novel Multifunctional Luminescent Electrospun Fluorescent Nanofiber Chemosensor-Filters and Their Versatile Sensing of pH, Temperature, and Metal Ions

Novel multifunctional fluorescent chemosensors composed of electrospun (ES) nanofibers with high sensitivity toward pH, mercury ions (Hg2+), and temperature were prepared from poly(N-Isopropylacrylamide-co-N-methylolacrylamide-co-rhodamine derivative) (poly(NIPAAm-co-NMA-co-RhBN2AM)) by employing an electrospinning process. NIPAAm and NMA moieties provide hydrophilic and thermo-responsive properties (absorption of Hg2+ in aqueous solutions), and chemical cross-linking sites (stabilization of the fibrous structure in aqueous solutions), respectively. The fluorescent probe, RhBN2AM is highly sensitive toward pH and Hg2+. The synthesis of poly(NIPAAm-co-NMA-co-RhBN2AM) with different compositions was carried on via free-radical polymerization. ES nanofibers prepared from sensory copolymers with a 71.1:28.4:0.5 NIPAAm:NMA:RhBN2AM ratio (P3 ES nanofibers) exhibited significant color change from non-fluorescent to red fluorescence while sensing pH (the λPL, max exhibited a 4.8-fold enhancement) or Hg2+ (at a constant Hg2+ concentration (10-3 M), the λPL, max of P3-fibers exhibited 4.7-fold enhancement), and high reversibility of on/off switchable fluorescence emission at least five times when Hg2+ and ethylenediaminetetraacetic acid (EDTA) were sequentially added. The P3 ES nanofibrous membranes had a higher surface-to-volume ratio to enhance their performance than did the corresponding thin films. In addition, the fluorescence emission of P3 ES nanofibrous membranes exhibited second enhancement above the lower critical solution temperature. Thus, the ES nanofibrous membranes prepared from P3 with on/off switchable capacity and thermo-responsive characteristics can be used as a multifunctional sensory device for specific heavy transition metal (HTM) in aqueous solutions.

Fluorescence Sensing with Cellulose-Based Materials

Cellulose-based materials functionalized with fluorescence sensors are highly topical and are employed in many areas of functional materials, including the sensing of heavy-metal ions and anions as well as being widely used as chemical sensors and tools for environmental applications. In this Review, we cover recent progress in the development of cellulose-based fluorescence sensors as parts of membranes and nanoscale materials for the detection of biological analytes. We believe that this Review will be of interest to chemists, chemical engineers, and biochemists in the sensor community as well as researchers working with biological material systems.

A selective fluorescence probe based on benzothiazole for the detection of Cr3+

A novel benzothiazole-functionalized Schiff-base derivative

Two-step FRET mediated metal ion induced signalling responses in a probe appended with three fluorophores

A tri-fluorophore appended Tren receptor based probe exhibited chelation induced ratiometric fluorescence signalling through a two-step FRET process; enhancement of F_An→ F_Rhenergy transfer efficiency through an F_NBDintermediate was observed.

Signalling probes appended with two rhodamine derivatives: inter-component preferences, Fe(iii)-ion selective fluorescence responses and bio-imaging in plant species

Molecular probes (1 and 2) incorporating two different xanthene dyes exhibited Fe(iii) selective dual mode signaling responses.

An unusual highly emissive water-soluble iridium lissamine-alanine complex and its use in a molecular logic gate

The interaction of iridium(iii) with a new lissamine rhodamine B sulfonyl derivative, bearing alanine as a building block, (1) with an orange emission in water results in a green highly emissive Ir@1 complex at room temperature. The new Ir@1 complex can sense the toxic Hg(2+) metal ion and cysteine. Based on such properties, a new sophisticated molecular logic gate with three inputs was designed.

A Method for the Highly Selective, Colorimetric and Ratiometric Detection of Hg(2+) in a 100% Aqueous Solution

Mercury (Hg) and its derivatives pose a serious threat to the environment and human health. Thus, the development of methods for the selective and sensitive determination of Hg(2+) is very important to understand its distribution, and to implement more detailed toxicological studies. Herein, we developed a new method for the detection of Hg(2+) based on the tricyanoethylene derivative and mercaptoethanol. This method could selectively detect Hg(2+) in a 100% aqueous solution by the naked-eye within the range of 1 - 60 μM. Importantly, this method also could detect Hg(2+) quantitatively by ratiometic absorption spectroscopy in the range of 0.1 - 6 μM with a detection limit of 55 nM. We anticipate that this proposed method will be used widely to monitor Hg(2+) in the environment.

Exploration of Energy Modulations in Novel RhB-TPE-Based Bichromophoric Materials via Interactions of Cu(2+) Ion under Various Semiaqueous and Micellar Conditions

Novel bichromophoric materials TR-A and TR-B consisting of an entirely new combination of TPE and RhB units were developed to explore the optimum conditions of energy modulations via pH variation and Cu(2+) interaction at various water contents of CH3CN. Interestingly, TR-A and TR-B, at 60 and 70% water contents, respectively, favored the optimum Cu(2+)-mediated energy modulations from TPE to RhB and thus achieve the brightest orange emissions of free RhB with complete disappearance of aggregation-induced emission (AIE) from TPE. Furthermore, various micellar conditions of triton-X-100, SDS, and CTAB were employed to adjust energy modulations of TR-A and TR-B at high water contents (at 80 and 90%, respectively). The incorporation of RhB into triton-X-100 micellar cavities disrupted AIE from TPE; thus, none of the energy modulations from TPE to RhB occurred even in the presence of Cu(2+) ion. Interestingly, the micellar conditions of anionic surfactant (SDS) favored the increased local concentration of Cu(2+) ions in the vicinity of scavangable RhB and facilitated the generation of noncyclic free RhB in situ via bright-orange emissions.

A sulfur-free iridium(III) complex for highly selective and multi-signaling mercury(II)-chemosensors

A sulfur-free iridium(III) complex (pbi)2Ir(mtpy) (1) was successfully prepared and adopted as a Hg(II)-chemosensor with high selectivity and sensitivity. Multi-signaling responses towards Hg(II) ions were observed by UV-vis absorption, phosphorescence and electrochemistry measurements. With addition of Hg(II) ions, complex 1 presented quenched emission in its phosphorescence spectrum and the detection limit was as low as 2.5 × 10(-7) M. Additionally, its redox peak currents showed a broad linear relationship with the concentration of Hg(II) ions ranging from 0 to 500 μM, which was beneficial for the quantitative detection. Based on the (1)H NMR and ESI-MS analyses, the probing mechanism was tentatively supposed to be the Hg(2+)-induced changes in the local environment of complex 1. Such a response process was useful for achieving simple and effective detection of Hg(II) ions as well as developing more chemosensors.

Highly sensitive and selective fluorescent probes for Hg2+ in Ag(i)/Cu(ii) 3D supramolecular architectures based on noncovalent interactions

Three novel Ag(i)/Cu(ii) metal–organic assemblies displayed 3D supramolecular architectures with the help of noncovalent interactions. 1 performs as a highly sensitive and selective fluorescent probe for Hg²⁺, and 2 shows a unique semiconductive nature.

Fluorescence “on–off–on” chemosensor for selective detection of Hg2+ and S2−: application to bioimaging in living cells

A phenothiazine based diamino-malenonitrile-linked (P-1) chromogenic and fluorogenic probe was synthesized and characterized for the specific detection of Hg²⁺ and S²⁻. The probe P-1 can be used for selective imaging of Hg²⁺ and S²⁻ in living cells.

Signaling preferences of substituted pyrrole coupled six-membered rhodamine spirocyclic probes for Hg2+ ion detection

Six-membered spiro-ring expanded probes in rhodamine scaffolds exhibit Hg²⁺ ion specific dual mode signaling responses; specificity is achieved with tuning substituents on the appended pyrrole receptor.

Fluorescence sensing of glucose using glucose oxidase incorporated into a fluorophore-containing PNIPAM hydrogel

We present a new composite material composed of pH sensitive fluorescent dyes in a poly(N-isopropylacrylamide)-based hydrogel and incorporating glucose oxidase (GOx), which provides a platform for fluorescence sensing of glucose.

Dual functional fluorescent sensor for selectively detecting acetone and Fe3+ based on {Cu2N4} substructure bridged Cu(i) coordination polymer

A novel red emission polymer can serve as a dual functional fluorescent sensor for selectively detecting trace amounts of acetone and Fe³⁺ though quenching the luminescence.

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.

Highly sensitive and selective colorimetric and off-on fluorescent reversible chemosensors for Al³⁺ based on the rhodamine fluorophore

A series of rhodamine derivatives L1-L3 have been prepared and characterized by IR, 1H-NMR, 13C-NMR and ESI-MS. These compounds exhibited selective and sensitive "turn-on" fluorescent and colorimetric responses to Al3+ in methanol. Upon the addition of Al(III), the spiro ring was opened and a metal-probe complex was formed in a 1:1 stoichiometry, as was further confirmed by ESI-MS spectroscopy. The chemo-dosimeters L1-L3 exhibited good binding constants and low detection limits towards Al(III). We also successfully demonstrate the reversibility of the metal to ligand complexation (opened ring to spirolactam ring).

A simple and dual responsive efficient new Schiff base chemoreceptor for selective sensing of F− and Hg2+: application to bioimaging in living cells and mimicking of molecular logic gates

A novel colorimetric hydrazine-functionalized Schiff base chemoreceptor, NPMP, was synthesized following a simple one-step Schiff base condensation pathway.

Dual mode signaling responses of a rhodamine based probe and its immobilization onto a silica gel surface for specific mercury ion detection

The amino-ethyl-rhodamine-B based probe 2 appended with a 3-aminomethyl-(2-amino-1-pyridyl) group retained its Hg(ii)-specific chromogenic and fluorogenic signaling responses in an aqueous medium even upon immobilization onto a silica gel surface for selective detection and extraction of Hg(ii) ions.

Rhodamine derived colorimetric and fluorescence mercury(ii) chemodosimeter for human breast cancer cell (MCF7) imaging

Condensation of rhodaminehydrazone with naphthalene-1-carboxaldehyde generates a colourless probe, RDHDNAP that can selectively detect Hg²⁺through generation of a pink color along with significant fluorescence enhancement.