New rhodamine B-based chromo-fluorogenic probes for highly selective detection of aluminium(iii) ions and their application in living cell imaging

Yolk-shell composite optical sensors with chiral L-histidine/Rhodamine 6G for high-sensitivity "turn-on" detection of L-proline

Chirality is a ubiquitous phenomenon in nature and has attracted wide attention in the biomedicine, pharmaceutics and biosensing research fields. Enantiomeric recognition of chiral compounds, especially chiral drugs and chiral amino acids, is important for human health and nutrition. In this work, through the encapsulation of L-His&R6G (L-His = L-Histidine; R6G = Rhodamine 6G) into MOF@MOF framework ZIF-67@ZIF-8, composited material L-His&R6G@ZIF-67@ZIF-8 can be obtained. Additionally, through the etching process, a unique yolk-shell ZIF-8 chiral composite optical sensors L-His&R6G@ZIF-8 (1) can be successfully prepared. Photo-luminescent (PL) experiment also reveals that 1 can highly sensitively detect L-Proline (L-Pro) through the "turn-on" detection strategy (KBH = 1.22 × 104 M-1 and detection limit 1.9 μM). Further yolk-shell L-His&R6G@ZIF-8-based fabricate flexible mixed-matrix membranes has been prepared using doctor-blading technique, which show significant fluorescence enhancement effect under ultraviolet lamp. This work also provides the unique example of preparing chiral yolk-shell framework composite sensors, which have broad application in chiral sensing area.

Preparation and performance study of rhodamine B naphthylamide, a fluorescent probe, for the detection of Fe3

Fe3+ is essential for humans, and its deficiency or excess can be harmful to human health; thus, it is crucial to detect Fe3+. Herein, a novel 1,8-naphthylimide rhodamine-based fluorescent probe (NA-RhBEA) was prepared from rhodamine B, anhydrous ethylenediamine, and 1,8-naphthoic anhydride. This fluorescent probe complexes Fe3+ with N and O on the carboxyl groups of its spironolactam structure and part of the 1,8-naphthalenedicarboxylic anhydride structure, which results in spironolactam ring-opening and fluorescence. NA-RhBEA has high selectivity for Fe3+ in ethanol/buffer solution (4 : 1, v/v), and fluorescence is detected at an excitation wavelength λEX = 500 nm, an absorption peak appears at 585 nm, and a significant color change appears. The effect of the fluorescence intensity of Fe3+ under a series of different concentration conditions was investigated, and it was concluded that the fluorescence intensity increased with increasing Fe3+ concentration in the range of 0-500 μmol, and its detection limit was 0.84 μmol L-1. In addition, we explored the detection ability of NA-RhBEA in solutions with different pH values, mixed metal ions, and different solvents, and the results showed that the fluorescent sensor also has good anti-interference properties and some practical applicability.

A rhodamine based chemodosimeter for the detection of Group 13 metal ions

A new rhodamine derivative, HL-CIN, derived from a reaction between N-(rhodamine-6G)lactam-ethylenediamine (L1) and trans-cinnamaldehyde, is reported here for the colorimetric and fluorogenic sensing of Group 13 trivalent cations, namely Al³⁺, Ga³⁺, In³⁺ and Tl³⁺. The absorption intensity of the probe increases significantly at 530 nm whereas the fluorescence intensity enhances massively at 558 nm upon interaction with these metal ions. Other relevant metal ions could not impart any noticeable color change or fluorescence enhancement. The quantum yield or fluorescence life time of HL-CIN increases considerably in the presence of these Group 13 metal ions. Different spectral studies such as ESI-mass, FT-IR, ¹H and ¹³C NMR spectra, establish that HL-CIN undergoes hydrolysis in the presence of the trivalent cations and a rhodamine species in its ring opened form (i.e. N-(2-aminoethyl)-2-((6Z)-3-(ethylamino)-6-(ethylimino)-2,7-dimethyl-6H-xanthen-9-yl)benzamide, (L2)) along with cinnamaldehyde are produced. The rhodamine species in its ring opened form (L2) is responsible for the color change and strong increment in the absorbance and fluorescence of HL-CIN with Group 13 cations. Interaction between L1 and these metal ions could not produce the same outcome. It has been used in test paper strips and to detect these cations in real samples.

A rhodamine based dual chemosensor for Al3+ and Hg2+: Application in the construction of advanced logic gates

A rhodamine-based compound (RBO), which has been constructed from the reaction between N-(rhodamine-6G)lactam-ethylenediamine and 2,1,3-benzoxadiazole-4-carbaldehyde, is reported here as a selective chemosensor for both Al³⁺ and Hg²⁺ ions in 10 mM HEPES buffer in water:ethanol (1:9, pH = 7.4). Absorption intensity of RBO increases considerably at 528 nm with these cations. It shows fluorescence enhancement at 550 nm by 1140- and 524-fold in the presence of Al³⁺ and Hg²⁺, respectively. LOD has been determined as 6.54 and 16.0 nM for Al³⁺ and Hg²⁺, respectively. Quantum yield and lifetime of RBO enhances with these metal ions. Fluorescence intensity of Al-probe complex or Hg-probe complex is quenched in the presence of fluoride or sulfide ion, respectively, opening a path for the construction logic gates. DFT analysis has been used to understand the spectral transitions. We have constructed a systematic development from single to five inputs complex circuit, and for the first time a time dependent five input complex logic circuit is reported herein.

Recent advances in the development of fluorescent chemosensors for Al3

Detection of Al3+ has become important as it is related to several health issues and other problems. Different fluorophoric platforms, such as naphthalene, benzene, rhodamine, etc., have been explored to sense Al3+ and a good number of research articles are being published. This article focuses on the synthesis of recently reported aluminum sensors constructed from 2-hydroxy-1-naphthaldehyde, salicylaldehyde, rhodamine, coumarin and different metal based-MOFs.

A novel fluorescent probe of aluminium ions based on rhodamine derivatives and its application in biological imaging

A new type of probe can be used for the detection of Al³⁺ in biological cells.

Multifunctional rhodamine B appended ROMP derived fluorescent probe detects Al3+ and selectively labels lysosomes in live cells

There a few reports of rhodamine-based fluorescent sensors for selective detection of only Al3+, due to the challenge of identifying a suitable ligand for binding Al3+ ion. The use of fluorophore moieties appended to a polymer backbone for sensing applications is far from mature. Here, we report a new fluorescent probe/monomer 4 and its ROMP derived polymer P for specific detection of Al3+ ions. Both monomer 4 and its polymer P exhibit high selectivity toward only Al3+ with no interference from other metal ions, having a limit detection of 0.5 and 2.1 µM, respectively. The reversible recognition of monomer 4 and P for Al3+ was also proved in presence of Na2EDTA by both UV-Vis and fluorometric titration. The experimental data indicates the behavior of 4 and P toward Al3+ is pH independent in medium conditions. In addition, the switch-on luminescence response of 4 at acidic pH (0 < 5.0), allowed us to specifically stain lysosomes (pH ~ 4.5-5.0) in live cells.

Thiazolidine based fluorescent chemosensors for aluminum ions and their applications in biological imaging

Utilization of fluorescent techniques in detection of various metal ions actively pursued allow ultrasensitive and selective detections of metal ions and prevent the adverse effect of cations such as aluminum (III) ions. In this study, two novel fluorescent chemosensors containing thiazole derivatives, ((E)-2-(4-hydroxy-3-(((2-hydroxyphenyl)imino)methyl)phenyl)-3-phenyl thiazolidin-4-one) AM1 and (2,3-bis(4-hydroxy-3-((E)-((2-hydroxyphenyl)imino) methyl) phenyl) thiazolidin-4-one) AM2, have been fabricated. The probes AM1 and AM2 were prepared using the condensation reaction between 2-hydroxy-5-(4-oxo-3-phenyl thiazolidin-2-yl) benzaldehyde and 2-aminophenol for the probe AM1 and 5,5'-(4-oxothiazolidine-2,3-diyl)bis(2-hydroxy benzaldehyde) and 2-aminophenol for the probe AM2. Afterwards, they were analyzed by various types of NMR and FT-IR spectroscopy, ESI-MS spectra, and elemental anayzer. As a second step, each fabricated chemosensor was able to use turn on fluorescence sensing for detecting of Al³⁺ ions in ACN/H₂O (v/v = 50/50, 10.0 μM, pH = 7.0) solution. Clear complexes formed between the probe AM1 and Al³⁺ ions and also the probe AM2 and Al³⁺ ions was determined by not only ¹H NMR titration study but also calculated by using the Job's plot. The limit of detection (LOD) value was found to be 0.11 μM (AM1) and 4.4 μM (AM2) for Al³⁺ ions. Likewise, cell imaging and in vitro cytotoxicity experiments of Al³⁺ ions in Human epithelium Lovo cells exhibited that prepared chemosensors had low cytotoxicity and blue fluorescence when they treated with of Al³⁺ ions in the cellular system.

A Review on Schiff Base Fluorescent Chemosensors for Cell Imaging Applications

Fluorescent determinations of analytes have proven to be a powerful method due to their simplicity, low cost, detection limit, rapid photoluminescence response, and applicability to bioimaging. Fluorescence imaging as a powerful tool for monitoring biomolecules within the living systems. Schiff base has been extensively used as strongly absorbing and colorful chromophores in the design of chemosensors. In recent years, Schiff base based fluorescent probes have been developed for the detection of various toxic analytes and imaging of various analytes in biological systems. This review gives an overview of the important fluorescent sensors which are based on Schiff base, their approaches for molecular recognition, and their potential application in bioimaging studies.

Multi-site probe for selective turn-on fluorescent detection of Al(III) in aqueous solution: synthesis, cation binding, mode of coordination, logic gate and cell imaging

An easy to make organic probe (hereafter called as R) possessing multiple ligating sites have been synthesized and characterized using spectral techniques. The probe exhibits selective and sensitive turn-on fluorescence response with Al(III) in aqueous dimethylformamide (DMF) (1:1 v/v) solution. Fluorescence titration experiment shows that the probe binds with Al(III) with a 1:1 stoichiometry and a binding constant of 6.6 × 10⁴ M^-1.The mode of coordination of R with Al(III) has been established suing ²⁷Al and ¹H NMR studies and the results suggest formation of an octahedral complex been them. The suggested point of attachment of R with Al(III) corroborates well with Density Functional Theory (DFT) optimized structure and Mulliken charges computed. Chelation-enhanced fluorescence (CHEF) is proposed as the mechanism of enhancement of fluorescence upon addition of Al(III) to R. The probe detects Al(III) in aqueous solution with a detection limit of 0.2 μM, which is much lower than the permissible limit of Al(III) set by the World Health Organization (WHO).The probe works in a wide pH range (4-11) and thus makes it a suitable candidate for environmental and biological applications. The fluorescence signals of R were used to construct an INHIBIT molecular logic gate. The confocal fluorescence microscope experiments show that R could be employed as a fluorescent probe for detecting Al(III) in living 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.

A novel turn on fluorescent probe for the determination of Al3+ and Zn2+ ions and its cells applications

Early detection of probes is very important for limiting toxic effects of various transition metal ions for example aluminum and zinc. Monitoring of these metal ions can be challenging via conventional methods since they are high cost instrumentations, time consuming and so on. We report facile preparation of a fluorescence probe containing biphenyl groups that effectively selective and superb sensitivity towards aluminum (III) and zinc (II) in neutral solutions without interference from each other and other ions. In neutral pH value, the probe FOB displayed the OFF-ON fluorescence enhancement at 464 nm and 512 nm toward aluminum (III) and zinc (II), respectively. The detection limit values of FOB for Al³⁺ and Zn²⁺ in neutral solutions were 1.27 and 1.02 nM, respectively and these values were significantly lower than permitted Al³⁺ and Zn²⁺ concentrations in drinking water determined by the World Health Organization (WHO) and European Water Quality. Also, fabricated cyano-biphenyl based probe is effective for sensing for aluminum (III) and zinc (II) in living human colon cancer cells even when employed at low concentrations (1.0 μM). Overall, this work allows us to obtain a great potential to be applied to detect Al³⁺ and Zn²⁺.