A fluorescence turn "on-off" imaging probe for sequential detection of Al3+ and L-Cysteine in HeLa cells.

At this "Aluminum Age", exposure to aluminum (metallic or ionic form) is inevitable and inestimable. The presence of aluminum in biological systems is evident but more often aluminum toxicity is less understood. Therefore, the presence of biologically reactive aluminum needs to be identified and quantified. Alongside metals, L-cysteine, an essential amino acid, plays a pivotal role in the homeostasis of cellular oxidative and reductive stress. However, excess (<7g) could be lethal and can lead to death. Thus, in-situ selective detection of aluminum and L-cysteine is of larger interest. Here we report a fluorogenic probe (R) for the sequential selective detection and quantification of Al3+ and L-cysteine in a semi-aqueous medium (3:7; water: DMSO). The probe (R) was synthesized by a one-step acid-mediated condensation reaction between pyridine-3,4-diamine and 2-hydroxy-1-napthaldehyde. The synthesized probe was characterized using 1H and 13C NMR, and HR-Mass spectroscopic techniques. The probe (R) is non-emissive in nature, but on recognition of Al3+, the probe R showed "turn-on" emission (bright yellow colour) showing two emission maxima (522 nm and 547 nm), and no naked eye observable color change. Other competing cations do not show any noticeable fluorescence outcome. The R + Al3+ ensemble can specifically detect L-cysteine among all the essential amino acids by showing a fluorescence "turn-off" response. The sensing mechanism of Al3+ is obeying the chelation-enhanced fluorescence (CHEF) effect. The binding constant of R + Al3+ is 0.3 × 104 M-1. The limit of detection (LoD) for Al3+ and L-cysteine are 2.02 × 10-7 M and 0.5 × 10-5 M respectively. The probe (R) can show maximum efficiency within the pH range (7.0-10.0). The probe is found non-toxic (>80 % cell viability with 15 µM concentration) and employed for the in-vitro fluorescence imaging in the HeLa cell.

Nanomolar Detection of H2S in an Aqueous Medium: Application in Endogenous and Exogenous Imaging of HeLa Cells and Zebrafish.

The homeostasis of short-lived reactive species such as hydrogen sulfide/hypochlorous acid (H2S/HOCl) in biological systems is essential for maintaining intercellular balance. An unchecked increase in biological H2S concentrations impedes homeostasis. In this report, we present a molecular probe pyrene-based sulfonyl hydrazone derived from pyrene for the selective detection of H2S endogenously as well as exogenously through a "turn-off" response in water. The structure of the receptor is confirmed by Fourier-transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction studies. The receptor shows excellent green emission in both the aqueous phase and solid state. Quenching of green emission of the receptor is observed only when H2S is present in water with a detection limit of 18 nM. Other competing anions and cations do not have any influence on the receptor's optical properties. The efficiency of H2S detection is not negatively impacted by other reactive sulfur species too. The sensing mechanism of H2S follows a chemodosimetric reductive elimination of sulfur dioxide, which is supported by product isolation. The receptor is found to be biocompatible, as evident by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and its utility is extended to endogenous and exogenous fluorescence imaging of HeLa cells and zebrafish.

Naphthalimide based smart sensor for CN-/Fe3+ and H2S. Synthesis and application in RAW264.7 cells and zebrafish imaging.

Achieving selective detection of target analytes in aqueous media continues to be an arduous proposition. Herein, we report the conceptualization and synthesis of a novel tailor-fit molecular probe R based on 1,8-naphthalimide which acts as a trifunctional molecular sensor for CN-, Fe3+ and H2S. R shows colorimetric and fluorometric "on-off" relay recognition for CN- (red colour and orange emission) and Fe3+ (no colour and no emission) in 5% H2O + DMSO medium which is experimentally ascertained to be a tandem deprotonation-protonation process and is supported by 1H-NMR titration. Among all RSS (Reactive Sulphur Species), R shows selectivity for H2S through red colouration. Other coexistent anions, cations and RSS cause no discernible perturbation to the detection process. The detection of H2S is attributed to a chemodosimetric reduction of the nitro to amino group as evidenced by a potentiometric titration assay. The experimental observations are well supported by DFT theoretical calculation. The K a for CN-/Fe3+ are 1.4 × 104 M-1, 6.07 × 104 M-1 respectively and photochemical yield of R + CN- is 0.86. Limit of detections for CN-, Fe3+ and H2S are 17.5 nM, 8.69 µM and 8.1 µM respectively. Receptor R is effective for real time applications, bio-compatible and has been successfully employed for confocal fluorescence imaging of RAW264.7 cell and zebrafish.

A Simple Red Emitting "Turn-On" Optical Relay Detector for Al3+ and CN-. Application in the Real Sample and RAW264.7 Cell Imaging.

A quantitative and qualitative fluorogenic molecular probe (R) has been designed and synthesized using Rhodamine-B hydrazide and 3,5-dibromo salicylaldehyde. The probe R has been applied for detection of ionic species and probe R turned out to be a prominent distinguisher among divalent and trivalent cations Al3+, Cr3+ and Fe3+ via the fluorometric response in acetonitrile medium. Colorimetric changes were observed for trivalent cations and Cu2+. Among all trivalent cations, Al3+ is possessing relay recognition for CN- even in the presence of other interfering anions with optimum precision. The association constant and the detection limit for R-Al3+ are 4.5 × 106 M-1 and 17.9 nM respectively. On the other hand, R + Al3++CN- exhibits an association constant and detection limit of 5.77 × 105 M-1 and 4.6 nM respectively. The stoichiometry of Al3+ binding with R is found to be 1:1. Quantum efficiency of probe R, R + Al3+ and R + Al3++CN- are found to be 0.2, 0.88 and 0.04 respectively. The receptor showed excellent real-time applicability for commercially available antiperspirant and apple seeds extract. The efficiency of the receptor further extended for fluorescent imaging of Al3+ and CN- in RAW264.7 cells.

Nanomolar colorimetric hypochlorite sensor in water.

Hypochlorous acid is present in several biological systems and plays a pivotal role in bioprocesses. The acid also finds application in industrial and synthetic spheres. The ecological toxicity of elevated hypochlorite concentrations in aqueous media has been thoroughly documented. As a consequence, there is a pressing need to develop quantitative and qualitative methods for the detection of hypochlorite in water. In this regard, nanomolar detectable, non-toxic and intensely coloured probes based on commercially available dyes such as Fuchsin basic, Methyl violet, Acid red-1, and Trypan blue have been successfully applied for hypochlorite detection in fully aqueous media. In all of these cases, specific and selective naked eye sensing of hypochlorite was achieved. As a rule of thumb, the addition of hypochlorite to a dye solution results in discoloration. The sensing mechanism follows an oxidative chemodosimetric approach and UV-Vis, as well as NMR titration experiments, support the oxidative cleaving of the molecular framework even in the presence of hypochlorite in trace amount (>1 nM). Furthermore, probes are subjected towards real-sample analysis of daily use water which contains bleaching agent and found to be promising in strip test too. Limits of detection of the dyes Fuchsin basic, Methyl violet, Acid red-1 and Trypan blue are 0.86 nM, 2.97 nM, 2.31 nM and 30 µM respectively. These dyes are promising analytical tools for the detection of hypochlorite.