A π-conjugated amphiphilic diketopyrrolopyrrole (PDPP-Amphi) forms crystalline 2D supramolecular nanosheets in water when compared to that from methyl cyclohexane. These nanosheets exhibit high fluorescence quantum yield in the solid-state with anisotropic charge-carrier mobility of 0.33 cm V s .

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Quantum dots and noble metal quantum cluster (QC) based fl uorescent probes are of interest for the detection of specifi c analytes of biological as well as nonbiological origin. [ 1 ] They exhibit size tunable fl uorescence emission ranging from UV/Vis to NIR region. [ 2 ] When compared to semiconductor quantum dots, gold clusters (AuCs) are advantageous due to the less toxicity of the latter. Applications of gold clusters include targeted cancer imaging, biological labeling, detection of proteases, glutaraldehyde, Cu 2 + , Hg 2 + , CN − , As 3 + as well as explosives such as TNT. [ 1e-m ] Majority of the QC based sensors are based on analyte induced fl uorescence variation in the UV/Vis region. While such sensors are useful for the analysis of a variety of samples, they are not appropriate for biological samples such as blood and other colloidal samples. For example, for the direct analysis of blood samples, due to the autofl uorescence and strong color, fl uorescent probes that emit in the NIR region are preferred over those emitting in the visible region. Herein, we report a gold cluster based nanosensor (AuC@Urease) for the selective and direct detection of urea in blood samples and hence has relevance in clinical diagnosis and health care. The main advantage of the proposed sensing mechanism is that it works directly on the blood whereas currently adopted clinical methods require serum separation for the detection of urea, as many of them work on colorimetric assay which is often hindered by the color of blood. Moreover, this highly sensitive and direct sensing method has the advantage of providing quick results as there is no need of serum separation.Urea is a byproduct of protein metabolism that is formed in the liver, carried by the blood and excreted through the kidney in urine. Therefore, urea is an important marker for evaluating uremic toxin levels and kidney and hepatocellular functions. [ 3 ] Urea detection is also important in the estimation of non-protein nitrogen in food products such as milk since it is known that urea adulteration is utilized as an indicator of protein feeding effi ciency. [ 4 ] Nanosensors based on metal nanoparticles (NPs) have got wide attention during the past couple of decades because of their enhanced selectivity and sensitivity towards specifi c analytes. [ 5 , 6 ] There are several reports on nanosensors for the detection of urea, most of which are based on electrochemical or amperometric sensing. [ 7 ] In a recent report, urease functionalized gold nanoparticles were used as a conductometric biosensor for the detection of urea. [ 7k ] The design of the nanosensor started with the preparation of AuC by the process of etching mercapto succinic acid conjugated gold nanoparticles (AuNPs, 5-7 nm, Figure S1) in the presence of glutathione (GSH) at 0 ° C followed by 20 min incubation and subsequent heating at 70 ° C, maintaining the pH at 1.5. The color of the solution changed from dark brown to light yellow ( Figure S2, inset) with etching process. The cluster was cha...

Cooperative p-p interactions and H-bonding are frequently exploited in supramolecular polymerization;h owever,c lose scrutiny of their mutual interplay has been largely unexplored. Herein, we compare the self-assembly behavior of aseries of C 2 -a nd C 3 -symmetrical oligophenyleneethynylenes differing in their amide topology (N-or C-centered). This subtle structural modification brings about drastic changes in their photophysical and supramolecular properties,h ighlighting the reciprocal impact of H-bonding vs.preorganization on the evolution and final outcome of supramolecular systems.

The design of fluorescent molecular platforms capable of responding to multiple analytes is a topic of great interest. Herein, the use of a Zn -complexed unsymmetrical squaraine dye, Sq-Zn , as a chemical platform for recognizing structurally distinct analytes is reported. The squaraine ring is substituted on one side with a dipicolylamine unit, which acts as the metal ion receptor, whereas the other part of the molecule carries a dibutylaniline moiety, which is an electron donor. The molecular system is unique because it can respond specifically to different types of analytes, namely, atmospheric carbon dioxide, cyclic phosphates, and picric acid. Moreover, the interaction of these analytes can be monitored colorimetrically and fluorimetrically, which favors both qualitative and quantitative analyses. The distinct response towards cyclic and linear phosphates, as well as the selective response towards picric acid, among the various nitroaromatic compounds was achieved with sensitivity at the ppm level. The flexible coordination offered by Zn plays a significant role in the discrimination of these analytes with high specificity. Dye Sq-Zn introduced herein is a single-molecule construct that can be used for the selective and sensitive response towards analytes of environmental and biological relevance.

Zinc, the essential trace element in human body exists either in the bound or free state, for both structural and functional roles. Insights on Zn2+ distribution and its dynamics are essential in view of the fact that Zn2+ dyshomeostasis is a risk factor for epileptic seizures, Alzheimer’s disease, depression, etc. Herein, a bipyridine bridged bispyrrole (BP) probe is used for ratiometric imaging and quantification of Zn2+ in hippocampal slices. The green fluorescence emission of BP shifts towards red in the presence of Zn2+. The probe is used to detect and quantify the exogenous and endogenous Zn2+ in glioma cells and hippocampal slices. The dynamics of chelatable zinc ions during epileptic condition is studied in the hippocampal neurons, in vitro wherein the translocation of Zn2+ from presynaptic to postsynaptic neuronal bodies is imaged and ratiometrically quantified. Raman mapping technique is used to confirm the dynamics of Zn2+ under epileptic condition. Finally, the Zn2+ distribution was imaged in vivo in epileptic rats and the total Zn2+ in rat brain was quantified. The results favour the use of BP as an excellent Zn2+ imaging probe in biological system to understand the zinc associated diseases and their management.

The excited state intra molecular charge transfer (ICT) property of fluorophores has been extensively used for the design of fluorescent chemosensors. Herein, we report the synthesis and properties of three donor–π-acceptor–π-donor (D–π-A–π-D) based molecular probes BP, BT and BA. Two heteroaromatic rings, pyrrole (BP), and thiophene (BT) and a non-heteroaromatic ring N-alkoxy aniline (BA) were selected as donor moieties which were linked to a bipyridine binding site through a vinylic linkage. The heteroaromatic systems BP and BT perform selective and ratiometric emission signalling for zinc ions whereas the non-heteroaromatic probe BA does not. The advantages of the D–π-A–π-D design strategy in the design of ICT based probes for the selective fluorescent ratiometric signalling of zinc ions in biological media is discussed. Further, the use of BP, BT and BA for imaging Zn(2+) ions from MCF-7 cell lines is demonstrated.

An unprecedented, positional effect of the isomeric repeat unit on chain folding in donor–acceptor-linked oligomers, which contain alternating bipyridine and carbazole moieties that are connected through an acetylinic linkage, is reported. 4,4′-Linked oligomer 1 adopts an intrachain helical conformation (CD-active) in CHCl3/MeCN (20:80 v/v), whereas oligomer 2, which contains an isomeric 6,6′-linkage, forms interchain randomly coiled aggregates (CD-inactive). The substitution position plays a significant role in controlling the variations in electronic effects and dipole moments around the bipyridyl moiety, which are responsible for this observed phenomenon. Two model compounds of oligomers 1 and 2 (3 and 4, respectively) were prepared and their properties were compared. A systematic investigation of the photophysical and CD properties of these structures, as well as theoretical studies, support our conclusions.