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...