Sensor citrate

The design of fluorescent sensors is of major importance because of the high demand in analytical chemistry, clinical biochemistry, medicine, the environment, etc. Numerous chemical and biochemical analytes can be detected by fluorescence methods cations (H+, Li+, Na+, K+, Ca2+, Mg2+, Zn2+, Pb2+, Al3+, Cd2+, etc.), anions (halide ions, citrates, carboxylates, phosphates, ATP, etc.), neutral molecules (sugars, e.g. glucose, etc.) and gases (O2, CO2, NO, etc.). There is already a wide choice of fluorescent molecular sensors for particular applications and many of them are commercially available. However, there is still a need for sensors with improved selectivity and minimum perturbation of the microenvironment to be probed. Moreover, there is the potential for progress in the development of fluorescent sensors for biochemical analytes (amino acids, coenzymes, carbohydrates, nucleosides, nucleotides, etc.). 

None of the involved species are fluorescent. Therefore, for fluorescence signaling of citrate recognition, carboxyfluorescein is first added to the medium because binding to the receptor in the absence of citrate is possible and causes deprotonation of carboxyfluorescein, which results in high fluorescence. Citrate is then added, and because it has a better affinity for the receptor than carboxyfluorescein, it replaces the latter, which emits less fluorescence in the bulk solvent as a result of protonation. Note that this molecular sensor operates in a similar fashion to antibody-based biosensors in immunoassays. It was succes-fully tested on a variety of soft drinks. 

Ammonium, citrate and oxalate 8 PVC sensors — Fermentation broth [97]... 

Triarylbenzoamido-crown ethers 71 and 72 [58] showed abilities as naked-eye sensors for F, H2PO4, AcO , citrate, trimesate, and isophthalate in the presence of potassium picrate in DMS0 H20 (1 1 v/v). Upon addition of the aforementioned anions to a solution of 71-K+ or 72-K+ picrate, the color of the solution changed from yellow to green. 

Willner and coworkers demonstrated three-dimensional networks of Au, Ag, and mixed composites of Au and Ag nanoparticles assembled on a conductive (indium-doped tin oxide) glass support by stepwise LbL assembly with A,A -bis(2-aminoethyl)-4,4 -bipyridinium as a redox-active cross-linker.8 37 The electrostatic attraction between the amino-bifunctional cross-linker and the citrate-protected metal particles led to the assembly of a multilayered composite nanoparticle network. The surface coverage of the metal nanoparticles and bipyridinium units associated with the Au nanoparticle assembly increased almost linearly upon the formation of the three-dimensional (3D) network. A coulometric analysis indicated an electroactive 3D nanoparticle array, implying that electron transport through the nanoparticles is feasible. A similar multilayered nanoparticle network was later used in a study on a sensor application by using bis-bipyridinium cyclophane as a cross-linker for Au nanoparticles and as a molecular receptor for rr-donor substrates.8... 

Many different applications for gold cysteine nanoclusters have been proposed. One application is the use of citrate capped nanoparticles as sensors for the detection of thiol containing stractures. This application rehes on the fact that thiols can easily displace oxygen coordinated moieties. Zhong et al. have studied this process between cysteine and homocysteine to develop an assay for the homocysteine biomarker, a correlate to cardiovascular disease. When citrate stabilized particles of 13 run were incubated with either thiolate structure, the solution color changed from a dark red to a deep blue. The displacement of citrate by these moieties resulted... 

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