Fluorescent signal transduction

Each of these goals requires the synthesis of a compound with sufficiently selective binding and concomitant fluorescent signal transduction in water. However, the scientific base on which to start the rational design process does not, at present, exist. We have set as our research agenda the evaluation of new ways in which an ion or molecule recognition event can be transduced into a fluorescence event. 

The requisite research issues essential to the creation of fluorescent chemosensors are (1) how can one bind a molecular entity with selectivity (preferably from water), (2) what molecular changes result in fluorescence changes, and (3) what mechanisms for binding and fluorescence signal transduction intersect. 

Chemical Mechanisms for Fluorescence Modulation. While UV/visible signalling almost always results from the ionization of a conjugated substituent, there exists a plethora of mechanisms by which fluorescence signal transduction may be engendered. It is useful to categorize the mechanisms for fluorescence modulation described to date via the type of measurement that is made. These are intensity, intensity-ratio, and lifetime. A pictoral summary of each is found in Figure 1 of the chapter by Szmacinski and Lakowicz. 

Fluorescent Signal Transduction in Molecular Sensors and Dosimeters... 

We will first summarize the fluorescence and spectroscopic assays that have been developed for the fluorometer and then describe their applications using flow cytometry. We will summarize research which exemplifies the utility of simultaneous measurement of responses and shows how these methods have provided Information about the signal transduction pathways and activation in neutrophils. 

The mDHFR protein complementation assay has been used to map a signal transduction network that controls the initiation of translation in eukaryotes (Remy and Michnick, 2001). A total of 35 different pairs of full-length proteins were analyzed and 14 interactions were identified using the survival selection of cells grown in the absence of nucleotides. In addition, the use of the fMTX reagent in combination with fluorescence microscopy was used to localize the protein complex within cells (Remy and Michnick, 2001). 

Fluorescence imaging with genetically encoded fluorophores is widely being used to study the dynamics and turnover of diverse proteins involved in different plant signal transduction pathways... 

Bastiaens, P. I. and Jovin, T. M. (1996). Microspectroscopic imaging tracks the intracellular processing of a signal transduction protein fluorescent-labeled protein kinase C beta I. Proc. Natl. Acad. Sci. USA 93, 8407-12. 

Few chemical sensing mechanisms (other than bulk quenching) have been described for neutral molecules nevertheless, many small analytes of interest are uncharged glucose, for example. Of course, most carbohydrates are neither fluorescent nor are they fluorescence quenchers novel signal transduction mechanisms are required. 

The signal transduction is obviously a very important aspect of the chemosensing scheme. Even if one exciton could sample an almost infinite number of binding sites, that would be of no benefit if the analyte was not able to alter its fluorescence. In other words, in order for there to be ampHfication, a signal must be present that can be amplified. There are several mechanisms by which signal... 

An ideal sensor recognizes analytes in a sensitive, selective, and reversible manner. This recognition is in turn reported as a clear response. In recent years, conducting polymers have emerged as practical and viable transducers for translating analyte-receptor and nonspecific interactions into observable signals. Transduction schemes include electronic sensors using conductometric and potentiometric methods and optical sensors based on colorimetric and fluorescence methods [1]. 

Bastiaens PIH, Verveer PJ, Squire A, Wouters F (2001) Fluorescence lifetime imaging microscopy of signal transduction protein reactions in cells. In Valeur B, Brochon JC (eds) Springer series on fluorescence 1 (New trends in fluorescence spectroscopy). Springer, Berlin Heidelberg New York p 297-302... 

Calixarenes may also bear excimer reporter sites, although the details of signal transduction are inherently different from those of CD-based excimer chemosensors. First, unlike Schemes 7 and 8, the fluorescent monomer units are not included within the calixarene bucket. Rather, calixarene functions as only a scaffold, bearing monomer subunits. Second, analyte seldom enters the calixarene bucket. The most common design for this type of chemosensor is shown in Scheme 9. A preformed excimer is disrupted by analyte binding at the... 

In one such approach we seek to exploit the potential signal transduction properties of the thermochromic Dawson [40] polyoxometalates and combine this with a fluorescent POM-hybrid to produce a device that could respond optically as a function of the local environment, see Figure 2.12. In this example, the clusters would be positioned on a gold surface using SAMs (Self-assembled monolayer) with a cationic tail and local positional control could be aimed using self-assembly, or even by means of an atomic force microscope tip. 

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