Sensitivity, single molecule

Willets KA, Callis PR, Moemer WE (2004) Experimental and theoretical investigations of environmentally sensitive single-molecule fluorophores. J Phys Chem B 108(29) 10465-10473... 

Among the different chemosensors, those which are fluorescence-based present many advantages such as high sensitivity (single molecule detection is possible), low cost, ease of performance, and versatility. The fluorescent-based sensors offer subnanometer spatial resolution with submicron visualization and submillisecond temporal resolution.20-26 Thus, numerous fluorescence-based chemosensors have been prepared and investigated.4-6 On the other hand, chromoionophores are also distinct and worthwhile subjects in their own right27-30... 

Willets, K.A., Callis, P.R., Moemer, W.E. Experimental and theoretical investigations of envirmuntaitally sensitive single-molecule fluorophores. J. Phys. Chem. B108,10465-10473 (2004)... 

Operating a micro-cantilever in the oscillating mode, enables e.g. to count the number of colloidal particles adsorbed onto the cantilever by antibody binding, due to significant shifts in resonance frequency. Coating the cantilever surface with specific receptors and labeling the analyte with beads results in an extremely sensitive single molecule sensor. 

The vast majority of single-molecule optical experiments employ one-photon excited spontaneous fluorescence as the spectroscopic observable because of its relative simplicity and inlierently high sensitivity. Many molecules fluoresce with quantum yields near unity, and spontaneous fluorescence lifetimes for chromophores with large oscillator strengths are a few nanoseconds, implying that with a sufficiently intense excitation source a single... 

Other sensor applications can be considered if some sensitive biological molecules (such as antibodies or receptors) are attached to the nanogranule. If, for example, an antibody molecule is attached to it, then the granule is placed between two electrodes, and single-electron current flows between them. The step value of the coulomb staircase depends on the capacity of the junctions. When the antibody molecule binds specific antigen, the capacity value will be changed, and, therefore, the step value of the VH characteristics will also change. 

Raman spectroscopy with single-molecule sensitivity. Rhys. Rev. B, 73, 193406-1-193406-4. 

Xu, H., Aizpurua, J., KaD, M. and Apell, P. (2000) Electromagnetic contributions to single-molecule sensitivity in surface-enhanced Raman scattering. Phys. Rev. E, 62, 4318-4324. 

Schwille, P., Korkach, J. and Webb, W. W. (1999) Fluorescence correlation spectroscopy with single-molecule sensitivity on cell and model membranes. Cytometry, 36, 176-182. 

In contrast to the C. sativa tincture, Marinol soft gel capsules possess clear advantages. Firstly, they contain a single component in an accurate dosage. Secondly, it uses sesame oil as the carrier, making resorption significantly more reliable and also stabilizing the rather sensitive THC molecule. 

Fluorescence techniques are the most sensitive. With proper dye selection and proper experimental conditions, the absolute sensitivity may reach the limit of single molecules. This feature is especially needed if the target exists in trace amounts. High sensitivity may allow avoiding time-consuming and costly target-enrichment steps. 

There are two important drawbacks of such an approach (1) a polarity scale based on a particular class of probes, in principle, does not account, for example, sizes of probes, which should strongly effect the interactions (2) betain dyes do not fluoresce, which restrict essentially the field of application of this approach, because in many cases, absorption spectrum could not be measured accurately (small volumes of samples, study of cells, and single molecules spectroscopy). Therefore, polarity-sensitive fluorescent dyes offer distinct advantage in many applications. 

Also here the small sensing volume makes this kind of sensors attractive devices for high-sensitivity sensing and detection down to the single molecule level. 

Figure 8.18 TbPc2-based molecular spin-tronic devices, (a) Graphene nanotransistor with sensitivity at the single-molecule level [39, 256], (b) Scheme of the supramolecular spin valve architecture [217]. (c) Scheme of the carbon nanotube NEMS. The magnetization reversal of a TbPc 2 SIMM from a spin state Jz = +6 to Jz = -6 results in a rotation...

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