Near infrared lifetimes

Lassiter, S.J., Stryjewski, W., Owens, C.V., Elanagan, J.H., Jr., Hammer, R.P., Khan, S., and Soper, S.A., Optimization of sequencing conditions using near-infrared lifetime identification methods in capillary gel electrophoresis, Electrophoresis, 23, 1480, 2002. 

Recently, SETA BioMedicals has developed a new near-infrared squaraine-based label Seta-633, which can be used to study the interaction between low-molecular-weight analytes and proteins using fluorescence lifetime as the readout parameter [19]. This label exhibits lower quantum yields and shorter fluorescence lifetimes when free in solution, but these values substantially increase upon interaction with proteins, which is contrary to tracers like Cy5 or Alexa 647. It was demonstrated in a model assay that a biotinylated Seta-633 binds to anti-biotin with high specificity. Importantly, the lifetime of Seta-633-biotin increases about 2.76 fold upon binding to a specific antibody (anti-biotin, MW =160 kDa), while the titration with BSA or nonspecific antibody does not result in a noticeable change in lifetime (Fig. 13). The label is compatible with readily available light sources (635 nm or 640 nm lasers) and filter sets (as for Cy5 or Alexa 647) and its... 

Berezin MY, Lee H, Akers W, Achilefu S (2007) Near infrared dyes as lifetime solvato-chromic probes for micropolarity measurements of biological systems. Biophysical J 93 2892-2899... 

Bloch, S., Lesage, F., McIntosh, L., Gandjbakhche, A., Liang, K. and Achilefu, S. (2005). Whole-body fluorescence lifetime imaging of a tumor-targeted near-infrared molecular probe in mice. J. Biomed. Opt. 10, 054003. 

D. J. S. Birch, G. Hungerford and R. E. Imhof, Near-infrared spark source excitation for fluorescence lifetime measurements, Rev. Sci. Instrum. 62, 2405-2408 (1991). 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

The purpose of the rotaxane is to protect the squaraine from nucleophilic attack, likely to occur under physiological conditions, and so enhance the lifetime of the probe in vivo. Indeed, the half-life of the probe is 100 times longer than a non-rotaxane analogue that incorporates a commercial sulfonated carbocyanine dye in place of the squaraine moiety. Furthermore the near infrared spectral nature of the dye means that it gives a strong signal even through centimetres of soft tissue. 

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