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Benzothiazole based cyanine dyes with bridged groups in the pentamethine chain were studied as potential far-red fluorescent probes for protein detection. Spectral-luminescent properties were characterized for unbound dyes and in the presence of serum albumins (bovine (BSA), human (HSA), equine (ESA)), and globular proteins (β-lactoglobulin, ovalbumin). We have observed that the addition of albumins leads to a significant increase in dyes fluorescence intensity. However, the fluorescent response of dyes in the presence of other globular proteins was notably lower. The value of fluorescence quantum yield for dye bearing a sulfonate group complexed with HSA amounted to 42% compared with 0.2% for the free dye. The detection limit of HSA by this dye was greater than 0.004 mg ml −1 which indicates the high sensitivity of dye to low HSA concentrations. Modelling of structure of the dyes complexes with albumin molecules was performed by molecular docking. According to these data, dyes could bind to up to five sites on the HSA molecule; the most preferable are the haemin-binding site in subdomain IB and the dye-binding site in the pocket between subdomains IA, IIA and IIIA. This work confirms that pentamethine cyanine dyes could be proposed as powerful far-red fluorescent probes applicable for highly sensitive detection of albumins.

Far-red pentamethine cyanine dyes as fluorescent probes for detection of serum albumins. The absorption spectra of the studied dyes (1μM) in acetonitrile, DMSO and MeOH

Additional file 1: Figure S1. Transmission electron microscopy (TEM) images of NPs_D2 with (a) and without (b) TEM contrast agent (phosphotungstic acid); NPs loaded PS and NIRFD without contrast agent (c). Figure S2. Fluorescence spectra of NF: polySt-poly(NIPAM-co-AA) NPs loaded with HPPH and dyes. a Fluorescence of HPPH emission loaded to NPs_D1 and NPs_D2 (excitation at 400 nm). b Fluorescence of NPs_D2 loaded with HPPH only and with HPPH and different concentration of JB 17-08; c Dependence of fluorescence intensity of JB 17-08 loaded NPs_D1 and NPs_D2 on dye concentration. Fluorescence was excited at 808 nm. Figure S3. Absorption (a) and fluorescence spectra (b, c) of HPPH and JB17-07 loaded to NPs_D2 before (black) and after (red) dialysis. Figure S4. Changes in absorption spectra of HPPH loaded to NPs_D2 under 532 nm laser irradiation. Samples were irradiated for 0,15,30 and 60 min. Figure S5. Confocal microscopy images of HeLa cells pre-incubated with HPPH/NIRFD NF, irradiated with laser at 405 nm and stained with propidium iodide (PI)24 h post irradiation. a Transmission (left and central columns) and PI fluorescence (right column) of cells treated with NPs_D2 loaded with HPPH and JB7-08. b NPs_D2 loaded with HPPH and JB17-08. Irradiated (laser scanned) area is marked by green dashed square.

Investigation of the influence of divalent metal cations on the induction of plasminogen catalytic activity by monoclonal antibody IV-Ic showed that the presence of metal cations in the reaction medium changes the induction by slowing down or accelerating the process. Ions of Zn(2+), Mn(2+), and Cu(2+) completely inhibit activation. Ions of Co(2+) and Ni(2+) decrease the rate of the first and second phases of the reaction more than 2 times. Ca(2+) ions do not have any effect on the activation rate. Ions of Mg(2+), Ba(2+), and Sr(2+) increase the rate of the first phase of the reaction by 1.5, 2.0, and 2.0 times and the rate of the second phase by 2.0, 3.8, and 4.7 times, correspondingly. Sr(2+) ions have the strongest stimulating effect on plasminogen activation by monoclonal antibody IV-Ic. Investigation of the dose dependent effect of Sr(2+) on the rate of plasminogen activation by monoclonal antibody IV-Ic showed stimulating effect of Sr(2+) at concentrations from 0.1 to 1.0 mM with half maximum at 0.6 mM. However, Sr(2+) ions do not affect amidolytic activity of plasmin and activation of plasminogen by streptokinase. Sr(2+) ions also do not affect monoclonal antibody IV-Ic binding to plasminogen. The effect of Sr(2+) is specific and mediated by the IV-Ic component. The presence of metal cations affects conformational changes in the process of active site formation. Metal cations also affect structure of the plasminogen molecule active site in the complex with monoclonal antibody IV-Ic and enzyme-substrate interaction. The effect of alpha(2)-antiplasmin on the induction of plasminogen catalytic activity by monoclonal antibody IV-Ic in range of concentrations from 5 to 30 nM has been studied. alpha(2)-Antiplasmin at concentration 30 nM almost completely inhibits induction of plasminogen catalytic activity by monoclonal antibody IV-Ic at the ratio plasminogen/alpha(2)-antiplasmin of 3 : 1. This can be explained by competition of alpha(2)-antiplasmin and monoclonal antibody IV-Ic for the lysine-binding sites of plasminogen and inhibition of the active center in activated complex plasminogen*-mAB IV-Ic. Divalent metal cations and alpha(2)-antiplasmin are important factors in induction of plasminogen catalytic activity by monoclonal antibody IV-Ic.

The method of using a saturable absorber to mode-lock the solid state laser is now a well established and simple technique1, 2. A number of polymethine dyes are presently known to be useful for passive mode locking of the solid state lasers in the 1.06 μm range3, 4. So far, reports on application of these dyes for mode-locked operation consider mostly dyes in solution rather than in plastic, although the polymethine dyes in plastic have some advantages. First, they can simplify the design of a mode-locked laser and, second, increase reproducibility of temporal and energetic parameters of the radiation. But this can be achieved only in the case if spectral, luminescence, and nonlinear optical characteristics of the dyes in the polymer matrix are not significantly different from the characteristics in liquid solutions. It was a difficult problem for a long time, and only now it has been solved by appropriate selection of the dye structure and the nature of the matrix containing it5.