Enhanced fluorescence cyanide detection at physiologically lethal levels: reduced ICT-based signal transduction

Abstract

Three water-soluble fluorescent probes have been specifically designed to determine free cyanide concentrations up to physiologically lethal levels, >20 microM. The probes have been designed in such a way as to afford many notable sensing features, which render them unique with regard to signal transduction, photophysical characteristics, and their application to physiological cyanide determination and safeguard. The probes are readily able to reversibly bind free aqueous cyanide with dissociation constants around 4 microM3. Subsequent cyanide binding modulates the intramolecular charge transfer within the probes, a change in the electronic properties within the probes, resulting in enhanced fluorescence optical signals as a function of increased solution cyanide concentration. The ground-state chelation with cyanide produces wavelength shifts, which also enable the probes to sense cyanide in both an excitation and emission ratiometric manner, in addition to enhanced fluorescence signaling. This has enabled a generic cyanide sensing platform to be realized that is not dependent on fluorescent probe concentration, probe photodegradation, or fluctuations in the intensity of any employed excitation sources, ideal for remote cyanide sensing applications. Further, the >600 nm fluorescence emission of the probes potentially allows for enhanced fluorescence ratiometric cyanide sensing in the optical window of tissues and blood, facilitating their use for the transdermal monitoring of cyanide for mammalian safeguard or postmortem in fire victims, both areas of active research.

Figure 1.

Molecular structures of cyanide.

Figure 2.

Complexation of DSPBA probes with aqueous free cyanide.

Figure 3.

Absorption spectra of DSP in water with increasing cyanide concentrations (top left), and for the ortho-, meta-, and para-DSPBA probes with increasing cyanide concentrations (top right, bottom left, and bottom right, respectively).

Figure 4.

Ratiometric response of the probes in water with increasing cyanide concentrations.

Figure 5.

Fluorescence emission of o-DSPBA in water with time when excited at 475 and 375 nm.

Figure 6.

Fluorescence emission spectra of o-DSPBA in water with cyanide for both 375 and 475 nm excitation (left), and the respective ratiometric plot for the intensity at 600 nm (i.e., 375/475 nm) (right).

Figure 7.

Fluorescence spectra of DSP in water with increasing cyanide concentrations (top left), and also for the ortho-, meta-, and para-DSPBA probes with increasing cyanide concentrations (top right, bottom left, and bottom right, respectively).

Figure 8.

Emission ratiometric response of the probes in water with increasing cyanide concentrations.

Figure 9.

Absorption and emission spectra of o-DSPBA in water with increasing cyanide concentration and having a 100 mM NaCl background (top), and the respective excitation and emission ratiometric plots (bottom).