A novel fluorescent probe is designed and synthesized for the determination of cysteine in biological samples by incorporating 2,4-dinitrobenzenesulfonyl (DBS) group as a quencher into the BODIPY skeleton. The BODIPY-based probe itself shows weak fluorescence due to the strong intramolecular charge transfer process. Upon reaction with cysteine, however, the probe produces a rapid and large fluorescence enhancement through the removal of the DBS unit by nucleophilic aromatic substitution. This valuable property leads to the development of a new and simple method for cysteine assay. Under the optimized conditions, the fluorescence enhancement value is directly proportional to the concentration of cysteine in the range 2–12 μM, with a detection limit of 30 nM (S/N = 3). The applicability of the developed method has been successfully demonstrated on the determination of non-protein cysteine in human serum. Compared to most of the existing fluorescent probes proposed for cysteine, the BODIPY-based one exhibits an excellent overall performance in terms of selectivity, sensitivity and simplicity.

Lipid peroxidation (LPO) in lysosomes is a valuable analyte because it is close associated with the evolutions of some major diseases. As a typical example, in the start-up phase of atherosclerosis, lysosomes get as swollen as foams, by accumulating a large amount of lipoproteins, which facilitates the free-radical chain propagation of LPO. Despite the existences of several fluorescent LPO probes, they are not appropriate for reporting the local extents of lysosomal LPO, for their unspecific intracellular localizations. Here, Foam-LPO, the first fluorescent LPO probe specifically targeting lysosomes, has been developed through straightforward synthesis using low-cost reagents. A basic tertiary amine group enables it to selectively localize in acidic lysosomes; and the conjugated diene moiety within the BODIPY fluorophore will degrade in response to lipid peroxidation, which results in fluorescence maximum shifting from 586 to 512 nm. Thus, under a confocal fluorescence microscope, Foam-LPO is able not only to visualize dynamic morphological changes of lysosomes during the evolution of foam cells, but also to relatively quantify local LPO extents in single lysosomes through ratiometric imaging. In addition, Foam-LPO proves applicable for two-color flow cytometry (FCM) analysis to make quantitative and high-throughput evaluation of LPO levels in large quantity of cells at different stages during the induction to form foam cells. Also importantly, with the aid of this new probe, the different roles played by low-density lipoprotein (LDL) and its oxidized form (ox-LDL) for the LPO processes of foam cells are distinguished and clarified, which benefits the understanding in the initiation and control factors of atherosclerosis.

2-Thienyl and 2,6-bisthienyl BODIPY derivatives (BS-SS and BS-DS) were prepared that show intense absorption (ε = 65000 M–1 cm–1 at 507 nm) and a large Stokes shift (96 nm) vs the small Stokes shift of typical BODIPY (<15 nm). Control compounds with a thienyl unit at the 8-position or phenyl substituents at the 2,6-positions were prepared (BS-1 and 9). BS-1 shows absorption/emission in the blue-shifted range and a small Stokes shift (12 nm). Compound 9 shows absorption in the red-shifted range, but the Stokes shift (<30 nm) is much smaller than that for BS-SS and BS-DS. DFT calculations propose the large Stokes shifts of BS-SS and BS-DS are due to the remarkable geometry relaxation upon photoexcitation and its substantial effect on the energy levels of molecular orbitals. For the dyes with small Stokes shifts, much smaller geometry relaxations were found. The fluorophores were used for fluorescent thiol probes, with 2,4-dinitrobenzenesulfonyl (DNBS) as the fluorescence switch. Both fluorescence OFF–ON and unprecedented ON–OFF transduction were observed, which are attributed to the different photoinduced intramolecular electron-transfer (PET) profile. All the photophysics were rationalized by DFT calculations based on the concept of “electronic states” instead of the very often used approximation of “molecular orbitals”.

A novel fluorescent probe is designed and synthesized for the determination of cysteine in biological samples by incorporating 2,4-dinitrobenzenesulfonyl (DBS) group as a quencher into the BODIPY skeleton. The BODIPY-based probe itself shows weak fluorescence due to the strong intramolecular charge transfer process. Upon reaction with cysteine, however, the probe produces a rapid and large fluorescence enhancement through the removal of the DBS unit by nucleophilic aromatic substitution. This valuable property leads to the development of a new and simple method for cysteine assay. Under the optimized conditions, the fluorescence enhancement value is directly proportional to the concentration of cysteine in the range 2–12 μM, with a detection limit of 30 nM (S/N = 3). The applicability of the developed method has been successfully demonstrated on the determination of non-protein cysteine in human serum. Compared to most of the existing fluorescent probes proposed for cysteine, the BODIPY-based one exhibits an excellent overall performance in terms of selectivity, sensitivity and simplicity.