Tracking Plasma Membrane Damage Using a Ruthenium(II) Complex Phosphorescent Indicator Paired with Cholesterol

Long-term in situ plasma membrane-targeted imaging is highly significant for investigating specific biological processes and functions, especially for the imaging and tracking of apoptosis processes of cells. However, currently developed membrane probes are rarely utilized to monitor the in situ damage of the plasma membrane. Herein, a transition-metal complex phosphorescent indicator, Ru-Chol, effectively paired with cholesterol, exhibits excellent properties on staining the plasma membrane, with excellent antipermeability, good photostability, large Stokes shift, and long luminescence lifetime. In addition, Ru-Chol not only has the potential to differentiate cancerous cells from normal cells but also tracks in real time the entire progression of cisplatin-induced plasma membrane damage and cell apoptosis. Therefore, Ru-Chol can serve as an efficient tool for the monitoring of morphological and physiological changes in the plasma membrane, providing assistance for drug screening and early diagnosis and treatment of diseases, such as immunodeficiency, diabetes, cirrhosis, and tumors.

Literature Review on Conjugated Polymers as Light-Sensitive Materials for Photovoltaic and Light-Emitting Devices in Photonic Biomaterial Applications

Due to their extended p-orbital delocalization, conjugated polymers absorb light in the range of visible-NIR frequencies. We attempt to exploit this property to create materials that compete with inorganic semiconductors in photovoltaic and light-emitting materials. Beyond competing for applications in photonic devices, organic conjugated compounds, polymers, and small molecules have also been extended to biomedical applications like phototherapy and biodetection. Recent research on conjugated polymers has focused on bioapplications based on the absorbed light energy conversions in electric impulses, chemical energy, heat, and light emission. In this review, we describe the working principles of those photonic devices that have been applied and researched in the field of biomaterials.

A short review article on conjugated polymers

This article provides a brief review of conjugated polymers and the various typical polymerization reactions exploited by the community to synthesise different conjugated polyelectrolytes with varied conjugated backbone systems. We further discuss with detailed emphasises the mechanism involved such as photo-induced electron transfer, resonance energy transfer, and intra-molecular charge transfer in the detection or sensing of various analytes. Owing to their excellent photo-physical properties, facile synthesis, ease of functionalization, good biocompatibility, optical stability, high quantum yield, and strong fluorescence emission. Conjugated polymers have been explored for wide applications such as chemical and biological sensors, drug delivery and drug screening, cancer therapeutics and imaging. As such we believe it will be a timely review article for the community.

Cancer Cell Membrane Labeling Fluorescent Doppelganger Enables In Situ Photoactivated Membrane Dynamics Tracking via Two-Photon Fluorescence Imaging Microscopy

Various suborganelles are delimited by lipid bilayers, in which high spatial and temporal morphological changes are essential to many physiological and pathological processes of cells. However, almost all the amphiphilic fluorescent molecules reported until now are not available for in situ precise tracking of membrane dynamics in cell apoptosis. Here, the MO (coumarin pyridine derivatives) was devised by engineering lipophilic coumarin and cationic pyridine salt, which not only lastingly anchored onto the plasma membrane in dark due to appropriate amphipathicity and electrostatic interactions but also in situ reflected the membrane damage and heterogeneity with secretion of extracellular vesicles (EVs) under reactive oxygen species regulation and was investigated by two-photon fluorescence lifetime imaging microscopy. This work opens up a new avenue for the development of plasma membrane staining and EV-based medicines for the early diagnosis and treatment of disease.

Conjugated polymer nanoparticles and their nanohybrids as smart photoluminescent and photoresponsive material for biosensing, imaging, and theranostics

The emergence of conjugated polymers (CPs) has provided a pathway to attain smart multifunctional conjugated polymer nanoparticles (CPNs) with enhanced properties and diverse applications. CPNs based on π-extended CPs exhibit high fluorescence brightness, low cytotoxicity, excellent photostability, reactive oxygen species (ROS) generation ability, high photothermal conversion efficiency (PCE), etc. which endorse them as an excellent theranostic tool. Furthermore, the unique light-harvesting and energy transfer properties of CPNs enables their transformation into smart functional nanohybrids with augmented performance. Owing to such numerous features, simple preparation method and an easy separation process, the CPNs and their hybrids have been constantly rising as a frontrunner in the domain of medicine and much work has been done in the respective research area. This review summarizes the recent progress that has been made in the field of CPNs for biological and biomedical applications with special emphasis on biosensing, imaging, and theranostics. Following an introduction into the field, a first large section provides overview of the conventional as well as recently established synthetic methods for various types of CPNs. Then, the CPNs-based fluorometric assays for biomolecules based on different detection strategies have been described. Later on, examples of CPNs-based probes for imaging, both in vitro and in vivo using cancer cells and animal models have been explored. The next section highlighted the vital theranostic applications of CPNs and corresponding nanohybrids, mainly via imaging-guided photodynamic therapy (PDT), photothermal therapy (PTT) and drug delivery. The last section summarizes the current challenges and gives an outlook on the potential future trends on CPNs as advanced healthcare material.

Graphene Oxide Composite for Selective Recognition, Capturing, Photothermal Killing of Bacteria over Mammalian Cells

The multifunctional photothermal therapy (PTT) platform with the ability to selectively kill bacteria over mammalian cells has received widespread attention recently. Herein, we prepared graphene oxide-amino(polyethyleneglycol) (GO-PEG-NH2) while using the hydrophobic interaction between heptadecyl end groups of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethyleneglycol)] (DSPE-PEG-NH2) and graphene oxide (GO). Based on GO-PEG-NH2, the versatile PTT system was constructed with simultaneous selective recognition, capturing, and photothermal killing of bacteria. When the cells undergo bacterial infection, owing to the poly(ethylene glycol) (PEG) chains and positively charged amino groups, GO-PEG-NH2 can specifically recognize and capture bacteria in the presence of cells. Meanwhile, the stable photothermal performance of GO-PEG-NH2 enables the captured bacteria to be efficiently photothermally ablated upon the irradiation of 808 nm laser. Besides, the GO-PEG-NH2 is highly stable in various biological media and it exhibits low cytotoxicity, suggesting that it holds great promise for biological applications. This work provides new insight into graphene-based materials as a PTT agent for the development of new therapeutic platforms.

Discrimination of live and dead cells with two different sets of signals and unique application in vivo imaging

Discriminating living and dead cells is of great significance for the study of apoptosis. In this work, we have developed a unique fluorescent probe (RPIC) for discriminating live and dead cells with duel-channel fluorescence imaging under double excitation and double emission mode. Dead cells treated with RPIC shows weak fluorescence signals in red channel, however, strong fluorescence signals are appeared in red channel in live cells. Weak and strong green fluorescence signals present at live cells and dead cells, respectively. Moreover, RPIC can detect successfully apoptosis of cancer cells. For in-vivo imaging, RPIC can discriminate successfully live and dead zebrafish with the same method. More interestingly, it is found that RPIC possesses the ability of discriminating normal mice and tumor mice.

Copper-based ionic liquid-catalyzed click polymerization of diazides and diynes toward functional polytriazoles for sensing applications

An efficient copper-based ionic liquid-catalyzed azide–alkyne click polymerization was developed, and functional polytriazoles were produced which could be used as sensors.

Fluorescent Probes for the Visualization of Cell Viability

Monitoring cell viability is a crucial task essential for the fundamental studies in apoptosis, necrosis, and drug discovery. Cell apoptosis and necrosis are significant to maintain the cell population, and their abnormality can lead to severe diseases including cancer. During cell death, significant changes occur in the intracellular contents and physical properties, such as decrease of esterase activity, depolarization of the mitochondrial membrane potential (ΔΨ_m), increase of caspase content, dissipation of membrane asymmetry, and loss of membrane integrity. To detect cell viability, the fluorescent probes have been developed by taking advantage of these biological parameters and using various fluorescence mechanisms. These fluorescent probes can serve as powerful tools to facilitate the research in biology and pathology. In this Account, the representative examples of the fluorescent probes for cell viability during the past decades have been summarized and classified into five types based on the biological changes. The basic principle, design strategy, fluorescence mechanisms, and molecular construction of these fluorescent probes have been discussed. Furthermore, the intrinsic characteristics and merits of these probes have been illustrated. Particularly, this Account describes our recent works for the design and synthesis of the fluorescent probes to detect cell viability in the dual-color and reversible modes. The dual-color and reversible fluorescent probes are highlighted owing to their unique benefits in accurate and dynamic detection of cell viability. In general, the dual-color fluorescent probes were constructed based on the loss of esterase activity during cell death. Excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) process were exploited for the probe design. The construction of such dual-color probes were realized by the acetate of the phenyl group on fluorophores. Esterases in healthy cells hydrolyze the acetate and bring a spectral shift to the probes. Moreover, reversible fluorescent probes for cell viability were designed based on the depolarization of ΔΨ_m, with relocalization properties dependent on ΔΨ_m. The probes target mitochondria in healthy cells with high ΔΨ_m, while they are relocalized into the nucleus in unhealthy cells with depolarized ΔΨ_m. As ΔΨ_m is reversibly changed according to the cell viability, these probes reversibly detect cell viability. The reversible and simultaneously dual-color fluorescent probes were developed based on the relocalization mode and aggregation-induced emission shift. The probes target mitochondria to form aggregates with deep-red emission, while they migrate into the nucleus to present in monomers with green fluorescence. In this manner, the probes enable dual-color and reversible detection of cell viability. Fluorescent probes for cell viability based on sensing the membrane integrity, caspase activity, and membrane symmetry are also presented. High-polarity and large-size fluorescent probes impermeable to the intact lipid bilayer selectively target apoptotic cells with a destructive plasma membrane. Fluorescent probes sensing caspases in a turn-on manner exclusively light up apoptotic cells with caspase expression. Membrane-impermeable probes with high affinity to phosphatidylserine (PS) specifically stain the plasma membrane of dead cells, since PS flip-flops to the outer leaflet of the membrane during cell death. In summary, this Account illustrates the basic principles, design strategies, characteristics, and advantages of the fluorescent probes for cell viability, and it highlights the dual-color and reversible probes, which can promote the development of fluorescent probes, apoptosis studies, drug discovery, and other relative areas.

Spectroscopic and Time-Dependent DFT Study of the Photophysical Properties of Substituted 1,4-Distyrylbenzenes

In this contribution, we examine the photophysical properties of 15 totally trans-trans 1,4-distyrylbenzene derivatives (DSBs) functionalized with different electron-donating (ED) and electron-withdrawing (EW) groups by experimental and computational methodologies. We use UV-vis and fluorescence spectroscopies to determine the experimental optical properties such as the maximum absorption (λ_abs^exp) and emission (λ_em^exp) wavelengths, the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps (ΔE_abs^exp), the molar extinction coefficients (ε), the fluorescence quantum yields (Φ_f), and the fluorescence lifetimes (τ). We also calculate the experimental spontaneous emission decay rate (k_r^exp) and correlate all of these magnitudes to the corresponding calculated properties, maximum absorption (λ_abs^cal) and emission (λ_em^cal) wavelengths, vertical transition energies (ΔE_abs^cal), oscillator strength (F_osc), and spontaneous emission decay rate (k_r^cal), obtained by the time-dependent density functional theory method. We analyze the effect of the electronic nature of the substituents on the properties of the DSBs, finding that the ED and EW groups lead to bathochromic shifts. This is consistent with the decrease of ΔE values as the strength of ED and EW substituents increases. We find excellent correlations between calculated and experimental values for λ_abs, λ_em, and ΔE_abs (r ∼ 0.99-0.95). Additionally, the correlations between the relative ε with F_osc values and the k_r values are in good agreement (r ∼ 0.88-0.72) with the experimental properties. Overall, we find that for substituted 1,4-DSBs, computational chemistry is an excellent tool to predict structure-property relationships, which can be useful to forecast the properties of their polymeric analogues, which are usually difficult to determine experimentally.

Novel polythiophene derivative for dual-channel cell imaging

Fluorescent materials play an extremely important role in understanding the microbiological world. New fluorescent materials which have good photophysical properties, low cytotoxicity, and multi-channel fluorescent imaging capability are still urgently needed, even though many kinds of fluorescent materials have already been synthesized. In this work, a new polythiophene derivative (PT-OH-PPR) modified with a porphyrin group in its side chain was designed and fabricated through FeCl₃ oxidative polymerization. The obtained PT-OH-PPR has wide absorption and emission spectral range, good water solubility and low cytotoxicity. Importantly it could be enriched in the cytoplasm of A549 cells and be excited by two excitation wavelengths (488 nm and 559 nm), which provides a promising application in dual-channel cell imaging.

PT-OH-PPR has good optical properties, good water solubility and low cytotoxicity, and could be used as a dual-channel cell imaging material.

Synthesis of Structurally Defined Cationic Polythiophenes for DNA Binding and Gene Delivery

Water-soluble conjugated polymers (WCPs) have prospective applications in the field of bioimaging, disease diagnosis, and therapy. However, the use of WCPs with controllability and regioregularity for bioapplications have scarcely been reported. In this work, we synthesized polythiophenes containing ester side chains (P3ET) via Kumada catalyst-transfer polycondensation (KCTP) and confirmed a quasi-"living" chain-growth mechanism. In addition, we obtained cationic regioregular polythiophenes (cPTs) by aminolysis of P3ET with varied chain lengths, and studied DNA binding capability and gene delivery performance. Benefiting from photocontrolled generation of intracellular reactive oxygen species (ROS), the cationic polythiophenes successfully delivered DNA into tumor cells without additional polymer species.

Sensitive Conjugated-Polymer-Based Fluorescent ATP Probes and Their Application in Cell Imaging

Three cationic conjugated polyelectrolytes (CPEs) with a common poly(p-phenylene ethynylene terthiophene) backbone and side chains of different lengths, named as PPET3-N1, PPET3-N2, and PPET3-N3, were designed and synthesized. The UV-vis absorption and fluorescence spectra of the polymers vary strongly with solvent composition, suggesting that the polymers are strongly aggregated in H2O. In addition, the spectroscopic properties of the polymers are affected by small-molecule ATP, characterized by significant fluorescence intensity decreases and red shifts of their absorption bands. Further application of these polymers in cell imaging was studied by confocal fluorescence microscopy, which demonstrated that all of the polymers were localized on the cell membrane and partially inside of cells and that the staining effect gradually increased with the length of the polymer side chains. On the basis of the low cytotoxicity and efficient quenching of PPET3-N2 by ATP, the dose and time effects of ATP on PPET3-N2 imaging were studied, and the results indicated that this polymer might have potential in cell imaging for ATP semiquantification in vivo.

New Red-Emitting Conjugated Polyelectrolyte: Stabilization by Interaction with Biomolecules and Potential Use as Drug Carriers and Bioimaging Probes

The design and development of fluorescent conjugated polyelectrolytes (CPEs) emitting in the red region of the visible spectrum is at present of great interest for bioimaging studies. However, despite the wide variety of CPEs available, stable bright red-emitters remain scarce due to their low solubility and instability in aqueous media, consequently limiting their applications. In this work, we have synthesized and characterized a new red-emitting cationic conjugated polyelectrolyte copoly-{[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]-2,7-(fluorene)-alt-1,4-(naphtho[2,3c]-1,2,5-thiadiazole)} bromide (HTMA-PFNT), based on the incorporation of naphtha[2,3c][1,2,5] thiadiazole on fluorene backbone to increase the bathochromic emission, extending the conjugation length in the polymer backbone. Water stabilization was achieved by binding the polyelectrolyte to two different biological systems which are currently used as nanocarriers: human serum albumin (HSA) and lipid vesicles. Using both systems, stable nanostructures of different composition were obtained and their properties were characterized. The properties of the protein-based nanoparticles are consistent with polyelectrolyte aggregates covered with HSA molecules, while the liposome system is composed of lipid vesicles coated with polyelectrolyte chains partially inserted in the bilayer. Both protein and vesicle structural integrity were not affected after their interaction with HTMA-PFNT, as well as the carrier properties, allowing for the binding and transport of ligands. In addition, the nanoparticles displayed the ability of labeling the cell membrane of living cells. All these results extend the potential applications of these novel multifunctional nanoparticles as therapeutic carriers and bioimaging probes.

Selective recognition and imaging of bacterial model membranes over mammalian ones by using cationic conjugated polyelectrolytes

This work describes the use of cationic polyfluorenes as fluorescent markers to selectively recognize bacterial membranes.

Co-self-assembled nanoaggregates of BODIPY amphiphiles for dual colour imaging of live cells

Co-self-assembled vesicular nanoparticles of two structurally comparable amphiphilic boron-dipyrromethene (BODIPY) dyes with dequenchable dual colour fluorescence were prepared for ratiometric imaging of live cells.

Imaging plasma membranes without cellular internalization: multisite membrane anchoring reagents based on glycol chitosan derivatives

Using a multisite membrane anchoring strategy, a new plasma membrane imaging reagent without cellular internalization was designed.

Cationic conjugated polymer/fluoresceinamine-hyaluronan complex for sensitive fluorescence detection of CD44 and tumor-targeted cell imaging

Simple, rapid, and sensitive detection of CD44 is of paramount importance since it plays pivotal roles in tumor initiation, growth and metastasis. Herein, we describe a novel method for sensitive, visual and facile fluorescence detection of CD44 and CD44-mediated cancer cell imaging, using a probe based on cationic conjugated polymer (CCP)-PFEP and fluoresceinamine-hyaluronan (FA-HA). HA is an anionic natural glycosaminoglycan that can specifically bind to the overexpressed CD44 on various kinds of cancer cells. PFEP and FA-HA formed a complex through electronic interactions, resulting in a highly efficient fluorescence resonance energy transfer (FRET) from PFEP to FA-HA; moreover, the efficiencies of FRET correlated with the concentrations of CD44 because the specific binding of HA-CD44 would separate FA-HA away from PFEP. This method did not require laborious and expensive dual-labeling or protein-labeling needed in previously reported detection methods of CD44. Just mix the sample and test solution containing the PFEP/FA-HA complex, and the results allowed naked-eye detection by observing fluorescent color of solutions with the assistance of a UV lamp. Most importantly, the use of a conjugated polymer with excellent amplification property as well as the specific binding of HA-CD44 endowed this method with high sensitivity and specificity, making it applicable for reliable quantitative detection of CD44. Furthermore, the PFEP/FA-HA complex formed nanoparticles in aqueous solution, and the nanoparticles can be selectively taken up by MCF-7 cells (cancer cell) through the HA-CD44 interaction, thereby giving rise to a dual-color tumor-targeted imaging probe with good photostability. The development of this fluorescent probe showed promising potential to make a reliable and routine method available for early diagnosis of cancer.

Selective Interaction of a Cationic Polyfluorene with Model Lipid Membranes: Anionic versus Zwitterionic Lipids

This paper explores the interaction mechanism between the conjugated polyelectrolyte {[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]fluorene-phenylene}bromide (HTMA-PFP) and model lipid membranes. The study was carried out using different biophysical techniques, mainly fluorescence spectroscopy and microscopy. Results show that despite the preferential interaction of HTMA-PFP with anionic lipids, HTMA-PFP shows affinity for zwitterionic lipids; although the interaction mechanism is different as well as HTMA-PFP's final membrane location. Whilst the polyelectrolyte is embedded within the lipid bilayer in the anionic membrane, it remains close to the surface, forming aggregates that are sensitive to the physical state of the lipid bilayer in the zwitterionic system. The different interaction mechanism is reflected in the polyelectrolyte fluorescence spectrum, since the maximum shifts to longer wavelengths in the zwitterionic system. The intrinsic fluorescence of HTMA-PFP was used to visualize the interaction between polymer and vesicles via fluorescence microscopy, thanks to its high quantum yield and photostability. This technique allows the selectivity of the polyelectrolyte and higher affinity for anionic membranes to be observed. The results confirmed the appropriateness of using HTMA-PFP as a membrane fluorescent marker and suggest that, given its different behaviour towards anionic and zwitterionic membranes, HTMA-PFP could be used for selective recognition and imaging of bacteria over mammalian cells.

Fluorescent conjugated polymers based on thiocarbonyl quinacridone for sensing mercury ion and bioimaging

Highly sensitive FRET-based thiocarbonyl quinacridone fluorescent conjugated polymers for the sensing and bioimaging of mercury ion have been developed.

Hyperbranched conjugated polyelectrolyte for dual-modality fluorescence and magnetic resonance cancer imaging

Herein is reported the synthesis of gadolinium ion (Gd(III))-chelated hyperbranched conjugated polyelectrolyte (HCPE-Gd) and its application in fluorescence and magnetic resonance (MR) dual imaging in live animals. The synthesized HCPE-Gd forms nanospheres with an average diameter of ∼42 nm measured by laser light scattering and a quantum yield of 10% in aqueous solution. The absorption spectrum of HCPE-Gd has two maxima at 318 and 417 nm, and its photoluminescence maximum centers at 591 nm. Confocal laser scanning microscopy studies indicate that the HCPE-Gd is internalized in MCF-7 cancer cell cytoplasm with good photostability and low cytotoxicity. Further fluorescence and MR imaging studies on hepatoma H22 tumor-bearing mouse model reveal that HCPE-Gd can serve as an efficient optical/MR dual-modal imaging nanoprobe for in vivo cancer diagnosis.

Fluorescence bioimaging with conjugated polyelectrolytes

This review summarizes the recent developments in fluorescent conjugated polyelectrolytes (CPEs) in bioimaging. The CPEs discussed include linear-, hyperbranched-, and polyhedral oligomeric silsesquioxanes (POSS)-based derivatives. Originating from their special optical properties, good photostability, low cytotoxicity, ease of bioconjugation and tuneable size, CPEs have shown wide applications in in vitro and in vivo protein and cell imaging, drug tracking and gene delivery. Moreover, some CPEs also possess antibacterial and anticancer characteristics as well as apoptosis imaging functions. Finally, this review discusses the future outlook of CPEs in bioimaging applications.

Highly sensitive method for assay of drug-induced apoptosis using fluorescence correlation spectroscopy

Apoptosis plays a crucial role in many biological processes and pathogenesis of various malignancies and diseases of the immune system. In this paper, we described a novel method for sensitive detection of drug-induced apoptosis by using fluorescence correlation spectroscopy (FCS). The principle of this method is based on the assay of DNA fragmentation in the process of the drug-induced apoptosis. FCS is a single molecule method, and it can be used for sensitive and selective assay of DNA fragmentation without separation. We first developed a highly sensitive method for characterization of DNA fragments using a home-built FCS system and SYBR Green I as fluorescent DNA-intercalating dye, and then established a model of drug-induced apoptosis using human pancreatic cancer cells and a drug lidamycin. Furthermore, FCS method established was used to directly detect the fragmentation of DNA extracted from apoptotic cells or in the apoptotic cell lysate. In FCS assay, the single-component model and the multiple-components model were used to fit raw FCS data. The characteristic diffusion time of DNA fragments was used as an important parameter to distinguish the apoptotic status of cells. The obtained data documented that the characteristic diffusion time of DNA fragments from apoptotic cells significantly decreased with an increase of lidamycin concentration, which implied that DNA fragmentation occurred in lidamycin-induced apoptosis. The FCS results are well in line with the data obtained from flow cytometer and gel electrophoresis. Compared to current methods, the method described here is sensitive and simple, and more importantly, our detection volume is less than 1 fL, and the sample requirement can easily be reduced to nL level using a droplets array technology. Therefore, our method probably becomes a high throughput detection platform for early detection of cell apoptosis and screening of apoptosis-based anticancer drugs.

Beyond annexin V: fluorescence response of cellular membranes to apoptosis

Dramatic changes in the structure of cell membranes on apoptosis allow easy, sensitive and non-destructive analysis of this process with the application of fluorescence methods. The strong plasma membrane asymmetry is present in living cells, and its loss on apoptosis is commonly detected with the probes interacting strongly and specifically with phosphatidylserine (PS). This phospholipid becomes exposed to the cell surface, and the application of annexin V labeled with fluorescent dye is presently the most popular tool for its detection. Several methods have been suggested recently that offer important advantages over annexin V assay with the ability to study apoptosis by spectroscopy of cell suspensions, flow cytometry and confocal or two-photon microscopy. The PS exposure marks the integrated changes in the outer leaflet of cell membrane that involve electrostatic potential and hydration, and the attempts are being made to provide direct probing of these changes. This review describes the basic mechanisms underlying the loss of membrane asymmetry during apoptosis and discusses, in comparison with the annexin V-binding assay, the novel fluorescence techniques of detecting apoptosis on cellular membrane level. In more detail we describe the detection method based on smart fluorescent dye F2N12S incorporated into outer leaflet of cell membrane and reporting on apoptotic cell transformation by easily detectable change of the spectral distribution of fluorescent emission. It can be adapted to any assay format.