Presence Of Oxygen Molecules Research Articles

Molecular near-infrared triplet-triplet annihilation upconversion with eigen oxygen immunity

Molecular triplet-triplet annihilation upconversion often experiences drastic luminescence quenching in the presence of oxygen molecules, posing a significant constraint on practical use in aerated conditions. We present an oxygen-immune near-infrared triplet-triplet annihilation upconversion system utilizing non-organometallic cyanine sensitizers (λex = 808 nm) and chemically synthesized benzo[4,5]thieno[2,3-b][1,2,5]thiadiazolo[3,4-g]quinoxaline dyes with a defined dimer structure as annihilators (λem = 650 nm). This system exhibits ultrastable upconversion under continuous laser irradiance (>480 mins) or extended storage (>7 days) in aerated solutions. Mechanistic investigations reveal rapid triplet-triplet energy transfer from sensitizer to annihilators, accompanied by remarkably low triplet oxygen quenching efficiencies (ηO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\eta }_{{{{\\mbox{O}}}}_{2}}$$\\end{document} < 13% for the sensitizer, <3.7% for the annihilator), endowing the bicomponent triplet-triplet annihilation system with inherent oxygen immunity. Our findings unlock the direct and potent utilization of triplet-triplet annihilation upconversion systems in real-world applications, demonstrated by the extended and sensitive nanosensing of peroxynitrite radicals in the liver under in vivo nitrosative stress.

Cholesterol inhibits oxygen permeation through biological membranes: mechanism against double-bond peroxidation.

The presence of oxygen molecules (O2) in biological membranes promotes lipid peroxidation of phospholipids with unsaturated acyl chains. On the other hand, cholesterol is considered to be an antioxidant molecule as it has a significant barrier effect on the permeation of O2 across membranes. However, a comprehensive explanation of how cholesterol affects the distribution and diffusion of O2 within lipid bilayers is yet to be established. In this study, we investigated the interaction of oxygen molecules with polyunsaturated lipid bilayers using molecular dynamics (MD) simulations. The degree of lipid unsaturation and the concentration of cholesterol were varied to study the permeation of O2. The free energy profile of O2 diffusing from the water phase to the lipid bilayer was calculated using biased umbrella MD simulations. The results show that O2 passively translocates into the membrane without changing the physical properties of the bilayer. Interestingly, in the unsaturated lipid bilayers the presence of cholesterol led to a significantly decreased permeation of O2 and an increase in the lipid chain order. Our results indicate that the hydroxyl groups of cholesterol strongly interact with the O2 molecules effectively inhibiting interactions between the oxygens and the double bonds in unsaturated lipid tails. In addition, a linear relationship between permeation and the ratio of membrane thickness and area per lipid was found. These insights can help our understanding of how the degree of unsaturation in a lipid tail and cholesterol affect lipid peroxidation at the molecular level.

Waste tires pyrolysis oil and its blend with diesel fuel spectral flame analysis, temperature contours, and emissions

The purpose of this research paper is to investigate the energy valorization from the pyrolysis of waste tires using coaxial continuous flame burners. For such an investigation, both the Tire Pyrolysis Oil (TPO) along with its blend (B1) with light diesel oil (LDO) were prepared, physically and chemically characterized, and then combusted in coaxial burners. To distinguish the spectral emission peaks, for the vaporization and combustion zone and the hot recirculation zone of the produced flame, flame spectroscopy techniques were utilized. The mass-specific emission indices and the axial inflame temperatures were used as indicators of the flame radiation intensity in the flame zones. The coaxial flame was inspected for excess air factors of 1.33, 1.04, and 0.9. In the study, a higher radiation intensity of TPO/LDO blend flame was recognized in the B1 flame length which was taller than that of LDO by 48% at λ=1.33. Furthermore, a decrease in CO emissions levels was also noticed in the combustion of waste tire pyrolysis oil and B1 by an average of 4%–12% compared to that from HDO, and the NOx emissions were also reduced by 8.5%–26%. The highest axial inflame temperature of 1,205 °C was recorded for TPO at condition λ=0.9, where the presence of oxygen molecules in fuel helps flame improvements.

Fine-tuning the encapsulation of a photosensitizer in nanoparticles reveals the relationship between internal structure and phototherapeutic effects.

Photodynamic therapy (PDT) is a cancer therapy that uses a photosensitizer (PS) in the presence of oxygen molecules. Since singlet oxygen is highly reactive, it is important to deliver it to the target site. Thus, an efficient drug delivery system (DDS) is essential for enhancing the efficacy of such a treatment and protecting against the side effects of PDT. Here, we report on attempts to increase the therapeutic effect of PDT by using a DDS, a lipid nanoparticle (LNP). We prepared a porphyrin analog, rTPA (PS) that was encapsulated in LNPs using a microfluidic device. The findings indicated that the internal structure of the prepared particles changed depending on the amount of rTPA in LNPs. The photoactivity and cell-killing effect of PS in LNPs also changed when the amount of the cargo increased. These results suggest that the internal structure of LNPs is important factors that affect drug efficacy.

Amphiphilic Protoporphyrin IX Derivatives as New Photosensitizing Agents for the Improvement of Photodynamic Therapy.

Photodynamic therapy (PDT) is a non-invasive therapeutic modality based on the interaction between a photosensitive molecule called photosensitizer (PS) and visible light irradiation in the presence of oxygen molecule. Protoporphyrin IX (PpIX), an efficient and widely used PS, is hampered in clinical PDT by its poor water-solubility and tendency to self-aggregate. These features are strongly related to the PS hydrophilic–lipophilic balance. In order to improve the chemical properties of PpIX, a series of amphiphilic PpIX derivatives endowed with PEG550 headgroups and hydrogenated or fluorinated tails was synthetized. Hydrophilic–lipophilic balance (HLB) and log p-values were computed for all of the prepared compounds. Their photochemical properties (spectroscopic characterization, photobleaching, and singlet oxygen quantum yield) were also evaluated followed by the in vitro studies of their cellular uptake, subcellular localization, and photocytotoxicity on three tumor cell lines (4T1, scc-U8, and WiDr cell lines). The results confirm the therapeutic potency of these new PpIX derivatives. Indeed, while all of the derivatives were perfectly water soluble, some of them exhibited an improved photodynamic effect compared to the parent PpIX.

Real-time observation and quantification of carbon black oxidation in an environmental transmission electron microscope: Impact of particle size and electron beam

Carbon black oxidation is a post-treatment method to control its properties for different applications, and its outcomes may depend on the particle size. Three different sizes of carbon blacks were oxidized in an environmental transmission electron microscope to study the size effect on their oxidation pathway and rate. The oxidation at the nanoscale has been quantified using the ASTM D3849-14a standard method for the carbon blacks and compared with the theory of solid particle burning, i.e., D2 law. This comparison confirms the validity of the diffusion-controlled burning model for all three samples oxidized at 800°C in the presence of oxygen molecules. Electron microscope images show surface burning is the governing mode under this condition. Oxidation under electron-beam irradiation shows that the oxidation rate reduces by ∼0%, 30%, and 80% for particles with 33, 112, and 356 nm in diameter, respectively. The results suggest that the electron beam is causing the atomic bonds to break and transform to the graphitic structure at relatively high temperatures (e.g., 800°C) that causes oxidation rate reduction in larger particles. Despite the reduction in oxidation rate as the initial size of carbon particles increases, observations show that surface burning is the dominant mode under electron-beam irradiation.

Gaseous and particulate emissions analysis using microalgae based dioctyl phthalate biofuel during cold, warm and hot engine operation

Presented in this study is an analysis of gaseous and particulate emissions for three selected fuels during cold, warm and hot engine operation; low sulphur neat diesel (D100), and 10 and 20% (% v/v) of dioctyl phthalate (DOP) blended with diesel. Experiments were conducted on a turbocharged common rail heavy-duty diesel engine over a custom-designed drive cycle. The impact of engine temperature and fuel properties during warm-up on emissions has been analysed. The presence of oxygen molecules in DOP was found to have a major influence on emissions. NOx emissions were higher by ∼ 10%, while the HC emissions were lower by ∼ 150% with DOP blended fuels, compared to D100, during cold engine operation. Total particle number (PN) concentration and total particle mass (PM) followed the same trend and decreased as the engine warmed up. Compared to both DOP blended fuels, total PN with D100 was higher during cold engine operation and reduced significantly as the engine warmed up. The particle count median diameter (CMD) was found to have an opposite trend with D100 (increasing with engine warm-up) compared to both DOP blended fuels (decreasing with engine warm-up).

Experimental assessment of performance, combustion and emission characteristics of diesel engine fuelled by combined non-edible blends with nanoparticles

This study emphasis the utilization of Candle nut and Soap nut biodiesel as a substitute for conventional fuel and investigates the emission characteristics and performance of engine using the above biodiesel by incorporating nanoalumina at the concentration of 25 ppm. Initially the samples were blended with 50% Candle nut and 50% Soap nut and later it was mixed with the neat diesel at the concentration of 20%, 30% and 40% (B20, B30 and B40) respectively. The investigation has been made using the biodiesel and compared with the conventional fuel at various load conditions. The biodiesel blends were mixed with nano alumina using a ultrasonicator and the performance of the nanoparticles incorporated biodiesel blends was assessed using compression ignition engine. This study revealed that nanoparticles incorporated biodiesel blends enhance the engine performance significantly and the enhancement in performance is due to more surface area to volume ratio of Al2O3. The Nitrous oxide, carbon monoxide and hydrocarbon emissions were reduced considerably due to the incorporation of nano alumina at higher concentration. In addition, the nitrous oxide emission was higher as compared with pure diesel. The presence of oxygen molecules in nanoalumina reacts with carbon monoxide and forms carbon dioxide. The above process reduces the carbon monoxide emissions significantly in nanoparticles incorporated biodiesel blends. Out of various biodiesel mix, 30B samples showed better results in terms of reducing the nitrous oxide, carbon monoxide and hydro carbon emissions.

Investigation of Photodynamic Therapy on Breast Cancer Cell Lines Using LaF3:Tb Nanoparticles Conjugated with Meso-tetra(4-carboxyphenyl) Porphine

Photodynamic therapy (PDT) is a clinically appropriate therapeutic procedure with a minimum invasion that can apply a selective cytotoxic effect toward intended cells. Generally, PDT involves the administration of light and a photosensitive drug (photosensitizer). In the presence of oxygen molecules, the excited photosensitizer can produce reactive oxygen species (ROS) to kill the cancerous cells. In PDT, drug or light can administrate in high doses at short time (acute PDT) or in low doses in a period of time (metronomic PDT). In addition, to solve the problem of light access to the tissues, new modality that named Self Light PDT (SLPDT), was introduced recently. According to the studies, LaF3:Tb conjugated with meso-tetra(4-carboxyphenyl) porphine (MTCP) nanosystem can function as an efficient nanosystem in SLPDT due to the ability of energy transfer between the light-exited NPs and MTCP to emissions which can generate ROS. In this research besides synthesizing and characterizing LaF3:Tb-MTCP nanosystems, we also studied energy transfer feasibility under UV radiation between NP and PS. Afterward, we tried to design several in vitro test using breast cancer cell lines, T47D and mcf-7, to understanding LaF3:Tb conjugated MTCP potentials for SLPDT or mPDT.

Capacitance response of solar cells based on amorphous Titanium dioxide (A-TiO&lt;sub&gt;2&lt;/sub&gt;) semiconducting heterojunctions

In the present study, we studied the capacitance frequency response of amorphous titanium dioxide (A-TiO2)/poly(3-hexylthiophene) (P3HT) solar cells. The capacitance was measured to provide information on interfacial layer between the two materials. At a low frequency, the capacitance increased because the frequency was lower than the relaxation time of the charge carriers, thus providing evidence of the formation of a depletion region at the P3HT/A-TiO2 interface. The loss tangent was measured for applied voltage ranging from 0 to 1.5 V and the frequencies from 20 Hz and 1 MHz. Peaks in the loss tangent appeared as a function of the applied voltage due to changes in the transport and accumulation mechanisms of charge at the interface and the presence of oxygen molecules in the TiO2. The resulting C-V curves were used to calculate dopant concentration and the barrier's potential, which was found to 1017 cm−3 and 0.6 V, respectively. This confirmed the presence of a depletion region placed in the P3HT region and the validated barrier's potential effect on the open circuit voltage value. It was also shown that the light J-V characteristics of the A-TiO2/P3HT solar cells were independent of the ambient conditions because the conductivity of P3HT and the depletion region were not affected.

Effect of rutin as flavonoid compound on photodynamic inactivation against P. aeruginosa and S. aureus.

Antimicrobial photodynamic therapy (aPDT) has drawn increasing attention for its potential to effectively kill multidrug-resistant pathogenic bacteria and also for its low tendency to induce drug resistance. Antimicrobial photodynamic therapy (aPDT) is the application of photoactive dye followed by light irradiation that leads to the death of microbial cells mainly by reactive oxygen species (ROS) production in the presence of oxygen molecules. Methylene Blue (MB) as a photosensitizer is a hydrophobic drug molecule and prone to aggregation and dimer formation which lead to its low phototoxicity. Rutin, a flavonoid compound which is derived from plants such as wheat, apple, and tea has many properties such as antibacterial activity. In this study, we investigated the effect of rutin as a flavonoid compound on photodynamic inactivation by MB on Pseudomonas aeruginosa and Staphylococcus aureus. After performing the Minimum Inhibitory Concentration (MIC) assay (to measure minimum inhibitory concentration) and the MTT assay (to evaluate methylene blue toxicity), the effect of aPDT at 660 nm and pretreatment or post treatment with rutin on bacteria in the forms of planktonic and biofilm were investigated. The results showed that by a combination of rutin (800 μg/mL) with methylene blue (MB 8 μg/mL) as a photosensitizer and aPDT (660 nm, 5 min), there is a more reduction in the number of bacteria in the planktonic condition and bacterial biofilm production in comparison to MB alone. MB-aPDT showed no toxic effect against human dermal fibroblast with the proposed strategy which could suggest its application with rutin as a novel approach in the treatment of bacteria in wound infection.

Insight into the enhanced activity of Ag/NiOx-MnO2 for catalytic oxidation of o-xylene at low temperatures

Ag/NiOx-MnO2 was synthesized by redox and deposition-precipitation methods and its catalytic performance for o-xylene oxidation was investigated. It exhibited higher activity than NiOx-MnO2 and OMS-2. The T20, T50 and T100 values were 72, 145 and 190 °C, respectively (500 ppm o-xylene/humid air, GHSV = 6000 h−1). Moreover, it showed excellent water-resistance and stability, demonstrating its potential for practical application. Characterization results revealed that the introduction of Ni and Ag increased the catalyst reducibility, the amount of electrophilic oxygen species, and the ability for oxygen molecules activation, resulting in the superior performance at low temperatures. In situ DRIFT study indicated that aromatic ring could be directly oxidized into maleate by the electrophilic lattice oxygen of Ag/NiOx-MnO2 in the absence of oxygen molecules, and the formed maleate could be oxidized into formate and/or carbonate in the presence of oxygen molecules. Finally, the possible degradation pathway of o-xylene in the presence or absence gaseous oxygen was discussed.

Theoretical Investigations of the Interaction of Gaseous Pollutants Molecules with the Polyacrylonitrile Surface

This work presents theoretical studies of the interaction of molecules of several gaseous pollutants with polyacrylonitrile (PAN) surface in the presence of a water and/or oxygen molecule. For this purpose, a PAN cluster model has been proposed by the methods of quantum chemical calculations and molecular modeling. The energy-favorable positions, in which the gas molecules are located relative to the surface of the PAN cluster, are determined and the thermodynamic and the following geometric parameters of the systems are calculated: “PAN cluster − oxygen molecule”, “PAN cluster − oxygen molecule − gas molecule”, “PAN cluster − water molecule − molecule of oxygen”, and “PAN cluster − a molecule of water − an oxygen molecule − a gas molecule”. It is concluded that PAN in atmospheric air in the presence of oxygen molecules is sensitive to carbon oxide (IV), sulfur (IV) oxide, chlorine, hydrogen sulfide and carbon oxide (II). In an anoxic environment, PAN films will show selective sensitivity to chlorine. The presence of water molecules in the investigated air should not affect the gas sensitivity of PAN films.

Effect of Coadsorbed Oxygen on the Photochemistry of Methane Embedded in Amorphous Solid Water

The photochemistry of methane caged within amorphous solid water (ASW) is interesting as a model for studying interstellar and high-altitude atmospheric pathways for the formation of more complex hydrocarbons. Here, we report on the photoreactivity of clean methane and in the presence of oxygen molecules, known as electron capture species, within two 50 monolayer-thick D2O-ASW films adsorbed on Ru(0001) substrate under ultrahigh vacuum conditions. Irradiation by 248 nm UV photons (5.0 eV), where none of the involved molecules absorb these photons in the gas phase, leads to the formation of diverse hydrocarbons. In all cases, the presence of oxygen results in significantly enhanced reactivity. The dissociative electron attachment mechanism with electrons generated within the metal substrate is thought to largely govern the photoreactivity in this system. Methyl radicals as the primary photoproducts subsequently react with the surrounding water and neighboring methane as well as with the stable O2– anion. P...

Nanomedicine associated with photodynamic therapy for glioblastoma treatment.

Glioblastoma, also known as glioblastoma multiforme (GBM), is the most recurrent and malignant astrocytic glioma found in adults. Biologically, GBMs are highly aggressive tumors that often show diffuse infiltration of the brain parenchyma, making complete surgical resection difficult. GBM is not curable with surgery alone because tumor cells typically invade the surrounding brain, rendering complete resection unsafe. Consequently, present-day therapy for malignant glioma remains a great challenge. The location of the invasive tumor cells presents several barriers to therapeutic delivery. The blood-brain barrier regulates the trafficking of molecules to and from the brain. While high-grade brain tumors contain some "leakiness" in their neovasculature, the mechanisms of GBM onset and progression remain largely unknown. Recent advances in the understanding of the signaling pathways that underlie GBM pathogenesis have led to the development of new therapeutic approaches targeting multiple oncogenic signaling aberrations associated with the GBM. Among these, drug delivery nanosystems have been produced to target therapeutic agents and improve their biodistribution and therapeutic index in the tumor. These systems mainly include polymer or lipid-based carriers such as liposomes, metal nanoparticles, polymeric nanospheres and nanocapsules, micelles, dendrimers, nanocrystals, and nanogold. Photodynamic therapy (PDT) is a promising treatment for a variety of oncological diseases. PDT is an efficient, simple, and versatile method that is based on a combination of a photosensitive drug and light (generally laser-diode or laser); these factors are separately relatively harmless but when used together in the presence of oxygen molecules, free radicals are produced that initiate a sequence of biological events, including phototoxicity, vascular damage, and immune responses. Photodynamic pathways activate a cascade of activities, including apoptotic and necrotic cell death in both the tumor and the neovasculature, leading to a permanent lesion and destruction of GBM cells that remain in the healthy tissue. Glioblastoma tumors differ at the molecular level. For example, gene amplification epidermal growth factor receptor and its receptor are more highly expressed in primary GBM than in secondary GBM. Despite these distinguishing features, both types of tumors (primary and secondary) arise as a result dysregulation of numerous intracellular signaling pathways and have standard features, such as increased cell proliferation, survival and resistance to apoptosis, and loss of adhesion and migration, and may show a high degree of invasiveness. PDT may promote significant tumor regression and extend the lifetime of patients who experience glioma progression.

Transport properties of Al or Cr-doped nickel oxide relevant to the thermal oxidation of dilute Ni-Al and Ni-Cr alloys

In the present study we have analysed the thermal oxidation of Ni and dilute (<1wt%) Ni-Al and Ni-Cr alloys between 700° and 1200°C, taking into account the transport properties of pure and Al or Cr-doped Ni1−xO single crystals. In the temperature range 900°–1200°C, Al3+ or Cr3+ additions decrease the oxidation rates of Ni1−xO single crystals in their stability range, due to the kinetic demixing of cations. At T<1000°C, Ni-Al alloys also oxidize slower than high-purity nickel, but faster above 1000°C, while on Ni-Cr alloys the oxide scales grow faster from 700°C. The higher oxidation kinetics of the alloys is explained by the presence of oxygen molecules, which penetrate along cracks or fissures through the oxide scales. The mechanism whereby these short-circuit pathways have been formed is associated with the growth of nickel oxide particles within the scale, leading to local tensile strengths. The way in which these particles develop is explained by a blocking effect of outward diffusion of nickel ions, due both to an extensive depletion of Al3+ and Cr3+ in the outer layer and to the decrease of the mobility of Ni2+ when the amount of Cr3+ or Al3+ decreases in Ni1−xO.

Degradation of black phosphorus: a real-time 31P NMR study

In this work, degradation behaviors and mechanisms of black phosphorus (BP) crystals in air under ambient conditions were investigated by nuclear magnetic resonance spectroscopy. It has been found that the 31P NMR line intensity for BP decreases exponentially during aging even at the very first several hours, suggesting the origin of the degradation of transport properties. In addition to phosphoric acid, new phosphorous acid was also well resolved in the final aging products. Moreover, BP has been found to be stable in water without the presence of oxygen molecules. These findings are relevant for better understanding of degradation behaviors of BP upon aging and should be helpful for overcoming a barrier that might hamper progress toward applications of BP as a 2D material.

Optical and photoelectrical properties of nanocrystalline indium oxide with small grains

Optical properties, spectral dependence of photoconductivity and photoconductivity decay in nanocrystalline indium oxide In2O3 are studied. A number of nanostructured In2O3 samples with various nanocrystals size are prepared by sol–gel method and characterized using various techniques. The mean nanocrystals size varies from 7 to 8nm to 39–41nm depending on the preparation conditions. Structural characterization of the In2O3 samples is performed by means of transmission electron microscopy and X-ray powder diffraction. The combined analysis of ultraviolet–visible absorption spectroscopy and diffuse reflectance spectroscopy shows that nanostructuring leads to the change in optical band gap: optical band gap of the In2O3 samples (with an average nanocrystal size from 7 to 41nm) is equal to 2.8eV. We find out the correlation between spectral dependence of photoconductivity and optical properties of nanocrystalline In2O3: sharp increase in photoconductivity was observed to begin at 2.8eV that is equal to the optical bandgap in the In2O3 samples, and reached its maximum at 3.2–3.3eV. The combined analysis of the slow photoconductivity decay in air, vacuum and argon, that was accurately fitted by a stretched-exponential function, and electron paramagnetic resonance (EPR) measurements shows that the kinetics of photoconductivity decay is strongly depended on the presence of oxygen molecules in the ambient of In2O3 nanocrystals. There is the quantitative correlation between EPR and photoconductivity data. Based on the obtained data we propose the model clearing up the phenomenon of permanent photoconductivity decay in nanocrystalline In2O3.

Negative impact of oxygen molecular activation on Cr(VI) removal with core–shell Fe@Fe2O3 nanowires

In this study, we demonstrate that the presence of oxygen molecule can inhibit Cr(VI) removal with core–shell Fe@Fe2O3 nanowires at neutral pH of 6.1. 100% of Cr(VI) removal was achieved by the Fe@Fe2O3 nanowires within 60min in the anoxic condition, in contrast, only 81.2% of Cr(VI) was sequestrated in the oxic condition. Removal kinetics analysis indicated that the presence of oxygen could inhibit the Cr(VI) removal efficiency by near 3 times. XRD, SEM, and XPS analysis revealed that either the anoxic or oxic Cr(VI) removal was involved with adsorption, reduction, co-precipitation, and re-adsorption processes. More Cr(VI) was bound in a reduced state of Cr(III) in the anoxic process, while a thicker Cr(III)/Fe(III)/Cr(VI) oxyhydroxides shell, leading to inhibiting the electron transfer, was found under the oxic process. The negative impact of oxygen molecule was attributed to the oxygen molecular activation which competed with Cr(VI) adsorbed for the consumption of donor electrons from Fe0 core and ferrous ions bound on the iron oxides surface under the oxic condition. This study sheds light on the understanding of the fate and transport of Cr(VI) in oxic and anoxic environment, as well provides helpful guide for optimizing Cr(VI) removal conditions in real applications.

Photodynamic therapy of cancer — Challenges of multidrug resistance

Photodynamic therapy (PDT) of cancer is a two-step drug-device combination modality, which involves the topical or systemic administration of a photosensitizer followed by light illumination of cancer site. In the presence of oxygen molecules, the light illumination of photosensitizer (PS) can lead to the generation of cytotoxic reactive oxygen species (ROS) and consequently destroy cancer. Similar to many other anticancer therapies, PDT is also subject to intrinsic cancer resistance mediated by multidrug resistance (MDR) mechanisms. This paper will review the recent progress in understanding the interaction between MDR transporters and PS uptake. The strategies that can be used in a clinical setting to overcome or bypass MDR will also be discussed.