TY - JOUR A1 - Schürmann, Robin Mathis A1 - Bald, Ilko T1 - Real-time monitoring of plasmon induced dissociative electron transfer to the potential DNA radiosensitizer 8-bromoadenine JF - Nanoscale N2 - The excitation of localized surface plasmons in noble metal nanoparticles (NPs) results in different nanoscale effects such as electric field enhancement, the generation of hot electrons and a temperature increase close to the NP surface. These effects are typically exploited in diverse fields such as surface-enhanced Raman scattering (SERS), NP catalysis and photothermal therapy (PTT). Halogenated nucleobases are applied as radiosensitizers in conventional radiation cancer therapy due to their high reactivity towards secondary electrons. Here, we use SERS to study the transformation of 8-bromoadenine ((8Br)A) into adenine on the surface of Au and AgNPs upon irradiation with a low-power continuous wave laser at 532, 633 and 785 nm, respectively. The dissociation of (8Br)A is ascribed to a hot-electron transfer reaction and the underlying kinetics are carefully explored. The reaction proceeds within seconds or even milliseconds. Similar dissociation reactions might also occur with other electrophilic molecules, which must be considered in the interpretation of respective SERS spectra. Furthermore, we suggest that hot-electron transfer induced dissociation of radiosensitizers such as (8Br)A can be applied in the future in PTT to enhance the damage of tumor tissue upon irradiation. Y1 - 2017 U6 - https://doi.org/10.1039/c6nr08695k SN - 2040-3364 SN - 2040-3372 VL - 9 SP - 1951 EP - 1955 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Meiling, Till Thomas A1 - Schürmann, Robin Mathis A1 - Vogel, Stefanie A1 - Ebel, Kenny A1 - Nicolas, Christophe A1 - Milosavljevic, Aleksandar R. A1 - Bald, Ilko T1 - Photophysics and Chemistry of Nitrogen-Doped Carbon Nanodots with High Photoluminescence Quantum Yield JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Fluorescent carbon nanodots (CNDs) are very promising nanomaterials for a broad range of applications because of their high photostability, presumed selective luminescence, and low cost at which they can be produced. In this respect, CNDs are superior to well-established semiconductor quantum dots and organic dyes. However, reported synthesis protocols for CNDs typically lead to low photoluminescence quantum yield (PLQY) and low reproducibility, resulting in a poor understanding of the CND chemistry and photophysics. Here, we report a one-step synthesis of nitrogen-doped carbon nanodots (N-CNDs) from various carboxylic acids, Tris, and ethylenediaminetetraacetic acid resulting in high PLQY of up to 90%. The reaction conditions in terms of starting materials, temperature, and reaction time are carefully optimized and their influence on the photophysical properties is characterized. We find that citric acid-derived N-CNDs can result in a very high PLQY of 90%, but they do not show selective luminescence. By contrast, acetic acid-derived N-CNDs show selective luminescence but a PLQY of 50%. The chemical composition of the surface and core of these two selected N-CND types is characterized among others by high-resolution synchrotron X-ray photoelectron spectroscopy using single isolated N-CND clusters. The results indicate that photoexcitation occurs in the N-CND core, whereas the emission properties are determined by the N-CND surface groups. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcc.8b00748 SN - 1932-7447 VL - 122 IS - 18 SP - 10217 EP - 10230 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schürmann, Robin Mathis A1 - Vogel, Stefanie A1 - Ebel, Kenny A1 - Bald, Ilko T1 - The physico-chemical basis of DNA radiosensitization BT - implications for cancer radiation therapy JF - Chemistry - a European journal N2 - High-energy radiation is used in combination with radiosensitizing therapeutics to treat cancer. The most common radiosensitizers are halogenated nucleosides and cisplatin derivatives, and recently also metal nanoparticles have been suggested as potential radiosensitizing agents. The radiosensitizing action of these compounds can at least partly be ascribed to an enhanced reactivity towards secondary low-energy electrons generated along the radiation track of the high-energy primary radiation, or to an additional emission of secondary reactive electrons close to the tumor tissue. This is referred to as physico-chemical radiosensitization. In this Concept article we present current experimental methods used to study fundamental processes of physico-chemical radiosensitization and discuss the most relevant classes of radiosensitizers. Open questions in the current discussions are identified and future directions outlined, which can lead to optimized treatment protocols or even novel therapeutic concepts. KW - cancer KW - dissociative electron attachment KW - low-energy electrons KW - radiation therapy KW - radiosensitizers Y1 - 2018 U6 - https://doi.org/10.1002/chem.201800804 SN - 0947-6539 SN - 1521-3765 VL - 24 IS - 41 SP - 10271 EP - 10279 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Vogel, Stefanie A1 - Ebel, Kenny A1 - Heck, Christian A1 - Schürmann, Robin Mathis A1 - Milosavljevic, Aleksandar R. A1 - Giuliani, Alexandre A1 - Bald, Ilko T1 - Vacuum-UV induced DNA strand breaks BT - influence of the radiosensitizers 5-bromouracil and 8-bromoadenine JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Radiation therapy is a basic part of cancer treatment. To increase the DNA damage in carcinogenic cells and preserve healthy tissue at the same time, radiosensitizing molecules such as halogenated nucleobase analogs can be incorporated into the DNA during the cell reproduction cycle. In the present study 8.44 eV photon irradiation induced single strand breaks (SSB) in DNA sequences modified with the radiosensitizer 5-bromouracil (U-5Br) and 8-bromoadenine ((8Br)A) are investigated. U-5Br was incorporated in the 13mer oligonucleotide flanked by different nucleobases. It was demonstrated that the highest SSB cross sections were reached, when cytosine and thymine were adjacent to U-5Br, whereas guanine as a neighboring nucleobase decreases the activity of U-5Br indicating that competing reaction mechanisms are active. This was further investigated with respect to the distance of guanine to U-5Br separated by an increasing number of adenine nucleotides. It was observed that the SSB cross sections were decreasing with an increasing number of adenine spacers between guanine and U-5Br until the SSB cross sections almost reached the level of a non-modified DNA sequence, which demonstrates the high sequence dependence of the sensitizing effect of U-5Br. (8Br)A was incorporated in a 13mer oligonucleotide as well and the strand breaks were quantified upon 8.44 eV photon irradiation in direct comparison to a non-modified DNA sequence of the same composition. No clear enhancement of the SSB yield of the modified in comparison to the non-modified DNA sequence could be observed. Additionally, secondary electrons with a maximum energy of 3.6 eV were generated when using Si as a substrate giving rise to further DNA damage. A clear enhancement in the SSB yield can be ascertained, but to the same degree for both the non-modified DNA sequence and the DNA sequence modified with (8Br)A. Y1 - 2019 U6 - https://doi.org/10.1039/c8cp06813e SN - 1463-9076 SN - 1463-9084 VL - 21 IS - 4 SP - 1972 EP - 1979 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Vogel, Stefanie A1 - Ebel, Kenny A1 - Schürmann, Robin Mathis A1 - Heck, Christian A1 - Meiling, Till A1 - Milosavljevic, Aleksandar R. A1 - Giuliani, Alexandre A1 - Bald, Ilko T1 - Vacuum-UV and Low-Energy Electron-Induced DNA Strand Breaks BT - Influence of the DNA Sequence and Substrate JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - DNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. In the present study we quantified photon and electron induced DNA strand breaks in four different 12mer oligonucleotides. They are irradiated directly with 8.44 eV vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF2 as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7-2.3x10(-16) cm(2). The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies <3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold. KW - DNA origami KW - DNA radiation damage KW - DNA strand breaks KW - low-energy electrons KW - vacuum-UV radiation Y1 - 2019 U6 - https://doi.org/10.1002/cphc.201801152 SN - 1439-4235 SN - 1439-7641 VL - 20 IS - 6 SP - 823 EP - 830 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Bald, Ilko A1 - Schürmann, Robin Mathis A1 - Ebel, Kenny A1 - Nicolas, Christophe A1 - Milosavljevic, Aleksandar R. T1 - Role of valence band states and plasmonic enhancement in electron-transfer-induced transformation of nitrothiophenol JF - The Journal of Physical Chemistry Letters N2 - Hot-electron-induced reactions are more and more recognized as a critical and ubiquitous reaction in heterogeneous catalysis. However, the kinetics of these reactions is still poorly understood, which is also due to the complexity of plasmonic nanostructures. We determined the reaction rates of the hot-electron-mediated reaction of 4-nitrothiophenol (NTP) on gold nanoparticles (AuNPs) using fractal kinetics as a function of the laser wavelength and compared them with the plasmonic enhancement of the system. The reaction rates can be only partially explained by the plasmonic response of the NPs. Hence, synchrotron X-ray photoelectron spectroscopy (XPS) measurements of isolated NTP-capped AuNP clusters have been performed for the first time. In this way, it was possible to determine the work function and the accessible valence band states of the NP systems. The results show that besides the plasmonic enhancement, the reaction rates are strongly influenced by the local density of the available electronic states of the system. Y1 - 2019 UR - https://pubs.acs.org/doi/10.1021/acs.jpclett.9b00848 U6 - https://doi.org/10.1021/acs.jpclett.9b00848 SN - 1948-7185 VL - 10 SP - 3153 EP - 3158 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Dutta, Anushree A1 - Schürmann, Robin Mathis A1 - Balko, Ilko T1 - Plasmon mediated decomposition of brominated nucleobases on silver nanoparticles BT - a surface enhanced Raman scattering (SERS) study JF - The european physical journal D N2 - The localized surface plasmon resonances (LSPRs) of silver nanoparticles (AgNPs) give rise to the generation of so called hot electrons and a high local electric field enhancement, which enable an application of AgNPs in different fields ranging from catalysis to sensing. Hot electrons generated upon the decay of LSPRs are transferred to molecules adsorbed on the surface of the NPs and trigger chemical reactions via dissociative electron attachment (DEA). Herein, we report on the hot electron induced decomposition of the brominated nucleobases – 8-bromoadenine, 8-bromoguanine, 5-bromocytosine and 5-bromouracil on laser illuminated AgNP surfaces. Surface enhanced Raman scattering (SERS) spectra of all canonical nucleobases and their brominated analogues have been recorded at different laser illumination times, and for the very first time we present SERS measurements of 8-bromoguanine and 5-bromocytosine. Reaction products have been identified by their vibrational fingerprint revealing the cleavage of the carbon bromide bond in all cases even under mild illumination conditions. These results indicate that the well-known reactions from DEA experiments in the gas phase (i) are also taking place on nanoparticle surfaces under ambient conditions, (ii) can be monitored by SERS, and (iii) are also of importance in analytical SERS applications involving electrophilic molecules, as the bands originating from reaction products need to be identified. Y1 - 2020 UR - https://link.springer.com/article/10.1140/epjd/e2019-100115-1 U6 - https://doi.org/10.1140/epjd/e2019-100115-1 SN - 1434-6079 SN - 1434-6060 VL - 74 IS - 19 PB - Springer CY - Berlin ER - TY - JOUR A1 - Schürmann, Robin Mathis A1 - Luxford, Thomas A1 - Vinklárek, Ivo A1 - Kočišek, Jaroslav A1 - Zawadzki, Mateusz A1 - Balko, Ilko T1 - Interaction of 4-nitrothiophenol with low energy electrons BT - implications for plasmon mediated reactions JF - Journal of chemical physics N2 - The reduction of 4-nitrothiophenol (NTP) to 4-4′-dimercaptoazobenzene (DMAB) on laser illuminated noble metal nanoparticles is one of the most widely studied plasmon mediated reactions. The reaction is most likely triggered by a transfer of low energy electrons from the nanoparticle to the adsorbed molecules. Besides the formation of DMAB, dissociative side reactions of NTP have also been observed. Here, we present a crossed electron-molecular beam study of free electron attachment to isolated NTP in the gas-phase. Negative ion yields are recorded as a function of the electron energy, which helps to assess the accessibility of single electron reduction pathways after photon induced electron transfer from nanoparticles. The dominant process observed with isolated NTP is associative electron attachment leading to the formation of the parent anion of NTP. Dissociative electron attachment pathways could be revealed with much lower intensities, leading mainly to the loss of functional groups. The energy gained by one electron reduction of NTP may also enhance the desorption of NTP from nanoparticles. Our supporting experiments with small clusters, then, show that further reaction steps are necessary after electron attachment to produce DMAB on the surfaces. Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?https://aip.scitation.org/doi/10.1063/5.0018784 SN - 1089-7690 SN - 0021-9606 VL - 153 SP - 104303 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Balderas-Valadez, Ruth Fabiola A1 - Schürmann, Robin Mathis A1 - Pacholski, Claudia T1 - One Spot-Two Sensors: Porous Silicon Interferometers in Combination With Gold Nanostructures Showing Localized Surface Plasmon Resonance JF - Frontiers in chemistry N2 - Sensors composed of a porous silicon monolayer covered with a film of nanostructured gold layer, which provide two optical signal transduction methods, are fabricated and thoroughly characterized concerning their sensing performance. For this purpose, silicon substrates were electrochemically etched in order to obtain porous silicon monolayers, which were subsequently immersed in gold salt solution facilitating the formation of a porous gold nanoparticle layer on top of the porous silicon. The deposition process was monitored by reflectance spectroscopy, and the appearance of a dip in the interference pattern of the porous silicon layer was observed. This dip can be assigned to the absorption of light by the deposited gold nanostructures leading to localized surface plasmon resonance. The bulk sensitivity of these sensors was determined by recording reflectance spectra in media having different refractive indices and compared to sensors exclusively based on porous silicon or gold nanostructures. A thorough analysis of resulting shifts of the different optical signals in the reflectance spectra on the wavelength scale indicated that the optical response of the porous silicon sensor is not influenced by the presence of a gold nanostructure on top. Moreover, the adsorption of thiol-terminated polystyrene to the sensor surface was solely detected by changes in the position of the dip in the reflectance spectrum, which is assigned to localized surface plasmon resonance in the gold nanostructures. The interference pattern resulting from the porous silicon layer is not shifted to longer wavelengths by the adsorption indicating the independence of the optical response of the two nanostructures, namely porous silicon and nanostructured gold layer, to refractive index changes and pointing to the successful realization of two sensors in one spot. KW - porous silicon KW - interferometry KW - gold nanostructures KW - surface plasmon resonance KW - optical sensor Y1 - 2019 U6 - https://doi.org/10.3389/fchem.2019.00593 SN - 2296-2646 VL - 7 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Schürmann, Robin Mathis A1 - Bald, Ilko T1 - Effect of adsorption kinetics on dissociation of DNA-nucleobases on gold nanoparticles under pulsed laser illumination JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Photothermal therapy is a novel approach to destroy cancer cells by an increase of temperature due to laser illumination of gold nanoparticles (GNPs) that are incorporated into the cells. Here, we study the decomposition of DNA nucleobases via irradiation of gold nanoparticles with ns-laser pulses. The kinetics of the adsorption and decomposition process is described by a theoretical model based on the Langmuir assumptions and correlated with experimentally determined reaction rates revealing a strong influence of the nucleobase specific adsorption. Beside the four nucleobases, their brominated analogs, which are potential radiosensitizers in cancer therapy, are also investigated and show a significant modification of the decomposition rates. The fastest decomposition rates are observed for adenine, 8-bromoadenine, 8-bromoguanine and 5-bromocytosine. These results are in good agreement with the relative adsorption rates that are determined from the aggregation kinetics of the GNPs taking the effect of an inhomogeneous surface into account. For adenine and its brominated analog, the decomposition products are further analyzed by surface enhanced Raman scattering (SERS) indicating a strong fragmentation of the molecules into their smallest subunits. Y1 - 2017 U6 - https://doi.org/10.1039/c6cp08433h SN - 1463-9076 SN - 1463-9084 VL - 19 SP - 10796 EP - 10803 PB - Royal Society of Chemistry CY - Cambridge ER -