Established and emerging nanocolloids: from synthesis & characterization to applications

Resume : Visual analysis of biomolecules is an integral avenue of basic and applied biological research. Quantum dots (QDs) are semiconductor inorganic nanoparticles that are emerging as alternative or complementary tools to the organic fluorescent dyes currently used in bioimaging. Although these QDs have great potential as probes for bioimaging, certain limitations may restrict their applications. Cytotoxicity strongly influencing is one of the major limiting factors for the application of II-VI QDs in efficient in vivo imaging. We propose silicon carbide (SiC) QDs for bioimaging in order to eliminate numerous disadvantages of traditional QDs. SiC is a stable, chemically inert wide band gap indirect semiconductor. Biocompatibility of bulk SiC and SiC QDs has been proven by several research teams. We developed a two-step experimental routine of producing SiC QDs. First, microcrystalline SiC (SiC MCs) is formed by reactive bonding method which, principally, allows us to produce highly doped SiC MCs in order to modulate the optical properties of the prepared SiC QDs made from them. SiC QDs form by electroless wet chemical etching of the SiC MCs [1]. These SiC QDs are less than 3 nm in diameter and make stable colloid sol in water thanks to the surface termination that was studied by infrared spectroscopy. We developed a simple separation method to overcome of the relatively large size distributon of collodial SiC QDs that could be suitable for two-photon study of neuron cells.

Resume : Understanding the interactions of nanoparticles with skin is of high importance for the development of new ways to deliver drugs efficiently but also in order to realize potential toxicity risks. The study of nanoparticle penetration through skin is a complex research task because it iis associated with a number of experimental parameters that can not be easily controlled related to the complexity of the skin structure and the physicochemical characteristics of nanoparticles. In this presentation we follow a thorough analytical approach to answer key questions concerning these interactions. We will particularly focus on how the charge, shape and function of nanoparticles influence the penetration through skin. For our studies we chose to work with gold nanoparticles due to the ease of their surface modification. To gain a good understanding, we employ a number of techniques such as ICP-OES to quantitatively measure the penetration of nanoparticles, as well as two-photon spectroscopy and tem cross sectioning to analytically detect the particles in the skin. Moreover we will hypothesize potential mechanisms of penetration.

Resume : Biomedical applications of nanodiamond (ND) have been investigated extensively due to its low toxicity, non-bleaching fluorescence, and high extensibility of the surface functionality through covalent organic functionalization. For in vivo applications such as drug carrier and imaging probe, ND should form a stable hydrosol under a physiological environment. In this context, we recently found that polyglycerol (PG) functionalization is very effective to impart the sufficient solubility and stability to ND [1]. In addition, the stable hydrogel of PG-functionalized ND (ND-PG) enabled precise characterization of the chemical structure by solution phase NMRs. Quantitative analyses were also conducted by elemental and thermogravimetric analyses. The ND-PG was subjected to further organic transformations at a number of hydroxyl groups on the PG layer to add more functions. As a result, we successfully prepared the ND-based drug carrier with acid-responsive platinum drug [2] and MR imaging probe with gadolinium [3] and applied them to in vivo and in vitro evaluations. [1] L. Zhao, N. Komatsu, Angew. Chem. Int. Ed., 50 (6), 1388-1392 (2011) [2] L. Zhao, N. Komatsu, X. Chen, submitted [3] L. Zhao, N. Komatsu, J. Nanosci. Nanotechnol. in press

Resume : Imaging cells at the single-molecule level reveals heterogeneities that are lost in ensemble imaging experiments. An ongoing challenge is the development of single-molecule probes with the requisite photostability, brightness, and continuous emission. Upconverting nanoparticles (UCNPs) overcome problems of photostability and continuous emission, and their upconverted emission can be excited with biologically benign NIR light at much lower powers than those required for conventional multiphoton imaging probes. The brightness of UCNPs, however, has been limited by open questions about energy transfer and relaxation within individual nanocrystals and unavoidable trade-offs between brightness and size. We have developed UCNPs with d < 10 nm that are over an order of magnitude brighter under single-particle imaging conditions than the brightest bulk compositions, allowing us to visualize single upconverting nanoparticles as small as fluorescent proteins. We use a combination of advanced single-particle characterization and theoretical modeling to find that surface effects become critical at d < 20 nm, and that the higher fluences used in single-molecule imaging fundamentally change the factors that determine nanocrystal brightness. We find that factors known to increase brightness in bulk experiments are unimportant at higher excitation powers, and that, paradoxically, the brightest probes under single-molecule excitation are barely luminescent at the ensemble level.

Resume : Noble metal nanostructures have attracted extensive research attentions due to their intriguing optical properties. In particular, silver nanoprisms are of great interest due to their size-dependent surface plasmon resonance bands that are tailorable in the visible and near-IR range. However, the poor stability of silver nanoprisms against oxidation and etching restricts their applications. Herein we demonstrate a simple process of gold-coating on silver nanoprisms. The resulting Ag@Au core–shell structure preserves the optical signatures of nanoprisms and offers versatile functionality and better stability against oxidation. Further, by slightly modifying the gold-coating process, we can obtain various functional Ag/Au bimetallic structures, such as Ag@Au-framed prisms and ultrathin nanoframes. [1,2]These interesting Ag/Au nanostructures are capable of showing high sensitivity in refractive sensing and strong enhancement of polaron yield in organic photovoltaics. Reference: [1] M. M. Shahjamali, M. Bosman, S. W. Cao, X. Huang, X. H. Cao, H. Zhang, S. S. Pramana, C. Xue*, Small 2013, 9, 2880-2886. [2] M. M. Shahjamali, M. Bosman, S. W. Cao, X. Huang, S. Saadat, E. Martinsson, D. Aili, Y. Y. Tay, B. Liedberg, S. C. J. Loo, H. Zhang, F. Boey, C. Xue*, Adv. Funct. Mater. 2012, 22, 849-854.

Resume : Gold nanoparticles, less than 5 nm, exhibit a catalytic activity in many chemical processes. However polydisperse particles obscure the interesting size-dependent catalytic activity of nanogold. Recently, atomically well defined thiolate-capped Au nanoclusters (denoted as Aun(SR)m) have been successfully isolated and their catalytic properties have been demonstrated. These monodispersed functionalized clusters, with gold core between less than 1 nm and more than 2 nm, hold promises as a new generation of catalysts. More importantly, these nanoclusters permit in-depth studies on the subtle correlation of structure and catalytic activity, since they are well defined and their crystallographic structures start to be solved. To investigate the influence of the size, the type of ligands at the surface and also the support effect, different nanoclusters have been synthesized. New clusters made of 4-aminothiophenol (HSPhNH2) have been synthesized, such as Au25(SPhNH2)17, and fully characterized by mass spectrometry, X-ray diffraction and XPS. Moreover these clusters exhibit absorption bands related to their molecular state. Catalytic activity for oxidation of alkene and alcohol derivatives of these colloidal or supported clusters were investigated and compared to the commonly used Aun(SCH2CH2Ph)m nanoclusters. At the opposite of the bare gold nanoparticles, the presence of the ligands around the clusters leads to a much better selectivity of the product.

Resume : In the field of emerging nanoscale materials with switchable properties chiral structures like helices or twisted ribbons are of great interest because of their intrinsic optical and mechanical properties. In this contribution, we present a study about the mechanical properties of SiO2 and SiO2@MxOy nanotubes and helical nanosprings synthesized by an original and simple technique from organic nanotubes through inorganic transcription. These nano-objects have potential applications in nano-electromechanical systems (NEMS), ranging from physical sensing and signal processing to ultra-low power radio frequency signal generation, thanks to their striking features. NEMS have been generally based on 1D nano-objects, such as carbon nanotubes [1] or silicon nanowires [2]. However, the use of 3D nanostructures such as nanohelices would allow a significant improvement the electromechanical performances of functional nanodevices, due to their specific properties. The originality of our synthesis method consists in the possibility to obtain 3D nanostructures with specific morphology and properties. In the present work, functional hybrid nano-helices are synthesized by use of amphiphilic organic chiral self-assemblies forming very well defined helix or ribbons structures and exploits them as templates for inorganic nanomaterial formation [3]. A bio-inspired mineralization of these self-assemblies allows creating silica nano-helices with very well controlled morphologies. We focus particularly on the formation of short helices (length control), individualized and well-dispersed in solution. Using this method, NTs and helical nanosprings with controlled dimensions were fabricated using inorganic materials usable in functional nanodevices such as sensors, actuators and resonators. To the best of our knowledge, nothing has been published concerning the mechanical properties of inorganic nanotubes or nanosprings templated from organic self-assemblies. Their elastic properties were determined by performing three-point bending tests on suspended NTs and nanosprings over micro-cavities using an atomic force microscope (AFM).. The SiO2 nano-objects were subjected to a load f at midpoint using an AFM tip by performing force vs. distance (F-d) curve measurements. The elastic modulus E was then determined using the beam bending theory of clamped-clamped beam [4], that gives the relationship between E and the elastic deformation of a suspended and clamped cylindrical beam or tube. For all tested NTs the average value of the elastic modulus E was determined to be 73.3 ± 6.7 GPa, which is comparable to that of bulk SiO2 [5] as well as amorphous SiO2 nanowires obtained using chemical vapor deposition [6]. On the other hand, the average value of E measured for helical nanospring was 70 ± 7 GPa, which is in very good agreement with the result obtained for the NTs. This is of paramount importance because the nanospring exhibit unconventional physical properties and can be advantageously used as building blocks in functional nanodevices. The first advantage concerns their helicity and periodicity that can be varied to tune the spring constant. In addition, due to their structural flexibility, the helical shape is also ideal for inducing polarization effects under mechanical stress [7]. The obtained results demonstrate that the proposed synthetic route for obtaining inorganic NTs is robust and reproducible. [1] K. Jensen, K. Kim, A. Zettl, Nature Nanotechnology, (2008) 3, 533 - 537. [2] Lih J. Chen J. Mater. Chem., (2007) 17, 4639-4643. [3] T. Delclos, C. Aimé, E. Pouget, A. Brizard, I. Huc, M.-H. Delville, R. Oda, Nano Lett. (2008), 8, 1929 - 1935, [4] J. M. Gere, S. P. Timoshenko, Mechanics of Materials, PWS-KENT, Boston, Massachusetts, (1990) Third Edition [5]. B. Bhushan, Handbook of Nanotechnology (Springer, Berlin, 2007) 2nd edition, p. 1040 [6] H. Ni, X. Li, H. and Gao, Appl. Phys. Lett. (2006) 88, 043108 [7]. J.P. Singh et al. Applied Physics Letters (2004) 84, 3657.

Resume : Alkaline-earth fluorides nanoparticles doped with Er3+/Yb3+ or Tm3+/Yb3+ lanthanide ions are efficient upconversion materials [1] that can find use in various technological fields, in particular in biomedical diagnostic. A recent paper describes the possibility of using upconverting Er3+/Yb3+ or Tm3+/Yb3+ codoped CaF2 nanoparticles for cellular imaging [2]. In this contribution, we describe the synthesis of water dispersible core-shell alkaline-earth fluoride nanoparticles and the study of the spectroscopic properties of the prepared nanostructures upon near infrared excitation. A hydrothermal procedure has been developed to prepare core-shell SrF2:Nd3+/Tm3+/Yb3+@SrF2:Nd3+ nanoparticles with hydrophilic capping agents. The behavior of the Tm3+ and Yb3+ ions luminescence upon excitation in the near infrared region and the Nd3+ - Yb3+ energy transfer processes have been investigated also as a function of the temperature for possible use of the nanoparticles as optical probes and nanothermometers. [1] M. Pedroni, F. Piccinelli, T. Passuello, S. Polizzi, J. Ueda, P. Haro-Gonzalez, L. M. Maestro, D. Jaque, J. Garcia-Sole, M. Bettinelli and A. Speghini, Cryst. Growth Des., 2013, 13, 4906-4913. [2] N. N. Dong, M. Pedroni, F. Piccinelli, G. Conti, A. Sbarbati, J. E. Ramirez-Hernandez, L. M. Maestro, M. C. Iglesias-de la Cruz, F. Sanz-Rodriguez, A. Juarranz, F. Chen, F. Vetrone, J. A. Capobianco, J. G. Sole, M. Bettinelli, D. Jaque and A. Speghini, ACS Nano, 2011, 5, 8665-8671.

Resume : Although Si is widely used for photovoltaic and electronic applications, light emission from Si is in general poor due to its indirect bandgap. Apart from Si, also Ge makes a good candidate for electronic devices. It has a rather large exciton Bohr radius (~18 nm) and bulk Ge has a direct bandgap of 0.8 eV. Therefore, Ge should also make a good candidate for QD-based devices. As reported in past literature, emission from (oxidized) Ge QDs is in general weak. Here, we discuss high-intensity PL emission bands from colloidal butyl-terminated Ge QDs. The PL bands blueshift with increasing excitation energy, indicating an ensemble of QDs with a broad size distribution. We observed PL lifetimes on a sub-nanosecond timescale. In addition, we discuss the intraband transitions in butyl-terminated Ge QDs. For that purpose, we use ultrafast transient induced absorption spectroscopy. The time-dependent evolution of absorption spectra provides information on relaxation and recombination processes within the excited states of QDs. This is done by probing intraband transitions of free carriers generated by the pump pulse. We demonstrate that the features observed by experiment agree well with theoretical modeling. We discuss implications of these findings for new applications of these bright emitting colloidal Ge QDs for photovoltaic and light emitting devices.

Resume : We discuss the optical properties of highly luminescent CdSe/CdS quantum dot-in-rods synthesized by seeded growth(1) and then transferred to water using a simple ligand-exchange method employing mercaptopropionic acid (MPA)(2). From a device fabrication point of view, water-soluble nanocrystals (NCs) are most desirable since they enable the preparation of multi-layer structures by exploiting orthogonal solvents, as well as the use of organic materials for the fabrication of a variety of photonic structures. Nevertheless, obtaining water-soluble CdSe/CdS NCs possessing similar optical properties to organic soluble ones has represented a major challenge. The water-soluble MPA-capped NCs here investigated possess a CdS rod with a diameter that is significantly larger than the CdSe core. The larger CdS rod prevents surface defects formed during the ligand-exchange reaction to affect the photophysics of the system, hence MPA-capped NCs show similar optical properties to the pristine (organic soluble) octadecylphosphonic acid functionalized NCs. More importantly, we demonstrate amplified spontaneous emission from the core or shell states(3) of films made from water-soluble CdSe/CdS dot-in-rods, providing further evidence that the desired properties are preserved after the ligand-exchange reaction. References: 1 Carbone L, et al. Nano Letters 2007, 7, 2942 2 Wuister S F, et al. Nano Letters 2003, 3 3 Krahne R, et al. Appl. Phys. Lett. 2011, 98, 063105

Resume : Arrays of metal nanoparticles interlinked by an organic matrix have attracted a lot of interest due to their diverse electronic and optoelectronic properties [1]. By controlling the nature of the matrix material and the interparticle distance, the electronic behavior of the nanoparticle array can be substantially tuned and controlled [1,2]. We have recently shown that nanoparticle arrays form a useful architecture to build networks of molecular junctions. Here, the nanoparticles act as electronic contacts to the molecules and a molecular functionality can be used to induce an overall functionality at the array scale. Using this approach, we have build nanoarticles arrays exhibiting for instance redox [3] and optical [4] switching behaviors. The later is made possible thanks to the excitation of surface plasmons in the nanoparticles. Thanks to this particular configuration, the molecules can easily be accessed by optical means. A resonant excitation of the molecules within the array will thus leads to a photoconductance enhancement at the array level [5]. Nanoparticle arrays thus represent an interesting architecture opening possibilities for the development of novel molecular scale electronic and optoelectronic devices. Their possible implementation as an information storage platform or even as computing networks thanks to a defect‐tolerant architecture is currently under investigation [6]. References 1. M.A. Mangold et al., Nanoparticles arrays, to appear in the Springer Handbook of Nanoparticles (2014). 2. M. Calame, Molecular junctions: from tunneling to function, Chimia Int. J. Chem, 64 (6), 391‐397 (2010). 3. J. Liao et al., Cyclic conductance switching in networks of redox‐active molecular junctions, Nano Letters, 10 (3) , 759–764 (2010). 4. S. van der Molen et al., Light‐controlled conductance switching of ordered metalmolecule‐ metal devices, Nano Letters, 9 , 76‐80 (2009). 5. M. A. Mangold et al., Resonant Photoconductance of Molecular Junctions Formed in Gold Nanoparticle Arrays, J. Am. Chem. Soc., 133 (31) , 12185–12191 (2011). 6. G. Wendin et al., Synaptic Molecular Networks for Bio‐Inspired Information Processing, Int. J. Unconv. Comp., 8 , 325‐332 (2012).

Resume : Recent advancements in colloidal chemistry indicate that two-dimensional single-crystalline sheets of semiconductors forming a honeycomb lattice can be synthesized from semiconductor nanocrystals [1]. We perform atomistic tight-binding calculations of the band structure of CdSe sheets with such a nano-geometry [2]. We predict in the conduction band Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has s-orbital character and is equivalent to the pi bands of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their p-orbital character. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. [1] W. H. Evers, B. Goris, S. Bals, M. Casavola, J. de Graaf, R. van Roij, M. Dijkstra, and D. Vanmaekelbergh, Nano Lett. 13, 2317 (2013). [2] E. Kalesaki, C. Delerue, C. Morais Smith, W. Beugeling, G. Allan, D. Vanmaekelbergh, Phys. Rev. X, in press.

Resume : Silicon quantum dots (Si QDs) are promising alternative to toxic, rare and expensive QDs of other materials that nowadays are being researched for or used in optoelectronics, photonics and bio-imaging. Radiative rates, though, are comparatively low, owing to the indirect bandgap nature of Si. Deeper understanding of the processes involved can be achieved from single QD spectroscopy, allowing study of individual quantum emitters, while avoiding ensemble averaging effects. Comparison of single QD characteristics with those of the ensemble gives insight into the microscopic processes that underlie ensemble photoluminescence (PL) and quantum yield (QY). As generally in all quantum emitters, the QY is critically influenced by blinking (PL intermittency), a cyclic transition between an emissive bright and a non-radiative dark state, that emerges on a microscopic level. The mechanism behind the blinking process is not yet fully understood, but could arise from charging of the QD or trapping into a nearby defect state. Surface states assume a major role in both models, but also influence the radiative rates through modification of the electron and hole wavefunctions. By single QD spectroscopy, as well as complementary ensemble measurements, we examine the effect of carbon- and silica oxide-based surface capping on blinking and PL of colloidal Si QDs, which will help the development of Si QDs for application in lighting technologies.

Resume : The photoactive properties of titanium dioxide are very attractive allowing many applications in the environmental domains. Its integration in hybrid organic solar cells, especially, requires the elaboration of layers to optimize collection and transport of photogenerated electrons. Solvothermal process allows us to adjust the size and variety of titanium dioxide by tuning pH or by using organic solvents. Depending on the chosen way, the hydrolysis-condensation is controlled; sols, gels and crystalline colloids can be prepared. Choosing to perform the synthesis in suitable solvents is a key parameter to obtain colloidal solutions, with the required physico-chemical properties for chemical solution deposition. In order to remain compatible with low temperature processes on plastic substrates, crystalline colloids are processed as thin film because no further annealing at high temperature is required. Their integration as interfacial layers allowed us to lengthen the lifetime of organic bulk heterojunction solar cells over 6500 hours, with a loss in photon conversion efficiency limited to less than 17% [1]. [1] Karpinski, A.; Berson, S.; Terrisse, H.; Mancini-Le Granvalet, M.; Guillerez, S,; Brohan, L.; Richard-Plouet, M. Solar Energy Mater. & Solar Cells 116, 27-33, 2013

Resume : Colloidal semiconductor nanocrystals (NCs) are a new class of versatile nanomaterials, whose properties are determined by their size, shape, and composition. Semiconductor NCs comprising two (or more) different materials joined together by heterointerfaces, i.e., heteronanocrystals (HNCs), offer even more exciting possibilities regarding property control. The spatial localization of charge carriers in HNCs can be manipulated by controlling the offsets between the energy levels of the materials that are combined at the heterointerface. Doping of NCs and HNCs enables further control over their electronic, optical, transport, and magnetic properties. Moreover, colloidal NCs and HNCs are coated with a layer of organic ligand molecules, which further extends their functionality, since it allows for easy surface manipulation and solution processing. These characteristics have turned colloidal semiconductor NCs and HNCs into promising materials for a myriad of applications, motivating extensive research into their synthesis. In this talk, we will discuss a synthesis approach that has been attracting increasing attention in recent years, and is establishing itself as a versatile strategy to fabricate shape-controlled NCs, HNCs, and doped NCs that are not attainable by conventional methods: Cation Exchange.

Resume : Colloidal systems are highly appealing to achieve a good control on inorganic nanoparticles size, size distribution, crystallinity and shape. Among them emulsions play a leading role and, in more detail, miniemulsions (MEs) represent a promising way to achieve a good control on the final material characteristics. Thanks to the high shear forces applied during homogenization, these systems reach the minimum droplet size possible, diffusion and collision phenomena are hindered, and droplets maintain their identity. A ME thus represents an ensemble of 1018-1020 independent droplets, where a reaction can take place in a parallel fashion. In these last years we exploited inverse MEs for the syntheses of a wide variety of inorganic materials. For example, ZnO nanostructures were obtained at RT, through an easy and reproducible route, which also enabled controlled doping (Eur. J. Inorg. Chem. 2013, 2291; J. Mater. Chem. 22, 1620). A similar approach was applied to the preparation of other lanthanide-doped binary and ternary systems, i.e., hydroxides, sulphides and halogenides. These materials showed good doping control, interesting luminescence properties and low cytotoxic effects, leading to appealing systems with potential bioimaging applications. The ME approach was also exploited for the photodecomposition in confined space of a tailored single-source Au/TiO2 precursor, enhancing catalytic properties with respect with the same materials prepared in a bulk (Nanoscale, 5, 10534).

Resume : In the last few years significant attention has been paid to the adjustment of optical properties of polymer nanocomposite materials by the employment of functionalized semiconductor inorganic nanocrystals (NCs). Zinc sulfide (ZnS) and zinc selenide (ZnSe) with band gap respectively about 3.6 eV and 2.8 eV are very good candidates as nanofillers for polymer systems because of their intense luminescence, narrow emission, broad absorption and chemical stability. Additionally, those materials due to the large band gap can be used as an efficient semiconductor hosts to dope different transition metal ions such as Mn2+. ZnS NCs doped with Mn2+ ion have been one of the best efficient electroluminescent phosphor materials in use. On the other hand, ZnSe NCs by having the smaller band gap is an attractive and suitable material for hybrid photovoltaic devices. In this work we report the fabrication and study of novel and transparent ZnSe:Mn/ZnS/PMMA and ZnS:Mn/PMMA hybrid nanocomposite thin films, including preparation techniques of colloidal ZnSe:Mn/ZnS and ZnS:Mn nanoparticles, their surface modification and the integration process with PMMA system in different solvents, as well as the consequences for their luminescence. Transparent ZnS:Mn/ZnS/PMMA and ZnS:Mn/PMMA nanocomposite materials via a film casting were obtained. Resulting colloidal nanocrystals and nanocomposite were characterized with respect to their optical and structural properties and their stability under ambient conditions. Additionally, in this work we present the latest research on preparation of one-dimensional (1D) ZnS and ZnSe NCs under microwaves irradiation and their surface modification as a potential component for polymer system.

Resume : A series of nanostructured TiO2 sensors and photoelectrochemical cells have been developed in our group for photoelectrochemical determination of organic compounds, leading to a series of commercialized patents [1] and commercial products. This sensing mechanism is based on photoelectrocatalytic oxidation of organic compounds in waters under UV radiation [2-4]. Recently, a hydrogenated nanostructured TiO2 photoanode was prepared by hydrogenating TiO2 nanorod arrays (H-TNRs) electrode. Hydrogenation is an efficient and effective means to extend light absorption to visible light region and improve electron conductivity of TiO2 via introduction of oxygen vacancy and mid-gap levels in TiO2 lattice. The H-TNRs photoanode was used as a sensor for organic compound detections under visible light illumination for the first time. Preliminary experiments demonstrate that the H-TNR electrode is able to sensitively determine various organic compounds in water with satisfactory stability. This suggests that the hydrogenation nanostructured TiO2 electrodes are promising in sensing organic compounds in waters and further to be further developed into commercial products. References: 1. Zhao, H., Zhang, S., Improved water analysis. PCT Int. Patent. (2008) WO 2008077191 2. Qiu J., Zhang S. , Zhao H., Recent Applications of TiO2 Nanomaterials in Chemical Sensing in Aqueous Media, Sensors & Actuators: B. Chemical, 2011, (2011); 160: 875-890 (Review) 3. Zhang S., Li H., Zhao H.,