Inorganic UV filters

Nowadays, concern over skin cancer has been growing more and more, especially in tropical countries where the incidence of UVA/B radiation is higher. The correct use of sunscreen is the most efficient way to prevent the development of this disease. The ingredients of sunscreen can be organic and/or inorganic sun filters. Inorganic filters present some advantages over organic filters, such as photostability, non-irritability and broad spectrum protection. Nevertheless, inorganic filters have a whitening effect in sunscreen formulations owing to the high refractive index, decreasing their esthetic appeal. Many techniques have been developed to overcome this problem and among them, the use of nanotechnology stands out. The estimated amount of nanomaterial in use must increase from 2000 tons in 2004 to a projected 58000 tons in 2020. In this context, this article aims to analyze critically both the different features of the production of inorganic filters (synthesis routes proposed in recent years) and the permeability, the safety and other characteristics of the new generation of inorganic filters

Desenvolvimento de sistemas líquido-cristalinos multifuncionais contendo nanopartículas de TiO2 para proteção solar e liberação controlada de terpinem-4-ol

A incidência de câncer de pele em todo o mundo cresce exponencialmente principalmente devido à exposição freqüente à radiação ultravioleta (UV). O uso de protetor solar é a medida mais eficaz para a sua prevenção. O dióxido de titânio (TiO2) é um filtro inorgânico que atua espalhando, refletindo e absorvendo a radiação UV, é fotoestável, hipoalergênico, entretanto, deixa a pele com aspecto esbranquiçado dependendo do tamanho da partícula. Hoje em dia há uma procura grande por produtos multifuncionais e o uso de estruturas líquido-cristalinas vem crescendo cada vez mais por promover a liberação controlada de ativos. O objetivo deste trabalho foi desenvolver sistemas multifuncionais líquido-cristalinos contendo nanopartículas de TiO2 transparentes capazes de agir como fotoprotetores e de liberar terpinem-4-ol (terpeno com atividade antioxidante) de forma controlada prevenindo e/ou tratando o câncer de pele. O teste de citotoxicidade mostrou que as nanopartículas de TiO2 obtidas através do processo sol-gel não foram citotóxicas para as duas linhagens de células testadas (queratinócitos de pele humana – HaCaT e fibroblastos de pulmão humano – MRC-5), evidenciando o uso deste material nos humanos sem causar danos. O potencial zeta das nanopartículas indicou que entre pH 5 e 7, que não é agressivo para pele humana, é possível evitar aglomeração das nanopartículas por estas apresentarem cargas superficiais significativas. Os dados de espalhamento de raios X a baixo ângulo e microscopia de luz polarizada mostraram que foi possível manter a estrutura líquido-cristalina das formulações com a presença de nanopartículas de TiO2 e terpinem-4-ol. O teste de liberação in vitro das formulações contendo 1 e 5% de terpinem-4-ol mostraram que o sistema líquido-cristalino controlou...The incidence of skin cancer growth exponentially in all the world mainly due to the frequent ultraviolet (UV) radiation exposition. The sunscreen use is one of the efficient manners to prevent the skin cancer. The titanium dioxide (TiO2) is an inorganic filter which works scattering, reflecting and absorbing the UV radiation, it is photostable, hypoalergenic, but it presents a whiteness appearance depending on the particle size. Nowadays there is a high demand for multifunctional products and the use of liquid crystal has been increasing because it promotes active controlled delivery. The propose of this work is to develop liquid crystalline multifunctional systems with transparent TiO2 nanoparticles able to photoprotect the skin and release in a controlled manner terpinem-4-ol (a terpen with antioxidant activity) to prevent and/or treat the skin cancer. The citotoxicity assay showed that TiO2 nanoparticles obtained by sol-gel process weren´t cytotoxics to the two cell lines tested (human skin keratinocites – HaCaT and human lung fibroblasts – MRC-5), evidencing the use of this material on the humans without dangers. The nanoparticles zeta potential indicated that at pH about 5 and 7, pH that is not irritative to the human skin, it´s possible to prevent nanoparticles aggregation due to their significative superficial charges. The small angle scattering X rays and light polarized microscopy data showed that it is possible to maintain the liquid crystalline structure of the formulations with the presence of TiO2 nanoparticles and terpinem-4-ol. The in vitro terpinem-4-ol release assay of the formulations containing 1 and 5% of terpinem-4-ol showed the controlled release of the liquid crystalline systems (liberation at about 13% in 12 hours), being zero order the best mathematical model that fit the release profile, indicating... (Complete abstract click electronic access below)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Pontos Quânticos à base de óxido de zinco (ZnO) para aplicações em bioimagem de nanocarreadores lipídicos

Sistemas teranósticos consistem em um único dispositivo contendo agentes terapêuticos e de diagnóstico e tem ganhado atenção nas pesquisas atuais por melhorar o tratamento de doenças como câncer, podendo diminuir efeitos colaterais, diminuir toxicidade em células não cancerígenas e permitir o monitoramento do tratamento. Os pontos quânticos (PQs) vem sendo usado como agentes de imagem para realizar o monitoramento ótico em investigações in vivo e in vitro. Dentre eles, o ZnO tem se destacado por ser mais barato, mais biocompatível e menos tóxico do que os utilizados comumente (SeCd, PbS, etc). O objetivo deste trabalho foi desenvolver sistemas teranósticos constituídos de nanocarreadores à base de lipídeos contendo pontos quânticos a base de ZnO, como guias luminescentes de células cancerígenas, e um fármaco modelo para tratamento do câncer. Primeiramente, foi estudada a síntese de pontos quânticos de ZnO/ZnS (estrutura de casca/caroço) pelo processo sol-gel, a fim de melhorar as propriedades luminescentes do ZnO através da passivação da sua superfície provocada pelo ZnS. Para isto, as reações de síntese tiveram como base (i) a solução precursora de acetato de Zinco e (ii) a suspensão coloidal de ZnO. Além disso, foram variadas as concentrações de tioacetamida (TAA) (1.5, 5 e 50mM), usada como fonte de íons de enxofre. Para diferenciar a formação de estruturas casca/caroço (ZnO/ZnS) e não uma mistura de partículas de ZnO e ZnS, várias técnicas foram utilizadas para caracterizar as amostras (DRX, XAS, SAXS, UV-vis, pH, HRTEM e PL). Dentre elas, XAS foi crucial para identificar que somente a reação realizada a partir da suspensão coloidal de ZnO com TAA 5mM deu origem à estrutura de ZnO/ZnS do tipo casca/caroço. Entretanto, os PQs de ZnO/ZnS não apresentaram maior intensidade da emissão na região do visível quando comparado ao ZnO. Portanto, PQs de ZnO foram dopados com Mg para gerar elétrons ou buracos extras na sua estrutura levando a mudanças em suas propriedades luminescentes. Diferentes quantidades de Mg (2.5, 5, 10 e 20 % em mol) foram usadas durante a síntese de ZnO pelo processo sol-gel para poder obter, assim, partículas com maior luminescência na região do visível. DRX, HRTEM, ICP-MS, SAXS, UV-Vis e PL foram usadas a fim de avaliar as características físico-químicas dos diferentes Zn1-xMgxO obtidos. Observou-se a diminuição do tamanho das partículas com o aumento da concentração de Mg. Quando se utilizou 20 % em mols em concentração nominal de íons Mg2+ no meio reacional (Zn0.8Mg0.2O), o rendimento quântico (RQ) foi seis vezes maior (RQ = 64%) do que a suspensão de ZnO não dopado (RQ = 10%). Para utilizar os PQs em meio biológico mantendo sua propriedade fotoluminescente, sua superfície normalmente é modificada com substâncias hidrofílicas para torná-los estáveis em água, ou com substâncias hidrofóbicas para permitir sua incorporação em sistemas/carreadores à base de lipídeos ou polímeros. Os PQs de ZnO e de Zn0.8Mg0.2O foram revestidos com ácido oleico (AO) formando uma dispersão coloidal estável em clorofórmio e tolueno. A espectroscopia RAMAN permitiu confirmar a modificação da superfície dos PQs pela presença dos grupamentos característicos do AO nessas amostras. O RQ do Zn0.8Mg0.2O revestido com AO foi em torno de 4 vezes maior (RQ = 40%) que o RQ de ZnO revestido com AO. Por fim, os PQs de Zn0.8Mg0.2O revestidos e não-revestidos com AO foram incorporados em nanocarreadores lipídicos para serem utilizados posteriormente nos estudos de internalização celular. Formulações à base de DPPC, DSPE-Peg e nanopartículas lipídicas sólidas (NLS) contendo PQs foram obtidos com diâmetro hidrodinâmico entre 100-220 nm. A formulação preparada com DSPE-Peg apresentou maior intensidade de emissão no visível quando comparadas com as NLS. O estudo de estabilidade realizado com as NLS luminescentes em diferentes meios (água, PBS, PBS com Mg e Ca, RPMI com soro à 10%) à 37°C durante 3 horas, mostrou que o tamanho delas não variou bruscamente no tempo analisado. Nesse estudo o tamanho máximo encontrado foi de 300 nm, mostrando que na presença de proteínas, elas não formam grandes agregados que podem favorecer a fagocitose pelo sistema mononuclear. Foram utilizados três métodos para realizar o estudo de internalização celular. O estudo da associação de fluorescência mostrou aumento da intensidade de emissão no visível de células de macrófagos J774 tratadas com 2 mg/mL de NLS luminescente durante 50 min, comparado com as células sem tratamento. Este resultado sugere internalização parcial das NLS nos macrófagos. A vídeo-microscopia e a microscopia de fluorescência não tiveram sucesso para realizar este estudo, uma vez que as condições experimentais utilizadas não puderam superar o efeito de auto-fluorescência das células. Para concluir, a síntese de PQs à base de ZnO pelo processo sol-gel possibilitou estudar as estruturas e propriedades luminescentes destes, permitindo otimizar sua síntese para adequá-los para uso como guias luminescentes. Desta forma, Zn0.8Mg0.2O com alto rendimento quântico foi incorporado em nanocarreadores lipídicos e sua aplicação como guia luminescente foi evidenciada através do teste de associação de fluorescência.Les systèmes théranostiques sont constitués d’un dispositif unique contenant des agents thérapeutiques et diagnostiques et attirent actuellement l'attention pour améliorer le traitement de maladies telles que le cancer ; ils pourraient réduire les effets secondaires (e.g. la toxicité pour les cellules non-cancéreuses) et permettre le suivi du traitement. Les quantum dots (QDs) sont utilisés comme agents d'imagerie in vitro et in vivo. Parmi ceux-ci, ZnO est moins cher, plus biocompatible et moins toxique que ceux utilisés couramment (SeCd, PbS, etc.). Le but de notre étude était de développer des systèmes théranostiques constitués de nanoparticules lipidiques contenant des QDs à base de ZnO comme agent luminescent, l’objectif final étant d’incorporer un principe actif pour le traitement du cancer. Nous avons d’abord étudié la synthèse de QDs de ZnO/ZnS (structure coeur/coquille) par le procédé sol-gel, afin d'améliorer les propriétés de luminescence de ZnO grâce à la passivation de la surface par le ZnS. Pour cela, deux voies de synthèse ont été explorées: le thioacétamide (TAA), utilisé comme source d'ions soufre, a été ajouté à (i) la solution de précurseur de l'acétate de zinc, et (ii) la suspension colloïdale de ZnO. Différentes concentrations de thioacétamide (TAA) ont été utilisées (1,5, 5 et 50 mM). Pour distinguer la formation de la structure coeur/coquille (ZnO / ZnS) d’un simple melange de particules de ZnO et ZnS, les échantillons ont été caractérisés par plusieurs techniques (DRX, XAS, SAXS, UV-vis, pH, HRTEM et PL). Parmi celles-ci, l’absorption des rayons X (XAS) a été essentielle pour montrer que seule la réaction effectuée à partir de la suspension colloïdale de ZnO contenant 5 mm de TAA donnait lieu à la structure ZnO/ZnS. Cependant, les QDs de ZnO/ZnS n'ont pas montré une intensité de l'émission dans le visible plus grande que celle des QDs de ZnO. Les QDs de ZnO ont donc été dopés pour générer des électrons ou des trous supplémentaires dans leur structure, entraînant des changements de leurs propriétés de luminescence. Différentes quantités de Mg (2,5, 5, 10 et 20% en mole) ont été ajoutées lors de la synthèse du ZnO par la voie sol-gel, afin d'obtenir des particules ayant une luminescence plus forte dans le visible. Plusieurs techniques (XRD, HRTEM, ICP-MS, SAXS, UV-Vis et PL) ont été utilisées pour déterminer les caractéristiques physico-chimiques des différents Zn1-xMgxO QDs obtenus. Il a été observé une diminution de la taille des particules avec l'augmentation de la concentration de Mg. Lors de l'ajout d’une concentration nominale de Mg2+ dans le milieu réactionnel de 20% molaire (Zn0.8Mg0.2O), le rendement quantique (QY) était six fois plus élevé (QY= 64%) que celui de la suspension de ZnO non dopé (QY= 10%). Pour utiliser les QDs dans un environnement biologique tout en conservant leurs propriétés de photoluminescence, leur surface est généralement modifiée par des substances hydrophiles pour les rendre stables dans l'eau, ou des substances hydrophobes pour permettre leur intégration dans des systèmes/nanoparticules à base de lipides ou de polymères. La surface des QDs de ZnO et Zn0.8Mg0.2O a été recouverte par de l'acide oléique (AO) ; les QDs ainsi modifiés forment une dispersion colloïdale stable dans le chloroforme et le toluène. La spectroscopie Raman a confirmé la présence d’acide oleique à la surface des QDs. Le rendement quantique des QDs de Zn0.8Mg0.2O recouverts d'AO était environ 4 fois plus élevé (QR = 40%) que celui des QDs de ZnO recouverts d’AO. Enfin, les QDs de Zn0.8Mg0.2O, recouverts ou non d’AO, ont été incorporés dans des nanoparticules lipidiques pour une utilisation ultérieure dans des études d'internalisation cellulaire. Des formulation à base de DPPC, DSPE-Peg et des nanoparticules lipidiques solides (SLN) contenant des QDs ont été préparées avec une taille hydrodynamique variant entre 100 et 220 nm. Les formulations à base de DSPE-Peg ont montré une intensité d'émission plus élevée dans le visible, comparé aux SLNs. L'étude de stabilité réalisée avec des SLNs luminescentes dans différents milieux (eau, PBS, PBS avec du Mg et du Ca, RPMI avec du sérum à 10%) à 37°C pendant 3 heures a montré que la taille ne changeait pas fortement au cours du temps. Dans cette étude, la taille maximale était de l’ordre de 300 nm, montrant que même en présence de protéines, il ne se forme pas de gros agrégats. Trois méthodes ont été utilisées pour l'étude de l'internalisation cellulaire dans des macrophages J774. Lorsque la longueur d’onde d’excitation correspond à celle des QDs, les mesures d’intensité de fluorescence sur les suspensions de cellules ont montré une faible augmentation de l’intensité de l’émission visible pour les cellules incubées avec 2 mg/mL de SLNs luminescentes pendant 50 minutes, en comparaison avec les cellules témoins. Ce résultat suggère une internalisation partielle des SLNs dans les macrophages. Malheureusement, ces résultats n’ont pas pu être confirmés par vidéo-microscopie et microscopie de fluorescence sur les cellules parce que les conditions expérimentales ( longueurs d’onde d’excitation et d’émission possibles) ne permettaient pas d’observer un signal supérieur à celui de l'auto-fluorescence des cellules. En conclusion, cette étude a permis d’optimiser la composition et la synthèse par voie sol-gel de QDs à base de ZnO pour les rendre aptes à être utilisés comme sondes luminescentes dans des nanoparticules lipidiques. La relation entre leur structure et leurs propriétés de luminescence a été étudiée; les QDs dopés Zn0.8Mg0.2O, qui ont le rendement quantique le plus élevé, ont pu être incorporés dans des nanoparticules lipidiques pouvant contenir des agents thérapeutiques.Theranostic systems consist of a single device containing therapeutics and diagnosis agents and have increased attention in the actual researches because these devices can improve the disease therapy such as cancer, decrease the side effects and the toxicity in no-cancer cells and permit monitoring the treatment. The aim of this work was to develop theranostic systems consisted of lipid based nanocarriers containing ZnO based quantum dots (QDs) as cancer cell luminescent guides, and a model drug for cancer therapy. Firstly, it was study the synthesis of ZnO/ZnS QDs aiming to achieve improved luminescent properties. In this step, X-Rays Absorption Spectroscopy, together with other usual characterization techniques, could identify the synthesis condition in which core-shell structures were formed. Nevertheless, the emission of ZnO/ZnS QDs in the visible range was not promising. Therefore, Mg-doped ZnO QDs were synthesized and their luminescence went through a maximum for a 20 mol% nominal concentration of Mg2+ ions in the reaction medium. Zn0.8Mg0.2O QDs presented quantum yield (QY) six times higher (QY = 64%) than undoped ones (QY = 10%). ZnO and Zn0.8Mg0.2O QDs capped by oleic acid (OA) were synthesized and formed stable colloidal dispersions in chloroform and toluene. The QY of OA-Zn0.8Mg0.2O was about 4 times (around 40%) higher than that of the OA-ZnO QDs. Zn0.8Mg0.2O QDs and OA-Zn0.8Mg0.2O QDs could be incorporated into lipid based nanocarriers of average hydrodynamic diameter around 100 – 220 nm. The luminescent solid lipid nanoparticles (SLN) were stable in different media at 37°C during 3 hours. The fluorescence association study showed enhanced emission of the J774 macrophage-like cells treated with 2 mg/mL of luminescent SLN during 50 min, suggesting partial internalization of the nanoparticles into the macrophages. The internalization study using the video-microscope and fluorescence microscope were not successfully, once the equipment condition used could not overcome the cells auto-fluorescence phenomena.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Inorganic UV filters

Nowadays, concern over skin cancer has been growing more and more, especially in tropical countries where the incidence of UVA/B radiation is higher. The correct use of sunscreen is the most efficient way to prevent the development of this disease. The ingredients of sunscreen can be organic and/or inorganic sun filters. Inorganic filters present some advantages over organic filters, such as photostability, non-irritability and broad spectrum protection. Nevertheless, inorganic filters have a whitening effect in sunscreen formulations owing to the high refractive index, decreasing their esthetic appeal. Many techniques have been developed to overcome this problem and among them, the use of nanotechnology stands out. The estimated amount of nanomaterial in use must increase from 2000 tons in 2004 to a projected 58000 tons in 2020. In this context, this article aims to analyze critically both the different features of the production of inorganic filters (synthesis routes proposed in recent years) and the permeability, the safety and other characteristics of the new generation of inorganic filters. Uniterms: Skin cancer. Sunscreen. Inorganic UV filter. A preocupação com o câncer de pele hoje em dia vem crescendo cada vez mais principalmente em países tropicais, onde a incidência da radiação UVA/B é maior. O uso correto de protetores solares é a forma mais eficaz de prevenir o aparecimento desta doença. Os ativos utilizados em protetores solares podem ser filtros orgânicos e inorgânicos. Filtros inorgânicos apresentam muitas vantagens em relação aos orgânicos, tais como fotoestabilidade, ausência de irritabilidade e amplo espectro de proteção. Entretanto, em razão de apresentarem alto índice de refração, os ativos inorgânicos conferem aos protetores solares aparência esbranquiçada, diminuindo sua atratividade estética. Muitas alternativas têm sido desenvolvidas no sentido de resolver este problema e dentre elas pode-se destacar o uso da nanotecnologia. Estima-se que o uso de nanomateriais deve crescer das atuais 2000 para 58000 toneladas até 2020. Neste sentido, este trabalho tem como objetivo fazer a análise crítica abordando diferentes aspectos envolvidos tanto na obtenção de protetores solares inorgânicos (rotas de sínteses propostas nos últimos anos) quanto na permeabilidade, na segurança e em outros aspectos relacionados à nova geração de filtros solares inorgânicos. Unitermos: Câncer de pele. Protetores solares. Filtros inorgânicos

Inorganic UV filters

Nowadays, concern over skin cancer has been growing more and more, especially in tropical countries where the incidence of UVA/B radiation is higher. The correct use of sunscreen is the most efficient way to prevent the development of this disease. The ingredients of sunscreen can be organic and/or inorganic sun filters. Inorganic filters present some advantages over organic filters, such as photostability, non-irritability and broad spectrum protection. Nevertheless, inorganic filters have a whitening effect in sunscreen formulations owing to the high refractive index, decreasing their esthetic appeal. Many techniques have been developed to overcome this problem and among them, the use of nanotechnology stands out. The estimated amount of nanomaterial in use must increase from 2000 tons in 2004 to a projected 58000 tons in 2020. In this context, this article aims to analyze critically both the different features of the production of inorganic filters (synthesis routes proposed in recent years) and the permeability, the safety and other characteristics of the new generation of inorganic filters.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Gel Based Sunscreen Containing Surface Modified TiO2 Obtained by Sol-Gel Process: Proposal for a Transparent UV Inorganic Filter

Inorganic UV filters, as titanium dioxide (TiO2), have become attractive because of their role in protecting the skin against the damage caused by the continuous exposure to the sun. However, their high refractive index, responsible for a white residue when applied on the skin, has led to the development of alternative inorganic materials, such as TiO2 nanoparticles. Thus, the aim of this study was the development of transparent and stable gel formulations containing surface modified TiO2 nanoparticles for application in sunscreens. Also, the physical and chemical properties of formulations containing TiO2 nanoparticles were evaluated. The UV absorption spectroscopy analyses indicated that the formulations containing TiO2 nanoparticles had a broad protection spectrum. The diffuse reflectance spectroscopy revealed that the use of PTSH surface modified TiO2 nanoparticles improved the transparency of the sunscreen formulations compared to that containing commercial ones. The rheology analyses showed that the amount of nanoparticles incorporated in the formulations influences the gel-like or liquid-like behavior. The results showed that the surface modified TiO2 nanoparticles are a promising innovative UV filter and the formulations containing these nanoparticles are interesting candidates for being used as sunscreen

Surface modified Mg-doped ZnO QDs for biological imaging

Nanocrystals of ZnO are currently attracting great interest as potential labels for biological applications, such as theranostic devices, due to their luminescent properties and low toxicity in vivo. It has been reported that doping with Mg2+ ions could enhance the luminescence of ZnO quantum dots (QDs). In the present study Mg-doped ZnO QDs were synthesized by a hydrolysis and condensation reaction. Surface modification of the QDs was performed using oleic acid (OA) to hinder their aggregation and to provide them colloidal stability in non-polar environments. Mg2+ ions could be incorporated into the ZnO wurtzite lattice owing to the very close values of the Mg2+ and Zn2+ ion radii. However, the dopant ions strongly influenced the growth and final size of ZnO nanocrystals, as evidenced by time-resolved synchrotron SAXS measurements. The presence of Mg prevented the aggregation of the primary nanoparticles. Doping with Mg2+ ions widened the band gap of ZnO QDs and enhanced their visible luminescence. With increasing proportion of Mg2+ ions, both the absorption and emission spectra experienced a blue shift. The luminescence went through a maximum for a 20 mol% nominal concentration of Mg2+ ions in the reaction medium. The quantum yield (QY) of 20 mol% Mg-doped ZnO colloidal suspension (64%) was about 6 times higher than that of the ZnO suspension (10%). Mg-doped ZnO QDs capped by OA formed stable colloidal dispersions in chloroforme, with strong visible fluorescence (QY=38%), promising for biological imaging.Fundação Amparo à Pesquisa Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Drug Delivery Systems Obtained from Silica Based Organic-Inorganic Hybrids

This is a review of hybrid materials based on silica as an inorganic phase used as drug delivery systems (DDS). Silica based DDS have shown effectivity when compared with traditional delivery systems. They present advantages such as: (a) ability to maintain the therapeutic range with minor variations; (b) prevention of local and systemic toxic effects; (c) plasma concentrations increase of substances with a short half-life; and (d) reduction of the number of daily doses, which may increase patient adherence to the treatment. These advantages occur due to the physical, chemical and optical properties of these materials. Therefore, we discuss the properties and characteristics of them and we present some applications, using different approaches of DDS to ensure therapeutic effectiveness and side effects reduction such as implantable biomaterial, film-forming materials, stimuli-responsive systems and others

The Critical Role of Thioacetamide Concentration in the Formation of ZnO/ZnS Heterostructures by Sol-Gel Process

ZnO/ZnS heterostructures have emerged as an attractive approach for tailoring the properties of particles comprising these semiconductors. They can be synthesized using low temperature sol-gel routes. The present work yields insight into the mechanisms involved in the formation of ZnO/ZnS nanostructures. ZnO colloidal suspensions, prepared by hydrolysis and condensation of a Zn acetate precursor solution, were allowed to react with an ethanolic thioacetamide solution (TAA) as sulfur source. The reactions were monitored in situ by Small Angle X-ray Scattering (SAXS) and UV-vis spectroscopy, and the final colloidal suspensions were characterized by High Resolution Transmission Electron Microscopy (HRTEM). The powders extracted at the end of the reactions were analyzed by X-ray Absorption spectroscopy (XAS) and X-ray diffraction (XRD). Depending on TAA concentration, different nanostructures were revealed. ZnO and ZnS phases were mainly obtained at low and high TAA concentrations, respectively. At intermediate TAA concentrations, we evidenced the formation of ZnO/ZnS heterostructures. ZnS formation could take place via direct crystal growth involving Zn ions remaining in solution and S ions provided by TAA and/or chemical conversion of ZnO to ZnS. The combination of all the characterization techniques was crucial to elucidate the reaction steps and the nature of the final products