Anitha Ethirajan

Toxicity of organometal halide perovskite solar cells

In the last few years, the advent of metal halide perovskite solar cells has revolutionized the prospects of next-generation photovoltaics. As this technology is maturing at an exceptional rate, research on its environmental impact is becoming increasingly relevant.

Assessing the toxicity of Pb- and Sn-based perovskite solar cells in model organism Danio rerio.

Intensive development of organometal halide perovskite solar cells has lead to a dramatic surge in power conversion efficiency up to 20%. Unfortunately, the most efficient perovskite solar cells all contain lead (Pb), which is an unsettling flaw that leads to severe environmental concerns and is therefore a stumbling block envisioning their large-scale application. Aiming for the retention of favorable electro-optical properties, tin (Sn) has been considered the most likely substitute. Preliminary studies have however shown that Sn-based perovskites are highly unstable and, moreover, Sn is also enlisted as a harmful chemical, with similar concerns regarding environment and health. To bring more clarity into the appropriateness of both metals in perovskite solar cells, we provide a case study with systematic comparison regarding the environmental impact of Pb- and Sn-based perovskites, using zebrafish (Danio Rerio) as model organism. Uncovering an unexpected route of intoxication in the form of acidification, it is shown that Sn based perovskite may not be the ideal Pb surrogate.

Synthesis and optimization of gelatin nanoparticles using the miniemulsion process

A convenient synthetic route based on the concept of nanoreactors using the versatility of the miniemulsion technique to synthesize glutardialdehyde cross-linked gelatin nanoparticles with tailored properties is reported. It is demonstrated that, independent of the molecular weight distribution of the gelatin used, stable nanoparticles can be produced with a small amount of surfactant. The amount of gelatin and the cross-linking degree in the particle can be well controlled. Different types of gelatin have been used without purification or fractionation. The stability of the dispersion, particle size, and the efficiency of cross-linking have been studied. Such nanoparticles with varying gelatin concentration and cross-linking density have high potential to be used for drug delivery applications, as nanoenvironment or template for synthesizing inorganic materials.

Selective Identification of Macrophages and Cancer Cells Based on Thermal Transport through Surface-Imprinted Polymer Layers

In this article, we describe a novel straightforward method for the specific identification of viable cells (macrophages and cancer cell lines MCF-7 and Jurkat) in a buffer solution. The detection of the various cell types is based on changes of the heat transfer resistance at the solid-liquid interface of a thermal sensor device induced by binding of the cells to a surface-imprinted polymer layer covering an aluminum chip. We observed that the binding of cells to the polymer layer results in a measurable increase of heat transfer resistance, meaning that the cells act as a thermally insulating layer. The detection limit was found to be on the order of 10(4) cells/mL, and mutual cross-selectivity effects between the cells and different types of imprints were carefully characterized. Finally, a rinsing method was applied, allowing for the specific detection of cancer cells with their respective imprints while the cross-selectivity toward peripheral blood mononuclear cells was negligible. The concept of the sensor platform is fast and low-cost while allowing also for repetitive measurements.

Nanostructured Coatings by Adhesion of Phosphonated Polystyrene Particles onto Titanium Surface for Implant Material Applications

Titanium that is covered with a native oxide layer is widely used as an implant material; however, it is only passively incorporated in the human bone. To increase the implant-bone interaction, one can graft multifunctional phosphonic compounds onto the implant material. Phosphonate groups show excellent adhesion properties onto metal oxide surfaces such as titanium dioxide, and therefore, they can be used as anchor groups. Here, we present an alternative coating material composed of phosphonate surface-functionalized polystyrene nanoparticles synthesized via free radical copolymerization in a direct (oil-in-water) miniemulsion process. Two types of functional monomers, namely, vinylphosphonic acid (VPA) and vinylbenzyl phosphonic acid (VBPA), were employed in the copolymerization reaction. Using VBPA as a comonomer leads to particles with a higher density of surface phosphonate groups in comparison to those obtained with VPA. VBPA-functionalized particles were used for the coating formation on the titanium surface. The particles monolayer was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) employing titanium and silicium tip with the native OH groups. Force versus distance curves proves the strong adhesion between the phosphonated particles and the titanium (or silicium) surfaces in contrast to the nonfunctionalized polystyrene particles. Finally, as a proof of concept, the particles adhered to the surface were further used to nucleate hydroxyapatite, which has high potential for bioimplants.

Functional Hybrid Materials with Polymer Nanoparticles as Templates

The use of polymeric nanoparticles as templates for producing inorganic materials is an intriguing approach as it offers the feasibility of synthesizing hybrid organic-inorganic functional materials for a broad spectrum of applications ranging from optoelectronics to biomedicine. The concept of using polymer nanoparticles as templates to produce hybrid materials has several advantages. On the one hand, the entire geometry of the nanoparticle can be used as a confined nano-environment to let the inorganic material grow inside the particle. On the other hand, the high surface area of nanoparticle can be exploited to let the inorganic material grow on the outside surface of the particles. One such application is presented here, in which polymer nanoparticles were used as biomimetic template to produce composite nanoparticles made of the bone mineral hydroxyapatite (HAP). The synthesized hybrid particle has a great potential to be used as regenerative filler or as scaffold for nucleation and growth of new bone material. In addition to be applied as coatings on implants, these nanoparticles also offer the feasibility of being injected directly into the damaged part or administered intravenously with functionalization. Within this overview, we will mainly focus on different polymer nanoparticles obtained by the miniemulsion technique and the different possibilities for them to be used as templates for the biomimetic mineralization of calcium phosphate in the aqueous phase.

Ligand switch in photoinduced copper-mediated polymerization: synthesis of methacrylate–acrylate block copolymers

The use of photo-induced copper-mediated radical polymerization (photoCMP) to synthesize mixed acrylate/methacrylate (methyl acrylate, MA and methyl methacrylate, MMA) block copolymers is investigated. Reactions in which only one type of ligand (Me6TREN) is used lead to unsuccessful outcomes of polymerization due to a mismatch in reactivity of the two monomers. A ligand exchange to PMDETA for methacrylate is required to obtain good block structures. Due to insufficient re-initiation of polyacrylates, methyl methacrylate needs to be polymerized first, before acrylate can be added for chain extension. A halogen exchange with CuCl is found to be beneficial to increase the re-initiation behaviour of the polyacrylate with respect to the acrylate chain propagation, but inherently compromises the livingness of the polymerization. Successful synthesis of block copolymers is only observed when the PMMA block is polymerized first and if all PMDETA ligand and residual monomer are removed prior to acrylate chain extension. The batch-type photoreactions are then transferred to a continuous flow tubular photoreactor, which leads to a significant acceleration of polymerizations, concomitant reduction in product dispersity and largely simplified block copolymer synthesis conditions.

Molecularly imprinted polymers as synthetic receptors for the QCM-D-based detection of l -nicotine in diluted saliva and urine samples

AbstractMolecularly imprinted polymers (MIPs) are synthetic receptors that are able to specifically bind their target molecules in complex samples, making them a versatile tool in biosensor technology. The combination of MIPs as a recognition element with quartz crystal microbalances (QCM-D with dissipation monitoring) gives a straightforward and sensitive device, which can simultaneously measure frequency and dissipation changes. In this work, bulk-polymerized l-nicotine MIPs were used to test the feasibility of l-nicotine detection in saliva and urine samples. First, l-nicotine-spiked saliva and urine were measured after dilution in demineralized water and 0.1× phosphate-buffered saline solution for proof-of-concept purposes. l-nicotine could indeed be detected specifically in the biologically relevant micromolar concentration range. After successfully testing on spiked samples, saliva was analyzed, which was collected during chewing of either nicotine tablets with different concentrations or of smokeless tobacco. The MIPs in combination with QCM-D were able to distinguish clearly between these samples: This proves the functioning of the concept with saliva, which mediates the oral uptake of nicotine as an alternative to the consumption of cigarettes. FigureSchematics of the sample-preparation procedure for l-nicotine spiked saliva- and urine samples with various concentration levels

UV-induced functionalization of poly(divinylbenzene) nanoparticles via efficient [2 + 2]-photocycloadditions

The efficient functionalization of poly(divinylbenzene) (polyDVB) nanoparticles via Paterno–Buchi type [2 + 2]-photocycloadditions is described. Initially polyDVB nanoparticles with high density of alkene groups on the surface are synthesized via radical miniemulsion polymerization. Subsequently, UV-induced [2 + 2]-photocycloadditions with different functionalized aldehydes have been performed on the surface under mild and catalyst-free conditions. In order to show the versatility and the accessibility towards incorporation of different functionalities with this strategy, surface modifications were carried out with ATRP initiators and NHS esters for bioconjugation, respectively. Finally, these photofunctionalized nanoparticles were grafted with poly(butyl acrylate) or with gold-labeled antibodies to prove the success of the reactions. PolyDVB nanoparticles before and after photofunctionalization are characterized by X-ray photoelectron spectroscopy (XPS), electron microscopy (SEM and TEM) and ATR-FTIR spectroscopy. Results show that the photoconjugation route is highly efficient and grafting densities of 4 to 5 molecules per nm2 on the entire surface of the particles are achieved.

Intracellular localization and dynamics of Hypericin loaded PLLA nanocarriers by image correlation spectroscopy

The study of cell-nanoparticle interactions is an important aspect for understanding drug delivery using nanocarriers. In this regard, advances in fluorescence based microscopy are useful for the investigation of temporal and spatial behavior of nanoparticles (NPs) within the intracellular environment. In this work, we focus on the delivery of the naturally-occurring hydrophobic photosensitizer Hypericin in human lung carcinoma A549 cells by using biodegradable poly L-lactic acid NPs. For the first time, Hypericin containing NPs are prepared by combining the miniemulsion technique with the solvent evaporation method. This approach yields an efficient loading of the NPs with Hypericin and allows for additional cargo molecules. To monitor the release of Hypercin from the NPs, an additional fluorescent lipophilic dye Coumarin-6 is incorporated in the NPs. Temporal and spatiotemporal image correlation spectroscopy is used to determine the fate of the NPs carrying the potential cargo. Both directed and non-directed motions are detected. By using image cross-correlation spectroscopy and specific fluorescent labeling of endosomes, lysosomes and mitochondria, the dynamics of the cargo loaded NPs in association with the organelles is studied.