Compound droplet manipulations on fiber arrays

Recent works demonstrated that fiber arrays may constitue the basis of an open digital microfluidics. Various processes, such as droplet motion, fragmentation, trapping, release, mixing and encapsulation, may be achieved on fiber arrays. However, handling a large number of tiny droplets resulting from the mixing of several liquid components is still a challenge for developing microreactors, smart sensors or microemulsifying drugs. Here, we show that the manipulation of tiny droplets onto fiber networks allows for creating compound droplets with a high complexity level. Moreover, this cost-effective and flexible method may also be implemented with optical fibers in order to develop fluorescence-based biosensor

Photochemical generation of reactive oxygen species using plasmonic nanoparticles

During his lecture entitled “ There is plenty of room at the bottom ”, Richard Feyn- man foresaw the possibility of manipulating material at the scale of individual atoms and molecules. Although Feynman’s conceptual idea of a nanoworld was evoked in 1959, the nanoscience and nanotechnology revolution began 30 years later with the ability to see at the atomic scale with the invention of electronic microscopy and related tools. The size range that has attracted so much attention over these last 30 years is typically from 100 nanometers down to the atomic level. Subsequently, nanomaterials were defined as materials, which have structured components with at least one dimension in this size range. For instance, material with three nanometric dimensions defines a nanoparticle. Among the variety of core materials available to synthesize nanoparticles, noble metal nanoparticles, i.e. gold and silver, have fascinated people for centuries owing to their bright and intense colors, used in particular as decorative pigments in cathedral stained glasses and artworks. The red and yellow colors displayed by gold and silver nanoparti- cles arise from their interaction with light, which one induces collective oscillations of free electrons at the nanoparticle surface in resonance with the light field. This phenomenon is commonly known as the localized surface plasmon resonance. Their remarkable optical properties and the intense electric field generated by plasmonics nanoparticles have brought these nanomaterials in the forefront of nanotechnology research, ranging from photonics to medicine. Shining light on plasmonic nanoparticles to push back limitations of light-activated therapy and so taking part to the societal challenge of cancer treatment improvement defines the global framework of the thesis. Falling within the nanomedicine topic, this one more precisely deals with the development of efficient plasmonic nano-drugs using light to cure diseases. Clearly, nanoplasmonics, which explores how electromagnetic field can be confined over dimension on the order or smaller than the wavelength of light, has come a long way since the stained glass of Roman times

Gold and silver nanomaterials based biosensors : a comparative study

Noble metal nanoparticles (NPs) are intensively studied due to their particular optical properties, mainly high optical absorption and diffusion yields, leading to interesting applications in biochemical sensing, molecular tracking and imaging, drug delivery and photothermal therapies [1]. These unique optical properties arise from a physical process named surface plasmon resonance (SPR) which is a resonant coupling of incident light to the collective motion of electrons along the nanoparticles surface [2]. Optical SPR biosensors are able to measure complex formation in real time. Indeed, the SPR absorption spectrum band of the NPs is sensitive to the shape, size, inter-particle distance and composition of the NP as well as the dielectric properties of the surrounding medium [2]. Due to the sensitivity of SPR to the local dielectric environment, plasmonic NPs can thus act as transducers that convert small changes in the local refractive index or in the inter-particle distance into spectral shifts and broadenings of the absorption spectral bands [3]. Among metals, silver and gold NPs have received considerable interest for many reasons. For instance, they are stable in ambient atmosphere and exhibit good biocompatibility even if particular surface treatments are sometimes required. The Ag and Au NPs are also relatively easy to fabricate with different sizes and shapes allowing the tuning of the SPR optical absorption band from the near ultraviolet (400 nm) to the near infrared (1000 nm) wavelengths. In this study, our aim is to characterize two biosensors based on silver and gold spherical NPs in order to detect which one seems the best. Both NPs have a diameter close to 15 nm. We use the well-known biocytin-avidin complex as a model system because the bonding of avidin with biocytin is extremely strong with a dissociation constant three order of magnitude higher than the typical constants of antigen-antibody interactions. More precisely, we compare the intensities, the band shapes and the spectral locations of the SPR adsorption bands before and after the biomolecular recognition of avidin by biocytin molecules adsorbed on the Ag and Au NPs. The kinetic of the interaction is also discussed. Before surface treatment with biocytin, the NPs SPR bands are located around 390 and 520 nm for Ag and Au NPs, respectively. The SPR band intensity is higher for silver than for gold. Biocytin adsorption does not significantly modify the SPR spectral features. NPs do not therefore form aggregates and the local refraction index has not significantly changed. After avidin addition, a SPR red-shift and a broadening of the SPR bands are observed with both NPs as shown on Figure 1. These parameters evolved with time and reach their final values after around 45 min for each system. The aforementioned spectral changes arise from the biomolecular recognition process between biotin and avidin which leads to the NPs aggregation. The recognition process also induces a variation of the local refractive index around these NPs which contributes to the red-shift. The maximum SPR shifts are equal to 25 nm and 12 nm for silver NPs and gold NPs, respectively. Our results highlight the smaller dielectric sensitivity of gold NPs compared to the silver NPs one for a same particles’ size and for an equivalent concentration of avidin. The detection limit, described as the lowest concentration for clear identification of wavelength shift due to biomolecular recognition, is equal to 4 nM for both silver and gold NPs. With this protein concentration, 3 nm is the typical wavelength shift. The specificity of the biocytin - avidin biosensors is verified by replacing avidin by Bovine Serum Albumina (BSA). When BSA is added, we observe a SPR band shift which is smaller than the detection limit of 3 nm attesting the biosensor selectivity. Our work demonstrates the superiority of Ag over Au NPs for the elaboration of biosensors based on SPR. However, it is well-known that Ag NPs are less biocompatible than gold. This problem can be circumvented by an appropriate coating of the NPs surface prior ligand adsorption

COMPARATIVE STUDY OF SPR BIOSENSORS BASED GOLD AND SILVER COLLOIDAL NANOPARTICLES

Noble metal nanoparticles (NPs) can be used as a robust tool for optical bio-sensing. These NPs are known for their strong interactions with light through their surface plasmon resonance (SPR), which corresponds to the collective oscillations of the conduction electrons on the particles [1]. Among metals, silver and gold NPs are of particular interest not only because they are air-stable but also because their SPR absorption bands are in the visible and near ultra-violet spectral regions, that appear as the most appropriate for technological applications [2]. The first advantage of such optical SPR biosensors is their ability to measure complex formation in real time. Indeed, the SPR absorption spectrum band of the NPs is sensitive to the shape, size, inter-particle distance and composition of the NP as well as the dielectric properties of the surrounding medium [2]. Because of the sensitivity of SPR to the local dielectric environment, plasmonic NPs can act as transducers that convert small changes in the local refractive index and the inter-particle distance into spectral shifts and broadening in the absorption spectra bands [3]. Biotin is a water-soluble B complex vitamin necessary for the production of fatty acids and the metabolism of fats and amino acids. The avidin is a tetrameric protein which can react with biotin to form the strongly bonded biotin-avidin complex.The prototypical biotin-avidin interaction forms the basis of a simple sol-based diagnostic technique for biological analytes. We focused on this well-known couple of bio-molecules to compare optical properties of silver and gold colloidal NPs. Gradual changes with time in the absorption spectra bands of biotinylated 10 nm silver and gold NPs were studied as a function of added avidin. After avidin addition, an increased red-shift of the SPR wavelength and a broadening of the absorption band with time are observed. These changes in the optical properties of colloidal NPs are due to the biomolecular recognition process between biotin and avidin which leads to aggregation of these NPs arising from cross-linking by the tetrameric protein. Moreover, the recognition process induces a variation of the local refractive index around these NPs and thus induces a red-shift of SPR also. The maximum SPR red-shift was reached after 45 minutes and was equal to 25 nm and 15 nm for silver NPs and gold NPs respectively. We concluded that the dielectric sensitivity of gold NPs is smaller than the silver NPs one for a same geometry and for an equivalent concentration of avidin. Therefore, the silver sol is more adapted to detection of avidin than the gold sol. The detection limit, described as the lowest concentration for clear identification of wavelength shift [4] due to biomolecular recognition is determined to be 4 nM for both silver and gold NPs. In this case, the corresponding wavelength shift is about 3 nm. The specificity of the interaction between biocytin and avidin was checked by replacing avidin by BSA. When BSA was added, we observed a SPR shift which was smaller than the detection limit of 3 nm. Future works will be devoted to transpose this kind of biomolecular recognition experiments on gold nanorods in order to improve the dynamic phototherapy efficiency of cancers

Comparative study of Ag and Au nanoparticles biosensors based on surface plasmon resonance phenomenon

The specific sensitivity of surface plasmon resonance to changes in the local environment of nanoparticles allows their use as platforms to probe chemical and biochemical binding events on their surfaces without any labeling [1- 4]. In this paper, we perform a comparative study of gold and silver nanoparticle based biosensors, prepared within the same conditions, in order to determine which metal seems the best for biological sensing. The prototypical biocytin-avidin interaction is used to study gradual changes over time and with avidin concentration in the absorption spectra bands of biocytinylated 10 nm silver and gold nanospheres. First, the Ag nanoparticles plasmon resonance absorbance signal is about 10 times larger than the Au one. Secondly, for an equivalent concentration of avidin, the optical properties modifications are more pronounced for silver nanoparticles than for gold ones of the same geometry. These observations attest the superiority of Ag on Au nanoparticles when optical considerations are only taken into account. Finally, with both biosensors, the specificity of the interaction, checked by replacing avidin with bovine serum albumin, is relatively poor and needs to be improved

Comparative study of gold and silver based nanobiosensors

Due to their particular optical properties, resulting from the surface plasmon resonance (SPR) phenomenon, silver and gold nanoparticles (NPs) can be used as robust tools for optical biosensing [1]. Optical SPR biosensors are able to measure complex formation in real time. Indeed, the SPR absorption spectrum band of the NPs is sensitive to the shape, size, inter-particle distance and composition of the NP as well as the dielectric properties of the surrounding medium [2]. Due to the sensitivity of SPR to the local dielectric environment, plasmonic NPs can act as transducers that convert small changes in the local refractive index and the inter-particle distance into spectral shifts and broadening in the absorption spectra bands [3]. In our study, the prototypical biocytin-avidin interaction was used to study gradual changes with time in the absorption spectra bands of biotinylated 10 nm silver and gold NPs as a function of added avidin. After avidin addition, a SPR red-shift and a broadening of the SPR bands were observed with both NPs. These optical changes evolved with time and reached their final values after around 45 min for each system. The maximum SPR red-shifts were equal to 25 nm and 15 nm for silver NPs and gold NPs, respectively. The detection limit, described as the lowest concentration for clear identification of wavelength shift due to biomolecular recognition, is determined to be 4 nM for both silver and gold NPs. The specificity of the biocytin-avidin biosensors was checked by replacing avidin by BSA. When BSA was added, we observed a SPR band shift which was smaller than the detection limit of 3 nm, attesting the biosensor selectivity. Our work demonstrates the superiority of Ag over Au NPs for the elaboration of biosensors based on SPR

Metal-Organic Framework Nanoparticles in Photodynamic Therapy: Current Status and Perspectives

This feature article covers the recent applications of metal-organic framework nanoparticles (MOF NPs) in photodynamic therapy (PDT) of cancer. It aims at giving the reader an overview about these two current research fields, i.e., MOF and PDT, and at highlighting the potential synergistic effect that could result from their association. After describing the general photophysics and photochemistry that underlie PDT, the relationship between photosensitizer (PS) properties and PDT requirements is discussed throughout the PSs historical development. This development reveals the advantages of using nanotechnology platforms for the creation of the ideal PS and leads us to define the fourth generation of PSs, which includes NPs built from the PS itself as porphysomes or PS-based MOF NPs. Especially, the precise spatial control over the PS assembly into well-defined MOF NPs, which keeps the PS in its monomeric form and prevents PS self-quenching, appears as a notable feature to solve PS solubility and aggregation issues and therefore improves the PDT efficiency. Finally, we discuss the future perspectives of MOF NPs in PDT and shed light on how promising these nanomaterials are. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimCRA2015; DFG-project WU 622/4-