The construction of hierarchical nanoparticle assemblies with well-defined surface control and stability has captured enormous attention because of their fascinating coupled properties and enhanced interfacial ability useful for catalysis, biomedical, and sensing applications. Progressively, the present work here introduces the preparation progress of hierarchical multicomponent assembly particles in which multilayered nanoparticles and microparticles have been fabricated via electrostatic surface interaction. Various types of metal nanoparticles were uniformly deposited on the surfaces of charged/swellable polymer nanoparticles, and the further deposition of these composite nanoparticles has been selectively applied on the surfaces of hydrogel microparticles. The fabrication procedure is based on microfluidic technology, which provides the advantages of homogeneous size distribution of particles and highly precise interfacial interaction. Layer-by-layer technology was used to combine oppositely charged nanoparticles through electrostatic interaction. A potential catalysis application is investigated by the reductive bleaching of an azo dye by sodium borohydride. The results show that the reaction rate is enhanced by the effect of composite particles. Because this fabrication method and the fabricated assembly particles are robust, showing potential in heterogeneous catalysis, the other types of metal nanoparticles can also be loaded onto the polymer microparticles, which may provide a platform to explore novel applications in future needs.

Microbial community in soil is a complex and dynamic system. Using traditional culture experiments it is difficult to model the stochastic distribution of single organisms of microbial communities in the soil pore's structure. Droplet-based micro-segmented flow technique allows the transfer of the principle of stochastic confinement of stochastically reduced communities from soil micro pores into nanoliter droplets. Microfluidics was applied for the investigation and comparison of soil samples from ancient mining areas by highly resolved concentration-dependent screenings. As results, the generation, incubation, and in situ optical characterization of nanoliter droplets of suspensions of unknown soil microbial communities allowed the identification of different response characteristics toward heavy metal exposition. The investigations proved the high potential of microfluidics for investigations of soil microbial communities. It may be in the future helpful to detect bacteria and consortia with special biosorption characteristics, which could be useful for the development of biological accumulation and detoxification strategies.

This work introduces the investigation of three-layered metal/polymer/polymer hierarchically structured composite particles, prepared by a microfluidic synthesis method combined with layer-by-layer (LBL) technology. Composite particles made of multiple length scales ranging from nanometer to submicrometer and submilimeter, and their potential application in catalysis is shown. In the first part, with the advantage of microreaction technology, platinum nanoparticles of a precise size were synthesized and electrostatically combined to oppositely charged surface-active polymer nanoparticles. After controlling the nanoparticles ratio and metal density on the polymer surface, nanocomposite particles of high specific surface to volume ratio were immobilized on the surface of microfluidically prepared polyacrylamide hydrogel particles, in second part. Platinum nanoparticles offer the possibility to be used as potential catalysts. For further study, the catalytic activity of the obtained hierarchical metal-polymer composite particles was evaluated by bleaching an azo-dye (Cochenille Red) with sodium borohydride. Different experiments have been conducted in the absence as well as in the presence of the composite particles. It has been found that a significant enhancement of the bleaching rate was realized in case of platinum containing composite particles. (C) 2017 Elsevier B.V. All rights reserved.

Novel composite films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold (AuNP) and iridium (IrNP) nanoparticles possessing diameters of 12.5 and 2.7 nm, respectively. The electrochemical responses of fabricated composite films, further denoted as N-MWCNTs/MNPs (M: Au and Ir), toward ferrocyanide/ferricyanide, [Fe(CN)6]3−/4− redox couple was probed by means of cyclic voltammetry and electrochemical impedance spectroscopy techniques. The findings demonstrate that both N-MWCNT/MNP composite films exhibit greater electrochemical response and sensitivity toward [Fe(CN)6]3−/4− compared to unmodified N-MWCNTs. The results verify that the N-MWCNT/MNP composite films are extremely promising for application in electrochemical sensing.

Simultaneous oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in phosphate puffer solution (pH 7.0) on films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) decorated with 2.7 nm rhodium (RhNPs), 2.6 nm palladium (PdNPs), 2.7 nm iridium (IrNPs), 2.7 nm platinum (PtNPs), and 14 nm gold (AuNPs) nanoparticles show a lower limit of detection towards simultaneous oxidation of AA (7.9, 6.8, 6.1, 3.1, and 0.9 mu M, respectively), DA (1.1, 0.8, 0.7, 0.6, and 0.3 mu M, respectively), and UA (4.1, 3.6, 3.1, 2.1, 0.4 mu M, respectively). The findings demonstrate that the film's lower limit of detection towards simultaneous oxidation of AA, DA, and UA tends to decrease with the order: N-MWCNTs > N-MWCNTs/RhNPs > N-MWCNTs/PdNPs > N-MWCNTs/IrNPs > N-MWCNTs/PtNPs > NMWCNTs/AuNPs. The findings suggest that N-MWCNTs/MNPs can be considered as potential electrode material for electrochemical simultaneous analysis of AA, DA, and UA. (C) 2016 Elsevier B.V. All rights reserved.

The photochemical synthesis of gold nanoparticles was transferred into a three-step micro-continuous flow process. A solution of tetrachloroaurate and a solution of a photoinitiator and polyvinylpyrrolidone were mixed within micro-fluid segments using a cross-injector. The segments (0.5 mm inner diameter) pass a focused UV ray after a short mixing by means of segment-internal convection. The nucleation of nanoparticles was initiated by this exposure, which lasted 30–300 ms depending on the applied flow rate. The growth of nanoparticles was completed by the passage of a residence loop of a length of 0.5 m. The obtained colloidal product solution was characterized by UV/VIS spectrophotometry, centrifugal sedimentation spectroscopy, dynamic light scattering, and SEM/TEM. In result, small gold nanoparticles with enhanced quality, compared to photochemical batch experiments, were obtained. The particle size can be tuned by variation of the composition of reactant solutions or flow rate between 2.5 and 4 nm. The small gold nanoparticles are suitable for use as seed particles for the formation of larger particles with an adjustable diameter.

The photochemical synthesis of small metal nanoparticles (Pd, Pt, Rh, Ir) was transmitted into a micro segmented flow process to control all aspects of the reaction. Solutions of noble metal salt, a photoinitiator, and a stabilizer were combined in a cross mixer and transferred in micro fluid segments. The start and termination of the photoinitiation, and thus the reduction of the noble metal salt, are defined by the entrance and the exit of fluid segments into the UV-ray of the irradiation source. The time of irradiation can be controlled by the flow rate. As a result, noble metal nanoparticles with comparatively high size homogeneity were obtained. The small nanoparticles are suitable as seed particles for the formation of larger particles with adjustable diameter.

Nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapour deposition technique and decorated with platinum (PtNPs), palladium (PdNPs), rhodium (RhNPs) and silver (AgNPs) nanoparticles possessing diameter 2.7, 2.6, 2.7 and 3.4 nm, respectively. The electrochemical responses of composite films, further denoted as N-MWCNTs/MNPs (M: Pt, Pd, Rh and Ag) towards ferrocyanide/ferricyanide, [Fe(CN)6]3−/4− were investigated in large concentration range (0.099–0.990 mM) in potassium chloride solution (1.0 M). The findings demonstrate that the electrochemical response and sensitivity of N-MWCNTs are improved significantly upon modification with metal nanoparticles. A strong dependence of film’s electrochemical fineness on type of metal nanoparticles used for modification can be observed. Namely, the current response, the charge-transfer kinetics, and the detection capability of novel composite films enhance with the following order: N-MWCNTs < N-MWCNTs/RhNPs < N-MWCNTs/PdNPs < N-MWCNTs/PtNPs < N-MWCNTs/AgNPs. The findings demonstrate that the novel N-MWCNTs/MNPs composite films can be considered as powerful and useful materials for electrochemical sensing.