We present an integrated, compact, lab on a chip (LoC) platform and protocol for rapid pathogen analysis in food samples. The proposed LoC is based on an oxygen plasma nanotextured polymeric chip combining in one microfluidic chamber bacteria immunoaffinity capturing on the chip surface, chemical lysis and DNA isothermal amplification, followed by label-free detection with a Surface Acoustic Wave (SAW) biosensor. The proposed operation protocol includes: 1) a short (3 h) off-chip pre-culturing step, starting from 1 to 5 CFUs in only 25 ml of spiked fresh or pasteurized milk, followed by a brief centrifugation step for concentration of the 25 ml down to 100 mu l, and, 2) injection of the preconcentrated sample on chip for automated bacterial capture, lysis, DNA amplification and acoustic detection. The sample-to-answer analysis time was less than 4.5 h, which is at least 5-times faster compared to conventional methods. Label-free detection of four different bacteria Salmonella, B. cereus, Listeria and E. coli in milk is demonstrated with minimal off chip handling and record fast analysis time.

In this work, the utilization of graphene oxide (GO), reduced graphene oxide (rGO), and carbon nanotube (CNT) thin films as hole transport and electron-blocking layers in polymer/nanocrystal hybrid solar cells is demonstrated. A simple method has been used to modify the anode of hybrid solar cells by depositing these two solution-processable nanocarbon materials between poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and transparent indium tin oxide (ITO) layers. Upon the use of an rGO interlayer, we found a substantial improvement in power conversion efficiency (PCE) from 2.5% to 3.2% due to a decrease in series resistance (Rs). This decrease has been obtained by a careful tuning of the reduction degree of rGO, inducing optimization of the energy band alignment at the solar cell anode. In addition, charge extraction by linearly increasing voltage (CELIV) measurements show an increase in light-induced charge extraction of ca. 50%. Finally, the utilization of rGO as replacement for PEDOT:PSS is also presented. The findings reported in this work demonstrate the excellent potential of rGO as an efficient hole transport material in hybrid solar cells.

Strict regulations govern food safety as the latter is of extremely high importance and a major public issue, while it is demanding in respect of analytical effort. The duration of common food analysis practices is typically 2-5 days. Microfluidics can reduce labor and analysis time to a few hours, proving its beneficial use and rendering the response of food industry as well as public safety agents faster. The aim of the present work is the fabrication and evaluation of a modular integrated Lab-on-Chip platform for sample preparation, accommodating bacteria capture, thermal lysis, DNA purification, and isothermal DNA amplification, addressing pathogen screening in milk samples for cell lysates corresponding to < 500 cells. We note that individual modules have been tested to work down to 10 cells.

The fast and efficient detection of foodborne pathogens is a societal priority, given the large number of food-poisoning outbreaks, and a scientific and technological challenge, given the need to detect as little as 1 viable cell in 25 gr of food. Here, we present the first approach that achieves the above goal, thanks to the use of a micro/nano-technology and the detection capability of acoustic wave sensors. Starting from 1 Salmonella cell in 25 ml of milk, we employ immuno-magnetic beads to capture cells after only 3 h of pre-enrichment and subsequently demonstrate efficient DNA amplification using the Loop Mediated Isothermal Amplification method (LAMP) and acoustic detection in an integrated platform, within an additional ½ h. The demonstrated 4 h sample-to-analysis time comes as a huge improvement to the current need of few days to obtain the same result. In addition, the work presents the first reported Lab-on-Chip platform that comprises an acoustic device as the sensing element, exhibiting impressive analytical features, namely, an acoustic limit of detection of 2 cells/μl or 3 aM of the DNA target and ability to detect in a label-free manner dsDNA amplicons in impure samples. The use of food samples together with the incorporation of the necessary pre-enrichment step and ability for multiple analysis with an internal control, make the proposed methodology highly relevant to real-world applications. Moreover, the work suggests that acoustic wave devices can be used as an attractive alternative to electrochemical sensors in integrated platforms for applications in food safety and the point-of-care diagnostics.

The development of integrated platforms incorporating an acoustic device as the detection element requires addressing simultaneously several challenges of technological and scientific nature. The present work was focused on the design of a microfluidic module, which, combined with a dual or array type Love wave acoustic chip could be applied to biomedical applications and molecular diagnostics. Based on a systematic study we optimized the mechanics of the flow cell attachment and the sealing material so that fluidic interfacing/encapsulation would impose minimal losses to the acoustic wave. We have also investigated combinations of operating frequencies with waveguide materials and thicknesses for maximum sensitivity during the detection of protein and DNA biomarkers. Within our investigations neutravidin was used as a model protein biomarker and unpurified PCR amplified Salmonella DNA as the model genetic target. Our results clearly indicate the need for experimental verification of the optimum engineering and analytical parameters, in order to develop commercially viable systems for integrated analysis. The good reproducibility of the signal together with the ability of the array biochip to detect multiple samples hold promise for the future use of the integrated system in a Lab-on-a-Chip platform for application to molecular diagnostics.

In this publication we show that the procedure to synthesize nanocrystals and the post-synthetic nanocrystal ligand sphere treatment have a great influence not only on the immediate performance of hybrid bulk heterojunction solar cells, but also on their thermal, long-term, and air stability. We herein demonstrate this for the particular case of spherical CdSe nanocrystals, post-synthetically treated with a hexanoic acid based treatment. We observe an influence from the duration of this post-synthetic treatment on the nanocrystal ligand sphere size, and also on the solar cell performance. By tuning the post-synthetic treatment to a certain degree, optimal device performance can be achieved. Moreover, we show how to effectively adapt the post-synthetic nanocrystal treatment protocol to different nanocrystal synthesis batches, hence increasing the reproducibility of hybrid nanocrystal:polymer bulk-heterojunction solar cells, which usually suffers due to the fluctuations in nanocrystal quality of different synthesis batches and synthesis procedures.

We present a significant efficiency enhancement of hybrid bulk heterojunction solar cells by utilizing CdSe quantum dots attached to reduced graphene oxide (rGO) as the electron accepting phase, blended with the PCPDTBT polymer. The quantum dot attachment to rGO was achieved following a self-assembly approach, recently developed, using thiolated reduced graphene oxide (TrGO) to form a TrGO-CdSe nanocomposite. Therefore, we are able to obtain TrGO-CdSe quantum dot/PCPDTBT bulk-heterojunction hybrid solar cells with power conversion efficiencies of up to 4.2%, compared with up to 3% for CdSe quantum dot/PCPDTBT devices. The improvement is mainly due to an increase of the open-circuit voltage from 0.55 V to 0.72 V. We found evidence for a significant change in the heterojunction donor-acceptor blend nanomorphology, observable by a more vertical alignment of the TrGO-quantum dot nanocomposites in the z-direction and a different nanophase separation in the x-y direction compared to the quantum dot only containing device. Moreover, an improved charge extraction and trap state reduction were observed for TrGO containing hybrid solar cells.

Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

In this work, the synthesis and characterization of thiol functionalized reduced graphene oxide (TrGO) as a novel base material for the generation of graphene-nanoparticle hybrid materials is reported. TrGO was directly synthesized by refluxing graphene oxide (GO) with phosphorus pentasulfide (P4S10). The introduction of sulfur containing chemical groups and the partial reduction of GO to TrGO were proven by UV–Vis, XPS and FTIR spectroscopy. CdSe nanocrystal-TrGO (CdSe-TrGO) as well as silver nanoparticle-TrGO (Ag-TrGO) hybrid materials are achieved by attachment of the respective nanoparticles to the thiol groups of the graphene using self-assembly decoration. The resulting hybrid materials were investigated by TEM and photoluminescence quenching experiments.

This chapter contains sections titled: Introduction Composite Materials Device Structure State of the Art of Hybrid Solar Cells Novel Approaches in Hybrid Solar Cell Development Outlook and Perspectives References

We report on the efficiency enhancement for bulk-heterojunction hybrid solar cells based on hexanoic acid treated trioctylphosphine/oleic acid-capped CdSe quantum dots (QDs) and low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) compared to devices based on poly(3-hexylthiophene) (P3HT). Photovoltaic devices with optimized polymer:QD weight ratio, photoactive film thickness, thermal annealing treatment, and cathode materials exhibited a power conversion efficiency of 2.7% after spectral mismatch correction, which is the highest reported value for spherical CdSe QD based photovoltaic devices. The efficiency enhancement is attributed to the surface treatment of the QDs together with the use of the low bandgap polymer PCPDTBT leading to an increased short-circuit current density due to additional light absorption between 650 and 850 nm. Our results suggest that the hexanoic acid treatment is generally applicable to various ligand-capped CdSe and confirm that low bandgap polymers with adequate HOMO and LUMO levels are promising to be incorporated into hybrid solar cells for further device performance improvement.

Inorganic‐organic hybrid films can act as photoactive layers in hybrid solar cells. The state of the art development of hybrid solar cells is briefly described and compared to other photovoltaic technologies in respect of device performance and regarding their potential for future use in applications.

We demonstrate the importance of the nanocrystal surface treatment and the inorganic composition for hybrid solar cells. Mixtures of CdSe nanorods and CdSe quantum dots integrated in hybrid solar cells together with the conjugated polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) perform better than nanorod and quantum dot only based devices. In addition larger sized quantum dots show a similar improvement after integration in respective solar cells. Power conversion efficiency values exceeding 3% are observed. A first result on the shelf lifetime of such a device is highlighted.

The interfacial charge transfer recombination processes under working conditions that limit the device performance in polymer:CdSe quantum dot bulk heterojunction hybrid solar cells have been measured. The recombination lifetimes for electrons and holes in the device show an exponential dependence in a similar way to that observed for other molecular based solar cells such as bulk heterojunction organic solar cells (OSC) and dye sensitized solar cells (DSSC). The implications of this unprecedented observation on the design of novel devices are discussed as well as the relationship between the charge accumulation in these devices under operation and the device open-circuit voltage.

Novel photovoltaic (PV) technologies are currently investigated and evaluated as approaches to contribute to a more environmental friendly energy supply in many countries. One of the driving forces are the aims to reduce the emission of green house gases and the dependency on importing fossil energy resources from political unstable countries. Additionally the wish to replace nuclear power by greener and less threatening technologies will enhance the development of regenerative energy supply in many countries especially after the recent nuclear catastrophe at Fukushima nuclear power plant in Japan in March 2011. This will include the more rapid implementation of existing mature PV technologies but also the development and improvement of novel PV approaches such as organic PV (OPV) and dye-sensitized solar cells (DSSCs) together with new efficient strategies for energy storage and distribution to make electric power, deriving from PVs, available whenever and wherever it is needed. The so-called 1st generation of solar cells based on e.g. bulk crystalline and polycrystalline silicon is still dominating the PV market. However, so-called 2nd generation solar cells mainly consisting out of thin film solar cells based on CdTe, Copper Indium Gallium Selenide (CIGS), and amorphous silicon gained distribution of ca. 25% in market share today worldwide. It is expected that this number will increase significantly within the next years. While for the 1st and 2nd generation solar cells commercial solar panels are available with decent power conversion efficiencies (PCEs) and lifetimes, the emerging 3rd generation solar cells such as OPV and DSSCs technologies are still in the development phase. Some commercially available products have recently entered the market such as e.g. solar bags representing niche products, which are so far not suitable for competing with traditional large scale applications of solar panels of the 1st and 2nd generations. In traditional solar panels the differences between best solar cell and average solar cell efficiencies are much smaller than for the emerging solar cell technologies with the consequence that modules of 3rd generation solar cells still suffer from too low performance. In Table 1 the best cell and module efficiencies of different PV technologies are compared. It has to be mentioned that especially for the emerging new PV technologies the average efficiencies are significantly lower than the results of the best cells.

Emerging alternative photovoltaic technologies such as dye sensitized solar cells (DSSCs) and organic solar cells (OSCs) have recently gained much attention as well as maturity and are on the step of being commercialized. Bulk heterojunction hybrid solar cells containing inorganic nanoparticles and semiconducting polymers are still lagging behind in respect of device performance although they have theoretically the potential to exhibit better performances than devices containing solely organic compounds. In this article we review the recent state of the art development of bulk heterojunction hybrid solar cells. Critical factors limiting the solar cell device performance are highlighted and strategies for further device improvement are demonstrated by giving recent examples from literature.

In this paper we present a new concept of creating and using capillary pressure gradients for passive degassing and passive methanol supply in direct methanol fuel cells (DMFCs). An anode flow field consisting of parallel tapered channels structures is applied to achieve the passive supply mechanism. The flow is propelled by the surface forces of deformed CO 2 bubbles, generated as a reaction product during DMFC operation. This work focuses on studying the influence of channel geometry and surface properties on the capillary-induced liquid flow rates at various bubbly gas flow rates. Besides the aspect ratios and opening angles of the tapered channels, the static contact angle as well as the effect of contact angle hysteresis has been identified to significantly influence the liquid flow rates induced by capillary forces at the bubble menisci. Applying the novel concept, we show that the liquid flow rates are up to thirteen times higher than the methanol oxidation reaction on the anode requires. Experimental results are presented that demonstrate the continuous passive operation of a DMFC for more than 15 h.