Zhisong Lu

Layered graphene/quantum dots for photovoltaic devices.

To meet the increasing demand of clean energy the harvesting of electricity from solar incident photons with high efficiency at economically viable cost is needed. Quantum dot (QD) based solar cells are poised to play a leading role in this revolution owing to their potential in exceeding the Shockley–Queissar limit, their size-tuned optical response, and their efficient multiple carrier generation. 6] A major challenge in developing high-performance QD solar cells is the effective separation of photogenerated electron–hole pairs and the transfer of the electrons to the electrode. Strategies that have been tried include the introduction of nanomaterials with a suitable band energy as efficient acceptors. Carbon, an environmentally friendly and inexpensive material, exists in a variety of nanostructures ranging from insulator/semiconducting diamond to metallic/semimetallic graphite, conducting/semiconducting fullerenes, and single-walled carbon nanotubes (SWNTs), 10] and recently has been widely used in QD solar cells. Particularly, SWNTs 12] and stacked-cup carbon nanotubes have been used as efficient acceptors to enhance photoinduced charge transfer for improved performance because of their unique one-dimensional nanostructure and appropriate band energy. However, the efficiency of carbon nanomaterial based QD solar cells reported so far is still low (incident photon-to-charge-carrier conversion efficiency (IPCE) 5 % and photocurrent response 0.4 mAcm 2 under light illumination of 100 mWcm ), which is still some distance from the requirement for the next generation of solar cells. Graphene, a new class of two-dimensional carbon material with single-atom-thick layer features different from balllike C60 and one-dimensional carbon nanotubes, has attracted attention in recent years. As a result of its high specific surface area for a large interface, high mobility up to 10000 cm V 1 s , and tunable band gap, graphene should be a very promising electron acceptor in photovoltaic devices. In this work, a novel layered nanofilm of graphene/QDs was constructed from all aqueous solutions to fabricate a photovoltaic device using graphene as acceptor, demonstrating the best performance (IPCE of 16% and photoresponse of 1.08 mAcm 2 under light illumination of 100 mWcm ) in all reported carbon/QD solar cells. For a better understanding of the mechanism of the graphene in improving the performance of the device, the graphene/QDs and SWNT/QDs photovoltaic devices are compared. The fabrication of the layered graphene/QDs device is shown schematically in Figure 1. Chemically reduced graphene was used not only because of its unique properties

Nanostructured Polyaniline/Titanium Dioxide Composite Anode for Microbial Fuel Cells

A unique nanostructured polyaniline (PANI)/mesoporous TiO(2) composite was synthesized and explored as an anode in Escherichia coli microbial fuel cells (MFCs). The results of X-ray diffraction, morphology, and nitrogen adsorption-desorption studies demonstrate a networked nanostructure with uniform nanopore distribution and high specific surface area of the composite. The composite MFC anode was fabricated and its catalytic behavior investigated. Optimization of the anode shows that the composite with 30 wt % PANI gives the best bio- and electrocatalytic performance. A possible mechanism to explain the excellent performance is proposed. In comparison to previously reported work with E. coli MFCs, the composite anode delivers 2-fold higher power density (1495 mW/m(2)). Thus, it has great potential to be used as the anode for a high-power MFC and may also provide a new universal approach for improving different types of MFCs.

Mechanism of antimicrobial activity of CdTe quantum dots.

The antimicrobial activity and mechanism of CdTe quantum dots (QDs) against Escherichia coli were investigated in this report. Colony-forming capability assay and atomic force microscopy (AFM) images show that the QDs can effectively kill the bacteria in a concentration-dependent manner. Results of photoluminescence spectrophotometry, confocal microscopy, and antioxidative response tests indicate that the QDs bind with bacteria and impair the functions of a cells antioxidative system, including down-regulations of antioxidative genes and decreases of antioxidative enzymes activities. The oxidative damage of protein and lipid is also observed with thiobarbituric reacting substances and protein carbonyl assays, respectively. On the basis of these results, it is proposed that the mechanism of the antimicrobial activity of CdTe QDs involves QDs-bacteria association and a reactive oxygen species-mediated pathway. Thus, CdTe QDs could have the potential to be formulated as a novel antimicrobial material with excellent optical properties.

Direct electrochemistry and electrocatalytic mechanism of evolved Escherichia coli cells in microbial fuel cells

E. coli cells evolved under electrochemical tension in a microbial fuel cell possess direct electrochemical behavior due to the excretion of hydroquinone derivatives through a highly permeable outer membrane, and their catalyzed fuel cell demonstrates excellent performance.

Extracellular microbial synthesis of biocompatible CdTe quantum dots.

An efficient bacterial synthesis method to harvest cadmium telluride (CdTe) quantum dots (QDs) with tunable fluorescence emission using Escherichia coli is demonstrated. Ultraviolet-visible, photoluminescence, X-ray diffraction and transmission electron microscopy analysis confirmed the superior size-tunable optical properties, with fluorescence emission from 488 to 551 nm, and the good crystallinity of the as synthesized QDs. A surface protein capping layer was confirmed by hydrodynamic size, zeta potential and Fourier transform infrared spectroscopy measurements, which could maintain the viability (92.9%) of cells in an environment with a QD concentration as high as 2 microM. After functionalization with folic acid the QDs were used to image cultured cervical cancer cells in vitro. Investigations of bacterial growth and morphology and the biosynthesis of CdTe QDs in Luria-Bertani medium containing E. coli-secreted proteins showed that extracellular synthesis directly relied on the E. coli-secreted proteins, and a mechanism for protein-assisted biosynthesis of QDs is proposed. This work provides an economical approach to fabricate highly fluorescent biocompatible CdTe QDs via an environmentally friendly production process. The biosynthesized QDs may have great potential in broad bio-imaging and bio-labeling applications.

Effect of inhaled formaldehyde on learning and memory of mice

UNLABELLED In this study, we investigated the effect of inhaled formaldehyde on learning and memory capacity. After exposure to 0 (control), 1 and 3 mg/m(3) of gaseous formaldehyde respectively, the behavior of mice in a Morris water maze, the expression of NR1, NR2B mRNA and oxidative damage levels in mice brain were analyzed. The water maze performance, the activities of dismutase superoxide (SOD) and levels of glutathione (GSH) decreased significantly in 3 mg/m(3) group (P < 0.01, compared with control group); while malondialdehyde (MDA) contents and expression of NR1 and NR2B genes increased significantly after exposure to 3 mg/m(3) of gaseous formaldehyde (P < 0.05, <0.01, <0.01, compared with control group). These findings indicate that inhaled formaldehyde negatively affects learning and memory at 3 mg/m(3) of gaseous formaldehyde but not at lower levels. Oxidative stress-induced neuron damages in the brain may be the possible mechanism for these effects. PRACTICAL IMPLICATIONS This study indicates that inhaled formaldehyde starts to negatively affect learning and memory at a middle concentration of formaldehyde without interference of other indoor air pollutants. Oxidative damage, and the alteration of NMDA receptor expression, which were induced by formaldehyde inhalation, may be the possible mechanism for gaseous formaldehyde-induced neurotoxicity.

Polydopamine-functionalization of graphene oxide to enable dual signal amplification for sensitive surface plasmon resonance imaging detection of biomarker.

Surface plasmon resonance imaging (SPRi) is one of the powerful tools for immunoassays with advantages of label-free, real-time, and high-throughput; however, it often suffers from limited sensitivity. Herein we report a dual signal amplification strategy utilizing polydopamine (PDA) functionalization of reduced graphene oxide (PDA-rGO) nanosheets for sensitive SPRi immunoassay in serum. The PDA-rGO nanosheet is synthesized by oxidative polymerization of dopamine in a gentle alkaline solution in the presence of graphene oxide (GO) sheets and then is antibody-conjugated via a spontaneous reaction between the protein and the PDA component. In the dual amplification mode, the first signal comes from capture of the antibody-conjugated PDA-rGO to form sandwiched immunocomplexes on the SPRi chip, followed by a PDA-induced spontaneous gold reductive deposition on PDA-rGO to further enhance the SPRi signal. The detection limit as low as 500 pg mL(-1) is achieved on a nonfouling SPRi chip with high specificity and a wide dynamic range for a model biomarker, carcinoembryonic antigen (CEA) in 10% human serum.

Aptamer induced assembly of fluorescent nitrogen-doped carbon dots on gold nanoparticles for sensitive detection of AFB1.

Novel fluorescent nitrogen-doped carbon dots (N,C-dots) were synthesized and assembled on aptamer modified gold nanoparticles (Aptamer/AuNPs) for the super sensitive detection of aflatoxin B1 (AFB1). Positively charged N,C-dots were synthesized by the hydrothermal treatment of pancreatin. The prepared N,C-dots were assembled on aptamer/AuNPs by electrostatic interactions. The fluorescence of the N,C-dots was efficiently quenched. When AFB1 was added to the assay solution, specific interactions between AFB1 and the aptamer caused release of the N,C-dots. The fluorescence of the N,C-dots recovered and the intensity increase could be used to calculate the amount of AFB1 added. The assay exhibits super-high sensitivity with a detection limit of 5 pg/mL (16 pM) and a wide range of linear response of 5 pg/mL to 2.00 ng/mL. A novel aptasensor is thus successfully constructed, it provides an efficient way for sensitive AFB1 sensing as well as a new technique for aptamer based novel sensor construction.

One-step aqueous synthesis of graphene–CdTe quantum dot-composed nanosheet and its enhanced photoresponses

Although CdTe nanocrystal has been applied in quantum dot (QD)-based solar cells, there is no report on a graphene-CdTe QD hybrid system and its photoresponses. In this work, graphene-CdTe QD composed nanosheets were one-step synthesized in aqueous solution using a hydrothermal method and demonstrated enhanced photoresponses, rendering potentials in optoelectronics applications. This work could provide an environmental-friendly and universal approach to fabricate graphene-based hybrid nanomaterials for various applications.

Sensitive human interleukin 5 impedimetric sensor based on polypyrrole-pyrrolepropylic acid-gold nanocomposite.

A sensitive impedimetric immunosensor was constructed by using an electropolymerized nanocomposite film containing polypyrrole (PPy), polypyrrolepropylic acid (PPa), and Au nanoparticles. The nanocomposite exhibits good stability, high porosity, high hydrophilicity, and efficient probe immobilization capability. In the film, PPa enhances the hydrophilicity while providing covalent probe attachment linkers, PPy promotes the conductivity and electroactivity, and Au nanoparticles result in good conductivity, high stability, and covalent binding linkers. These combined advantages significantly improve the detection sensitivity in comparison to the conventional methods. As a model, a human interleukin 5 (IL-5) immunosensor, an important sensor for disease pathology study, clinic diagnosis, and pharmaceutical research, was fabricated with the new nanocomposite film. Various optimization works were conducted to improve the detection sensitivity. With the optimal fabrication parameters, the detection limit for IL-5 was 10 fg/mL in phosphate buffered saline (PBS) and 1 pg/mL in 1% human serum with good specificity and a dynamic range of 3 orders of magnitude. This work demonstrates a new approach to develop a sensitive and labeless impedimetric immunosensor for potential broad applications in clinical diagnosis and drug discovery.