The presence of microorganisms, such as Escherichia coli, Salmonella, Listeria, and Vibrio, in food can be a serious threat to health, especially for infants, the elderly, and immunodeficient patients. The most reliable and accurate method for detecting food-borne pathogens is the conventional culture method, which includes a culture process and phenotypic or metabolic fingerprinting. [1] However, this method has the drawbacks that it is labor-intensive and requires at least 1-2 days to identify the pathogen(s). Therefore, researchers are looking for new methods that are fast, inexpensive, lightweight, and highly sensitive. Nanotechnology combined with biotechnology could potentially form the basis for such a method, and there have been efforts to develop fast and ultrasensitive nanosensors that can detect pathogens. To date, various platforms for pathogen detection have been developed, including metallic striped nanowires, [2] fluorescent nanobarcodes, [3] nanoparticles, [4,5] nanoelectromechanical systems (NEMs), [6] and microfluidic modules. [7,8] Herein, we demonstrate a screening tool for microorganisms such as E. coli, based on aptamer-functionalized single-walled carbon-nanotube field-effect transistor (SWNT-FET) arrays combined with the most probable number (MPN) method. Nanoscale biosensors based on FETs have been shown to be sufficiently sensitive to detect single viruses, [9] tumor-specific antigens, [10,11] and small molecules. [12] Moreover, in a previous study we showed that aptamer-functionalized SWNT-FET sensors can be used as sensitive, recyclable biosensors. [13] Nanosensors require only very small sample volumes (on the order of microliters), a characteristic that is advantageous in many instances but which can be a problem for inhomogeneous samples. Specifically, the probability that a collection of microorganisms in water will be distributed perfectly uniformly throughout the solution is very low. For example, if a 1-mL solution contains 10 3 E. coli cells, it does not necessarily mean that every 1-mL aliquot of the solution contains a single cell; rather, some aliquots will contain more than one cell, and others will not contain any cells. Thus, although each aliquot contains a single E. coli cell on average, there is a high possibility of recording a false signal if only a small volume of the solution is sampled. Microfluidic channels combined with nanosensors can solve this problem to some extent, but the volumes used are too small to avoid statistical errors. Moreover, motile bacteria such as E. coli can move at % 20 mm s À1 in a favorable medium, [14] which increases the difficulty of detecting these microorganisms using sensors with nanometer-sized sensing areas.Microbiologists have solved this problem by using a simple method called MPN. [15] First developed in 1933, MPN is still considered to be an important technique in estimating microbial populations in soils, waters, the food industry, etc. In MPN, to determine the cell titer in a particular solution, that solution is diluted at l...

BackgroundMetabolic engineering of cyanobacteria has enabled photosynthetic conversion of CO2 to value-added chemicals as bio-solar cell factories. However, the production levels of isoprenoids in engineered cyanobacteria were quite low, compared to other microbial hosts. Therefore, modular optimization of multiple gene expressions for metabolic engineering of cyanobacteria is required for the production of farnesyl diphosphate-derived isoprenoids from CO2.ResultsHere, we engineered Synechococcus elongatus PCC 7942 with modular metabolic pathways consisting of the methylerythritol phosphate pathway enzymes and the amorphadiene synthase for production of amorpha-4,11-diene, resulting in significantly increased levels (23-fold) of amorpha-4,11-diene (19.8 mg/L) in the best strain relative to a parental strain. Replacing amorphadiene synthase with squalene synthase led to the synthesis of a high amount of squalene (4.98 mg/L/OD730). Overexpression of farnesyl diphosphate synthase is the most critical factor for the significant production, whereas overexpression of 1-deoxy-d-xylulose 5-phosphate reductase is detrimental to the cell growth and the production. Additionally, the cyanobacterial growth inhibition was alleviated by expressing a terpene synthase in S. elongatus PCC 7942 strain with the optimized MEP pathway only (SeHL33).ConclusionsThis is the first demonstration of photosynthetic production of amorpha-4,11-diene from CO2 in cyanobacteria and production of squalene in S. elongatus PCC 7942. Our optimized modular OverMEP strain (SeHL33) with either co-expression of ADS or SQS demonstrated the highest production levels of amorpha-4,11-diene and squalene, which could expand the list of farnesyl diphosphate-derived isoprenoids from CO2 as bio-solar cell factories.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0617-8) contains supplementary material, which is available to authorized users.

Active manipulation of light in optical fibres has been extensively studied with great interest because of its compatibility with diverse fibre-optic systems. While graphene exhibits a strong electro-optic effect originating from its gapless Dirac-fermionic band structure, electric control of all-fibre graphene devices remains still highly challenging. Here we report electrically manipulable in-line graphene devices by integrating graphene-based field effect transistors on a side-polished fibre. Ion liquid used in the present work critically acts both as an efficient gating medium with wide electrochemical windows and transparent over-cladding facilitating light–matter interaction. Combined study of unique features in gate-variable electrical transport and optical transition at monolayer and randomly stacked multilayer graphene reveals that the device exhibits significant optical transmission change (>90%) with high efficiency-loss figure of merit. This subsequently modifies nonlinear saturable absorption characteristics of the device, enabling electrically tunable fibre laser at various operational regimes. The proposed device will open promising way for actively controlled optoelectronic and nonlinear photonic devices in all-fibre platform with greatly enhanced graphene–light interaction.

Here, we report that Nb doping of two-dimensional (2D) MoSe layered nanomaterials is a promising approach to improve their gas sensing performance. In this study, Nb atoms were incorporated into a 2D MoSe host matrix, and the Nb doping concentration could be precisely controlled by varying the number of NbO deposition cycles in the plasma enhanced atomic layer deposition process. At relatively low Nb dopant concentrations, MoSe showed enhanced device durability as well as NO gas response, attributed to its small grains and stabilized grain boundaries. Meanwhile, an increase in the Nb doping concentration deteriorated the NO gas response. This might be attributed to a considerable increase in the number of metallic NbSe regions, which do not respond to gas molecules. This novel method of doping 2D transition metal dichalcogenide-based nanomaterials with metal atoms is a promising approach to improve the performance such as stability and gas response of 2D gas sensors.

Single‐walled carbon‐nanotube absorbers are experimentally demonstrated for laser mode‐locking. A saturable absorber device is used to mode‐lock three different bulk solid‐state lasers in a 500 nm‐wide wavelength interval. The devices exhibit a low saturation fluence of <10 µJ cm−2, low scattering losses, and an exceptionally rapid relaxation, with time constants reaching <100 fs. The latter two properties are explained by a decreased curling tendency and increased tube‐to‐tube interactions of the nanotubes, respectively. These properties are the result of an optimized manufacturing procedure in combination with the use of a starting material with a higher microscopic order. The decreased scattering enables universal use of these devices in bulk solid‐state lasers, which tend to be highly sensitive against non‐saturable device losses as caused by scattering. The favorable saturable absorption properties are experimentally verified by mode‐locking the three lasers, which all exhibit near transform‐limited performance with about 100 fs pulse duration. The complete and unconditional absence of Q‐switching side bands verifies the small saturation fluence of these devices.

Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1-xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices.

Stable and self-starting mode-locking of a Tm:KLu(WO(4))(2) crystal laser is demonstrated using a transmission-type single-walled carbon nanotube (SWCNT) based saturable absorber (SA). These experiments in the 2 microm regime utilize the E11 transition of the SWCNTs for nonlinear saturable absorption. The recovery time of the SWCNT-SA is measured by pump-probe measurements as approximately 1.2 ps. The mode-locked laser delivers approximately 10 ps pulses near 1.95 microm with a maximum output power of up to 240 mW at 126 MHz repetition rate.

High-quality monolayer graphene as large as 1.2×1.2 cm² was synthesized by chemical vapor deposition and used as a transmitting saturable absorber for efficient passive mode-locking of a femtosecond bulk solid-state laser. The monolayer graphene mode-locked Cr:forsterite laser was tunable around 1.25 μm and delivered sub-100 fs pulses with output powers up to 230 mW. The nonlinear optical characteristics of the monolayer graphene saturable absorber and the mode-locked operation were then compared with the case of the bilayer graphene saturable absorber.