RSC Advances

Mattsson, Leena; Wegner, K. David; Hildebrandt, Niko; Soukka, Tero

doi: 10.1039/c5ra00397kpmid: N/A

Both upconverting nanoparticles (UCNPs) and semiconductor quantum dots (QDs) have revolutionized optical biosensing because of their unique photophysical properties. However, their outstanding photostability, near-infrared (NIR) excitability, and colour tunability have never been combined for homogeneous mix-and-measure FRET (Förster resonance energy transfer) biosensors that do not require any washing or separation steps. Here we demonstrate that UCNP-to-QD FRET systems can be used for rapid homogeneous bioassays, which are essential tools for clinical diagnostics. One of the main drawbacks of UCNPs for FRET, namely their very low photoluminescence (PL) quantum yields, was efficiently overcome by using QD FRET acceptors with very strong spectral overlap with the UCNP donors. This resulted in unrivalled Förster distances for UCNP-based FRET pairs of up to 6 nm. We could quantify the prototypical analyte biotin (vitamin H) at low nanomolar concentrations and steady-state and time-resolved PL analysis showed that UCNP-to-QD FRET was caused by streptavidin-to-biotin binding. Immediate applicability in biosensing was demonstrated by biotin replacement assays over a large concentration range with IC50 values between 8 nM and 250 nM and detection limits down to 5 nM. The high photostability of the double-nanoparticle biosensor, the NIR excitation of UCNPs for minimal autofluorescence, and the spectral multiplexing capability of QDs offer a large potential for spectroscopy and imaging-based biosensing beyond in vitro diagnostics.

Kumar, Vanish; Chopra, Aditi; Arora, Shweta; Yadav, Shriniwas; Kumar, Suresh; Kaur, Inderpreet

doi: 10.1039/c4ra12594kpmid: N/A

Sensing of urea is the key component in the diagnosis of kidney related diseases and milk adulteration. Until now, the methods developed for urea sensing are not easy to perform, and very little attention has been paid to commercialization of such sensors. Herein, for the first time we report the low cost graphene nanoplatelets (GNPlts) based sensing platform for urea. Specifically edge functionalized GNPlts are used for keeping graphitic activity of graphene planes intact. We have successfully sensed variable ranges of urea concentrations from 0.1–0.8 mg ml−1. The amperometeric characterization showed a linear variation in current as a function of urea concentration. The developed platform has a rapid response time of 15 s with good sensitivity (33 μA (mg ml−1)−1) and specificity. This developed nanoplatform could be highly beneficial for the development of an ultrasensitive, disposable, routine use sensor for urea.

Kaur, Navjot; Ali, Amjad

doi: 10.1039/c4ra14786cpmid: N/A

Molybdenum impregnated calcium oxide (Mo/CaO) was prepared via a wet impregnation method by varying Mo loading (1–5 wt%) and calcination temperature (300–800 °C). Powder X-ray diffraction study of the Mo/CaO catalyst supported the homogeneous doping of Mo in CaO as no peak corresponding to molybdenum oxide was obtained. The prepared catalyst was successfully employed for the ethanolysis of high free fatty acid (up to 18 wt%) containing vegetable oils with ethanol to give >99% fatty acid ethyl ester (FAEE) yield under the optimal reaction conditions of ethanol to oil molar ratio of 12 : 1, catalyst concentration of 5 wt% (catalyst/oil) and reaction temperature of 65 °C. The catalyst was recovered and reused five times without significant loss in its activity. The Koros–Nowak criterion test demonstrated that catalytic activity was independent from the mass transport phenomenon. Under optimized reaction conditions the activation energy (Ea) for Mo/CaO catalyzed ethanolysis was found to be 66.02 kJ mol−1. Thermodynamic activation parameters of the reactions were evaluated based on activation complex theory (ACT) and obtained values of ΔG‡ = 43.62 kJ mol−1, ΔH‡ = 64.10 kJ mol−1 and ΔS‡ = −60.58 J mol−1 K−1 supported an unspontaneous, endothermic and associative mechanism of reaction.

Zhang, Shuidong; Wang, Peng; Tan, Lingcao; Huang, Hanxiong; Jiang, Guo

doi: 10.1039/c4ra13114bpmid: N/A

Considering environmental protection and economic requirements, the use of recycled glass fiber reinforced flame retardant nylon 46 (RGFFRPA46) is of significant importance. In this work, the mechanical, thermal, rheological and flame retardant properties of the recycled RGFFRPA46 were evaluated by varying shear screws. To establish the relationship between the screw structure and the properties of RGFFRPA46, the carboxyl content (CC) and viscosity-average molecular weight () of PA46, the distribution and average length of glass fiber (L̄) and microscopic appearance of RGFFRPA46 were investigated. The results showed that the shear force resistance time of RGFFRPA46 increased with the increase of the shear strain and with the ratio of length to diameter of the used extruder. As a result, of PA46, L̄ and the percentage of glass fiber length (Vj), which was higher than critical length, decreased, whereas the CC of PA46 increased significantly. The mechanical and rheological properties were sensitive to these variations, particularly the decrease in impact, tensile, flexural strength and shear viscosity of RGFFRPA46. Furthermore, the influence of degradation on of PA46 and L̄ were negative to the thermal properties of RGFFRPA46 after extrusion. However, the flame retardant properties of RGFFRPA46 were independent of the degradation. All of them achieved a UL-94 V-0 classification, and passed the glow wire ignition temperature (775 °C) test along with LOI of 36.7%. When RGFFRPA46 was extruded by a single screw extruder with the lowest shear force, a decrease of only 5.8% was observed in mechanical properties with negligible reductions in thermal and flame retardant properties.

Huang, Chang-Bo; Huang, Junhai; Xu, Lin

doi: 10.1039/c4ra08337gpmid: N/A

A new naphthalimide-based fluorescent probe NPA for detection of nitric oxide (NO) is reported. NPA responds to NO quickly and shows a 25-fold fluorescence enhancement within 10 seconds. To the best of our knowledge, NPA exhibits the fastest detection rate for NO based on o-phenylenediamine receptor. Moreover, NPA can detect NO quantitatively in aqueous solution with an estimated detection limit of 0.87 × 10−8 M.

Bernardim, Barbara; Hardman-Baldwin, Andrea M.; Burtoloso, Antonio C. B.

doi: 10.1039/c4ra15670fpmid: N/A

The Wolff rearrangement is one of the best methods for chain homologation. However, it still suffers from many drawbacks with respect to its practical execution in the laboratory. We wish to demonstrate the use of commercial LED lamps as a sustainable alternative for the classic experimental protocols typically used for Wolff rearrangements.

Kong, Junhua; Yao, Xiayin; Wei, Yuefan; Zhao, Chenyang; Ang, Jia Ming; Lu, Xuehong

doi: 10.1039/c4ra16460apmid: N/A

In this work, highly mesoporous carbon nanofibers in free-standing mat form are successfully fabricated by single-spinneret electrospinning of polystyrene (PS) followed by coating the porous PS nanofibers via in situ polymerization of dopamine and subsequent annealing. The pores inside the nanofibers are mainly in the range of 10–50 nm and interconnected to each other, forming nanochannels. ZnFe2O4 crystals can then be grown from the nanofibers via a solution route. Strikingly, ZnFe2O4 nanoneedles are formed, which have diameter and length of about 8 nm and 70 nm, respectively, and are located evenly not only on the surface of the nanofibers but also inside the nanochannels. The ZnFe2O4/carbon composite nanofibers exhibit excellent cyclability and rate performance as anodes of lithium ion batteries (LIBs), in which the ZnFe2O4 nanoneedles are the major active component with normalized capacity of 1000–1700 mA h g−1 at 0.1 A g−1 and 560 mA h g−1 at 5 A g−1, respectively. The excellent properties can be ascribed to the very small diameter of the nanoneedles that ensures complete conversion reactions and alloying/de-alloying between Zn and lithium, the good contact of the nanoneedles with polydopamine-derived N-doped graphitic carbon that offer efficient electrical conduction, and the nanochannels that allow facile transport of the electrolyte and lithium ions.

Luo, Lin-Bao; Zhang, Shun-Hang; Lu, Rui; Sun, Wei; Fang, Qun-Ling; Wu, Chun-Yan; Hu, Ji-Gang; Wang, Li

doi: 10.1039/c4ra14096fpmid: N/A

Although significant progress has been achieved in the synthesis and doping of ZnTe nanostructures, it remains a major challenge to rationally tune their transport properties for nanodevice applications. In this work, p-type ZnTe nanowires (NWs) with tunable conductivity were synthesized by employing Ga/Ga2O3 as a dopant via a simple thermal evaporation method. Electrical measurements of back-gate metal-oxide field-effect-transistors based on a single NW revealed that when the Ga content in the ZnTe NWs increases from 1.3 to 5.1 and 8.7%, the hole mobility and hole concentration will increase from 0.0069 to 0.33 to 0.46 cm2 V−1 s−1, respectively. It was also found that the photodetector composed of a ZnTe:Ga NW/graphene Schottky diode exhibited high sensitivity to visible light illumination with an on/off ratio as high as 102 at reverse bias, with good reproducibility. The responsivity and detectivity were estimated to be 4.17 × 103 A W−1 and 3.19 × 1013 cm Hz1/2 W−1, higher than other ZnTe nanostructure based photodetectors. It is expected that the ZnTe:Ga NWs with controlled p-type conductivity are promising building blocks for fabricating high performance nano-optoelectronic devices in the future.

Ng, T. N.; Chen, X. Q.; Yeung, K. L.

doi: 10.1039/c4ra16679epmid: N/A

The precision by which the fluid mixing, flow pattern, and reaction can be manipulated in a flow-synthesis reactor enables the deliberate preparation of ordered mesoporous silicas (OMS) of controlled particle size (ca. 50 to 650 nm) and shapes (i.e., spheres and random), as well as complex microstructures (i.e., hollow spheres). Fluid mixing and flow pattern were generated using Tee- and slit interdigital micromixers under laminar and Taylor flow conditions, while hydrolysis reactions was governed by the alkoxide precursors (i.e. TEOS & TMOS) and temperature. The hollow OMS spheres can host molecules and clusters as demonstrated by the incorporation of ferrocene and iron nanoparticles.

Shen, Shi-Li; Zhang, Xiao-Fan; Bai, Su-Yun; Miao, Jun-Ying; Zhao, Bao-Xiang

doi: 10.1039/c4ra16398bpmid: N/A

In this study, a novel ratiometric pH probe RC1 was successfully developed. RC1 was constructed by integrating a coumarin fluorophore as a fluorescence resonance energy transfer (FRET) donor into a rhodamine B fluorophore as a FRET acceptor, which is associated with rhodamine B dyes possessing spirocyclic (non-fluorescent) and ring-opening (fluorescent) forms with response to pH. At weak basic pH, the photo-induced electron transfer (PET) process of the N atom of aromatic imino in the rhodamine moiety partly quenches the coumarin emission. At acidic pH, the PET process is gradually inhibited upon acidification, enhancing the fluorescence intensity of coumarin remarkably; at the same time, the spirolactam form of rhodamine changes to a ring-opening form followed by the FRET process between coumarin and rhodamine. Hence, the emission intensities of coumarin and the rhodamine moiety simultaneously increase along with the pH decrease. The sensing mechanism is an integration of the PET and FRET processes. Based on the ratios of fluorescence intensity at 583 nm and 470 nm (I583/I470), RC1 with a pKa of 3.21 could be used in the ratiometric detection of pH in the range 2.20–4.20 with high selectivity. Furthermore, it can be applied to visualize extreme acidity in bacteria. The results demonstrate that RC1 can serve as an ideal probe for extremely acidic pH levels with excellent biological significance.