Urease immobilized fluorescent gold nanoparticles for urea sensing.

We report a surfactant-free synthesis of monodispersed gold nanoparticles (AuNPs) with average size of 15 nm. An approach for visual and fluorescent sensing of urea in aqueous solution based on shift in surface plasmon band (SPB) maxima as well as quench in fluorescence intensity. To enable the urea detection, we functionalized the thiol-capped gold nanoparticles with urease, the enzyme specific to urea using carbodiimide chemistry. The visible color changed of the gold colloidal solution from red to blue (or purple); this was evident from quenching in absorbance and fluorescence intensity, is the principle applied here for the sensing of urea. The solution turns blue when the urea concentration exceeds 8 mg/dL which reveals visual lower detection limit. The lower detection limits governed by the fluorescence quenching were found 5 mg/dL (R(2) = 0.99) which is highly sensitive and selective compared to shift in SPB maxima. The approach depicted here seems to be important in clinical diagnosis.

Graphene oxide-based biosensor for food toxin detection.

We report results of the studies relating to the fabrication of a highly sensitive label free biosensor based on graphene oxide (GO) platform for the detection of aflatoxin B1 (AFB1) which is most toxic and predominant food toxin, using electrochemical impedance spectroscopy. The structural and optical characterization of GO/Au and anti-AFB1/GO/Au has been done by electron microscopy, Raman, X-ray diffraction (XRD), UV-vis and electrochemical impedance spectroscopy (EIS). The impedimetric sensing response of immunoelectrode as a function of AFB1 concentration reveals wider linear detection range (0.5-5 ng/ml), high sensitivity (639 Ω ng(-1) ml), improved detection limit (0.23 ng ml(-1)) and good stability (5 weeks) for the label-free detection. Association constant (k a) for antigen-antibody interaction obtained as 0.46 ng ml(-1) indicates high affinity.

Study of mechanism of enhanced antibacterial activity by green synthesis of silver nanoparticles.

The extensive use of silver nanoparticles needs a synthesis process that is greener without compromising their properties. The present study describes a novel green synthesis of silver nanoparticles using Guava (Psidium guajava) leaf extract. In order to compare with the conventionally synthesized ones, we also prepared Ag-NPs by chemical reduction. Their optical and morphological characteristics were thoroughly investigated and tested for their antibacterial properties on Escherichia coli. The green synthesized silver nanoparticles showed better antibacterial properties than their chemical counterparts even though there was not much difference between their morphologies. Fourier transform infrared (FTIR) spectroscopic analysis of the used extract and as-synthesized silver nanoparticles suggests the possible reduction of Ag(+) by the water-soluble ingredients of the guava leaf like tannins, eugenol and flavonoids. The possible reaction mechanism for the reduction of Ag(+) has been proposed and discussed. The time-dependent electron micrographs and the simulation studies indicated that a physical interaction between the silver nanoparticles and the bacterial cell membrane may be responsible for this effect. Based on the findings, it seems very reasonable to believe that this greener way of synthesizing silver nanoparticles is not just an environmentally viable technique but it also opens up scope to improve their antibacterial properties.

Single step synthesis of graphene nanoribbons by catalyst particle size dependent cutting of multiwalled carbon nanotubes.

Graphene nanoribbons are emerging as an interesting material for the study of low dimensional physics and for the applications in future electronics due to its finite energy band gap. However, its applicability for large scale nanoelectronics may not be effectively realized unless graphene nanoribbons could be produced using a simple, viable, cost-effective and scalable technique. Here, we report the one step facile synthesis of few layered graphene nanoribbons (GNRs) by catalytically unzipping multi-walled carbon nanotubes (MWCNTs) based on the solubility of carbon atoms in transition metals. The process is free from aggressive oxidants (such as KMnO(4), KClO(4), H(2)SO(4), HNO(3), etc.) and utilizes the in situ grown nickel nanoparticles for nanotube unzipping. This is an additional advantage over previously used techniques to synthesize GNRs. To observe the effect of catalyst particle size and reaction temperature on cutting length of the nanotubes, a simulation study has been done based on solubility of carbon atoms in metal nanoparticles.