An ultrasmall chitosan nanosphere encapsulating carbon dots and rhodamine B as a ratiometric probe for the determination of Hg2.

Hg2+-sensitive carbon dots (CDs) were synthesized by microwave-assisted pyrolysis of citric acid, sodium fluoride, and urea. The CDs as a signal report unit and rhodamine B (RhB) as a reference were then encapsulated in a nanosphere of chitosan assembled by a nonsolvent-induced chitosan colloidal formation and in situ cross-linking to construct a ratiometric probe for Hg2+ (chitosan-CDs-RhB). Interestingly, without any assistance from acids to improve the solubility of chitosan, the nanosphere containing CDs and RhB had an ultrasmall size of 9.7 nm with only approximately 1.1-nm-thick layers of chitosan enclosing one dot. In order to keep the residual functional groups on the nanosphere from compromising the fluorescence response of CDs to Hg2+, Co2+ was used as a fluorescently intact metal ion to saturate the functional groups. The saturated chitosan-CDs-RhB was thus potentially developed for determining Hg2+ in the fruit bodies and mycelia of edible and medicinal fungi. Limits of detection (LODs) of 2.24, 5.29, and 2.03 µM and recoveries in the ranges 98.3 to 101.8%, 99.5 to 104.6%, and 97.4 to 100.9% were estimated for the determination of Hg2+ in the fruit bodies of Pleurotus ostreatus, Lentinus edodes, and Hypsizygus marmoreus, respectively. Chitosan-CDs-RhB was further developed as a fluorescent ratiometric probe for quantitatively determining intracellular Hg2+ in fungal mycelia with a linear calibration curve of RIgreen/Ired = - 0.145c + 1.69 within the range 0.013 to 0.356 µg g-1. Graphical abstract An ultrasmall chitosan nanosphere encapsulating carbon dots and rhodamine B as a ratiometric probe for the determination of Hg2+.

Saccharification of poplar biomass by using lignocellulases from Pholiota adiposa.

A basidiomycetous fungus, identified as Pholiota adiposa SKU0714 on the basis of morphological and phylogenetic analyses, was found to secrete efficient lignocellulose degrading enzymes. The strain showed maximum endoglucanase, cellobiohydrolase and ß-glucosidase activities of 26, 32 and 39 U/mL, respectively and also secreted xylanase, laccase, mannanase, and lignin peroxidase with activities of 1680, 0.12, 65 and 0.41 U/mL, respectively when grown with rice straw as a carbon source. Among the various plant biomasses tested for saccharification, poplar biomass produced the maximum amount of reducing sugar. Response surface methodology was used to optimize hydrolysis parameters. A maximum saccharification yield of 83.4% (667 mg/g-substrate), the highest yield from any plant biomass, was obtained with Populus biomass after 24h of hydrolysis. P. adiposa was proven to be a good choice for the production of reducing sugars from cellulosic biomass.