Synthesis And Applications Of Gold Nanoparticles Supported By Modified Yeast Cells

Gold nanoparticles ?AuNPs? have been widely used in the fields of analysis, biological medicine, catalysis and environmental pollutant treatment duo to its unique physicochemical properoties and biocompatibility. S. cerevisiae supported gold nanoparticles ?Au@SC? was green synthesized by the reduction of chloroauric acid with modified yeast cells as stabilizer and reductant in the presence of sodium hydroxide. The prepared Au@SC was characterized by X-ray diffraction pattern ?XRD? and UV-Vis spectroscopy. The optimum synthesis conditions of Au@SC were obtained by maximizing the catalytic efficiency of Au@SC in the 4-nitrophenol ?4-NP? reduction. The application of this prepared Au@SC in the catalytic reduction of 4-NP and the dechlorination of 2,4-dichlorophenol ?2,4-DCP?, as well as in the detection of trace Cu²⁺ in food, were investigated also. The results are as follows:?1? The influence of synthesis condition on the particle size of AuNPs and the catalytic efficiency of Au@SC in the reduction of 4-NP were investigated. These synthesis conditions include the modification of yeast cells, the dosage of yeasts, the concentration of HAuCl4 and NaOH, the temperature as well as the reaction time. The results show that the synthesis of Au@SC is much more rapid with the modification of yeast cells as compared to that of the untreated yeasts, and lead to a smaller AuNPs particle size and a higher catalytic efficiency in the reducing of 4-NP. The most effective Au@SC will synthesized by adding 20.0 mg of modified yeast cells in the solution of 1.67 mmol·L^-1 HAuCl4 and 500 mmol·L^-1 NaOH, and the reaction will conducted for 24 h at 37 ?.?2? The effects of the Au@SC dosage, the NaBH₄ concentration, the temperature, the ionic strength as well as the initial 4-NP concentration on the reduction of 4-NP were investigated. The results show that the reduction of 4-NP catalyzed by Au@SC follows pseudo-first-order kinetic model with a maximum rate constant of 1.6960 min-1 for the 0.1 mmol·L^-1 of 4-NP under the optimum conditions. This optimum catalytic reduction of 4-NP by NaBH₄ is done with 1.4 mg Au@SC added in 6.0 mmol·L^-1 NaBH₄ under 45 ?. The existence of NaCl will decrease the reduction ratio of 4-NP. The efficiency of Au@SC to reduce 4-NP decreases with the increases of recycle, and the reduction ratio of 4-NP decreases from 100%?within 21 min? to 10%?within 720 min? when the Au@SC is used the third recycle under the optimum conductions.?3? The dechlorination degradation of 2,4-DCP catalyzed by Au@SC follows pseudo-first-order kinetic model with a maximum rate constant of 0.0205 h-1 for the 0.01 mmol·L^-1 of 2,4-DCP under the optimum condition. This optimum catalytic dechlorination of 2,4-DCP by NaBH₄ is done with 1.0 mg Au@SC added in the mixture of 125 mmol·L^-1 NaBH₄ and 25 mmol·L^-1 NaOH under 40 ?. The efficiency of Au@SC to dechlorinate 2, 4-DCP decreases with the increases of recycle, and the dechlorination ratio of 2,4-DCP decreases from 80% to 2% when the Au@SC is used the fourth recycle under the optimum conductions.?4? The maximum fluorescence quenching of AuNPs induced by Cu²⁺ is obtained when the reaction is conducted in 50 mmol·L^-1 PBS solution ?pH 11.5? for 30 minutes. The results indicate that the quenched fluorescence of AuNPs is linearly proportional to the concentration of Cu²⁺ ranging from 0.001 ?g·mL^-1 to 0.2 ?g·mL^-1. The accuracy and precision of the developed method meet the requirements of food analysis, and has been successfully applied in the detection of copper ion in rice and dried tofu with a relative error of -4.2% and -0.71%, respectively.