Bio-fabrication of gold nanoparticles using aqueous extract of red tomato and its use as a colorimetric sensor

Abstract

In this work, we report a green method for the synthesis of gold nanoparticles (GNP) using the aqueous extract of red tomato (Lycopersicon esculentum). We believe that citric acid and ascorbic acid present in tomato juice are responsible for the reduction of gold ions. This biosynthesized GNP in the presence of sodium dodecyl sulfate has been used as a colorimetric sensor to detect and estimate the pesticide, methyl parathion. The GNP in the presence of methyl parathion shows a new peak at 400 nm due to the formation of 4-nitrophenolate ion by catalytic hydrolysis of methyl parathion in alkaline medium. A calibration curve between the absorption coefficients of the 400-nm peak versus the concentration of the pesticide allows the quantitative estimation of the 4-nitrophenolate ion, thereby enabling indirect estimation of methyl parathion present in the system.

Figure 1

Schematic diagram of formation of GNP, catalytic hydrolysis of methyl parathion and aggregation of GNP.

Figure 2

UV–VIS absorption spectra of GNP at different compositions of tomato extract and SDS capped GNP in alkaline medium. UV-VIS spectra of (A) GNP at different compositions and (B) SDS-capped GNP. Insets are digital photographic images of A and B.

Figure 3

UV–vis spectra of GNP and with methyl parathion, calibration curve (absorbance versus methyl parathion), and control spectrum. (A) UV–vis spectra of GNP and GNP with various concentrations of methyl parathion 10 to 200 ppm; (inset) digital photographic images of color changes due to addition of methyl parathion. (B) Calibration curve between absorbance of 400-nm peak versus concentration of methyl parathion. (C) Spectrum of pure methyl parathion (control experiment).

Figure 4

TEM micrographs, particle size distribution histogram, and SAED pattern of GNP. (A) TEM micrographs of GNP with tomato extract. (B) Particle size distribution histogram of spherical GNP, and (C) corresponding SAED pattern of GNP.

Figure 5

TEM micrographs, particle size distribution histogram, SDS-capped GNP with methyl parathion, and SAED pattern of GNP. (A) TEM micrographs of SDS-capped GNP with tomato extract. (B) Particle size distribution histogram of spherical GNP. (C) SDS-capped GNP in the presence of methyl parathion, and (D) corresponding SAED pattern of GNP.

Figure 6

FTIR spectra of vacuum-dried powder of red tomato and GNP synthesized from aqueous red tomato extract. (A) FTIR spectra of vacuum-dried powder of red tomato (Lycopersicon esculentum) and (B) GNP synthesized from aqueous red tomato extract.

Figure 7

XRD of SDS capped GNP and GNP in presence of methyl parathion. XRD of GNP (A) before and (B) after addition of methyl parathion.