AuNPs/colloidal properties

As mentioned in the previous section, the response, the stability and the enzyme activity found greatly enhanced at the MWCNT platform. Other than CNTs, AuNPs also possess some unique properties and recent years it has been widely employed in the biosensors to immobilize biomolecules. Thus in this section we discuss about the application of AuNP matrix for the immobilization of AChE for pesticide sensor development. With the use of AuNPs, the efficiency and the stability of the pesticide sensor gets greatly amplified. Moreover, the nanoparticles matrix offers much friendly environment for the immobilized enzyme and thus the catalytic activity of the enzyme got greatly amplified. Interestingly, Shulga et al. applied AChE immobilized colloidal AuNPs sensor for the nM determination of carbofuran, a CA pesticide [16], The enzyme-modified electrode sensor was also utilized for the sensitive electrochemical detection of thiocholine from the enzyme catalyzed hydrolysis of acetylthiocholine chloride (ATCl). The fabrication and the enzyme catalyzed reaction at the AuNPs coated electrode surface is shown in Fig. 6. 

AuNPs in Liquid-State Environment Solute pure and monolayer-coated ( capped ) AuNPs are central targets in colloid and surface science also with a historical dimension [258-262]. Facile chemical syntheses introduced by Schmid et al. [260] and by Brust et al. [263] have boosted AuNP and other metal nanoparticle science towards characterization of the physical properties and use of these nanoscale metallic entities by multifarious techniques and in a variety of environments. Physical properties in focus have been the surface plasmon optical extinction band [264—269], scanning and transmission electron microscopy properties, and electrochemical properties of surface-immobilized coated AuNPs [173, 268-276], To this can be added a variety of AuNP crosslinked molecular and biomolecular... 

ICP analyses were carried out to check the accurate concentration of the An precursor compoimds (Au-pa, Au-pb, Au-pc) in aqueous solution using an Optima 3000XL device (Perkin-Elmer). Optical properties (absorbance) of colloidal solutions were acquired with UV-Vis spectrometer (Avantes-2048). Particle size distribution and zeta potential values were obtained at room temperature from dynamic light scattering and zeta potential measurements, respectively, which were performed on a Malvern Instrument (ZS ZEN 4003). Size analysis (i.e. size, shape, morphology etc.) of colloidal AuNPs was further confirmed with HRTEM (JEM-2 lOOF) at a voltage of 200 kV. 

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