Gold Nanoparticles for Colorimetric detection of hydrolysis of antibiotics by penicillin G acylase

A simple inexpensive method of monitoring hydrolysis of an antibiotic penicillin G (pen G) and subsequent enzyme detection using gold nanoparticles is presented. Gold nanoparticles capped with Cetyl trimethyl ammonium bromide (CTAB) are synthesized using chemical route. The particles could be used for detection of Penicillin G acylase (PGA) enzyme by incorporating hydrolysis reaction with pen G. This hydrolysis reaction leads to a shift in the surface plasmon band of gold nanoparticles from 527 nm to 545 nm accompanied by a visual colorimetric change in the solution from red to blue. The process is attributed to aggregation of nanoparticles caused due to displacement of CTAB bilayer by byproducts of the hydrolysis reaction. It is proposed that the presence of 0.007 mg/ml of PGA can be detected by a color change of gold nanoparticles solution without requiring any complicated instrument or highly trained operator to conduct the test. The method could also identify the presence of different penicillins by showing different spectral shifts. Thus the work presented here would be useful not only for the detection of the pharmaceutically important drug Pen G, but also represents a general methodology for the detection of enzymes, eg PGA.