Assessment of nonlinear optical refractive index in identification of bacterial infection

This study evaluates the Z-scan technique in determining Pseudomonas aeruginosa (P. aeruginosa), Staphylococcus aureus (S. aureus), and Escherichia coli (E. coli) titration. Ten in vitro samples were prepared for each bacteria. Closed-aperture Z-scan technique was employed for measuring the sign and magnitude of the nonlinear refractive index of each sample. Seven concentrations were used to design a standard graph model and three concentrations for each bacteria were used to test the model. Prior to application of Z-scan technique, all samples were fixed with 1 ml of 5% paraformaldehyde. The sign of nonlinear refractive index for P. aeruginosa and S. aureus was positive and negative for E. coli. The value of nonlinear refractive index decreases with increasing concentration of the samples. The results show that nonlinear refractive index has good potential in predicting the concentration of blind samples. The proposed method demonstrates that Z-scan technique is a reliable detection method with the potential to characterize bacterial samples of different concentrations. Nonlinear refractive index could also be used as a new identification technique for the evaluation of infections. (paper)