A facile method for fabrication of buckled PDMS silver nanorod arrays as active 3D SERS cages for bacterial sensing


Pseudomonas aeruginosa is an opportunistic pathogen that colonizes on damaged sites prone to infection such as burns, surgical wounds, respiratory tract and physically damaged eyes. Conventional techniques used to identify bacteria include biochemical tests such as Gram stain, enzyme activity tests and antibiotic susceptibility tests. All these tests can be applied only on pure bacteria after incubating them in suitable growth medium. However, culturing bacteria is a time consuming procedure and cannot provide rapid identification and response. Recently, surface enhanced Raman scattering (SERS) has emerged as a promising technique for chemical and biological sensing. Although SERS has emerged as a potential technique for chemical and biological sensing it has few limitations like all the other techniques. One of the limitations of these SERS substrates lies in the fact that they are mostly two-dimensional (2D) planar systems. In 2D ordered substrates the number of hotspots is limited to only one Cartesian x–y plane. Whereas three-dimensional (3D) cage-like structures can supply more hotspots which results in large enhancement of the Raman signal as compared to their 2D counterparts. We report a facile method to fabricate highly sensitive flexible Ag nanorod (AgNR) array based SERS substrates on buckled poly(dimethylsiloxane) (PDMS) for the detection of P. aeruginosa. The AgNRs were deposited on 30% pre-stretched PDMS using oblique angle deposition. The bacterial suspension (3 μL, 108 cells mL−1) was pipetted directly onto the AgNRs grown on a stretched PDMS substrate. After performing SERS measurements on the stretched AgNR-PDMS SERS substrate, the stress was released and SERS measurements were repeated. This AgNR-PDMS buckled system increases the number of hotspots and also provides better entrapment of the bacteria P. aeruginosa onto the AgNRs giving rise to enhancement in the Raman signal. The buckled AgNR-PDMS array substrates exhibit about eleven-fold Raman signal enhancement compared to the pre-stretched AgNR-PDMS film. This excellent SERS enhancement may be attributed to the formation of high density hotspots among the AgNRs and increase in the area for better interaction of bacteria with the metal surface which is supported by finite difference time domain (FDTD) simulations. These substrates can be promising candidates for chemical and biological sensing applications. http://pubs.rsc.org/En/content/articlelanding/2015/cc/c5cc03604f#!divAbstract

Contact details: 

Dr. J. P. Singh

Department of Physics