A bimodal (SERS and colorimetric) aptasensor for the detection of Pseudomonas aeruginosa

An aptamer based assay is described for the determination of Pseudomonas aeruginosa (P. aeruginosa). It is bimodal in that both surface enhanced Raman spectroscopy (SERS) and colorimetry are applied for quantitation. The aptamer against P. aeruginosa and its corresponding complementary DNA fragment (cDNA) were conjugated to two kinds of differently sized gold nanoparticles (AuNPs). The 30 nm AuNPs carrying the aptamer are used as color signal probes, while the cDNA-15nm AuNP conjugates serve as SERS signalling probes. In the absence of P. aeruginosa, the two probes assemble to form the duplex structure. When the probes are exposed to P. aeruginosa, the aptamer dissociates from its cDNA and binds the target. After centrifugation, the SERS signal from the supernatant decreased, due to the decreased electromagnetic effect. On addition of 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide, a relatively rapid catalytic reaction between horseradish peroxidase(linked to the aptamer on the 30-nm AuNPs) and TMB occurred, resulting in the formation of agreen color with an absorption peak at 640 nm. The reliability of the approach was validated by detecting different levels of P. aeruginosa in spiked tap water and chickenmeat samples. The average recoveries ranged from 88% to 112%, confirming the practicality of this method. In our perception, this dual mode aptasensor paves the way for accurate and reliable determination of P. aeruginosa. Conceivably, the method has a wide scope in that it may be extended to the determination of various other species for which respective aptamers are available.