a) Representative results recorded visually after acid addition. Blank, positive, and negative denotes sample tubes containing PBS, genomic DNA of Escherichia coli and Pseudomonas aeruginosa respectively. Red color shows the presence of target and purple indicates the absence. b) UV-Vis spectra of the respective samples. c) Visual observation of minimum detection limit of AuNP- oligo probes hybridized with serial dilutions of Escherichia coli genomic DNA in 50 μl volume. d) UV-Vis spectra of the respective samples showing characteristic absorption at 520 nm upto 54 ng DNA and broad spectral shift for samples containing less than 54 ng DNA and control sample.