A simple colorimetric pH alarm constructed from DNA–gold nanoparticles

Because of their unique characteristics, DNAs have been widely studied for uses in biosensors. In this work, we utilize single-stranded homopolymeric deoxyadenosines (abbreviated as poly (dA)) as recognition elements and gold nanoparticles (abbreviated as AuNPs) as reporter parts for the construction of pH alarms, which are able to produce sharp colorimetric responses upon specific pH thresholds within the range from pH 2 to 4. These biosensors are convenient to prepare and easy to operate. Their pH thresholds for colorimetric response can be easily tuned by changes of DNA strand length, concentration and DNA sequence. With an increase in the number of nucleotide bases per DNA chain while keeping the overall number of nucleotide base in the system constant, the pH threshold can be raised. Increasing the concentration of the single-stranded poly (dA) DNA lowers the pH response threshold. Moreover, as they can sense a range as narrow as a 0.4 pH unit which equals to 2.5 fold [H+] change, they can be used as a potential pH alarm for specific pH range.

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► It is the first time that poly (dA) ssDNAs have been attempted in pH sensing.
► The system can provide very sharp, naked-eyes detectable colorimetric responses upon a specific media pH.
► The approach is simple and detection threshold can be modulated.