A QCM-based ‘on–off’ mechanistic study of gas adsorption by plasmid DNA and DNA–[Bmim][PF6] construct

The study of the adsorption behavior of disease markers such as ammonia (NH3) and acetaldehyde (CH3CHO) with biomaterialsis important, as it will improve our understanding of their interaction behavior and enable the development of self-diagnosistechnologies, among others. In this study, three types of DNA-based biomaterialswere synthesized (pGFP plasmid DNAisolated from E. coli DH5α, a DNA–ionic liquid construct ( DNA–IL) and DNA–ionic liquid–gold chloride ( DNA–IL–Au)) and their adsorption capacities for NH3 and CH3CHO were tested by utilizing a gravimetric transducer, namely, a quartz crystal microbalance (QCM). Pristine DNAitself displayed high sensitivity towards both gases, with a pristine DNA-based QCM displaying magnitudes of response of ∼3.74 and 2.62 ng cm−2 μg−1 following 10 minutes of exposure to 600 ppm NH3 and CH3CHO, respectively. Interestingly, no response was observed when these gases were exposed to the DNA–IL complex, which comprised DNAmodified with the hydrophobic IL [Bmim][PF6]. However, when the DNA–IL complex was further treated with HAuCl4, the biomaterial( DNA–IL–Au) regained its adsorption capacity, exhibiting magnitudes of adsorption/response up to 140% and 36% higher than its DNAcounterpart toward NH3 and CH3CHO, respectively. It was also observed that the utilization of DNA–IL–Au significantly reduced the sensitivity of the QCM device to humidity content, which indicates that the developed biomaterialcan be readily employed to detect NH3 and CH3CHO in humid environments. Further study showed that the magnitudes of the QCM response of the DNAand DNA–IL–Au materials toward the different concentrations of NH3 and CH3CHO that were tested follow the loading ratio correlation (LRC), which thus indicates that the developed materials can potentially be utilized as sensitive layers for the detection of biomarker gases that are produced in the body as a result of biomedical disorders. In addition, a plausible sorption mechanism has also been proposed on the basis of the interaction of DNAwith the ionic liquid and HAuCl4 (experimentally proved by XPS and FTIR), which strongly indicates the role of the phosphates and nucleobasesof DNAfor the electrostatic binding of NH3 and CH3CHO, respectively.