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

Abstract

The study of the adsorption behavior of disease markers such as ammonia (NH₃) and acetaldehyde (CH₃CHO) with biomaterials is important, as it will improve our understanding of their interaction behavior and enable the development of self-diagnosis technologies, among others. In this study, three types of DNA-based biomaterials were synthesized (pGFP plasmid DNA isolated 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 DNA itself 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 DNA modified 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 DNA counterpart 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 biomaterial can be readily employed to detect NH₃ and CH₃CHO in humid environments. Further study showed that the magnitudes of the QCM response of the DNA and 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 DNA with the ionic liquid and HAuCl₄ (experimentally proved by XPS and FTIR), which strongly indicates the role of the phosphates and nucleobases of DNA for the electrostatic binding of NH₃ and CH₃CHO, respectively.