DNA-Functionalized Gold Nanoparticles for Chemiresistive Vapor Sensing

Chemiresistive sensing with functionalized gold nanoparticles is a powerful new technology for vapor sensing. Utilizing changes in behavior of electron tunneling through conductive gold nanoparticles and insulating organic capping layers upon analyte adsorption, this system can achieve intrinsically high sensitivity and rapid response time. A number of thiol-based small-molecule organic ligands have already been successfully used to functionalize gold nanoparticles, yielding an array of organic sensors having various sensitivities towards different organic vapors. With the aid of chemometric analysis tools, gold nanoparticle-based chemiresistive sensors have been rapidly maturing into a vapor quantification and identification technology. A limiting factor for its success, as has been the case for many types of sensors based on reversible physical adsorption, is the lack of specific interaction between sensor material and the vapor analytes. Therefore, the vapor identification capability is limited. A method to overcome this, using DNA-functionalized gold nanoparticles, is proposed in this study. Although highly specific molecular recognition is not yet achievable, this preliminary reveals many characteristics of DNA-functionalized gold nanoparticle for sensing purpose. Using non-specially designed DNA sequences, gold nanoparticle sensors display similar kinds of swelling-dominated response behavior with sequence-dependent response patterns towards organic vapors. Due to the polyelectrolyte nature of DNA molecules, the sensors behave specially towards water vapor, displaying a dichotomous behavior. At low relative humidities, the sensors are swelling-dominated, showing an increase in sensor response with increasing relative humidity. At medium to high relative humidities, the sensors are ionic-conduction dominated, showing a rapid decrease in resistivity by a few orders of magnitude with increasing relative humidity. Sensor responses towards organic vapor analytes are mediated by environmental relative humidity, with both a response sign switch and response enhancement observed. The chemiresistive effects of DNA-functionalized nanoparticles were also influenced by the DNA chain length, with higher response exhibited by longer DNA chain length. However, the response magnitude normalized by chain length is approximately constant. Lastly, the sequence-dependence behavior is explored by using two DNA molecules of identical composition but different nucleobase sequences. A comparison with alkanethiol-functionalized gold nanoparticles indicates that the sensors respond by swelling behavior under dry conditions, but possibly conformational-dependent response is present. The findings in this preliminary but comprehensive study of DNA-functionalized gold nanoparticles suggest the potential future developments of highly selective and highly diverse chemiresistive sensors for specific vapor analytes