Effect of Nanoporous Gold Thin Film Morphology on Electrochemical DNA Sensing

Abstract

Advances in materials science and chemistry have led to the development of a wide range of nanostructured materials for building novel electrochemical biosensors. A systematic understanding of the challenges related to electrode morphology involved in designing such sensors is essential for developing effective biosensing tools. In this study, we use nanoporous gold (npAu) thin film electrode coatings with sub-micron thicknesses, as a model system to investigate the influence of nanostructuring on DNA-methylene blue (MB) interactions and their application for DNA biosensors. The interaction of single-and double-stranded DNA immobilized onto morphologically different np-Au films with MB was electrochemically interrogated via square wave voltammetry (SWV). The electrochemical signal from these electrodes in response to MB decayed progressively with each SWV scan. The decay rate was governed by accessibility of the electrochemically-active np-Au surface by the analyte. The optimum frequency for extracting the maximum signal via SWV was influenced by the film morphology, where the optimum frequency was lower for the nanoporous morphology with lower density of molecular access points into the porous coating. Overall, the np-Au electrodes exhibited a 10-fold enhancement in probe grafting density and approximately 10-fold higher electrochemical current upon probetarget hybridization as compared to the planar Au electrodes. The np-Au electrodes enabled sensitive detection with a dynamic range of 10 nM to 100 nM that shifts by an order of magnitude for coarsened np-Au morphology due to increased target penetration into the porous network and hence enhanced hybridization efficiency. These findings provide insight into the influence of nanostructuring on the transport mechanisms of small molecules and nucleic acids, and yield an understanding of diverse sensor performance parameters such as DNA grafting density, hybridization efficiency, sensitivity and dynamic range.

Sequence-Specific Electrical Purification of Nucleic Acids with Nanoporous Gold Electrodes

“…The total number of grafted probes was estimated to be 4.3 x 10 12 molecules, which translates into a grafting density that is 10 times that of its planar gold counterpart 24 . This 10-fold increase in the grafting density is in agreement with the surface area enhancement, indicating that most of the porous surface of the electrode is covered with recognition molecules and MB molecules can access the deeper surfaces of the porous electrode 24 . We then challenged the sensor with the DNA target spiked into FBS solution to simulate the complex environment.…”

“…We then challenged the sensor with the DNA target spiked into FBS solution to simulate the complex environment. We used a loading concentration of 300 nM (2.4 ng/µL), as this corresponds to the concentration that led to sensor saturation in our previous study 24 . Upon target hybridization, the SWV peak current dropped, indicating successful target hybridization ( Figure 2A).…”

“…Owing to its catalytic properties, tunable morphology, microfabrication compatibility and excellent thiol-gold chemistry, np-Au is an emerging material for biosensing applications [20][21][22] . We recently demonstrated that np-Au electrochemical sensors exhibit excellent biofouling-resilience in the presence of complex media such as serum while preserving the sensitive DNA detection capabilities 23,24 . In addition, as the np-Au thin film electrodes can be easily produced using conventional microfabrication techniques, they are highly amenable to seamless integration with microfluidics and other microsystem components to build complete sample-in-answer-out platforms 25 .…”

Nanostructured Inorganic Materials at Work in Electrochemical Sensing and Biofuel Cells

“…The great excitement generated by the above glucose and H 2 O 2 sensors was mostly motivated by the tunable physical, morphological and catalytic properties of nanoscale materials. To take advantage of the fascinating properties of nanomaterials, such as larger specific surface areas and the higher density of surface active sites, various methods have been developed by different groups to prepare nanostructured materials to trace other substrates within biofluids such as DNA [8,148,149], ascorbic acid [12,150,151], dopamine [11,152], acetylsalicylic acid (aspirin) [12,153], and paracetamol [9,10]. At the physiological level, ascorbic acid, commonly known as vitamin C, is a compound of great biomedical interest that plays a very important role in regulating metabolism and central nervous system functions.…”

Electrochemically Triggered Pore Expansion in Nanoporous Gold Thin Films

“…As a model system for nanoporous metals produced by dealloying, we use nanoporous gold (np-Au), which has been the most popular material system as it embodies numerous advantages, including high electrical conductivity 22 , compatibility with microfabrication processes 19 , well-established gold-thiol chemistry for surface functionalization 23 , tunable mechanical properties [24][25] , and biocompatibility 26 . By employing electrochemical etching at time-varying potentials, we probe the underlying etch mechanisms and discuss its implications to catalysis and sensing applications.…”