Interplay of Effective Surface Area, Mass Transport, and Electrochemical Features in Nanoporous Nucleic Acid Sensors

Abstract

Four different film thicknesses of np-Au were sputtered using Lesker Labline Sputter System. For each of the sets, piranha-cleaned glass coverslips were sputter-coated with 160 nm-thick Cr layer to serve as an adhesive layer between the glass substrate and 80 nm-thick seed layer of Au. Ag and Au were co-sputtered on top of the Au-seed layer to obtain 36% Au and 64% Ag (atomic %) alloy 1. Alloy co-sputtering time was varied to allow for fabrication of varying film thicknesses (t = 5, 10, 20 and 30 min). All metal depositions were performed in argon ambient at a pressure of 10 mTorr without breaking the vacuum between deposition of different metal layers. To obtain unannealed np-Au morphology, the alloy samples were dealloyed in 70% nitric acid at 55 °C for 15 min, followed by copious rinsing under deionized water (DI) water stream. This process is a chemical corrosion process, in which nitric acid dissolves less noble metal (Ag) from the AuAg alloy as gold atoms go under surface diffusion to assemble the bi-continuous porous structure with interconnected nanochannels. To obtain coarser, yet self-similar morphologies, thermal annealing was used. Final product of the fabrication process were 8 sets of varying properties thin films (4 thicknesses and 2 morphologiesunannealed and annealed np-Au).

Nanoporous Gold for the Miniaturization of In Vivo Electrochemical Aptamer-Based Sensors

“…The increase in the EAB signal we observe is smaller than the 75-to 100-fold increase in the microscopic surface area seen for nanoporous electrodes (Figure 2). This discrepancy, which is consistent with recent observations by Vesilinovic et al, who examined the impact of nanoporous gold surfaces on the signaling of a different class of electrochemical biosensors, 24 may result from two sources. First, hindered diffusion of the aptamer into the smallest pores in the matrix might reduce the number of aptamers per unit of the microscopic surface area.…”

“…Because it allows the attachment of more aptamers to an electrode of a given size, increasing the microscopic surface area of the gold provides a route toward smaller EAB sensors. To this end, many techniques exist that enhance the microscopic surface area of gold, including a number of electrochemical etching/deposition approaches, − co-sputtering, − or the leaching of commercially available gold alloy foils. ,, Co-sputtering and the leaching of gold foil, however, are incompatible with the wire format of our implantable sensors. In contrast, electrochemical surface area enhancement techniques are readily compatible with our sensor architecture.…”

Real-Time Intracellular Analysis of Kanamycin Using Microaptasensors

“…This packing density is much lower than that of the commonly used macroelectrodes . The decrease in packing density at aptamer-modified nanoporous surfaces has been previously investigated by Veselinovic et al In their study, they demonstrated that the hindered diffusion of aptamers to smaller pores in a nonporous surface decreased the packing density . For our sensors, the lower packing density might be explained by the slower diffusion of aptamers near dendrite junctions.…”

Mass Transport in Nanoporous Gold and Correlation with Surface Pores for EC1 Mechanism: Case of Ascorbic Acid

“…electrochemical processes on NPG films with small pore size has already been reported. [29][30] Interestingly, a different behavior was noticed in similar plots obtained for the AA electrode process for NPG films prepared at a fixed E D (-4 V) but for varying t D (in the range of 50 to 600 s) (Figure 7). At the shorter t D value (50 s), E 1/2 is reported instead of E p because the voltammogram recorded with this electrode presented a steady-state feature instead of a peak-shaped profile.…”

“…This has also been demonstrated in the recent work of Veselinovic et al, according to which the sensitivity for nucleic acid detection was not linearly proportional to the NPG electrochemical surface area (ECSA). [29] Therefore, a trade-off between mass transport limitation and ECSA is always noticed to improve the electroanalytical performance of NPG-based platforms. [30] This balance depends on two important factors: the kinetics and mechanism of the electrode reactions, and the pore size in the NPG films.…”