Molecular release from patterned nanoporous gold thin films

Abstract

Nanostructured materials have shown significant potential for biomedical applications that require high loading capacity and controlled release of drugs. Nanoporous gold (np-Au), produced by an alloy corrosion process, is a promising novel material that benefits from compatibility with microfabrication, tunable pore morphology, electrical conductivity, well-established gold-thiol conjugate chemistry, and biocompatibility. While np-Au's non-biological applications are abundant, its performance in the biomedical field is nascent. In this work, we employ a combination of techniques including nanoporous thin film synthesis, quantitative electron microscopy, fluorospectrometry, and electrochemical surface characterization to study loading capacity and molecular release kinetics as a function of film properties and discuss underlying mechanisms. The sub-micron-thick sputter-coated nanoporous gold films provide small-molecule loading capacities up to 1.12 mg cm À2 and molecular release half-lives between 3.6 hours to 12.8 hours. A systematic set of studies reveals that effective surface area of the np-Au thin films on glass substrates plays the largest role in determining loading capacity. The release kinetics on the other hand depends on a complex interplay of micro-and nano-scale morphological features.

Effect of Nanoporous Gold Thin Film Morphology on Electrochemical DNA Sensing

“…Transport limitations, especially for MB to penetrate the porous structure once dispersed into the electrolyte, are more prominent in np-Au films owing to their highly tortuous structure 21 . Hence the extent of signal reduction was greater in np-Au (65%) compared to planar Au (50%).…”

Effect of Surface–Molecule Interactions on Molecular Loading Capacity of Nanoporous Gold Thin Films

“…Tensile stress accumulation during the dealloying step results in hairline cracks (large connected darker regions in top SEM view) throughout the film, which were included in the determination of pore width 19 . The influence of cracks on loading capacity and release kinetics have been reported previously 11 . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 …”

“…Our previous work describes the detailed fabrication of patterned np-Au thin films used in the release experiments 11,16 . Briefly, in order to fabricate the release chips (also referred to as release samples) used for molecular release from 3 mm x 3 mm np-Au patterns, we sputtered a stack of metal layers through a laser-cut PDMS stencil mask temporarily placed on glass coverslips.…”

“…After the rinse, each chip was placed into a new microcentrifuge tube filled with release medium of interest (DI water or PBS) to initiate fluorescein release from the np-Au chips. At successive time points, 10 μL of solution was sampled from the elution tube (following pipet agitation to ensure homogeneity) and mixed with 10 μL of 50 mM NaOH to enhance fluorescence intensity 11,16 . The fluorescence intensity of the resulting solution was quantified with NanoDrop 3300 fluorospectrometer at a peak emission wavelength of 515 nm.…”

“…Properties of the drug molecules (e.g., electrical charge, size, chemical reactivity), the materials (e.g., morphology, surface charge), and the liquid medium where the molecules are delivered (e.g., ionic strength, pH) are all crucial factors in dictating drug delivery performance 2,6 . Nanoporous gold (np-Au), with its high effective surface area, well established gold-thiol-mediated surface modifications, and tunable pore morphology, is a promising material for drug delivery applications and studying the influence of physicochemical surface properties on the moleculeloading capacity and release kinetics [8][9][10][11][12][13][14][15] . Our previous studies have focused on the effect of pore morphology and elution medium constituents on the molecular release from np-Au coatings 11,16 .…”