Self-assembled monolayers on gold for the fabrication of radioactive stents

An innovative and easily applicable method for the fabrication of radioactive stents, to be used for the treatment of restenosis, is presented. By incorporating the b-emitting radioisotopes 186Re, 188Re, 90Y, or 32P into sulfur-containing adsorbates, it becomes possible to cover a gold surface with a radioactive self-assembled monolayer (SAM). Two methods have been investigated. In the first, SAMs consisting of potentially radioactive rhenium-, yttrium-, and phosphorus-containing adsorbates have been assembled on 2D gold substrates, after which they have been studied by wettability measurements, electrochemistry, and X-ray photoelectron spectroscopy (XPS). The stability of these SAMs under simulated physiological conditions (phosphate buffered saline, PBS solution) for periods up to two months has been demonstrated. Alternatively, potentially radioactive monolayers have been prepared by exposure of SAMs of mono-, bi-, and tridentate ligands to a solution containing a radiometal (rhenium) in order to bind the metal to the monolayer. The polydentate ligands exhibit excellent binding capacity, leading to SAMs containing over 10±10 mol/cm2 of the radiometal, which is more than sufficient to make this system viable for the delivery of therapeutical dosages of radiation

Cation sensing by patterned self-assembled monolayers on gold

X-Ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to study the interactions between self-assembled monolayers (SAMs) of crown ether adsorbates and metal ions. Both analytical techniques confirmed the selectivities of the 12-crown-4 and 15-crown-5 SAMs that had previously been determined by electrochemical impedance spectroscopy. AFM has also been used to characterize microcontact-printed crown ether monolayers. The electrochemical patterning of monolayers on gold allowed the design of a dual sensor for the electrochemical detection of cations. However, due to cross-contamination of both monolayers during the patterning process a significant selectivity reduction of the layers was observed. Nevertheless, the remaining Na+ selectivity of the 12-crown-4 SAM and the K+ selectivity of the 15-crown-5 SAM allowed the unambiguous discrimination between both metal ions. \u

Self-assembled monolayers of heptapodant ß-cyclodextrins on gold

A route was developed for the synthesis of three different cyclodextrin adsorbates: heptakis{6-O-[3-(thiomethyl)propionyl)]-2,3-di-O-methyl}-ß\ud -cyclodextrin, heptakis{6-O-[12-(thiododecyl)dodecanoyl)]-2,3-di-O-methyl}-ß\ud -cyclodextrin (a short and long alkyl chain sulfide cyclodextrin adsorbate, respectively), and heptakis[6-deoxy-6-(3-mercaptopropionamidyl)-2,3-di-O-methyl]-ß-cyclodextrin (a short alkyl chain thiol adsorbate). Self-assembled monolayers on gold of these three cyclodextrin adsorbates with seven sulfur moieties were fully characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The electrochemical capacitance measurements show the differences between the thicknesses of the ß-cyclodextrin monolayers, and the XPS-(S2p) measurements show the different effectivenesses of the sulfur moieties of the three monolayers in their binding to the gold surface. Sulfide-based -cyclodextrin monolayers use on average 4.5 of the 7 attachment points whereas the thiol-based cyclodextrin monolayer only uses 3.2 of the 7 sulfurs. These experiments show that, for adsorbates with multiple attachment points, sulfides may be more effective than thiols. TOF-SIMS measurements confirm the robust attachment of these adsorbates on gold obtained by XPS