Reproducible carbon/molecule/Cu molecular junctions are made with high yield using diazonium reduction of aromatic molecules on carbon with direct evaporation of Cu as a top contact. This report investigates the stability of these devices in response to fabrication steps. Raman spectroscopy through a transparent support shows that direct deposition of Au or Cu causes little change in molecular layer structure, while Ti and Pt deposition cause signifi cant damage to the molecules. AFM, Raman, and XPS examination of Au, Cu, and Ti devices after removal of deposited metal confi rm that Cu and Au have minimal effects on molecular structure. However, the molecular layer is rougher after Au deposition, probably due to partial penetration of Au atoms into the molecular layer. Completed carbon/molecule/Cu devices can be heated to 250 ° C without signifi cant changes in electronic behaviour while nitroazobenzene molecular layers on carbon were unaffected by photolithography or by 5 min at 400 ° C in vacuum. Completed devices could be sealed with parylene-N, stabilizing them to aqueous etching solution. The stability of carbon/molecule/Cu junctions is due, in part, to the strong carbon-carbon bonding and aggressive nature of diazonium surface modifi cation. The results signifi cantly expand the range of processing variables compatible with molecular electronic junctions.

The neurotransmitter acetylcholine (ACh) plays a key role in the pathophysiology of brain disorders such as Alzheimer's disease. Understanding the dynamics of ACh concentration changes and kinetics of ACh degradation in the living brain is crucial to unravel the pathophysiology of such diseases and the rational design of therapeutics. In this work, an electrochemical sensor capable of dynamic, label-free, selective, and in situ detection of ACh in a range of 1 nM to 1 mM (with temporal resolution of less than one second) was developed. The sensor was employed for the direct detection of ACh in artificial cerebrospinal fluid and rat brain homogenate, without any prior separation steps. A potentiometric receptor-doped ion-selective electrode (ISE) with selectivity for ACh was designed by taking advantage of the positive charge of ACh. The dynamic range, limit of detection (LOD), and the selectivity of the sensor were optimized stepwise by (i) screening of hydrophobic biomimetic calixarenes to identify receptors that strongly bind to ACh based on shape-selective multitopic recognition, (ii) doping of the ISE sensing membrane with an ACh-binding hydrophobic calixarene to enable selective detection of ACh in complex matrices, (iii) utilizing a hydrophilic calixarene in the inner filling solution of the ISE to buffer the concentration of ACh and, thereby, lower the LOD of the sensor, and (iv) introducing a surface treatment step prior to the measurement by placing the sensor for ∼1 min in a solution of a hydrophilic calixarene to lower the LOD of the sensor even further.

This paper presents a method to derivatize a wide variety of substrate materials that are frequently used in spectroscopic characterizations with molecular layers through the reduction of aromatic diazonium reagents. The method relies on an ultrathin (5 nm) layer of a reactive metal (e.g., Ti or Al) deposited as a primer that subsequently mediates the reduction of aromatic diazonium reagents from acetonitrile solution. Following surface modification, the Ti can be oxidized to provide a passivated support surface. Raman, Infrared, UV-vis and X-ray photoelectron spectroscopic techniques are used to characterize the molecular layers on the metal primer surface. When a Ti primer layer is derivatized via diazonium reduction, the molecule is shown to be present on the ultrathin Ti layer on Au, Al, quartz, Si/SiO(x), glass, and polyethylene surfaces. For molecules bound to a Ti primer, the molecular layer was found to be stable to sonication in acetone or acetonitrile, a 1 h exposure to boiling water, and a 30 min exposure to 0.1 M acid or base. The approach also permits spectroscopic characterization of buried thin-film molecular layers on optically transparent substrates after deposition of thick top metal contacts.

No abstract